Open MOFs with Unique Hexatopic Zinc-5,15-bis(4â²-carboxyphenyl

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Open MOFs with the unique hexatopic zinc-5,15-bis(4'carboxyphenyl)-10,20-bis(3',5'-dicarboxyphenyl)porphyrin linker Bharat Kumar Tripuramallu, SOUMYABRATA GOSWAMI, and Israel Goldberg Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.7b01171 • Publication Date (Web): 28 Nov 2017 Downloaded from http://pubs.acs.org on November 29, 2017

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Crystal Growth & Design

Open MOFs with the unique hexatopic zinc-5,15-bis(4'carboxyphenyl)-10,20-bis(3',5'-dicarboxyphenyl)porphyrin linker Bharat Kumar Tripuramallu,*1,2 Soumyabrata Goswami,1 Israel Goldberg*1 1

School of Chemistry, Sackler Faculty of Exact Sciences, Tel-Aviv University, Ramat-Aviv, 69978 Tel-Aviv, Israel; 2Chemistry Division, Department of Sciences and Humanities, Vignan Foundation for Science Technology and Research, Vadlamudi, Guntur 522213, Andhra Pradesh, India.

---------------------------------------------------------------------------------------------------------------ABSTRACT: Characteristic coordination modes of tetrapodal and octapodal porphyrin linkers were combined in the design of a new hexapodal porphyrin linker. The customdesigned [(5,15-bis(4-carboxyphenyl)-10,20-bis(3,5-dicarboxyphenyl)]porphyrin (H6HCPP) contains

two

trans-related

4-carboxyphenyl

coordination

sites

similar

to

tetra(carboxyphenyl)porphyrin (H4TCPP) linker and two other 3,5-dicarboxyphenyl (isopthalate-type) functions related to octa(carboxyphenyl)porphyrin (H8OCPP) moiety. Synthesis of the H6HCPP was optimized for higher yields by utilizing excess concentration of TFA. The supramolecular reactions of zinc metallated linker Zn-H6HCPP with different metal centers afforded open hexacarboxy-metalloporphyrin frameworks (hcMPFs) perforated by wide intra-lattice voids. A 6-connected uninodal and 6,6-connected binodal frameworks Mn-hcMPF (1), Co-hcMPF (2) and Zn-hcMPF (3)

were obtained by employing transition

metals Mn(II), Co(II) and Zn(II) as the exocyclic inter-porphyrin binding nodes. These frameworks feature a dinuclear Mn2 and Zn2 paddlewheels in 1 and 3, and trinuclear Co3 trigonal prisms in 2, as inorganic building units. Among p-block elements In(III) from the 13th group and Pb(II) from the 14th group of the periodic table form In-hcMPF (4) and PbhcMPF (5) frameworks tessellated by InNa2 and Pb2 clusters as building units. Similar reactions with rare earth elements yielded the formation of Ln-hcMPFs (Ln=Pr(III), Gd(III) and

Yb(III))

structures

(6-8)

stabilized

by

1D

{Ln(COO)5Na2(H2O)2(µ2-H2O)2}n

heterometallic helical chains with tetragonal shaped inter-porphyrin channel voids in 6 and 7, and homometallic dinuclear Yb2 cluster in 8. All the frameworks are non-interpenetrated and provide wide solvent accessible intra-lattice voids, which account for about 53-64% of the crystal volume. Thermal and powder diffraction analyses provided additional insights into the homogeneity and stability of these frameworks. ---------------------------------------------------------------------------------------------------------------1 ACS Paragon Plus Environment

Crystal Growth & Design 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

INTRODUCTION Metal-metalloporphyrin frameworks (MMPFs) belong to a class of highly tunable porous materials, being considered as promising candidates for applications in the fields of light harvesting and catalysis.1-4 A vast number of MMPFs fabricated for catalytic transformations were inspired from the functions performed by the porphyrin ring of chlorophyll molecules in natural processes, like photosynthesis and biological catalytic reactions.5-6 Owing to the presence of quadrangular coordination arms, the porphyrin building blocks can form versatile open coordination architectures when reacted with metal ion connectors.7-9 Porphyrin macrocycles can be easily tuned at the meso- and β-positions to introduce different coordination groups on the periphery of the porphyrin backbones. A major part of research of such materials have focused on symmetrically functionalized (A4) porphyrin building units with various coordinating arms (e.g., carboxylates, tetrazoles, imidazoles, pyrazoles, pyridine and phosphonates).10-15 Yet, only limited examples of MMPFs based on A2B2 porphyrin building blocks are available in the literature. Synthetic difficulties aroused in the preparation of A2B2-type porphyrin molecules and crystallization of the corresponding metal-organic frameworks, which may account for the scarcity of the latter. The available examples include porphyrin moieties that bear 4'-pyridine or 4'-imidazole substituents at 5,15-positions, and non-coordinating groups as 4'-cyanophenyl, 4'-iodophenyl, and pentaflourophenyl at the 10,20-positions.17-18 Such entities have been used as linear pillaring linkers. In a similar way, materials based on A2B2-porphyrin building units with trans-related carboxyl coordinating groups have been reported.18-20 In all these cases the porphyrins have two potentially active coordination A-sites (at 5,15 meso-positions) and two coordination-inert B-sites (at 10,20positions). Coordination networking of such porphyrin linkers is oftentimes associated with the formation of open-architecture materials of potential utility in the fields of catalysis, light harvesting and ultrafast energy migrations. 21 In the present article we report on the efficient synthesis of A2B2 tetraarylporphyrins with coordinating groups placed on all four meso-substituted arms (a natural expansion of earlierstudied concepts) and of their MMPFs. To this end, we have synthesized the [(5,15-bis(4'carboxyphenyl)-10,20-bis(3',5'-dicarboxyphenyl)]porphyrin (H6HCPP) ligand that is a kind of a linker in which the coordination characteristics are similar to the well-known tetra(4carboxy)phenylporphyrin (H4TCPP) and the tetra(3,5-dicarboxy)phenyl porphyrin (H8OCPP) linkers. The preparation of the H6HCPP followed the principles of our previously reported scalable synthesis of A2B2-type porphyrins (carefully controlling the concentration of TFA).22 2 ACS Paragon Plus Environment

