StructuralâSpectrochemical Correlations of Variable Dimensionality

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Structural-spectrochemical correlations of variable dimensionality crystalline metal organic framework materials in hydrothermal reactivity patterns of binary-ternary systems of Pb(II) with (a)cyclic (poly)carboxylate and aromatic chelator ligands. Athanasios Salifoglou, Catherine Gabriel, Angelos Vangelis, Catherine Raptopoulou, Aris Terzis, Vassilis Psycharis, Maria Zervou, and Marko Bertmer Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.5b00861 • Publication Date (Web): 14 Sep 2015 Downloaded from http://pubs.acs.org on September 27, 2015

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Crystal Growth & Design

Structural-spectrochemical correlations of variable dimensionality crystalline metal organic framework materials in hydrothermal reactivity patterns of binary-ternary systems of Pb(II) with (a)cyclic (poly)carboxylate and aromatic chelator ligands.

Catherine Gabriel,

a

a

Angelos A. Vangelis,

b

c

b

Catherine P. Raptopoulou,

d

Aris Terzis,

b

Vassilis

a

Psycharis, Maria Zervou, Marko Bertmer, Athanasios Salifoglou * a

Department of Chemical Engineering, Laboratory of Inorganic Chemistry, Aristotle University of

Thessaloniki, Thessaloniki 54124, Greece.

b

Institute of Nanoscience and Nanotechnology, NCSR

“Demokritos”, Aghia Paraskevi 15310, Attiki, Greece.

c

Laboratory of Molecular Analysis, Institute of

Organic and Pharmaceutical Chemistry, National Hellenic Research Foundation, Athens 11635, Greece. d Institut für Experimentelle Physik II, Universität Leipzig, Leipzig 04103, Germany.

Abstract Efforts to comprehend the structural-spectrochemical correlations of crystalline metal-organic framework materials of Pb(II) with (a)cyclic and aromatic chelators linked to photoluminescent applications

led

to

the

hydrothermal

. [Pb{H2BTC}(phen)(H2O)]n 2nH2O(1),

pH-specific

synthesis

of

crystalline

materials

.

[Pb2{CBTC}]n(2), [Pb4(phen)8{CBTC}2(H2O)4]3 70.3H2O(3), and

.

[Pb{HCTA}(H2O)2]n nH2O(4). X-ray studies showed that 1-4 exhibit unique architectures linked to 2D3D coordination polymers formulated by Z-type units composed of Pb2O2 cores, unusually high number of lattice-water molecules, and π-π and H-bond interactions. The contribution of the naturestructure-properties of the aliphatic-(a)cyclic organic (poly)carboxylic/aromatic chelators-ligands to binary-ternary Pb(II) reactivity weaves into the assembly of supramolecular networks, thereby providing

clear

structural-spectroscopic

inter-relationships

exemplifying

the

observed

photoluminescent activity in a distinct MOF-linked fashion.

*Author to whom correspondence should be addressed: Athanasios Salifoglou, Dept. of Chemical Engineering, Laboratory of Inorganic Chemistry, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece. Tel: +30-2310-996-179 Fax: +30-2310-996-196 E-mail: [email protected]

ACS Paragon Plus Environment


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Structural-spectrochemical correlations of variable dimensionality crystalline metal organic framework materials in hydrothermal reactivity patterns of binary-ternary systems of Pb(II) with (a)cyclic (poly)carboxylate and aromatic chelator ligands.

Catherine Gabriel,

a

a

Angelos A. Vangelis,

b

c

b

Catherine P. Raptopoulou,

d

Aris Terzis,

b

Vassilis

a

Psycharis, Maria Zervou, Marko Bertmer, Athanasios Salifoglou * a

Department of Chemical Engineering, Laboratory of Inorganic Chemistry, Aristotle University of

Thessaloniki, Thessaloniki 54124, Greece.

b

Institute of Nanoscience and Nanotechnology, NCSR

“Demokritos”, Aghia Paraskevi 15310, Attiki, Greece.

c

Laboratory of Molecular Analysis, Institute of

Organic and Pharmaceutical Chemistry, National Hellenic Research Foundation, Athens 11635, Greece. d Institut für Experimentelle Physik II, Universität Leipzig, Leipzig 04103, Germany.

Abstract Efforts to comprehend the structural-spectrochemical correlations of crystalline metal-organic framework materials of Pb(II) with (a)cyclic and aromatic chelators linked to photoluminescent applications

led

to

the

hydrothermal

. [Pb{H2BTC}(phen)(H2O)]n 2nH2O(1),

pH-specific

synthesis

of

crystalline

materials

.

[Pb2{CBTC}]n(2), [Pb4(phen)8{CBTC}2(H2O)4]3 70.3H2O(3), and

.

[Pb{HCTA}(H2O)2]n nH2O(4). X-ray studies showed that 1-4 exhibit unique architectures linked to 2D3D coordination polymers formulated by Z-type units composed of Pb2O2 cores, unusually high number of lattice-water molecules, and π-π and H-bond interactions. The contribution of the naturestructure-properties of the aliphatic-cyclic organic (poly)carboxylic/aromatic chelators-ligands to binaryternary Pb(II) reactivity weaves into the assembly of supramolecular networks, thereby providing clear structural-spectroscopic inter-relationships exemplifying the observed photoluminescent activity in a distinct MOF-linked fashion.

*Author to whom correspondence should be addressed: Athanasios Salifoglou, Dept. of Chemical Engineering, Laboratory of Inorganic Chemistry, Aristotle University of Thessaloniki, Thessaloniki 54124, Greece. Tel: +30-2310-996-179 Fax: +30-2310-996-196 E-mail: [email protected]


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Crystal Growth & Design 3

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Abstract Efforts to comprehend the structural-spectrochemical correlations of crystalline metal-organic framework materials of Pb(II) with (a)cyclic and aromatic chelators linked to photoluminescent applications led to the hydrothermal pH-specific investigation of binary-ternary systems containing (poly)carboxylic acids and 1,10-phenanthroline (phen). The synthesis led to crystalline materials .

.

[Pb{H2BTC}(phen)(H2O)]n 2nH2O(1), [Pb2{CBTC}]n(2), [Pb4(phen)8{CBTC}2(H2O)4]3 70.3H2O(3), and [Pb{HCTA}(H2O)2]n.nH2O(4). X-ray studies showed that 1 is a 3D coordination polymer with a unique architecture formulated by water-containing lattice channels. Coordination polymer 2 features Z-type units composed of Pb2O2 cores creating a 3D framework. In non-polymeric 3, a 2D layered-structure is supported by π-π and H-bond interactions, while containing an unusually high-number of latticewater molecules. Finally, 4 is a 2D coordination polymer with Pb6O6 units arising from Pb2O2 cores and supported through H-bonds, affording a supramolecular 3D network. The open-closed aliphatic organic-rings bearing variable numbers of carboxylate moieties and the aromatic bulky-chelator phenanthroline define the interplay with Pb(II), profusely influencing the nature-physicochemical profiles of 1-4, delineated by elemental analysis, FT-IR, (13C,207Pb) CP-MASNMR, luminescence and X-ray crystallography. The contribution of the nature-structure-properties of the aliphatic-(a)cyclic organic (poly)carboxylic/aromatic chelators-ligands to binary-ternary Pb(II) reactivity weaves into the supramolecular assemblies of 1-4, thereby providing clear structural-spectroscopic inter-relationships exemplifying the observed photoluminescent activity in a distinct MOF-linked fashion.



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Introduction The advent of new metal organic framework (MOF) materials has revolutionized the science and engineering of chemistry over the past decades. As a result, a large variety of MOFs encompassing coordination polymers have been synthesized in pursuit of emerging and promising applications in magnetic materials, gas adsorption, catalysis, molecular recognition, and sensors. Key to synthetic strategies linked to coordination polymers is their careful design and metal-involved assembly built up by variably structured organic ligands, such as 1,10-phenanthroline (phen), pyridine,

1,2

carboxylates

3-6

and phosphonates,7,8 thereby driving considerable interest toward micro-porous materials for industrial applications, including ion exchange, sorption and catalysts.

9-11

Considerable attention in this area of research has been focused on coordination polymers with multifunctional ligands.12-15 To this end, various polycarboxylate ligands (rigid and flexible O-donor organic binders) have been used to prepare coordination polymers of transition metals or lanthanides, among them included being aliphatic α,ω-dicarboxylates.16-30 Given the choice between aliphatic and aromatic ligand binders, in contrast to seeking binding between rigid organic ligands and metal ions in a relatively invariable sense,

31-33

flexible organic ligands do not possess or impose the structural

restrictions of benzene or non-aromatic cyclic rings in the metal-embodied assemblies. Therefore, their chemistry emerges upon binding metal ions in a plethora of modes dictated by equally varying modes rotation and twisting of their flexible skeletons.

34-37

However, the characteristic of enhanced

flexibility makes it difficult and often challenging to control the ultimate metal-organic frameworks. Balancing the aforementioned structural rigidity-flexibility ligand attributes stands as a challenge when designing new coordination polymeric materials of specified properties. Among the numerous such organic metal ion binders, a typical flexible ligand, 1,2,3,4-butanetetracarboxylic acid (H4BTC) appears to be a promising organic linker containing four carboxylic acid groups capable of establishing bridges between several contiguous metal centers through variable coordination modes. In this regard, a host of coordination polymers with transition metal ions, such as Mn(II), Co(II), Ni(II), and Zn(II), have thus far been obtained.

38-41

On the other hand, heterometallic coordination polymers based on H4BTC are

relatively unexplored. Cycloalkane (poly)carboxylate derivatives could also serve as ligand-spacers for the construction of coordination polymers with metals and lanthanides, with due attention drawn to them by the research community as there has been considerable progress toward application of hybrid materials in molecular recognition, enantioselective sensing and photoluminescence.42,43 In such materials, the envisioned and potentially adopted conformations of such ligands in axial and/or equatorial positions around the metal ion center depend upon intrinsic characteristics of polycarboxylate nature, reaction temperatures and pH conditions in aqueous solution. The correlation between the conformation of free nascent polycarboxylic acids and those of the produced hybrid metal-polycarboxylate coordination polymers has not been probed into and understood in detail, in view of the fact that the thermodynamic parameters of molecular conformation(s) may seriously control the crystal structure, architecture, lattice dimensionality and reactivity properties of resulting products. 1,2,3,4-cyclobutanetetracarboxylic acid (H4CBTC) used in this study could adopt a variable number of different structures, with the resulting coordination polymer(s) being expected to involve various conformations of the attached carboxylate groups in the crystal structures. On an equal footing,


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another ligand in the same family of metal ion binders is 1,3,5-cyclohexanetricarboxylic acid (H3CTA). Recently, it was shown that such ligands, with their donor groups arranged around a cyclohexane backbone, could exhibit sufficient flexibility to direct the assembly of interesting polynuclear clusters and extended networks, with the rigidity of the cyclohexane backbone preventing formation of amorphous polymers.

44,45

Systematic work by our lab in the field has a) relied on the aforementioned logic, and b) provided a number of new metal organic framework materials of Pb(II).46-49

It is in this respect that the drive for

new knowledge in the factors a) influencing metal ion-ligand assembly b) controlling the nature, lattice dimensionality, structure architecture of hybrid metal organic framework materials, and c) correlating with the physicochemical properties of arising hybrid materials of specified optical properties, has prompted the in-depth study of binary and ternary systems of Pb(II) with 1. aliphatic (H4BTC) and cyclic (poly)carboxylic acids (H4CBTC, H3CTA), and 2. aromatic binding chelators in aqueous media and in a pH-specific fashion (Scheme 1).

The emerging polymeric crystalline materials exemplify

trends in the assembly of the structural architecture and lattice dimensionality that correlate distinctly with their spectroscopic properties and specifically their luminescence activity.

CH2COOH CHCOOH CHCOOH CH2COOH 1,2,3,4-Butanetetracarboxylic acid H4BTC

HOOC

COOH

HOOC

COOH

1,2,3,4-Cyclobutanetetracarboxylic acid H4CBTC

COOH

HOOC

COOH

1,3,5-Cyclohexanetricarboxylic acid H3CTA

N

N

1,10-Phenanthroline (phen)

Scheme 1: Tri- and Tetra-carboxylic acids along with aromatic N,N-chelator phen in this work.

Experimental Section Materials and methods. All experiments were carried out under aerobic conditions. All reagents were purchased from Fluka or Aldrich. Analytical determination of C, H, N (%) was performed on a Thermo-Finnigan Flash EA 1112 CHNS elemental analyser. FT-Infrared spectra were recorded on a Thermo, Nicolet IR 200 FT-infrared spectrometer. A TA Instruments thermal analyzer, model Q 600, system was used to run TGA experiments. Luminescence measurements were carried out on a Hitachi F7000 spectrophotometer.

13

C CPMAS NMR spectra were obtained on a Varian 400 MHz



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spectrometer operating at 100.53 MHz. The high resolution solid state natural abundance 207Pb Magic Angle Spinning (MAS) NMR spectra were recorded on a Bruker Avance 750 NMR spectrometer at a frequency of 156.71 MHz.

50,51

More details about the physical measurements are given in the

Supporting Information. Preparation of [Pb{H2BTC}(phen)(H2O)]n.2nH2O (1) .

A quantity of Pb(CH3COO)2 3H2O (0.37 g, 1.0 mmol), H4BTC acid (0.47 g, 2.0 mmol) and phen (0.20 g, 1.0 mmol) were placed in a flask and dissolved in 10 mL of H2O. The final pH value was ~4.5. The o

resulting solution was then placed in a 23 mL teflon-lined stainless steel reactor and heated to 160 C for 85 h. At the end of that period, the reactor was allowed to cool to room temperature. The resulting solution was allowed to stand at room temperature and a few days later white crystals appeared. .

Yield: 0.13 g (20 %). Anal. Calcd for 1, [Pb(H2BTC)(phen)(H2O)]n 2nH2O (1) (C20H22N2O11Pb, Mr 673.59): C 35.66, H 3.29, N 4.16. Found: C 36,04, H 3.34, N 3.94. FT-IR (KBr, cm-1) for 1: νas(COO–): -1

–

-1

1688cm , νs(COO ): 1550-1514 cm . Preparation of [Pb2{CBTC}]n (2) A quantity of Pb(NO3)2 (0.20 g, 0.60 mmol) and H4CBTC acid (0.28 g, 1.2 mmol) were placed in a flask and dissolved in 10 mL of H2O, with a final pH~1.5. The resulting reaction solution was then placed in a 23 mL teflon-lined stainless steel reactor and heated to 160oC for 85 h. Subsequently, the reactor was allowed to return to room temperature, with crystals appearing at the bottom of the teflon vessel. Yield: 0.13 g (64 %). Anal. Calcd for 2, [Pb2(CBTC)]n (2) (C8H4O8Pb2, Mr 642.49): C 14.95, H 0.63, Found: C 15.10, H 0.63. FT-IR (KBr, cm-1) for 2: νas(COO–): 1550 cm-1, νs(COO–): 1383 cm-1. .

Preparation of [Pb4(phen)8(CBTC)2(H2O)4]3 70.3H2O (3) A quantity of Pb(NO3)2 (0.33 g, 1.0 mmol), H4CBTC acid (0.46 g, 2.0 mmol) and phen (0.20 g, 1.0 mmol) were placed in a flask and dissolved in 10 mL of H2O. Then, slow addition of a solution of sodium hydroxide solution helped adjust the pH to a final value of ~9. The resulting reaction mixture was then placed in a 23 mL teflon-lined stainless steel reactor and heated to 160oC for 85 h. At the end of that period, the reactor was allowed to return to room temperature, with gray crystals observed at the bottom of the teflon vessel. Yield: 0.20 g (74%). Anal. Calcd for 3, [Pb4(phen)8(CBTC)2(H2O)4]3 .

70.3H2O (3) (C336H380.6N48O130.3Pb12, Mr 9662.57): C 41.72, H 3.98, N 6.99. Found: C 41.90 H 4.10, N -1

–

-1

–

-1

6.80. FT-IR (KBr, cm ) for 3: νas(COO ): 1566-1511 cm , νs(COO ): 1395-1344 cm . .

Preparation of [Pb{HCTA}(H2O)2]n nH2O (4) A quantity of Pb(NO3)2 (0.2 g, 0.60 mmol) and H3CTA acid (0.25 g, 1.2 mmol) were placed in a flask and dissolved in 10 mL of H2O with a final pH value at ~1.5. The resulting reaction solution was then placed in a 23 mL teflon-lined stainless steel reactor and heated to 160oC for 85 h. Subsequently, the reactor was allowed to cool to room temperature, with crystals ultimately appearing at the bottom of .

the teflon vessel. Yield: 0.095 g (33%). Anal. Calcd for 4, [Pb(HCTA)(H2O)2]n nH2O (4) (C9H16O9Pb, Mr 475.41): C 22.72, H 3.37. Found: C 22.90, H 3.45. FT-IR (KBr, cm-1) for 4: νas(COO–): 1543 cm-1, –

-1

νs(COO ): 1398-1324 cm . X-ray crystal structure determination. X-ray quality crystals of compounds 1-4 were grown from aqueous solutions subjected to hydrothermal reactivity conditions. Single crystals, with dimensions 0.21 x 0.27 x 0.35 mm (1), 0.17 x


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0.22 x 0.32 mm (2), 0.13 x 0.28 x 0.42 mm (3) and 0.02 x 0.10 x 0.53 mm (4) were taken from the mother liquor and immediately cooled to -93 oC (1, 3, 4) or mounted in capillary (2).

Diffraction

measurements were made on a Rigaku R-AXIS SPIDER Image Plate diffractometer, using graphite monochromated Mo Kα radiation for 1 and 2, and Cu Kα for 3 and 4. Data collection (ω-scans) and processing (cell refinement, data reduction, and empirical/numerical absorption correction) were carried out using the CrystalClear program package.

52

Crystallographic details are given in Table 1.

The structures of compounds 1-4 were solved by direct methods using SHELXS-97,53 and refined by 2

full-matrix least-squares techniques on F

with SHELXL-97.

54

All non-H atoms were refined

anisotropically. Hydrogen atoms were either located by difference maps and refined isotropically or introduced at calculated positions as riding on bonded atoms. In the asymmetric unit of the structure of 3 there are 70.3 lattice water molecules, with the hydrogen atoms for these molecules not having been located. Plots of all structures were drawn using the Diamond 3.1 crystallographic package.55 Results and Discussion Synthesis. The hydrothermal synthesis of colorless crystalline compound 1 was pursued through a .

reaction between Pb(CH3COO)2 3H2O, H4BTC and phen in water at pH~4.5 (Reaction 1):

CH2COOH N n Pb(CH3COO)2 + n

CHCOOH CHCOOH

+

pH 4.5 3

n N

3 H 2O

CH2COOH

[Pb(H2BTC)(phen)(H2O)]n.2nH2O + 2n CH3COOH

In a similar reaction, Pb(NO3)2 and H4CBTC acid reacted in water at pH~1.5 and led to synthesis and isolation of crystalline compound 2 (Reaction 2):



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HOOC

COOH

pH 1.5

2n Pb(NO3)2 + n HOOC

COOH

[Pb2(CBTC)]n + 4n HNO3

In a ternary system encompassing the aromatic chelator phen, compound 3 emerged as a result of the reaction involving Pb(NO3)2, H4CBTC acid and phen, in water at pH~9 (Reaction 3):

HOOC

N

COOH

12 Pb(NO3)2 + 6

pH 9 + 24

HOOC

+ N

COOH

82.3 H2O NaOH

[Pb4(phen)8(CBTC)2(H2O)4]3 . 70.3 H2O + 24 HNO3 Finally, in a similar binary system, Pb(NO3)2 and H3CTA acid reacted in water, at pH~1.5, affording the crystalline compound 4 (Reaction 4):

COOH pH 1.5 n Pb(NO3)2 +

n

+ 3 H2O

HOOC

COOH

[Pb(HCTA)(H2O)2]n.nH2O + 2n HNO3

The isolated materials were easily retrieved in pure crystalline form following hydrothermal synthesis. Elemental analysis of the isolated crystalline products projected the molecular formulation [Pb{H2BTC}(phen)(H2O)]

.