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Formulation of single-crystalline MMPFs with Zn-H6HCPP is elusive due to the multiple coordination ability of this ligand. Their successful synthesis was achieved following our recently reported ameliorated methodology, i.e the use of NaOH as modulator in the reaction mixture.23-24 As a result, single-crystalline MMPFs based on the HCPP linker (named as hcMPFs) with different metal connectors from p, d and f blocks of the periodic table. Here we report on the synthesis and crystal structures of Mn-hcMPF (1), Co-hcMPF(2) and ZnhcMPF(3) from transition metals, In-hcMPF (4), Pb-hcMPF(5) from p-block elements and finally Ln-hcMPFs (Ln=Pr (6), Gd (7), Yb (8)) with rare earth elements. These structures possess the characteristic connectivity’s of both tetrapodal and octapodal linkers. Paddlewheel and trigonal prismatic SBUs (Secondary Building Units) feature in the Mn/ZnhcMPFs and Co-hcMPFs respectively, simple trimer and dimer SBUs (InNa2 and Pb2) feature in In-hcMPF and Pb-hcMPF, whereas infinite 1D helical rod dominate in Ln-hcMPFs. All the reported hcMPFs are thermally stable and characterized by open coordination-polymeric architectures with intra-lattice voids (occupied either partly or fully by crystallization solvent) accounting for more than 50% of the crystal volume.

Experimental Section (a) Materials and methods: Unless otherwise specified all the chemicals were received as analytical grade reagents and used

without

further

purification.

4-carboxydipyrromethane

and

dicarboethoxydipyrromethane were prepared according to the literature procedure.

3,520,25

All

reactions requiring anhydrous conditions were conducted under an atmosphere of argon in oven-dried glassware in dry solvents. Thin layer chromatography (TLC) was performed on silica gel plates Merck 60 F254. Flash column chromatography was carried out using alumina. (b) Synthesis (Scheme 1): (1) Synthesis of 5,15-Bis(4′-carbomethoxyphenyl)-10,20-bis(3′5′-biscarboethoxyphenyl) porphyrin In a typical procedure a solution of aldehyde (1.0 mmol) and dipyrromethane (1.0 mmol) in 250.0 ml of DCM was degassed for 10 min. To this solution TFA (0.15 ml, 2.02 mmol for Route A and 3.825 ml, 48.0 mmol for Route B; Scheme 1) was slowly added, and the reaction vessel was shielded from sunlight by wrapping with aluminum foil. The mixture was stirred under room temperature for 1 hour, followed by addition of DDQ (0.507 g, 2.24 mmol) and continued stirring for another 1 hour. Aqueous saturated NaHCO3 was added to wash the organic phase and then was extracted by chloroform (3x50 mL), dried over Na2SO4 3 ACS Paragon Plus Environment


and concentrated under vacuum. Purification by column chromatography (Al2O3, 2% EtOAc in CHCl3) gave the desired trans-porphyrin in 8 % yield for Route A, and 20 % yield for Route B. 1H NMR (400 MHz, CDCl3) δ 9.16 (s, 2H, Ar-H), 9.06 (s, 4H, Ar-H), 8.84 (d, J = 4.2 Hz, 4H, β-pyrrole-H), 8.78 (d, J = 4.2 Hz, 4H, β-pyrrole-H), 8.47 (d, J = 8.3 Hz, 4H, ArH), 8.32 (d, J = 8.3 Hz, 4H), 4.51 (q, J=7.0 Hz, 8H, OEt) 4.12 (s, 6H, OCH3) 1.44 (t, J=7.1 Hz, 12H, OCH2CH3) -2.96 (s, 2H, N-H) 13C NMR (101 MHz, DMSO) δ 167.5, 166.8, 152.1, 149.2, 145.64, 138.1, 134.4, 132.1, 129.8, 127.5, 40.1, 29.2, λabs/nm (THF), (ε/105 M-1 cm-1 ): 412, 543, 582 HRMS-ESI calcd. for C60H51N4O12 [M+H]+:1019.3425; found: 1019.3503 ----------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------Scheme 1: Synthetic protocol implemented for obtaining the Zn-H6HCPP porphyrin linker.

Synthesis of 5,15-Bis(4′-carbomethoxyphenyl)-10,20-bis(3′5′-biscarboethoxyphenyl) porphyrinato zinc(II): Metallation of porphyrin esters was carried out by mixing the hexa-ester porphyrin (0.05 mmol) and Zn(OAc)2·2H2O (5.0 mmol) in 20.0 ml of DMF followed by reflux for 4 hours. To the resultant reaction mixture 30.0 ml of H2O was added and the organic phase was extracted thrice with CHCl3. The organic fractions were collected and were dried using Na2SO4 and the solvent was evaporated to obtain metallated porphyrin ester in quantitative yield. λabs/nm (THF), (ε/105 M-1 cm-1 ): 427, 558, 597

Synthesis of 5,15-Bis(4′-carboxyphenyl)-10,20-bis(3′5′-biscarboxyphenyl) porphyrinato zinc(II) (Zn-H6HCPP):

4 ACS Paragon Plus Environment

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The metallated porphyrin hexa-ester (0.05 mmol) was dissolved in THF-methanol (2:1) mixture followed by addition of powdered KOH (5.0 mmol) in 1.0 ml of H2O. The reaction mixture was refluxed overnight and the solvent was evaporated. The residue was dissolved in water, and 2N HCl was added slowly to bring the reaction mixture to acidic pH, which was accompanied by precipitation of the porphyrin. The precipitate was filtered, and washed several times with water and air dried to obtain Zn-H6HCPP in a quantitative yield. 1

H NMR (400 MHz, DMSO-d6) δ 9.07 (s, 2H, Ar-H), 9.02 (m, 4H, Ar-H), 8.97-8.91 (m, 8H,

β-pyrrole-H), 8.51 (d, J = 8.2 Hz, 4H, Ar-H), 8.46 (d, J = 8.3 Hz, 4H, Ar-H), 13C NMR (101 MHz, DMSO-d6) δ 166.8, 149.7, 145.6, 143.5, 137.4, 134.4, 131.9, 129.9, 127.0, 29.2 λabs/nm (THF), (ε/105 M-1 cm-1): 426, 516, 556, 596 λem/nm (THF): 656, 715; HRMS-ESI calcd. for C50H27N4O12Zn [M-H]¯: 940.0995; found: 939.0919.