2H2O (1), [Pb2{CBTC}] (2), [Pb4(phen)8(CBTC)2(H2O)4]3 70.3H2O (3), and

[Pb{HCTA}(H2O)2].H2O (4). Alternative reaction conditions leading to discrete and polymeric Pb(II) species of H4BTC, H4CBTC and H3CTA at the binary and ternary level are currently being


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investigated. Compounds 1-4 are insoluble in water and stable in the crystalline form in air at room temperature. Description of crystallographic structures. The molecular structure of compound 1 reveals a 3D coordination polymer. Compound 1 crystallizes in the monoclinic space group P21/n. The asymmetric unit contains one Pb(II) metal ion, one phen 2–

molecule, two crystallographically independent [H2BTC]

ligand ions, each of which resides on an

inversion center located in the middle of C(22)-C(22'') ('' = -x, 1-y, 2-z) and C(32)-C(32*) (* = -x, -y, 1z) bonds, respectively, and three water molecules (one coordinated and two lattice). Therefore, the repeating unit is [Pb{H2BTC}(phen)(H2O)]. Pb(II) is bound to five carboxylato oxygen atoms from three different [H2BTC]2– ligands, one oxygen atom from the water molecule and two nitrogen atoms from the phen molecule. As a result, the coordination number around Pb(II) is eight (Figure 1A) (Table 2). 2–

One of the two [H2BTC]

ligands, adopts the µ4-[H2BTC]

2–

(Scheme 2) coordination mode and its two

deprotonated carboxylato units are asymmetrically bound to two Pb(II) ions (Pb and Pb* Figure 1A, (*): -x, -y, 1-z) in trans arrangement [Pb-O(31)(=Pb*-O(31*))=2.799(3) and Pb-O(32)(=Pb*O(32*))=2.658(3) Å]. The two terminal neutral carboxylate groups of µ4-[H2BTC]2– bind the other two Pb(II) (Pb*** and Pb!, Figure 1A, (***): 0.5-x, -0.5+y, 1.5-z; (!): -0.5+x, 0.5-y, -0.5+z) ions also in trans arrangement, in a monodentate fashion [Pb-O(33')(=Pb!-O(33*)=Pb(***)-O(33)=2.999(3) Å, Figure 1A]. 2–

This particular coordination mode of the µ4-[H2BTC]

coordinated ligand results in the formation of

metallocyclic rings, which can be described as a 2D (4,4) network extending parallel to the (101) plane (Figure 1B). The second [H2BTC]2– ligand (defined by O(21), O(22) oxygen atoms), adopts the µ2[H2BTC]2– coordination mode (Scheme 2) and utilizes only its two central deprotonated carboxylato units in trans arrangement to asymmetrically bind two Pb(II) ions (Pb and Pb″, Figure 1A, (″): -x, 1-y, 2-z) in a bidentate fashion [Pb-O(21)(=Pb″-O(21)″)=2.649(3) and Pb-O(22)(=Pb″-O(22)″)=2.573(3) Å]. The terminal neutral carboxylate groups (defined by O23, O24 oxygen atoms) are pointing away from the coordination sphere of the metal ions and form hydrogen bonds with the coordinated water molecule O(2W) (Table 6) and O(32) oxygen atom of a neighboring molecule µ2-[H2BTC] 2–

These µ2-[H2BTC]

2–

ligand.

ligands contribute to the assembly of the 3D architecture of the structure of 1 by

linking neighboring 2D (4,4) networks through the Pb-O(21) and Pb-O(22) bonds from one end of the ligand and through the centrosymmetrically related other end of the ligand (indicated by O(21″) and O(22″) oxygen atoms in Figure 1A). In Figure 1C, a top view of a small part of the 3D framework of 1 2–

is presented, i.e. two layers with the ligands of the first of the two µ4-[H2BTC]

belonging to the bottom

one being in turquoise color and those of the same ligand belonging to the top one in red color. These 2–

two layers are linked through the µ2-[H2BTC]

ligand, which is bright green in color. A side view of the

same part of the structure along [101] direction is shown in Figure 1D, where channels running parallel to this direction are clearly seen and filled with lattice water molecules (O(1W) and O(3W)) interacting with hydrogen bonds with each other and with the lattice (Table 6). The presence of these channels classifies this structure in the category of MOFs. The molecular lattice structure of compound 2 reveals a 3D coordination polymer.

Compound 2

crystallizes in the triclinic space group Pī, with the asymmetric unit containing two Pb(II) metal ions and one [CBTC]4– ligand; therefore, the repeating unit is [Pb2{CBTC}]. Pb(1) is bound to eight



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carboxylato oxygen atoms from five different [CBTC]4– ligands (Figure 2A). Pb(2) also exhibits a coordination number eight, formulated by carboxylato oxygen atoms from four different [CBTC]4– 4–

ligands (Figure 2B) (Table 3). Each [CBTC] 2

2

2

ligand binds nine Pb(II) metal ions, five Pb(1) and four

2

Pb(2), thus exhibiting a µ9-κ Ο:κ Ο':κ Ο'':κ Ο''':κ2O'''':κ2O''''':κ2O'''''':κ2O''''''':κ2Ο'''''''' coordination mode 4–

(Scheme 2, Figure 2A). Each one of the four carboxylato moieties of [CBTC] 2

binds four Pb(II) ions in

2

the chelate-bis(monoatomic) bridging mode (µ3-κ O:κ O') (Figure 2A). In addition, each carboxylato oxygen is also coordinated in an asymmetric fashion bridging two neighboring Pb(II) ions. Pb-O distances are in the range 2.445(4)-3.029(5) Å and through these bonds a 3D architecture is built in 2. In the 3D polymeric crystal lattice of compound 2 there exist three different types of dinuclear units containing a Pb2O2 core, which is very common in Pb(II)-O compounds. Two of those cores are defined by atoms Pb(2)-O(2)-Pb(1)-O(4) and Pb(1)-O(7)-Pb(1)-O(7), and create a repeating unit of three corner-sharing Pb2O2 cores through a center of symmetry in the middle of Pb(1)-O(7)-Pb(1)O(7). These three Pb2O2 repeating units are linked through both of their ends to a pair of a third type of Pb2O2 core defined by atoms Pb(2)-O(3)-O(3)-Pb(2), thereby forming a Z-type unit consisting of five Pb2O2 units. In Figure 2C, the bonds within the Z-type units are highlighted in red. The closest Pb···Pb interatomic distances within the Pb2O2 cores are Pb(2)···Pb(1) = 4.469 Å, Pb(1)···Pb(1) = 4.080 Å and Pb(2)···Pb(2) = 4.092 Å. Further bridging of Pb(1) and Pb(2) atoms forming the Z-type units, with those of neighboring ones, through monoatomic bridges O(1), O(5) and O(6) (indicated in blue in Figure 2C) result in the formation of a 2D network (Figure 2C). Figure 2D shows the 2D layer which extents parallel to the (101) plane in polyhedral presentation. Polyhedra around Pb(1) and Pb(2) atoms are indicated in pink and plum colors, respectively, and the Z-type units actually indicate the paths along which the Pb polyhedra are linked through edge sharing. The polyhedra forming each Z unit are linked with the polyhedra of neighboring Z-units by sharing corners (monoatomic bridges indicated in blue in Figure 2C). Figure 2E presents a side view of the arrangement of layers, which are stacked along the [101] direction, forming a 3D polymeric structure and rendering clear the double role played by the [CBTC]

4–

ligand, i.e. bridging Pb(II) ions resulting in a layer structure and bridging

neighboring layers resulting in a 3D coordination polymer. The molecular lattice of compound 3 reveals a 2D layer structure based on π-π interactions and a layer of lattice water molecules. The asymmetric unit consists of three clusters formed by four Pb(II) ions coordinated by four water molecules, eight phen molecules and two [CBTC]4– ligands each, and 70.3 lattice water molecules forming layers. 3.3 of the lattice water molecules partially occupy 7 different positions. Each of the clusters has the formula [Pb4(phen)8(CBTC)2(H2O)4]. Pb(1) and Pb(3) ions from the first cluster, Pb(5) and Pb(7) from the second one, and Pb(9) and Pb(11) from the third 4–

one are seven-coordinate, and bound to one carboxylato oxygen atom from one [CBTC]

ligand, two

oxygen atoms from two different water molecules and four nitrogen atoms from two different phen molecules. Pb(2) and Pb(4) from the first unit, Pb6 and Pb8 from the second one, and Pb(10) and Pb(12) ions from the third cluster are eight coordinate and bound to two pairs of carboxylato oxygen atoms from two different [CBTC]4– ligands, and four nitrogen atoms from two different phen molecules (Figure 3A, Table 4).

4–

The [CBTC]

ligands coordinated to the Pb(II) ions all have the same

2

coordination mode µ3-κO:κO':κO'':κ O''' (Scheme 2) in all three clusters.


The closest PbPb

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interatomic distances bridged through carboxylato oxygen atoms of the [CBTC]4– ligand are in the range of 4.0-4.5 Å and those through the µ3-κO:κO':κO'':κ2O''' ligand are in the range of 6.6-7.35 Å. This particular coordination of the two [CBTC]

4–

ligands in each of the three symmetry-independent

tetranuclear Pb(II) clusters results in the formation of three eighteen member metallocyclic rings. Only two of the carboxylate ends of all [CBTC]

4–

ligands are coordinated to Pb(II) ions, with the other two

ends extending above and below the metallocyclic rings and interacting through hydrogen bonds with lattice water molecules. The phen molecules coordinated to Pb(II) ions from the long side (those approximately 7 Å apart) of the cluster interact through π-π contacts with the corresponding phen molecules of neighboring clusters, forming chains along the b axis. Phen molecules from neighboring clusters and chains coordinated to Pb(II) ions lying on the short side (those approximately 4 Å apart) of the cluster interact through π-π contacts, resulting in a 2D layer parallel to the (100) crystallographic plane (Figure 3B). The planes of phen molecules contributing to chain formation are almost parallel o

with interplanar angles in the range 0.7-6.2 , interplanar distances in the range 3.341-3.656 Å and centroid-centroid distances in the range 4.119-4.671 Å.

The phen molecules contributing to the

interchain π-π interactions also have almost parallel planes with interplanar angles in the range 0.8o

2.5 , interplanar distances in the range 3.341-3.458 Å and centroid-centroid distances in the range 3.819-4.215 Å. As has already been mentioned in the experimental part, the hydrogen atoms of lattice water molecules have not been located and as the distances among them are in the range 2.58-3.11 Å, they are likely to interact through hydrogen bonds and form stripes extending parallel to the c axis (Figure 3C). The water molecules forming these stripes also interact with carboxylate oxygens not 4–

bonded to Pb(II) ions of the coordinated [CBTC]

ligands, thus resulting in a 2D network of oxygen

atoms interacting through hydrogen bonds. The so derived network lies between the layers formed by the clusters (Figure 3D). The molecular lattice of compound 4 reveals a 2D coordination polymer. Compound 4 crystallizes in the monoclinic space group C2/c and the asymmetric unit contains one Pb(II) ion, one [HCTA]2– ligand, two coordinated water molecules and two partial occupancy lattice water molecules. The repeating unit of the 2D coordination polymer consists of [Pb{HCTA}(H2O)2] (4).

Each Pb(II) ion, is eight-

coordinate and bound to six carboxylato oxygen atoms from four [HCTA]2– ligands and two water 2–

molecules (Figure 4A, Table 5). The [HCTA]

ligand is doubly deprotonated and binds to four Pb(II) 2

2

metal ions through two carboxylato groups adopting a µ4-κ O:κ O':κO'':κO''' mode (Scheme 2). The two bridging carboxylato groups are asymmetrically coordinated to two Pb(II) ions in the chelate monoatomic bridge mode, with Pb-O bond distances in the range 2.500(4)-2.823(4) Å, with the third one not being coordinated to any Pb(II) ion (Figure 4A). As a result of the coordination modes of [HCTA]2– ligands, one type of Pb2O2 unit is observed and defined by atoms Pb-O(1)-Pb-O(1) with Pb···Pb interatomic distance 4.250 Å (Figure 4B). The Pb2O2 units are linked through O(4)-Pb-O(4) units and form Pb6O6 rings, which define the 2D inorganic skeleton of the structure. The closest Pb···Pb interatomic distance through the O(4) bridge is 5.121 Å. Figure 4C shows the polyhedral representation of the structure of layers in compound 4. The [HCTA]

2–

ligands are oriented above and

below the 2D inorganic skeleton, which extends parallel to the bc crystallographic plane (Figures 4BD). The layers of 4 are further linked through hydrogen bonding interactions between the protonated



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carboxylato oxygen of [HCTA]2– ligand O(6) and the carboxylato oxygen O(3) of a neighboring ligand in the same layer [O(6)···O(3) = 2.692 Å (1-x, y, 1.5-z), H(6O)···O(3) = 1.874Å, O(6)-H(6O)···O(3) = o

164.0 ] (Table 6) and result in a supramolecular 3D structure of 4 (Figure 4D). The coordinated and lattice water molecules, which reside in channels formed between the layers and parallel to the c axis, also participate in hydrogen bonds and contribute to the formation of the 3D lattice structure (Table 6). The Pb-O bond distances in 1-4 are quite similar and analogous to those observed in other previously reported materials (Table 7).46-49,56-64 NMR spectroscopy. The

13

C spectrum of 1 exhibits two resonances at 36.6 ppm and 47.7 ppm, which are assigned to the

–CH and –CH2 groups of the [H2BTC]2– ligand, and another two resonances at 176.4 and 184.4 ppm for the [H2BTC]

2–

–

–COO carbons bound to the Pb(II) ion.

In addition, there are several signals

between 126.2 and 153.6 ppm stemming from the phen molecule in the coordination sphere of Pb(II) 4–

(Figure 5). The spectrum of 2 exhibits a resonance at 47.6 ppm for the –CH groups of the [CBTC] –

ligand and resonances at 181.3 and 184.2 ppm indicative of the presence of the –COO carbon of the [CBTC]4– ligand bound to the Pb(II) ion (Figure 6). The spectrum of 3 exhibits one resonance at 45.6 4–

ppm projecting the presence of –CH groups of the [CBTC] –

for the –COO carbon of the [CBTC]

4–

ligand and one resonance at 183.2 ppm

bound to the Pb(II) ion. The resonances appearing between

125.1 and 151.0 ppm are due to carbon atoms of the phen molecule in the coordination sphere of Pb(II) (Figure 7). The spectrum of 4 exhibits two sets of resonances between 32.4 to 28.3 ppm and 40.5 to 49.1 ppm due to the –CH and –CH2 groups of the [HCTA]2– ligand. Furthermore, there are two 2–

resonances at 178 ppm and 187 ppm, for the [HCTA]

–

–COO carbon bound to the Pb(II) ion (Figure

8). All of the resonances lie at lower fields in contrast to the free ligands. The signal assignments are consistent with the structural composition of all compounds investigated and have been confirmed by X-ray crystallography. 207

Pb MAS NMR spectra could only be successfully recorded in the case of compounds 2 and 4

(efforts in the case of compound 1 and 3 did not succeed, most likely because of the long spin-lattice relaxation times when nitrogen coordinating atoms are involved. The

207

Pb nucleus has a spin of 1/2,

a property previously used to gain insight into the structural identification of Pb(II) compounds.65-69 The spectra of 2 and 4 are shown in Figure 9 and 10, respectively. Included is also the quality of the fit obtained through the program dmfit.

70

The identity of the isotropic signal was confirmed by running

experiments with variable spinning frequencies in the case of 2 and from line shape analysis for 4. The spectrum of 2 exhibits isotropic signals at –2051 and -1672 ppm (Figure 9), whereas the spectrum of 4 exhibits an isotropic signal at –2412 ppm (Figure 10). The number of isotropic signals is in congruence with the observed crystal structure. The anisotropy parameters ∆σ of -67 kHz (η=0.40) and -43 kHz (η=0.33) for 2 and ∆σ of 87 kHz (η=0.84) for 4 indicate the symmetry of the surroundings of the lead center. The

207

Pb chemical (isotropic and anisotropic) shifts are very sensitive to the

electronic structure of Pb(II), with the coordination number and symmetry likely not being the only contributors to the observed chemical shifts. Further in depth perusal of the issue requires DFT calculations, beyond the scope of the current manuscript.


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Thermal studies.

The thermal decomposition of all compounds was studied by TGA under an

atmosphere of oxygen. Compound [Pb(H2BTC)(phen)(H2O)]n.2nH2O (1) is thermally stable up to 158 o

C (Figure 11A). From that point on, there are contiguous process steps between 158 and 499 °C for

1, involving decomposition of the organic part in line with the tentatively proposed reactivity depicted below:

[Pb(C8H8O8)(C12H8N2)(H2O)]n . 2nH2O

+

20.5n O2

n PbO + 20n CO2

+

n N2 +

11n H2O

Compound [Pb2(CBTC)]n (2) is thermally stable up to 338 °C (Figure 11B). From that point on, there is one consecutive process step between 338 and 496 °C for 2, involving decomposition of the organic part, in line with the tentatively proposed reactivity shown below:

[Pb2(C8H4O8)]n

+

6n O2 2n PbO + 8n CO2

Compound [Pb4(phen)8(CBTC)2(H2O)4]3

.

+

2n H2O

70.3H2O (3) is thermally stable up to 174°C (Figure 11C).

From that point on, there are three consecutive steps between 174 and 462°C for 3, involving the decomposition of the organic part of the compound and loss of water molecules in question. No clear plateaus are reached in these stages, suggesting that the derived products are unstable and decompose further.

[Pb4(C12H8N2)8(C8H4O8)2(H2O)4]3.70.3H2O

+

12 PbO + 336 CO2

372 O2 +

24 N2

+

190.3 H2O

Compound [Pb(HCTA)(H2O)2]n.nH2O (4) is thermally stable up to 398 °C (Figure 11D). From that point on, there is one process step between 398 and 490 °C for 4, involving decomposition of the organic part, in line with the following tentative reactivity profile depicted below:

[Pb(C9H10O6)(H2O)2]n . nH2O

+

9n O2

n PbO + 9n CO2

+

8n H2O

Mass loss calculations are in line with the final decomposition product being PbO for all compounds 14. Decomposition is complete at 499 oC for 1, at 496 °C for 2, at 462 °C for 3 and 490 °C for 4. Luminescence. Functional metal–organic frameworks based on d10 metal ion configuration have been reported, with notable photoluminescence properties and some potential applications.

71-73

The

solid-state photoluminescence spectrums of 1-4 and H4BTC, H4CBTC, H3CTA ligands have been studied at room temperature (Figure 12). The results at hand suggest that free H4BTC does not possess any luminescence at room temperature. In the case of the free H4CBTC ligand, the main



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emission bands emerge at 450 nm and 469 nm (λex 300 nm), which could be attributed to the π*― n transitions. For H3CTA the results show that, the main emission band emerges at 570 nm (λex 360 nm), which could be attributed to the π*― n transitions. The strongest emission band for the free phen ligand appears at 417 nm (λex 368 nm) and could attributed to the π*― π transitions. When the aforementioned ligands are bound to Pb(II) in the herein studied materials, the emission spectrum of 1 shows a band at 446 nm (λex = 340 nm). It was also observed that a strong emission occurred at 467 nm (λex = 315 nm) for compound 2, with 3 showing two strong features at 417 nm and 444 nm (λex = 370 nm). The observed features in 2 and 3 could be assigned to ligand-to-metalcharge-transfer (LMCT) processes.74,75 These observations suggest that coordination polymers 2 and 3 could be considered as potential fluorescent porous materials. In the case of 4, two strong emission bands were also observed at 474 nm and 494 nm (λex = 305 nm), blue shifted compared to the free ligand. The blue shifted emission band could be assigned to ligand-to-metal-charge-transfer (LMCT) processes compared to the free ligand. The fact that the free ligands (H4BTC) do not possess any luminescence at room temperature suggests that compounds 1 could be considered as a potential fluorescent porous material. Discussion Diversity in Pb(II) chemical reactivity with acyclic and cyclic substrates. The nature of organic carboxylic acids and their incipient properties a) play a significant role in the chemical reactivity of Pb(II), and b) influence profusely the nature and physicochemical profile of arising coordination polymeric networks. In this regard, the present work focused on the chemical reactivity of binary and ternary systems of Pb(II) with congener acyclic and cyclic (poly)carboxylic acids as organic substrate carriers further enriching the potential interactions of distinctly different ligands inside the system through incorporation of N,N-aromatic metal ionic chelator binder phen. In all cases, perusal of the requisite systems took place under optimally selected hydrothermal conditions.

In a structurally-

correlated ligand-associated synthetic strategy, the initial attempts were made with the acyclic H4BTC acid and its cyclic H4CBTC acid variant. pH-specific synthetic investigation of the ternary system of Pb(II) with H4BTC in the presence of phen led to the isolation of a new coordination polymer [[Pb{H2BTC)}(phen)(H2O)]n.2nH2O (1).

Further switching to cyclic derivative acids, the synthetic

investigation of the binary system Pb(II)-H4CBTC led to a binary coordination polymer [Pb2{CBTC}]n (2) followed by an extension of the observed chemical reactivity into the ternary system encompassing phen, with the latter leading to the coordination polymer [Pb4(phen)8(CBTC)2(H2O)4]3 . 70.3H2O (3), all exhibiting unique lattice features. Finally, expansion of the cyclic ring from the cyclobutane to cyclo hexane with concomitant reduction of the carboxylic acid moieties from 4 to 3 led to the H3CTA acid. Its chemical reactivity with Pb(II) in the requisite aqueous binary system led to the isolation of the .

coordination polymer [Pb{HCTA)}(H2O)2]n nH2O (4) . In the case of the acyclic acid-containing coordination polymer 1, the Pb(II) ion center in the repeating unit is bound to a variably formulated O,N-ligand environment earmarked by chelators and further characterized by a water molecule. The presence of the water molecule in the coordination sphere of the Pb(II) atom appears to be very important as it can easily be exchanged for (O-, N-, S-)-containing


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ligand. Such a prospect presents an additional opportunities in enriching and/or even extending the coordination sphere and geometry of the Pb(II) center. Structural diversity in supramolecular architectures The structural differentiation of lattices between compounds 2 and 3 is a result of the presence of a) the distinctly configured ligand acting as a chelator, and b) the aromatic chelator phen ligand coordinated to Pb(II) in a bidentate fashion. In coordination polymer 2, there are two different Pb(II) ions coordinated to eight carboxylato oxygen atoms each, albeit in Pb(1) the oxygen anchors belong 4–

to five [CBTC]

ligands and in Pb(2) originate from four such ligands.