(2) Synthesis of hcMPFs: (i) Synthesis of Mn-hcMPF (1): To the solution of Zn-H6HCPP (2.5 mg, 2.6 µmol) in 0.8 ml of DMF, a solution of Mn(NO3)2·xH2O (5.3 mg, 30 µmol) in 100.0 µL of 1.0 M HNO3 was added and stirred to obtain clear solution. The mixture was sealed in a screw cap vial, was heated at 90°C in a bath reactor for 3 days and cooled slowly to obtain block shaped crystals. The crystals were harvested by filtration, washed several times with DMF and air dried for further characterizations. (Yield 45% based on Mn). FT-IR (cm-1): 3412, 2954, 1668, 1610, 1595, 1571, 1555, 1434, 1333, 1112, 1050, 777, 634. (ii) Synthesis of Co-hcMPF (2): Compound 2 was obtained by the same procedure as that for the preparation of compound 1 except for using Co(NO3)3·6H2O (5.8 mg , 20.0 µmol) instead of Mn(NO3)2·xH2O. Dark red block shaped crystals suitable for X-ray diffraction were collected, washed with DMF and air-dried (Yield 35 % based on Co). FT-IR (cm-1): 3377, 2986 (m), 1667, 1645, 1578, 1403, 1384, 1316, 1097, 1064, 786, 661. (iii) Synthesis of Zn-hcMPF (3): The preparation of 3 was similar to that of 2, but using the metal salt Zn(NO3)3·6H2O (6.0 mg 20.0 µmol). Purple block crystals were harvested by filtration in 20.2 % yield. FTIR (cm-1): FTIR (cm-1): 3319, 2934, 1710, 1660, 1620, 1445, 1425, 1333, 1300, 1002, 950. (iv) Synthesis of In-hcMPF (4): A mixture of Zn-H6HCPP (2.5 mg, 2.6 µmol) in 300.0 µL DMF, and InNO3·6H2O (6.0 mg, 20.0 µmol) in 100.0 µL of 1M HNO3 was sealed in a screw cap vial and heated at 120°C in a bath reactor. After few hours, to the hot reaction mixture 275.0 µL of 1N NaOH was added and sonicated to obtain a purple coloured turbid 5 ACS Paragon Plus Environment


solution, which was then heated at same temperature for 7 days to obtain a block shaped crystals of In-hcMPF along with white powder. The crystals were separated by filtration, washed with DMF, acetone and water several times, and air dried for further characterizations Yield: ~25 %. FTIR (cm-1): 3425, 2960, 1685, 1625, 1520, 1444, 1370, 1322, 1265, 1050, 775, 650. (v) Synthesis of Pb-hcMPF (5): The preparation of 5 was similar to that of 4, but using the metal salt Pb(NO3)2 (6.6 mg 20.0 µmol). Red block crystals were harvested by filtration in ~22 % yield. FTIR (cm-1): 3418, 2850, 1645, 1605, 1555, 1420, 1350, 1303, 1249, 1045, 888, 674, 654. (vi) Synthesis of Ln-hcMPF Ln= Pr(6), Gd(7), Yb(8): All the Ln-hcMPFs were obtained according to the same synthetic procedure described above for 4, but Ln(NO3)3·xH2O (x=6 for Pr, Gd and x=5 for Yb) (20.0 µmol) was used instead of the In reagent. Purple coloured tetragonal crystals were isolated by filtration. Yield for Gd-hcMPF: ~22 %. FTIR (cm-1): 3400, 2927, 1650, 1607, 1538, 1415, 1373, 1251, 1204, 1097, 995, 933, 661. (c) Physical measurements: 1

H NMR (400 MHz) and

13

C NMR (100 MHz) spectra were recorded on Bruker-400

spectrometers, in DMSO-d6 with residual DMSO-d5 (1H, 2.50 ppm) or DMSO-d6 (13C, 39.52 ppm); or in CDCl3 or CDCl3/TFA 1:1 with residual CHCl3 (1H, 7.26 ppm) or CDCl3 (13C, 77.16 ppm) as an internal standard. Absorption spectra were recorded on Shimadzu UV-1650 PC spectrophotometer at room temperature in quartz cuvettes. Emission spectra were measured on Horiba Jobin Yvon FL3-11 spectrofluorometer at room temperature. Fouriertransform (FT)-IR spectra were recorded on a Bruker Tensor 27 system spectrophotometer in ATR mode. Powder X-ray diffraction data were recorded on Bruker D8 Advance diffractometer using CuKα radiation (λ = 1.54056 Å) over a 2θ range of 5-50° at a scan rate of 1° min-1. Thermogravimetric analyses were carried out on an STA 409 PC analyzer, and corresponding masses were analyzed by a QMS 403 C mass analyzer, under a flow of N2 gas with a heating rate of 5 °C min−1 in the temperature range of 40−600 °C Single crystal X-ray diffraction measurement: The X-ray measurements [Bruker-Apex Duo diffractometer, IµS micro-focus MoKα radiation] were carried out at ca. 110(2) K on crystals coated with a thin layer of amorphous oil. These structures were solved by direct and Fourier methods and refined by full-matrix least-squares (using standard crystallographic software (SHELXT-2014, SHELXL-2014).26-27 They were found to contain severely disordered crystallization solvent (usually an unknown combination of DMF and water), and 6 ACS Paragon Plus Environment

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occasionally also dissociation products of the DMF solvent (hydrolyzed in the solvothermal conditions of the supramolecular reactions) within the intra-lattice voids. The solvent content could not be reliably identified, and modeled by discrete atoms. Correspondingly, the contribution of the disordered solvent moieties was subtracted from the diffraction pattern by the SQUEEZE procedure and PLATON software.28 Due to the loose crystal packing in these compounds and the large amounts of disordered solvents contained therein they diffracted to low θ-angles only (for crystals of 2 significant data could be measured only to θ = 20°). In 13, 5 and 8 the five-coordinate Zn(H2O)-OCPP entity was found to exhibit twofold disorder, with the Zn(H2O) fragment displaced in a given unit either above or below the porphyrin macrocycle. The solvent accessible voids in all the structures are in the range of 53-64% of the crystal volume. The TOPOS software package was used to analyze the topological features of the available framework solids.29 Analysis of the coordination geometries around the metal centers was performed by using the SHAPE 2.1 program (details on the geometric analysis are described in ESI).30 The crystal data of the available structures are: (1) C50H26Mn2N4O13Zn (framework only) Mr = 1066.00, monoclinic, space group C2/c (No. 15), a = 40.6571(17), b = 9.5969(5), c = 30.057(2) Å, β =129.830(1), V = 9006.1(9) Å3, T = 110 K, Z = 4, µ(MoKα) = 0.58 mm-1, ρ(calcd) = 0.79 g·cm-3, 17063 reflections measured to θ = 25.07°, of which 7949 were unique (Rint = 0.030) and 5735 with I > 2σ(I). Final R1 = 0.081 (wR2 = 0.229) for the 5735 data above the intensity threshold, and R1 = 0.101 (wR2 = 0.243) for all unique data. Solvent accessible void space in the unit cell is 5568 Å3 (62% of the crystal volume with residual electron count of 1096 e). CCDC 1565825. (2) C50H28Co3N4O16Zn (framework only), Mr = 1182.92, orthorhombic, space group Pnma (No. 62), a = 29.131(2), b = 33.601(3), c = 9.8382(8) Å, V = 9629.9(13) Å3, T = 110 K, Z = 4, µ(MoKα) = 0.79 mm-1, ρ(calcd) = 0.81 g·cm-3, 21797 reflections measured to θ = 20.80°, of which 5126 were unique (Rint = 0.176) and 5126 with I > 2σ(I). Final R1 = 0.143 (wR2 = 0.333) for the 5126 data above the intensity threshold, and R1 = 0.214 (wR2 = 0.356) for all unique data. The intra-lattice void space accommodating the disordered solvent is 5759 Å3/unit-cell (64% of the crystal volume with residual electron count of 1201 e). CCDC 1565826. (3) C50H26N4O13Zn3 (framework only), Mr = 1086.86, monoclinic, space group C2/c (No. 15), a = 40.576(4), b = 9.3912(9), c = 29.635(3) Å, β =129.337(2), V = 8733.9(15) Å3, T = 110 K, Z = 4, µ(MoKα) = 0.85 mm-1, ρ(calcd) = 0.83 g·cm-3, 19720 reflections measured to θ = 23.64°, of which 6516 were unique (Rint = 0.054) and 4229 with I > 2σ(I). Final R1 = 7 ACS Paragon Plus Environment