In 3, there are three

tetranuclear molecules linked through π-π interactions to form a supramolecular layer. In each molecule, the four different Pb(II) ions present two different coordination numbers. Pb(1)/Pb(3), Pb(5)/Pb(7) and Pb(9)/Pb(11) from the three tetranuclear molecules are seven coordinate, whereas Pb(2)/Pb(4), Pb(6)/Pb(8) and Pb(10)/Pb(12) are eight coordinate with the coordination sites being occupied by O,N anchors of the [CBTC]

4–

and phen ligands; two coordination sites in the seven 4–

coordinate Pb(II) ions are occupied by two water molecules. It is worth noting that the [CBTC]

ligand

is fully deprotonated, as in 1, but the coordination mode is different (Scheme 2), with the most interesting feature being that in only two of the four carboxylates the oxygen atoms participate in the coordination sphere of Pb(II) ions. In the chemical reactivity of the binary system Pb(II)-H3CTA leading to the binary species .

[Pb{HCTA}(H2O)2]n nH2O (4), the Pb(II) center is eight coordinate, with the coordination sites being occupied only by O anchors of the [HCTA]2– ligand and by two water molecules. Pb(II) coordination number and geometry. Literature reports cite that the coordination geometry of the PbOn polyhedra in Pb(II) materials can be described as hemidirected for low coordination numbers (2–5), holodirected for high coordination numbers (9,10), with either a hemidirected or holodirected stereochemistry observed for intermediate coordination numbers (6–8).

76,77

It has been found through

ab initio molecular orbital calculations on Pb(II) complexes in the gas-phase that a hemidirected geometry reflects hard ligands, the ligand coordination number is low and attractive interactions emerge between the ligands.

78,79

To this end, in 1, the eight-coordinate Pb(II) centers exhibit a

hemidirected geometry. The eight coordinate Pb(1) and Pb(2) centers in 2 exhibit a holodirected geometry.

For the seven coordinate Pb(1)/Pb(3), Pb(5)/Pb(7) and Pb(9)/Pb(11) centers in 3, a

hemidirected geometry is observed, with the eight-coordinate Pb(2)/Pb(4), Pb(6)/Pb(8) and Pb(10)/Pb(12) centers in 3 exhibiting a holodirected geometry. Finally the eight coordinate Pb(II) centers in 4, exhibit a holodirected geometry. In light of the aforementioned assignments on the coordination geometry of the title materials, the X-ray crystal structures of the investigated metalloassemblies concur with the analytical and physicochemical data (FT-IR and solid state NMR) on all four cases. To this end, useful information is extracted from the NMR of the compounds in the solid state, with the MAS NMR spectra projecting the specific coordination geometry of the investigated centers in the corresponding lattice architectures. earmarking specific regions in the five up to ten.

49,80,81,82,83

Past reports had revealed various patterns,

207

Pb spectrum reflecting Pb(II) coordination numbers ranging from

In the present work, the emerging

207

Pb data are in line with coordination

numbers six and seven (2) and six (4), thereby signifying the importance of that nucleus to the



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detection of lattice-specific structural properties of Pb(II)-containing hybrid inorganic–organic materials. Work in this direction is currently ongoing in our labs. Lattice dimensionality From ‘aliphatic’-H4BTC ligand to ‘cyclo’-H4CBTC in the presence of phen In the present work, three different ligands were used for the synthesis and isolation of four new complexes. Two of the ligands have a similar structure, with the first one being an aliphatic butanetetracarboxylic acid and the other one a cyclo-butene-tetracarboxylic acid. The presence of phen influences profusely the nature of the produced coordination polymers. The ternary system Pb(II)-H4BTC-phen containing the acyclic tetracarboxylic acid is linked to a coordination polymer [Pb{H2BTC}(phen)(H2O)]n.2nH2O (1), whereas the ternary system Pb(II)H4CBTC-phen containing the cyclic congener is associated with a non-polymeric molecular species [Pb4(phen)8(CBTC)2(H2O)4]3 . 70.3H2O (3) forming supramolecular network through π-π interactions. In the case of 1, the H4BTC ligand is doubly deprotonated and the ratio between the Pb(II) ion and the ligand is 1:1 whereas in complex 3 the H4CBTC ligand is fully deprotonated and the ratio between the Pb(II) ion and the ligand is 2:1. The repeating unit in 1 contains one Pb(II) ion, one [H2BTC]2– ligand, one phen molecule and one water molecule. In 3, the repeating unit contains four Pb(II) ions, two [CBTC]4– ligands, eight phen molecules, and four water molecules. In 1, the H4BTC ligand is doubly deprotonated and coordinated to the Pb(II) ions through all carboxylato oxygens, whereas in 3 the H4CBTC ligand is fully deprotonated and coordinated only through two carboxylato groups. In both compounds there are water molecules in the coordination sphere of the Pb(II) ions that can easily be replaced by other ligands and lead to different structures. Undoubtedly, the acyclic vs. cyclic aliphatic nature of the organic tetracarboxylic acid ligand plays a significant role in the chemical reactivity toward Pb(II), which is further influenced by the aromatic chelator phen, with its hydrophobicity, bulk structure and thermodynamically driven bidentate chelation potential supporting the uniquely defined architecture of the arising hybrid crystalline polymeric assemblies. The eight coordinate Pb(II) centers in 1 participate in the formation of 2D networks linked so as to give rise to an overall 3D framework. From the binary Pb(II)-H4CBTC system to the ternary Pb(II)-H4CBTC-phen system Incorporation of the phen ligand in the reaction mixture of Pb(II) and the cyclic aliphatic organic acid reveals the actual contribution of that aromatic chelator in the formulation of the nature of the emerging product, turning the binary polymeric 2 into the non-polymeric yet molecularly discrete species 3. Surprisingly, the [CBTC]4- ligand in 2 is coordinated to the Pb(II) ions through all of the available carboxylato groups attached to the cyclic core, whereas in complex 3 the same fully deprotonated ligand employs only two of its available carboxylato groups to pursue binding to Pb(II) ion centers. Of paramount uniqueness to the structure of 3 is a) the thee tetranuclear Pb(II) units comprising the molecular assembly, and b) the extremely high number of lattice water molecules in the lattice architecture, collectively formulating a distinct identity to the emerging ternary species. In both compounds the H4CBTC ligand is fully deprotonated and the ratio between the Pb(II) ion and the ligand is 2:1. As a result, metallocyclic rings and channels arise in the lattice of 2 thereby promoting formation of unique Z-type units composed of Pb2O2 cores through the formed network. Consequently, a 3D framework emerges that constitutes the molecular imprint of 2. In the crystal


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lattice in 3, on the other hand, interactions between adjacent phen rings through π-π contacts further supplemented by hydrogen bonds lead to the formation of a 2D framework.

Ostensibly, upon

maintenance of the organic ligand in its full deprotonation state, the incorporation of phen aromatic chelators in binary 2 induces significant variations in the structural architecture of the 3D framework, ultimately reducing the lattice dimensionality in 3 to 2, even in the presence of π-π interactions and hydrogen bonds. From cyclo-butene-tetracarboxylic to cyclo-hexane-tricarboxylic cyclic Pb(II)-binders Structural modification of the cyclic ligand by a) increasing the number of carbon atoms, and b) reducing the number of carboxylic acid moieties presents a convincing case of influence of the ligand on the nature of the derived crystalline product. Given the binary nature of the materials derived (2 and 4), distinct similarities and differences arise that give emphasis to the contribution of the nature of the ligand to the nature of the crystalline structure: a) both 2 and 4 are polymeric in nature, b) .

[Pb2{CBTC}]n (2) and [Pb{HCTA}(H2O)2]n nH2O (4) contain the respective ligands in variably deprotonated forms, i.e. fully deprotonated [CBTC]

4–

2–

and doubly deprotonated [HCTA] , c) the ratio of

metal to ligand is 2:1 (2) and 1:1 (4), quite distinct in the two cases of materials, d) 2 is binary, whereas 4 is characterized by the presence of the water molecules bound to Pb(II) in the repeating unit of the polymer and lattice water molecules. In contrast to complex 2, where the fully deprotonated [CBTC]4– ligand employs all four available carboxylate groups to promote binding to Pb(II), in the doubly deprotonated [HCTA]

2–

of 4 the

protonated group is not coordinated to the Pb(II) ions. Therefore, in view of the increase of the size in the cyclic ligand (from 4 to 6) and concurrent reduction in the number of carboxylic acid moieties from 4 to 3, the architecture of 4 reveals an initial formation of a 2D polymeric structure emerging by way of Pb2O2 units forming Pb6O6 rings, eventually giving rise to a 3D supramolecular network through hydrogen bonding interactions. Finally, in both 2 and 4 crystalline polymeric materials, the distinct nature of the ligands promoting Pb(II) binding in connection with the specific interactions characterizing the emerging assemblies give rise to lattices with an ultimate 3D dimensionality. Collectively, the results point to the following: a) all crystalline polymeric materials (1,2,4) exhibit 3D framework networks, with the non-polymeric yet large cluster of 3 exhibiting a 2D lattice dimensionality. b) In all cases, the open aliphatic and cyclic four and six-membered ring ligands bearing three to four carboxylic acid moieties support the emergence of 2D-3D lattice dimensionality architectures at both binary and ternary systems incorporating the aromatic chelator phen. c) Significant roles in the formulation of the conditions under which high dimensionality lattice architectures are supported are supported by π-π interactions, when ternary systems involve phen incorporation, hydrogen bonds, and Pb2O2-based cores formulating Z-type (2) and Pb6O6 ring motifs (4) in the presence and absence of lattice water molecules, respectively. Luminescence vs structural architecture The photoluminescence properties of 1-4 could be classified in categories reflecting a) acyclic and cyclic substrates, and b) binary and ternary systems of variable lattice dimensionality. At the binary vs ternary level, 1 is comprised of a 3D structural architecture involving Pb(II):acyclic [H2BTC]2-:phen with 4-

a ratio 1:1:1, whereas 3 provides a 2D structural architecture containing Pb(II):cylic [CBTC] :phen with