0.094 (wR2 = 0.237) for the 4229 data above the intensity threshold, and R1 = 0.130 (wR2 = 0.260) for all unique data. The intra-lattice void space accommodating the disordered solvent is 5235 Å3/unit-cell (60% of the crystal volume with residual electron count of 1061 e). CCDC 1565827. (4): C50H26InN4Na2O15Zn (framework only) Mr = 1148.93, monoclinic, space group P21/c (No. 14), a = 15.8380(13), b = 16.5852(16), c=31.823(2) Å, β = 97.707(4) V = 8283.5(12) Å3, T = 110 K, Z = 4, µ(MoKα) = 0.62 mm-1, ρ(calcd) = 0.92 g·cm-3, 33054 reflections measured to θ = 23.29°, of which 11846 were unique (Rint = 0.068) and 6808 with I > 2σ(I). Final R1 = 0.098 (wR2 = 0.276) for the 6808 data above the intensity threshold, and R1 = 0.149 (wR2 = 0.319) for all unique data. The total solvent accessible void space in the unit cell is 4535 Å3 (approximately 55% of the crystal volume with residual electron count of 1102 e). CCDC 1565828. (5): C100H46N8O25Pb4Zn2 (framework only), Mr = 2718.95, monoclinic, space group P21 (No. 4), 15.6141(9), 17.0338(9), 16.3128(9) Å, β = 115.824(2) V = 3905.4(4) Å3, T = 110 K, Z = 1, µ(MoKα) = 4.65 mm-1, ρ(calcd) = 1.16 g·cm-3, 18312 reflections measured to θ = 25.24°, of which 12750 were unique (Rint = 0.029) and 11174 with I > 2σ(I). Final R1 = 0.040 (wR2 = 0.095) for the 11174 data above the intensity threshold, and R1 = 0.049 (wR2 = 0.099) for all unique data. The total solvent accessible void space in the unit cell is 2079 Å3 (53% of the crystal volume with residual electron count of 524 e). CCDC 1565829. (6): C50H31N4Na2O16PrZn (framework only) Mr = 1196.05, monoclinic, space group P21/c (No. 14), a = 16.4186(6), b = 16.9421(7), c = 31.7145(12) Å, β = 96.867(2), V = 8758.6(6) (1) Å3, T = 110 K, Z = 4, µ(MoKα) = 0.88 mm-1, ρ(calcd) = 0.91 g·cm-3, 71684 reflections measured to θ = 25.09°, of which 15392 were unique (Rint = 0.068) and 11241 with I > 2σ(I). Final R1 = 0.071 (wR2 = 0.193) for the 11241 data above the intensity threshold, and R1 = 0.092 (wR2 = 0.206) for all unique data. The solvent accessible void space in the unit cell is 4840 Å3 (55% of the crystal volume with residual electron count of 1378 e). CCDC 1565830. (7): C50H31GdN4Na2O16Zn (framework only) Mr = 1212.39, monoclinic, space group P21/c (No. 14), a = 16.2149(6), b = 16.8506(7), c = 31.8606(14) Å, β = 96.948(2) V = 8641.4(6) Å3, T = 110 K, Z = 4, µ(MoKa) = 1.09 mm-1, ρ(calcd) = 0.93 g·cm-3, 104181 reflections measured to θ = 25.16°, of which 15374 were unique (Rint = 0.037) and 13184 with I > 2σ(I). Final R1 = 0.064 (wR2 = 0.156) for the 13184 data above the intensity threshold, and R1 = 0.074 (wR2 = 0.163) for all unique data. The solvent accessible void space in the unit 8 ACS Paragon Plus Environment

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cell is 4631 Å3 (54% of the crystal volume with residual electron count of 1289 e). CCDC 1565831. (8): C50H28N4O16Yb2Zn (framework only) Mr = 1352.21, monoclinic, space group C2/c (No. 15) a = 31.729(2), b = 17.4765(11), c = 16.8361(11) Å, β = 110.431(1)°, V = 8748.4(10), T = 110 K, Z = 4, µ(MoKa) = 2.44 mm-1, ρ(calcd) = 1.03 g·cm-3, 29029 reflections measured to θ = 28.37°, of which 10929 were unique (Rint = 0.031) and 7955 with I > 2σ(I). Final R1 = 0.049 (wR2 = 0.124) for the 7955 data above the intensity threshold, and R1 = 0.077 (wR2 = 0.148) for all unique data. The solvent accessible void space in the unit cell is 5085 Å3 (58% of the crystal volume with residual electron count of 1232 e). CCDC 1565832.

Results and Discussion Synthesis Synthesis of the porphyrin linker Zn-H6HCPP was performed by acid catalyzed one pot reaction through McDonald 2+2 condensation of dipyrromethane and aldehyde. 32 The yield of the desired porphyrin was optimized by varying the concentration of the trifluoroacetic acid (TFA) (Scheme 1). When stiochiometric ratio of TFA (2.0 mmol for 1.0 mmol of reactants) was used in condensation of 4-carboxydipyrromethane and 3,5-dicarboethoxy benzaldehyde, a single product of the trans-porphyrin was obtained in 8-10% yield. By increasing the concentration of TFA (from 2.0 mmol to 48.0 mmol) the yield of the trans porphyrin increased to nearly 20 %, without any scrambling products. Similar effect of increasing the concentration of TFA was obtained for condensation of 3,5-dicarboethoxy dipyrromethane and 4-carboxybenzaldehyde (Table S1). The porphyrin ester was metallated with zinc acetate, followed by hydrolysis with KOH, to yield the desired Zn-H6HCPP porphyrin in quantitative yield. The crystalline metalloporphyrin frameworks (hcMPFs) with the Zn-H6HCPP linker and various exocyclic connectors were obtained through the NaOH-modulator synthetic approach. Multitopic porphyrin linkers tend to form rapidly amorphous precipitates, rather than single crystals, on reacting with metal sources. The use of excess NaOH solubilizes the precipitate, forming a mixture of metal hydroxides and porphyrin salts, which at a later stage undergoes an exchange reaction to yield the desired crystalline frameworks.23,24

By

employing this synthetic protocol we obtained sizeable crystals of the Ln-hcMPFs (Ln=Pr,



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Gd, Yb), as well as of the In-hcMPF and Pb-hcMPF. Similar procedure with light transition metals resulted in very low yields. This can be attributed to the reluctance of the corresponding metal hydroxides to exchange the hydroxyl ions from their stable coordination sphere with porphyrin linkers. Correspondingly, in the synthesis of Mn-hcMPF, Co-hcMPF and Zn-hcMPF the reactants were heated in presence of 1M HNO3 at 90°c to achieve sizeable crystallites (Scheme 2). The Infrared spectra of all the compounds are consistent with their single crystal structures. The bands arising from the coordinated and uncoordinated water molecules displays stretching frequencies in the range 3200 to 3400 cm-1 in all the compounds. The aromatic C-H stretching bands are obtained in the range 2900 to 3000 cm-1. The asymmetric and symmetric stretching frequencies of C-O bonds of carboxylate groups are observed in the region 1600 to 1700 cm-1. The aromatic stretching frequencies of porphyrin rings are observed in the region 1200 to 1600 cm-1 in all the compounds. ----------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------Scheme 2. Schematic representation of octahedral-like disposition of the functional groups of ZnH6HCPP and the protocol employed in the synthesis of the reported framework solids

Description of the crystal structures Mn-hcMPF (1). Red block crystals of Mn-hcMPF (C2/c) were obtained by heating stiochiometric ratio of Mn(NO3)2 and Zn-H6HCPP in a mixture of DMF and HNO3 solvent at 90°C.

The

{Mn2[Zn(H2O)-H2HCPP]}·13DMF·3H2O formula

characterizes

the

3D

framework in 1, with binuclear Mn2(COO)4(COOH)2 paddlewheel synthons of pseudo 10 ACS Paragon Plus Environment

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octahedral geometry (centered on inversion) that connect between the porphyrin entities. The two manganese ions are bridged by four carboxylate functions of four different porphyrins. Each of the Mn-centers is further coordinated to a carboxylic acid group of yet another ligand (Figure 1a). Thus, the binuclear Mn2–cluster acts as a 6-connector node (6-c) that involves four porphyrin units in paddlewheel formation and two other porphyrins connected in a monodentate fashion to apical positions. The Mn-O bond lengths range from 2.033 to 2.127 Å as typically observed for Mn(II) ions. As shown in Scheme 2 the Zn-H6HCPP linker has unique connectivity modes: two of its aryl arms have isopthalate-type connectivity represented as (3,5-connectivity) and the other two have p-type connectivity represented as (4-connected). In 1, one of the two 3,5-connectivity groups is part of the paddlewheel through bidentate chelating mode (µ2-η1η1) to manganese ions, while the other is coordinated to only one of the metal centers in a monodentate fashion (µ1-η1η0). This mode of coordination generates infinite two dimensional layers, projecting the (4-connectivity) arms above and below the layers (Figure.S1). The 4-connectivity arms of one layer coordinate to the Mn2 units of another layer and complete the paddlewheel formation (Figure 1). ----------------------------------------------------------------------------------------------------------------



Figure 1. (a) Six connected Mn2-centered paddlewheel in 1. (b) Connectivity of every Zn-H2CPP with six Mn2 paddlewheel synthons. (c) Fraction of the 3D framework projected parallel to the ac plane, showing open 1D intra-lattice channels that propagate parallel to the b-axis of the crystal.(Color code: gray – C, blue – N, red – O, magenta – Co, cyan– Zn)

As shown in Figure 1b, every porphyrin linker in the structure connects between six Mn2 paddlewheels, leading to the formation of an open 3D coordination-polymeric framework. The latter reveals 1D intra-lattice (solvent accessible) channels that propagate along the baxis of the crystal with cross-sectional (atom-to-atom) dimensions of 17.8 x 18.1 Å2 (Figure 1c). As assessed by PLATON,28 the solvent-accessible voids account for 58.8% of the crystal volume. From figure 1a it is clear that each Mn2-paddlewheel connects to six porphyrin linkers hence paddlewheel unit can be considered as 6-connected node in a similar way from figure 1b each porphyrin connects to six paddlewheels and hence it is also considered as 6connected node. The topology of the framework was then derived by considering the Mn2 paddlewheel units and the Zn-H2HCPP linkers as 6-connected octahedral nodes. Correspondingly, the observed framework is best described as a 6-connected uninodal net with Schafli symbol {410.65} and belongs to wxyl topological type. (Figure S2).31 Co-hcMPF (2). Next we reacted the title ligand with another d-block ion, Co(II), known of its ability to tessellate MOFs either in a mononuclear or polynuclear (cluster) form. The crystals of Co-hcMPF (space group Pnma) were harvested by solvothermal week-long reaction of Zn-H6HCPP and Co(NO3)2 in DMF and HNO3 at 90°C. -------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------Figure 2. (Left) Representation of trigonal prismatic water-bridged Co3 cluster in 2 (Right) hexapodal connectivity of Zn-HCPP linker and the associated framework that forms (Color code: dark gray – C, blue – N, red – O, magenta – Co, cyan– Zn, light gray– H)