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a ratio of 2:1:4. Compound 3 shows higher intensity excitation and emission features than 1, a) consistent with the presence of the cyclic ligand in the distinctly differentiated structure, and b) profusely affected by the variably distinct presence of phen. Both 1 and 3 are red-shifted compared to the phen aromatic chelator ligand alone. In the systems containing the same ligand as a common 4-

factor, 2 is a binary species with a structural architecture bearing Pb(II):cylic [CBTC] with a ratio of 2:1 and 3D lattice dimensionality, whereas 3 is a 2D ternary material. Along with the change from binary to ternary, lattice dimensionality also changes, concurrently projecting in both materials intense features that could be assigned to ligand-to-metal-charge-transfer (LMCT) processes. Ostensibly, therefore, introduction of the acyclic ligand in a Pb(II) lattice, results in luminescence, thereby signifying the importance of coordination in bringing out metal organic framework electronic signatures. On the other hand, cyclization of the initially employed H4BTC ligand a) retains the ternary character of the arisen materials albeit through assembly of commensurably higher Pb(II):ligand:phen ratios (from 1 to 3), b) lowers lattice dimensionality from 3D to 2D, and c) red-shifts the electronic features observed compared to the free aromatic chelator. For the same cyclic ligand (in 2 and 3), the transition from the binary to the ternary species is associated with a) a reduction in lattice dimensionality from 3D to 2D, and b) luminescence features (λem) blue-shifted compared to the free ligand yet red-shifted compared to the aromatic chelator. Increasing the size of the cyclic substrate from four to six, while concomitantly reducing the number of carboxylic acid moieties by one and symmetrically locating them around the ring, affords 4, a binary structure bearing an architecture containing Pb(II):[HCTC]2- with a ratio of 1:1 and a supramolecular 3D lattice dimensionality not unlike that in the corresponding material 2. Both 2 and 4 show intense emission bands that could be assigned to ligand-to-metal-charge-transfer (LMCT) processes. In both cases, the observed bands are blue-shifted compared to the free ligands. Consequently, under the structural constraints of the employed ligands, retention of the binary nature of the arisen polymeric metal organic framework materials is associated with a) retention in the Pb(II):ligand ratio in the arisen structure despite the structural differentiation imposed by the ligands, b) retention in lattice dimensionality, and c) intense LMCT electronic features (λem) variably shifted compared to the corresponding free ligands. Collectively, the electronic signature of 1-4 reflect quite well their structural architecture, lattice dimensionality, and binary-ternary nature of their assembly, with the emerging correlations based on ligand nature formulating cross-relationships useful in their global profile as metal organic framework materials. More in-depth work a) delving into the contribution of factors, such as hydrogen bonds, π-π interactions, to the design and assembly of MOFs bearing distinct electronic signatures, and b) combined with synthetic tuning of structural parameters involved in the assembly of distinct architecture and lattice dimensionality MOFs, is expected to provide further insight into such correlations. Such work is currently ongoing in our labs. Conclusions pH-Specific hydrothermal synthetic reactivity of H4BTC, H4CBTC and H3CTA acids with Pb(II) salts afforded new metal-organic framework species 1-4. Compound 1 is a 3D coordination polymer of a ternary Pb(II)-H4BTC-phen composition. The binary material 2 is a 3D coordination polymer of the


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binary system of Pb(II) and H4CBTC revealing the emergence of Z-type units composed of Pb2O2 cores, with 3 consisting of tetranuclear molecular entities of the ternary system Pb(II)-H4CBTC-phen. In the latter system, the organic ligand phen is introduced in the lattice, thereby turning a 2D layered architecture supported by π-π and H-bond interactions in the presence of a large number of water molecules. Compound 4 is a 2D coordination polymer of the binary system of Pb(II)-H3CTA with Pb6O6 units arising from Pb2O2 cores, eventually switching to a 3D supramolecular structure due to the presence of hydrogen bonds. The gradual transformation of the organic ligands from open chain aliphatic tetracarboxylic acids to closed cyclic carboxylic acid-containing rings of variable size (initially four ultimately reduced to three, with a concomitant change of the carried carboxylic moieties) signifies the contribution of the nature and associated chemical properties of the organic substrates in influencing Pb(II) chemical reactivity, and dictating the assembly of polymeric or non-polymeric crystalline materials, in the presence and absence of large hydrophobic and aromatic chelator phen. In a so developing reactivity at the binary and ternary level, a) unusual structural motifs (channel and Ztype), b) the presence of unusually high number of lattice water molecules, and c) π-π interactions (due to phen incorporation) and H-bonding interactions, contribute to the emergence of high 2D-3D lattice architectures, essentially accounting for the individual and collective influence of the aforementioned factors leading to extensive structural networks. The collective structural profiles of the arisen materials are intimately linked with their physicochemical properties, thereby providing essential correlations to a) their molecular imprint and b) photoluminescence activity. The analysis and subsequent identification of the factors influencing Pb(II) chemical reactivity formulate a significant strategy toward the design and synthesis of MOF materials linked to optical applications relying on structural-spectrochemical correlations. Acknowledgments: Financial support “ΙΚΥ Fellowships of Excellence for Postgraduate studies in Greece – Siemens Program" is gratefully acknowledged. We thank the DFG (German Research Foundation) and the Experimental Physics Institutes of the Leipzig University for support with the Avance 750 MHz NMR spectrometer. Supporting Information Description: X-ray crystal crystallographic files, in CIF format, (CCDC 1405495 (1), 1405496 (2), 1405497 (3), and 1405498 (4)), and listings of positional and thermal parameters and H-bond distances and angles for 1-4. The material is available free of charge via Internet at http://pubs.acs.org. References [1]

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Page 24 of 48 24

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Table

1:

Summary

of

Crystal,

[Pb{H2BTC}(phen)(H2O)]n.2nH2O

Intensity

Collection

(1), [Pb2{CBTC}]n (2),

and

Refinement

Data

[Pb4(phen)8(CBTC)2(H2O)4]3.70.3H2O

for

(3) and

.

[Pb{HCTA}(H2O)2]n nH2O (4). 1

2

3

4

C20H22N2O11 Pb

C8H4O8Pb2

C336H380.6N48O130.3Pb12

C9H16O9Pb

formula weight

673.59

642.49

9662.57

475.41

T, K

180(2)

293(2)

180(2)

180(2)

MoKα 0.71073

MoKα 0.71073

CuKα 1.54178

CuKα 1.54178

Monoclinic

Triclinic

Monoclinic

monoclinic

P21/n

Pī

Pn

C2/c

a (Ǻ)

12.8713(3)

7.9520(2)

24.6700(4)

22.1353(3)

b (Ǻ)

13.7355(4)

8.1662(2)

43.4593(8)

13.7831(2)

c (Ǻ)

12.8720(4)

8.7137(2)

17.0949(3)

8.7343(1)

α, deg

90

72.380(1)

90

90

β, deg

105.091(1)

66.270(1)

97.165(1)

92.025(1)

γ, deg

90

73.574(1)

90

90

2197.21(11)

485.23(2)

18185.0(5)

2663.11(6)

4

2

2

8

2.036

4.397

1.765

2.371

7.744

34.686

11.394

25.040

formula

wavelength, λ (Ǻ) space group

3

V, (Ǻ ) Z -3

Dcalcd (Mg m ) -1

abs.coeff. (µ), mm

R = 0.0238

R indices (1)

(1)

Rw = 0.0432

Rw = 0.0528

R = 0.0544

(2)

Rw = 0.1380

R values are based on F values, Rw values are based on F2.

R=

∑F −F ∑(F ) o

c

o

(2)

R =0.0217

(2)

,

Rw =

∑ [w( F

2 o

− Fc2 ) 2

]

∑ [w( F ) ] 2 2 o

[(1): 3578, (2): 2114, (3): 54590, and (4): 1961 reflections with I>2σ(I)]


(2)

R =0.0380 Rw = 0.0831

(2)

Page 25 of 48


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Table 2: Selected bond lengths [Å] and angles [deg] for [Pb{H2BTC}(phen)(H2O)]n .2nH2O (1) Distances (Å) Pb-N(2)

2.520(3)

Pb-O(32)

2.657(3)

Pb-N(1)

2.526(3)

Pb-O(31)

2.799(3)

Pb-O(22)

2.572(3)

Pb-O(2w)

2.923(4)

Pb-O(21)

2.648(3)

Pb-O(33')

2.999(3)

o

Angles ( ) N(2)-Pb-N(1)

66.16(11)

O(22)-Pb-O(21)

49.91(8)

N(2)-Pb-O(22)

76.66(9)

N(2)-Pb-O(32)

72.44(9)

N(1)-Pb-O(22)

83.40(9)

N(1)-Pb-O(32)

77.24(9)

N(2)-Pb-O(21)

77.97(9)

O(22)-Pb-O(32)

148.13(8)

N(1)-Pb-O(21)

126.83(10)

O(21)-Pb-O(32)

127.98(8)

N(1)-Pb-O(31)

77.53(8)

N(2)-Pb-O(31)

115.00(9)

N(1)-Pb-O(2w)

134.27(10)

N(2)-Pb-O(2w)

78.59(10)

N(1)-Pb-O(33')

74.63(9)

N(2)-Pb-O(33')

132.57(10)

O(21)-Pb-O(31)

155.47(8)

O(22)-Pb-O(31)

150.15(8)

O(21)-Pb-O(2w)

68.27(9)

O(22)-Pb-O(2w)

116.61(10)

O(21)-Pb-O(33')

107.61(8)

O(22)-Pb-O(33')

73.27(8)

O(31)-Pb-O(32)

47.35(8)

O(32)-Pb-O(2w)

64.61(10)

O(31)-Pb-O(2w)

93.04(10)

O(32)-Pb-O(33')

124.00(8)

O(31)-Pb-O(33')

79.60(7)

O(2w)-Pb-O(33')

148.23(9)

Symmetry operations: (') 0.5-x, 0.5+y, 1.5-z



Page 26 of 48 26

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Table 3: Selected bond lengths [Å] and angles [deg] for [Pb2{CBTC}]n (2). Distances (Å) Pb(1)-O(7')

2.445(4)

Pb(2)-O(3*)

2.450(4)

Pb(1)-O(2')

2.485(6)

Pb(2)-O(3**)

2.510(4)

Pb(1)-O(6'')

2.544(4)

Pb(2)-O(5***)

2.548(5)

Pb(1)-O(1)

2.582(4)

Pb(2)-O(2)

2.661(4)

Pb(1)-O(7''')

2.614(6)

Pb(2)-O(8***)

2.714(7)

Pb(1)-O(4'''')

2.831(4)

Pb(2)-O(4**)

2.768(7)

Pb(1)-O(8''')

2.972(9)

Pb(2)-O(1)

2.873(5)

Pb(1)-O(5'')

3.029(5)

O(1)-Pb(1)-O(2')

79.5(2)

O(1)-Pb(2)-O(2)

46.9(1)

O(1)-Pb(1)-O(7')

74.4(2)

O(1)-Pb(2)-O(3*)

76.6(2)

O(1)-Pb(1)-O(6'')

149.1(1)

O(1)-Pb(2)-O(3**)

132.1(2)

O(1)-Pb(1)-O(5'')

144.9(1)

O(1)-Pb(2)-O(4**)

111.1(2)

O(1)-Pb(1)-O(7''')

94.1(1)

O(1)-Pb(2)-O(5***)

123.5(2)

O(1)-Pb(1)-O(8''')

85.6(2)

O(1)-Pb(2)-O(8***)

138.7(2)

O(1)-Pb(1)-O(4'''')

99.9(1)

O(1)-Pb(2)-O(6*)

62.0(2)

O(2')-Pb(1)-O(7')

83.6(2)

O(2)-Pb(2)-O(3*)

74.0(1)

O(2')-Pb(1)-O(6'')

99.6(2)

O(2)-Pb(2)-O(3**)

91.2(1)

O(2')-Pb(1)-O(5'')

65.3(1)

O(2)-Pb(2)-O(4**)

66.1(1)

O(2')-Pb(1)-O(7''')

156.1(2)

O(2)-Pb(2)-O(5***)

147.1(1)

O(2')-Pb(1)-O(8''')

153.7(2)

O(2)-Pb(2)-O(8***)

129.1(2)

O(2')-Pb(1)-O(4'''') O(7')-Pb(1)-O(6'')

67.4(1)

108.7(1)

74.8(2)

O(2)-Pb(2)-O(6*) O(3*)-Pb(2)-O(3**)

68.8(1)

O(7')-Pb(1)-O(5'')

100.1(2)

O(3*)-Pb(2)-O(4**)

101.7(1)

O(7')-Pb(1)-O(7''')

72.5(2)

O(3*)-Pb(2)-O(5***)

73.1(1)

O(7')-Pb(1)-O(8''')

113.2(2)

O(3*)-Pb(2)-O(8***)

144.5(2)

O(7')-Pb(1)-O(4'''')

150.9(2)

O(3*)-Pb(2)-O(6*)

87.2(1)

O(6'')-Pb(1)-O(5'')

45.6(1)

O(3**)-Pb(2)-O(4**)

49.0(2)

O(6'')-Pb(1)-O(7''')

74.2(1)

O(3**)-Pb(2)-O(5***)

76.8(1)

O(6'')-Pb(1)-O(8''')

104.2(2)

O(3**)-Pb(2)-O(8***)

82.7(2)

O(6'')-Pb(1)-O(4'''')

108.2(1)

O(3**)-Pb(2)-O(6*)

143.5(1)

O(5'')-Pb(1)-O(7''')

117.8(1)

O(4**)-Pb(2)-O(5***)

121.0(1)

O(5'')-Pb(1)-O(8''')

126.7(2)

O(4**)-Pb(2)-O(8***)

72.4(2)

O(5'')-Pb(1)-O(4'''')

67.8(1)

O(4**)-Pb(2)-O(6*)

167.4(2)

O(7''')-Pb(1)-O(8''')

45.8(2)

O(5***)-Pb(2)-O(8***)

80.2(2)

O(7''')-Pb(1)-O(4'''')

136.5(1)

O(5***)-Pb(2)-O(6*)

69.9(1)

O(8''')-Pb(1)-O(4'''')

94.3(2)

O(8***)-Pb(2)-O(6*)

105.4(2)

Pb(2)-O(6*) Angles (o)


3.008(7)

Page 27 of 48


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Symmetry operations: (') 1-x, 1-y, -z; ('') x, -1+y, 1+z; (''') x, -1+y, z; ('''') –x, 1-y, -z; (*) 1-x, 1-y, -1-z; (**) 1+x, y, z; (***) 1+x, -1+y, z.



Page 28 of 48 28

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Table 4: Selected bond lengths [Å] and angles [deg] for [Pb4(phen)8(CBTC)2(H2O)4]3 . 70.3H2O (3). Distances (Å) Pb(1)-OW

2.634(5), 2.792(7)

Pb(2)-Ocarboxylato

2.540(5)-2.689(5)

Pb(1)-Ocarboxylato

2.658(5)

Pb(2)-Nphen

2.661(7)-2.809(9)

Pb(1)-Nphen

2.561(7)-2.809(7)

Pb(3)-OW

2.631(5), 2.759(7)

Pb(4)-Ocarboxylato

2.540(5)-2.733(5)

Pb(3)-Ocarboxylato

2.700(5)

Pb(4)-Nphen

2.686(7)-2.817(7)

Pb(3)-Nphen

2.552(8)-2.778(7)

Pb(5)-OW

2.653(5), 2.742(17)

Pb(6)-Ocarboxylato

2.465(6)-2.699(5)

Pb(5)-Ocarboxylato

2.573(5)

Pb(6)-Nphen

2.694(9)-2.771(8)

Pb(5)-Nphen

2.461(8)-2.742(7)

Pb(7)-OW

2.669(5), 2.758(7)

Pb(8)-Ocarboxylato

2.505(7)-2.718(5)

Pb(7)-Ocarboxylato

2.652(5)

Pb(8)-Nphen

2.681(9)-2.761(8)

Pb(7)-Nphen

2.533(8)-2.720(6)

Pb(9)-OW

2.674(5), 2.708(7)

Pb(10)-Ocarboxylato

2.494(5)-2.691(5)

Pb(9)-Ocarboxylato

2.684(5)

Pb(10)-Nphen

2.671(7)-2.820(8)

Pb(9)-Nphen

2.597(8)-2.770(7)

Pb(11)-OW

2.629(7), 2.2.854(7)

Pb(12)-Ocarboxylato

2.583(5)-2.711(5)

Pb(11)-Ocarboxylato

2.639(5)

Pb(12)-Nphen

2.671(9)-2.751(8)

Pb(11)-Nphen

2.488(8)-2.735(7) o

Angles ( ) Nphen-Pb(1)-Nphen

61.2(2), 64.5(2)

Nphen-Pb(2)-Nphen

59.0(2), 61.6(2)

Oaqua-Pb(1)-Oaqua

84.7(2)

Ocarboxylato-Pb(2)-Ocarboxylato

48.9(2), 49.9(2)

Ocarboxylato-Pb(1)-Nphen

72.5(2)-152.9(2)

Nphen-Pb(2)-Ocarboxylato

80.7(2)-161.6(2)

Ocarboxylato-Pb(1)-Oaqua

80.7(2), 114.6(2)

Nphen-Pb(3)-Nphen

60.4(2), 62.8(2)

Nphen-Pb(4)-Nphen

58.5(2), 62.8(2)

Oaqua-Pb(3)-Oaqua

87.7(2)


48.1(2), 50.5(2)


73.5(2)-155.1(2)


80.6(2)-159.1(2)


82.4(2), 110.3(2)

Nphen-Pb(5)-Nphen

61.5(2), 65.5(2)

Nphen-Pb(6)-Nphen

59.9(2), 60.8(2)

Oaqua-Pb(5)-Oaqua

83.7(5)


48.4(2), 50.2(2)


73.5(2)-148.8(2)


75.5(2)-166.7(2)


80.2(2), 118.5(4)

Nphen-Pb(7)-Nphen

61.0(2), 64.4(2)

Nphen-Pb(8)-Nphen

60.7(2), 61.2(2)

Oaqua-Pb(7)-Oaqua

85.3(2)


48.9(2), 50.6(2)


73.7(2)-150.8(2)


75.9(2)-161.3(2)


81.1(2), 114.5(2)

Nphen-Pb(9)-Nphen

63.2(2), 63.8(2)

Nphen-Pb(10)-Nphen

59.5(2), 60.7(2)

Oaqua-Pb(9)-Oaqua

83.9(2)


49.1(2), 50.8(2)


71.3(2)-155.6(2)


82.5(2)-159.8(2)


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83.5(2), 107.9(2)

Nphen-Pb(11)-Nphen

60.1(2), 64.1(2)

Nphen-Pb(12)-Nphen

60.4(2), 62.8(2)

Oaqua-Pb(11)-Oaqua

79.5(2)


48.9(2), 49.7(2)


73.3(2)-151.9(2)


76.1(2)-155.7(2)


81.3(2), 114.7(2)

Symmetry operations: (') x, y, z; ('') x+1/2, -y, z+1/2



Page 30 of 48 30

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Table 5: Selected bond lengths [Å] and angles [deg] for [Pb{HCTA}(H2O)2]n.nH2O (4). Distances (Å) Pb-Ο(1)

2.500(4)

Pb-Ο(3''')

2.605(5)

Pb-Ο(1w)

2.556(6)

Pb-Ο(2w)

2.748(4)

Pb-O(1ʹ)

2.587(4)

Pb-O(4'')

2.759(4)

Pb-O(2)

2.599(6)

Pb-O(4''') o Angles ( )

2.823(4)

O(1)-Pb-O(1w)

75.7(2)

O(1')-Pb-O(3''')

70.5(1)

O(1)-Pb-O(1')

66.7(1)

O(1')-Pb-O(2w)

154.5(1)

O(1)-Pb-O(2)

50.4(1)

O(1')-Pb-O(4'')

86.0(1)

O(1)-Pb-O(3''')

84.3(2)

O(1')-Pb-O(4''')

118.0(1)

O(1)-Pb-O(2w)

114.0(1)

O(2)-Pb-O(3''')

88.6(2)

O(1)-Pb-O(4'')

147.6(1)

O(2)-Pb-O(2w)

77.6(1)

O(1)-Pb-O(4''')

104.5(1)

O(2)-Pb-O(4'')

158.2(1)

O(1w)-Pb-O(1')

77.5(2)

O(2)-Pb-O(4''')

71.1(1)

O(1w)-Pb-O(2)

98.1(2)

O(3''')-Pb-O(2w)

134.6(1)

O(1w)-Pb-O(3''')

147.0(2)

O(3''')-Pb-O(4'')

103.4(1)

O(1w)-Pb-O(2w)

78.2(2)

O(3''')-Pb-O(4''')

47.5(1)

O(1w)-Pb-O(4'')

81.8(1)

O(2w)-Pb-O(4'')

83.1(1)

O(1w)-Pb-O(4''')

163.7(2)

O(2w)-Pb-O(4''')

87.1(1)

O(1')-Pb-O(2)

115.4(1)

O(4'')-Pb-O(4''')

103.5(1)

Symmetry operations: (') 0.5-x, 0.5-y, -z; ('') 0.5-x, -0.5+y, 0.5-z; (''') 0.5-x, 0.5-y, 1-z.