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The porphyrin units in the resulting 3D framework, {[Co3(H2O)3](Zn(H2O)-HCPP)}· 7DMF ·2H2O, are inter-connected via a trigonal prismatic Co3(H2O)3 cluster (located in the crystal on a mirror plane) as a secondary building unit (SBU) (Figure 2).33 The three Co(II) ions in the cluster are bridged by µ3-H2O in the center. Two of the Co(II) ions located in general positions and related by the mirror symmetry are linked by another water species (in a µ2-H2O form). The third water is bound to the mirror-located cation. The trinuclear Cocluster coordinates (the binding geometry around individual ions being octahedral) to carboxylate groups of six different Zn-HCPP units. Correspondingly, every Zn-HCPP connects to six different Co3 clusters. The (4-connectvity) and one of the two (3,5connectivity)-type carboxylate arms of the ligand associate to a given Co-ion in a bidentate fashion, while the other carboxylates bind to two different Co-ions in a monodentate mode. Topological analyses were performed to gain better insights in to a crystal structure. The topology of the framework was obtained by reducing Co3 cluster and Zn-HCPP6- as two different 6-connected nodes. Hence topology of the framework (Figure 3) is a (6,6)connected binodal net with nia topology [point symbol: (412.63)(49.66)]. It is known that combination of 6-connected trigonal prism SBU (as the Co-cluster) with octahedral linker (as approximately the Zn-HCPP) results in the formation of nia topological networks (Figure S2).34 View of the structure down the c-axis reveals channel type solvent-accessible voids with tetragonal 11.0 Å wide cross-section. These voids account for about 58% of the crystal volume. ---------------------------------------------------------------------------------------------------------------



---------------------------------------------------------------------------------------------------------------Figure 3. (Left) Representation of the 3D open framework in 2 projected on the ab-plane. (Right) Side view of the solvent-accessible voids that propagate through the crystal parallel to the c-axis (Color code: orange – C, blue – N, red – O, magenta – Co, cyan– Zn)

Zn-hcMPF(3).

Purple colored tetragonal crystals of Zn-hcMPF were obtained

solvothermally by reacting the Zn(NO3)2 and Zn-H6HCPP reagents in DMF/HNO3 mixture at 90°C. The material crystallized in monoclinic space group C2/c and turned out to be isomorphous and isostructural with the Mn-hcMPF(1). The experimental data for this structure are given in the corresponding CIF. In-hcMPF (4). In(III) ions have been widely used in various formulations of porphyrinbased framework solids. In many of these frameworks the dominant connecting synthon involves mono-nuclear In(COO)4 SBUs.35-36 In our previous report related to the NaOHmodulated synthesis of MOFs with the tetra(3,5-dicarboxyphenyl)porphyrin linker (ZnH8OCPP) as the organic component, we observed the occurrence of a tri-nuclear In2Na inorganic connector.21 In this work a similar attempt was made utilizing Zn-H6HCPP as the linker. Dark purple block crystals of In-hcMPF were obtained by heating stiochiometric ratio of Zn-H6HCPP and In(NO3)3 in DMF and HNO3 followed by addition of excess NaOH. The crystalline material (space group P21/c) reveals an open 3D framework as well (Figure 4). It consists of the Zn-HHCPP5- porphyrin as the organic linker and a rather peculiar inorganic building unit, {InNa2(COO)5(H2O)3}. Topological expression of the framework is derived by considering the porphyrin linker as 6-connected moiety and the InNa2 clusters as 5-connected node. The framework is then a 5,6-connected binodal net with network topology {46.53.6}{46.56.62.7}, and belongs to the tcj/hc topological type. (Figure S2). The topology of the network is identified by the transformation symbol tcj-hc P63/mmc-P21/c (-a-b, a-b, c); bond sets: 4,6,7,8,9: tcj in the TOPOS binodal database. The symbol designate that the net is derived from the tcj-hc by decreasing its space-group symmetry from P63/mmc to P21/c with transformation of the unit cell by (-a-b, a-b, c) vector.37


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----------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------Figure 4. (a) Polyhedral representation of 5-c InNa2 cluster in 4. (b) Porphyrin dimer formed by coordination of one of the meta-carboxylate to the endocyclic Zn(II) center of a neighboring species. (c) A fraction of the 3D framework viewed along the ac plane. (d) 1D zig-zag channels running parallel to the b-axis of the crystal. (Color code:medium gray – C, blue – N, red – O, dark gray– Na, light blue– In, cyan– Zn, light gray– H)

In the structure, every Zn-HHCPP porphyrin linker connects to five different InNa2 nodes through five carboxylate groups, while the sixth carboxylate group of the porphyrin coordinates to the endocyclic metal center Zn(II) of an adjacent porphyrin moiety to form a dimer unit (Figure 4b). An uneven coordination was observed with the coordination arms of Zn-HHCPP. As a result, the porphyrin plane ruffled to some extent by 10.202°(10) (Cα– N···N–Cα) (Table S2) and the core metal Zn(II) was slightly deformed out of the plane. Among the benzoate arms of the porphyrin, the (3,5-connected) arms are nearly perpendicular to the plane of the core macrocycle. On the other hand the (4-connectvity) arms were found rotated with respect to the core plane by about 25-28°. The inorganic cluster InNa2 is 5-connected. In the trinuclear cluster In(III) is in octahedral coordination sphere furnished by oxygen atoms from the five carboxylate groups. Then, one of the sodium ions (Na1) adopts an octahedral coordination environment, while the other (Na2) has a tetrahedral neighborhood. The two ions are connected to each other through a bridging water molecule (Figure. 4a). Three carboxylate groups bridge between the In(III) and the two Na(I) ions, yielding together a distorted trigonal prism cluster. The octahedral coordination sphere of 15 ACS Paragon Plus Environment