Page 31 of 48


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Table 6. Hydrogen bonds in 1-4. Interaction

D···A (Å)

H···A (Å)

D-H···A (o)

Symmetry operation

1 O(23)-H(23O)···O(32)

2.526

1.746

169.7

0.5+x, 0.5-y, 0.5+z

O(34)-H(34O)···O(w1)

2.626

1.976

175.1

x, y, z

O(w1)-H(w1A)···O(21)

2.732

2.096

165.7

-x, -y, 2-z

O(w1)-H(w1B)···O(w3)

2.680

1.745

168.7

x, y, z

O(w2)-H(w2B)···O(24)

2.813

2.034

164.3

-0.5+x, 0.5-y, -0.5+z

O(w3)-H(w3A)···O(31)

2.673

1.890

162.0

0.5-x, -0.5+y, 1.5-z

O(w3)-H(w3B)···O(22)

2.729

1.746

173.4

x, -1+y, z

4 O(6)-H(6O)···O(3)

2.692

1.874

164.0

1-x, y, 1.5-z

O(1w)-H(1wA)···O(3)

2.898

2.003

176.3

x, y, -1+z

O(2w)-H(2wA)···O(1w)

2.813

2.255

121.0

x, -y, 0.5+z

O(2w)-H(2wB)···O(4w)

2.830

2.316

117.3

x, y, z



Page 32 of 48 32

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Table 7: Pb-O (Ǻ) bond distances in Pb(II)-ligand compounds

Pb --- O (Ǻ)

Compound .

Reference

[Pb(H2BTC)(phen)(H2O)]n 2nH2O (1)

2.572(3)-2.999(3)

This work

[Pb2(CBTC)]n (2)

2.445(4)-3.029(5), 2.450(4)-3.008(7)

This work

[Pb4(phen)8(CBTC)2(H2O)4]3 70.3H2O (3)

2.465(6)-2.733(5)

This work

. Pb(HCTA)(H2O)2]n nH2O

2.500(4)-2.823(4)

This work

{[Pb2(BTC)(H2O)2] (H2O)2}n

2.354(9)-2.459(9)

56

{[Pb(BTC)0.5H2O]H2O}n

2.367(4)-2.581(4)

57

{[Pb(BTCA)0.5]}n

2.447(13)-2.74(2)

57

Pb4(oda)3(NO3)2 H2O

2.464(13)-2.890(13)

58

[Pb(oda)(H2O)]

2.490(3)-2.91(2)

59

[Pb(phen)(suc)]n

2.646(5)-2.882(7)

49

.

(4)

.

.

.

[Pb3(phen)3(glu)3]n 7nH2O

2.515(6)-3.006(6), 2.547(6)-3.215(5), 2.496(6)-3.166(5)

49

[Pb3(tca)2]n

2.363(6)-2.899(7), 2.379(6)-3.091(7)

49

. [Pb2(phen)2(tcaH)2]n nH2O

2.337(5)-3.151(5)

49

[Pb2(phen)4(fum)](NO3)2

2.538 (3)-2.624(3)

46

. [Pb2(phen)4(CO3)(fum)]n 6nH2O

2.451(5)-2.872(7)

46

[Pb2(phen)(fum)2]n

2.439(3)-2.853(3)

46

[Pb(phen)(fum)]n 2nH2O

2.454(5)-2.656(5)

46

[Pb(phen)(Heida)]4H2O

2.454(6)-2.699(6)

47

[Pb3(NO3)(Dpot)]n

2.379(6)-2.880(6)

47

[Pb3(oda)3]n

2.494(5)-2.818(1), 2.551(6)-2.862(5)

48

[Pb(phen)(oda)]n

2.635(4)-2.747(6)

48

[Pb(tda)]n

2.404(8)-2.841(7)

48

[Pb(phen)(tda)]n

2.313(2)-2.785(3)

48

2.483(8)-2.586(8)

60

{[Pb2(fum)2(H2O)4] 2H2O}n

2.517(5)-2.858(5)

61

[Pb(fum)]n

2.399(5)-2.811(5)

61

[Pb(suc)]

2.44(1)-2.91(1)

62

Pb2(phen)4(suc)(NO3)2

2.490(3)-2.638(3)

63

[Pb(citr)]n

2.397(7)-2.847(1)

64

.

[Pb(nic)(fum)0.5] .


Page 33 of 48


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FIGURE CAPTIONS

Figure 1:

(A) Partially labeled plot showing the coordination environment around Pb in 1 (inset: the coordination polyhedron around the Pb ion). Symmetry operations: ('): 0.5-x, 0.5+y, 1.5-z; (''): -x, 1-y, 2-z; (*): -x, -y, 1-z; (**): 0.5+x, 0.5-y, 0.5+z; (***): 0.5-x, -0.5+y, 1.5-z; (!): -0.5+x, 2–

0.5-y,-0.5+z. (B) A small part of the 2D (4,4) structure of 1 through µ4-[H2BTC]

ligands.

Color code: Pb: magenta; O, red; N, blue; C, grey. (C) A top view of a small part of the overall 3D structure of 1 built through µ4-[H2BTC]2– and µ2-[H2BTC]2– ligands. The ligands at the bottom layer are in turquoise color (µ4-[H2BTC] 2–

top layer are colored red (µ4-[H2BTC]

2–

coordination mode), those at the

coordination mode) and the bridging ligands of the

two layers are in light green color (µ2-[H2BTC]2– coordination mode). Phen molecules are colored blue and the polyhedrons belonging to the bottom layer are shown in light pink color. (D) A side view of the characteristic MOF architecture of material 1 along the [101] direction showing the channels and the lattice water molecules (colored orange) residing in them. Hydrogen bonds between channel lattice molecules are indicated with dashed orange lines, with the rest of the color code being as in Figure 1C. Figure 2:

Partially labeled plot of the coordination environment around Pb(1), binding mode of 4–

[CBTC]

(A) and Pb(2) (B) in 2 (inset: the coordination polyhedron around each Pb(II)

ion). Symmetry operations: ('): 1-x, 1-y, -z; (''): x, -1+y, 1+z; ('''): x, -1+y, z; (''''): -x, 1-y, -z; (*): 1-x, 1-y, -1-z; (**): 1+x, y, z; (***): 1+x,-1+y, z; (!): x,1+y, z; (!!): -1+x, 1+y, z; (!!!): x, 1+y, -1+z; (#): -1+x, y, z. (C) A small fragment of the 2D structure of 2 due to five member Pb2O2 Z-shaped repeating units. The two oxygen links are shown in red and the single oxygen one with blue lines. (D) Polyhedral presentation of the layer structure of compound 2 (see text for details). (E) A small part of the overall 3D structure showing layer characteristic structure of compound 2 (See text for details) Figure 3:

(A) The three tetranuclear clusters showing the coordination environment around the Pb(II) ions in 3. (B) Plot of the 2D network extending parallel to the bc plane, formed through π-π interactions of phen molecules coordinated to Pb(II) forming the tetranuclear clusters. Dark green dashed lines indicate the intra-chain π-π and the light green indicate the corresponding inter-chain interactions. (C) Plot of the stripes formed by the lattice water molecules through hydrogen bond interactions. The orange thick lines indicate hydrogen bond interaction formed among lattice water molecules and the dark red lines indicate hydrogen bond interactions among the non-coordinated carboxylate oxygen 4–

atoms of [CBTC]

ligands from the layer of clusters lying above (light blue) and below

(dark blue) the stripes of lattice water molecules. (D) Side view of the arrangement of layers of clusters and stripes formed by lattice water molecules as seen along c-axis. Figure 4:

(A) Partially labeled plot showing the coordination environment around the Pb ion and the binding mode of [HCTA]2– ligand in 4 (inset: the coordination polyhedron around the metal ion). Symmetry operations: ('): 0.5-x, 0.5-y, -z; (''): 0.5-x, -0.5+y, 0.5-z; ('''): 0.5-x, 0.5-y, 1-



Page 34 of 48 34

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z; (*): 0.5-x, 0.5+y, 0.5-z. (B) A small part of the 2D structure of 4. (C) Polyhedral presentation of the layer structure of 4. Color code: Pb, magenta; O, red; C, grey. (D) A small part of the supramolecular 3D structure of 4 due to intermolecular hydrogen bonding interactions (orange dashed lines) between neighboring layers. Atoms in red, in the middle of the channels, are lattice water molecules, Figure 5:

13

Figure 6:

13

Figure 7:

13

Figure 8:

13

Figure 9:

207

Figure 10:

207

C CPMAS NMR spectrum of 1. C CPMAS-NMR spectrum of 2. C CPMAS-NMR spectrum of 3. C CPMAS-NMR spectrum of 4. Pb MAS NMR spectrum of 2 (blue) and simulated spectrum (red) in the solid state. The

individual fit for the two sites is also included. Pb MAS NMR spectrum of 4 (blue) and simulated spectrum (red) in the solid state

Figure 11: TGA diagram of 1-4. Figure 12: Solid-state excitation-emission spectra of 1-4 at room temperature.


Page 35 of 48

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35



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Page 36 of 48

36


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37



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Page 38 of 48

38


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39



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1,10 phenanthroline

C=O

200

ppm

150

100

CH / CH2

50

0

Figure 5

CH

C=O

ppm

200

150

100

Figure 6


50

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1,10 phenanthroline

CH

C=O

ppm

200

150

100

50

0

Figure 7

CH – , CH2 –

C═ O

Figure 8



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Figure 9

Figure 10


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Figure 11



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Figure 12


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Scheme 2. The coordination modes of the [H2BTC]2–, [CBTC]4– and [HCTA]2– in 1-4.



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For Table of Contents Use Only Structural-spectrochemical correlations of variable dimensionality crystalline metal organic framework materials in hydrothermal reactivity patterns of binary-ternary systems of Pb(II) with (a)cyclic (poly)carboxylate and aromatic chelator ligands. Catherine Gabriel,a Angelos A. Vangelis,a Catherine P. Raptopoulou,b b

c

d

Aris Terzis,b Vassilis

a

Psycharis, Maria Zervou, Marko Bertmer, Athanasios Salifoglou *

Synopsis Hydrothermal pH-specific reactivity in Pb(II)-H4BTC/phen, Pb(II)-H4CBTC/phen and Pb(II)-H4CTA systems afforded crystalline hybrid-materials [Pb{H2BTC}(phen)(H2O)]n.2nH2O(1), [Pb2{CBTC}]n(2), [Pb4(phen)8(CBTC)2(H2O)4]3.70.3H2O(3), and [Pb{HCTA}(H2O)2]n.nH2O(4). All compounds are 2D-3D coordination polymers with unusual structural motifs and π-π/H-bond interactions contributing to distinct architecture/lattice-dimensionality.

Structural-spectrochemical correlations denote the

emerging luminescence activity, emphasizing aliphatic-cyclic (poly)carboxylic/aromatic chelator-ligand contributions to binary-ternary Pb(II) reactivity affording MOF supramolecular networks. Synopsis Figure


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A



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C

B

D

Figure 3 Environment ACS Paragon Plus

StructuralâSpectrochemical Correlations of Variable Dimensionality

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StructuralâSpectrochemical Correlations of Variable Dimensionality