In(III) is completed by two other carboxylate groups that bind in a monodentate manner, whereas that of the Na ions are fulfilled by three aqua ligands. The resulting framework show open 1D zig-zag solvent-accessible channels that propagate parallel to the b-axis, with cross-sections of 15.9x20.2 and 16.0x20.3 Å2 (Figure 4c). The surface of these channels is lined with water molecules attached to the Na(I) centres, which imparts hydrophilicity to the channel walls (Figure 3d). The crystal structure contains nearly 52.6% of intra-lattice void space filled with solvent molecules and charge neutralizing counter ions. Pb-hcMPF (5). Only a small number of metalloporphyrin frameworks associated with Pb(II) as the inorganic connector, have been reported in the literature.38-39 This can be attributed to the flexible coordination sphere and 6s2 outer-sphere electronic configuration of this ion.40 In the present work, we isolated dark red crystals of Pb-hcMPF from Zn-H6HCPP and Pb(NO3)2 in a quantitative yield through the NaOH-ameliorated synthetic approach (Figure 5). Crystallographic and thermogravimetric analysis established the formula of the framework as {Pb2[Zn(H2O)-H2HCPP]}·3DMF·H2O The resulting crystals (space group P21) accommodate the DMF/H2O crystallization solvent within the intra-lattice voids. A stable dinuclear cluster Pb2(COO)6 was formed in situ bridging between six-different Zn-H2HCPP4linkers, yielding a 3D coordination-polymeric Pb-hcMPF framework (Figure 5a). In the coordination sphere around Pb(II) all the coordinating oxygen atoms are located on one side. This is due to the presence of a stereochemically active lone electron pair.41 By considering both strong and weak Pb···O bonds, the coordination spheres around the two crystallographically independent Pb(II) centres can be regarded as Johnson's pentagonal pyramid (CN=6) and capped trigonal prism (CN=7) (Figure 4b). These spheres are furnished by two carboxylate groups in a µ1-η1η1 bridging mode for each metal, and by two bridging carboxylates in µ2-η1η0 and µ2-η2η1 coordination interaction. The coordination of each ZnHCPP linker with six Pb2 dimers results in the formation of a 3D open framework with solvent accessible channel voids running along the b-axis of the crystal (Figure S3). The channel walls are decorated by water molecules protruding from the Zn(II) coordination sphere (Figure 5c). --------------------------------------------------------------------------------------------------------------


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Figure 5. (a) SBU representing the dinuclear homo-metallic Pb2 cluster in 5. (b) Hemi directional coordination spheres representing the location of oxygen atoms on one side of the Pb-ion. (c) Fraction of the framework, viewed down the b-axis of the crystal, showing the two different types of solvent-accessible channels. (d) Representation of pcu alpha-Po primitive cubic topological type. (Color code:orange – C, blue – N, red – O, light blue– Pb, cyan– Zn)

Topological expression of the framework was derived by reducing Pb2 cluster and porphyrin moiety to octahedral 6-connected nodes. Consequently, the structure of Pb-hcMPF can be described as 6-connected uninodal network, which belongs to the pcu alpha-Po primitive cubic topological type with a Schlafli symbol of {412.63} (Figure 5d). Ln-hcMPFs were prepared by solvothermal

Ln-hcMPFs [Ln=Pr(6), Gd(7), Yb(8)]

reaction of the hexatopic linker Zn-H6HCPP with Ln(NO3)3 (Ln=Pr, Gd, Yb) in DMF through NaOH modulated synthetic methodology. Two different structural patterns were observed with lanthanoid connectors. The early lanthanoid centers (Pr and Gd) formed isostructural Pr-hcMPF (6) and Gd-hcMPF (7) solids, whereas the late lanthanide Yb formed Yb-hcMPF (8) with a different structure. The isomorphous structures of compounds 6 and 7 are presented by that of the Gdderivative. The observed framework in 7 exhibits infinite 1D rod-like SBUs {Gd(COO)5Na2(H2O)2(µ2-H2O)2}n associated with the Zn-HHCPP5- building units. Among six carboxylate groups on a given porphyrin, five functions coordinate to the Gd(III) metal 17 ACS Paragon Plus Environment


centre through the (µ1-η1η1) coordination mode (Figure 6a). The sixth carboxylate group is involved in coordination with the endocyclic Zn-center of a neighboring porphyrin to form a porphyrin "dimer" entity. ----------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------Figure 6. (a) Connectivity pattern adopted in 7 by the Zn-HHCPP linker with Gd(III) and the endocyclic Zn(II) center of an adjacent ligand. (b) 1D {Gd(COO)5Na2(H2O)2(µ2-H2O)2}n rod helical chains in wireframe and polyhedral representations. (c) Illustration of the 3D framework along the ab plane (cyan colored polyhedron represents Gd(COO)5 coordination spheres). (d) 1D channels running parallel to the c- axis of the crystal with pore opening of nearly 1.0 nm (Colour code:medium gray – C, blue – N, red – O, green– Gd, sky blue– Na, cyan– Zn).

The coordination sphere around Gd(III) centre is tetradecahedron constituted of the five coordinating (in a monodentate fashion) carboxylate groups, in such a way that four groups are from the porphyrin units aligned on the same plane (2D layer) (Figure. S4). The fifth carboxylate group is from porphyrin of an adjacent layer, creating a 3D coordination pattern. The sixth carboxylate group of each porphyrin connects to the endocyclic zinc-center of a neighboring unit. The resulting 3D architecture sustained by coordination is an open 3D framework perforated by ~10 Å wide-open channels. Adjacent Gd(COO)5 polyhedra are connected to each other by the hydrated sodium dimers Na2(H2O)2(µ2-H2O)2, affording the framework structure (Figure 6b). The Na atoms are in an octahedral coordination 18 ACS Paragon Plus Environment

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environment from two bridging- and one coordinated-water molecules and three carboxylate oxygen atoms from the Gd(COO)5 polyhedra. The open nature of the MOF is illustrated in Figures 6c and 6d. Topological analyses were performed by dividing the framework into two parts: the porphyrin (Zn-HHCPP) and 1D polymeric connecting chain. Later the 1D coordination polymeric chains are split into smaller cluster nodes {Gd(COO)5Na2(H2O)2(µ2H2O)2. Hence the topology of the framework is best described as 6,7-connected binodal net with a Schläfli symbol of {3.410.53.6}{32.410.57.62} and belongs to tcj/hc topological type. The porphyrin entities are forming six bonds of which five are with the Gd-clusters and the sixth with another porphyrin. Every Gd-cluster is involved in seven coordination bonds of which five are with other porphyrins and the remaining two with adjacent Gd-clusters (Figure S2). The topology of the network is identified by the transformation symbol tcj-hc P63/mmcP21/c (-a-b, a-b, c); bond sets: 3,4,6,7,8,9,14: tcj in the TOPOS binodal database. The symbol designate that the net is derived from the tcj-hc by decreasing its space-group symmetry from P63/mmc to P21/c with transformation of the unit cell by (-a-b, a-b, c) vector.37 The late lanthanide element Yb(III) forms different structural pattern compared to former (Pr) and central lanthanide (Gd) elements: Yb-hcMPF (8) is built from the Yb2(COO)6 (H2O)3 dinuclear cluster and the fully deprotonated Zn-HCPP linker. Even by using NaOH as a modulator the building block does not include the Na(I) ions, as observed in 7 and 8. The dinuclear Yb2 cluster is 6-connected and the two Yb(III) ions in the cluster are in capped trigonal prism geometry. These atoms are bridged by two carboxylate groups and one water molecule (Figure 7a). The porphyrin building block Zn-HCPP also behaves as a 6-connected linker by involving all the six coordination groups on the skeleton in coordination. Overall connectivity results in the formation of 6-connected uninodal net projecting the solventaccessible channels along the b-axis (Figure 7b). The framework expresses the pcu alpha-Po primitive cubic topological type with a Schlafli symbol of {412.63}. ----------------------------------------------------------------------------------------------------------------



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---------------------------------------------------------------------------------------------------------------Figure 7. (a) Dinuclear Yb2 building block involved in the construction of the framework architecture in 8. (b) View of the 3D framework down the b-axis of the crystal. (Color code:medium gray – C, blue – N, red – O, green– Yb, pink– H, cyan– Zn).

Structural comparison with H4TCPP- and H8OCPP-based MOFs The H6HCPP linker is the mixed representation of the better known H4TCPP and H8OCPP porphyrin building units (Scheme 3). The geometric disposition of its six functional substituents allow for coordination patterns of pseudo-octahedral shape with metal ions. The carboxylic groups present on the trans-related (3,5-connectivity) arms constitute the basal plane, while the (4-connectvity) arms the apical coordination sites (Scheme 2). Analysis of the coordination schemes observed for the hcMPFs in this work, in relation to other tetracarboxy-based

and

octacarboxy-based

frameworks,

provides

some

interesting

observations. For example, MOFs with H4TCPP represent most often 4,4-connected pts networks,42-43 while those with H8OCPP form 6,8,8-connected msq networks.44,7 On the other hand, the structures with H6HCPP described above are characterized by either 6connected uninodal or binodal networks with nia, tcj/hc and pcu network topologies.


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---------------------------------------------------------------------------------------------------------------Scheme 3: Representation of the structural characteristics of H6HCPP vs. those of H4TCPP and H8OCPP ------------------------------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------Figure 8. Structural comparison of paddlewheels generated in three types of frameworks built from H4TCPP, H6HCPP and H8OCPP with Mn(II) as exocyclic connector.

ZJU-1844 and [Mn3(TCPP)(H2O)4]·nD45 represent the frameworks corresponding to H8OCPP and H4TCPP with Mn(II) exocyclic connecters featuring two SBUs Mn2 paddlewheel along with Mn3 linear cluster in the former and Mn2 paddlewheel in the later (Figure 8). In ZJU-18 meta-phenylcarboxylate groups (carboxylate on 3-position) of H8OCPP 21 ACS Paragon Plus Environment


constitute paddlewheels to generate 2D layers, which are further extended into 3D material by another meta-carboxylate group (i.e in 5th position) with the aid of Mn3 linear clusters. In the H4TCPP case para-carboxylate groups on H4TCPP are involved in the formation of paddlewheel units to generate 2D layers. The paddlewheels formed in both cases are 4connected as the apical positions of these units are occupied by Cl- anion in the former case and H2O in the latter example. In the case of H6HCPP in Mn-hcMPF the paddlewheels are composed of para (from 4-connectivity arm) and meta (from 3,5-connectvity arm) carboxylate groups, which then generate a 3D framework. The other carboxylate group on a 3,5-connected arm connects to the apical positions of these paddlewheels, imparting 6connectivity. In the above examples with H8OCPP and H4TCPP the connectivity schemes through the paddlewheels are of the 2D type, while with H6HCPP a 3D coordination framework is formed (Figure 8). ----------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------Figure 9. Comparison of SBUs and coordination modes of H8OCPP in MMPF-2 with H6HCPP in Co-hcMPF


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In another example when Co(II) is used as the exocyclic connector, H4TCPP forms PIZA-146 and H8OCPP forms MMPF-2 type frameworks.7 These two frameworks feature Co3 clusters which are linear in the case of PIZA-1 and cyclic in MMPF-2. A cyclic trinuclear Co3 cluster of trigonal prismatic shape characterizes the binding nodes in Co-hcMPF with the H6HCPP linker (2). Yet, different coordination modes are exhibited by compounds MMPF-2 and Co-hcMPF (Figure 9). By employing Zn(II) as the connecting node, H6HCPP forms Zn2 paddlewheels in ZnhcMPF (3) and the structural features are similar to Mn2 paddlewheels in Mn-hcMPF (1). BNAS-1147 and MMPF-448 represent the corresponding frameworks built by H4TCPP and H8OCPP, respectively. The former is 2D layered polymer featuring Zn2 paddle wheels, while the latter is a highly symmetrical pcu topological network built by Zn2 dimers. The coordination characteristics displayed by H6HCPP in 1 and 3 are somewhat similar to those observed in BNAS-11, but don't reveal any features related to the H8OCPP-MOF. ----------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------Figure 10. Representation of different types of building units formed with tetrapodal, hexapodal and octapodal linkers when In(III) is used as the connecting unit.

MOFs MMPF-743 and In-Co(TBP)47 involve In(III) ions as the connecting nodes and H4TCPP as the organic component. They reveal In(COO)4 as the inter-porphyrin synthons and 4,4-connected networks of pts topology. On the other hand, H8OCPP-based InMPF compound synthesized by the NaOH-modulated synthetic approach revealed 6,8,8-c msq network.23 In the latter case, the Na ions were included in the formation of the In2Na 6-c trinuclear cluster. In In-hcMPF (4) involving the H6HCPP ligand the obtained framework is 5,6-connected net which is tessellated by a 5-c tri-nuclear InNa2 cluster. In 4, two porphyrin units are directly coordinated to each other as one meta-carboxylate group on 3,5-arm links to 23 ACS Paragon Plus Environment


the endocyclic Zn(II) center of an adjacent species, which has not been observed in the other examples (Figure 10). Only a few examples of Pb-MPFs with H4TCPP have been reported,38 but none with H8OCPP. They commonly reveal 1D {Pb(COO)2}n chains as the connecting pillars between the H4TCPP linkers. The Pb(II) atoms in these chains are doubly and triply bridged by carboxylate groups with mean Pb(II)···Pb(II) distances spanned in the range of 3.99-4.49 Å. In the case of Pb-hcMPF in 5 a dinuclear cluster doubly bridged by meta-carboxylate groups with Pb(II)···Pb(II) distance of 4.09 Å was observed. Only monodentate carboxylate···Pb coordination modes were observed in 5. ----------------------------------------------------------------------------------------------------------------

---------------------------------------------------------------------------------------------------------------Figure 11. Representation of three different 1D building chains formed as building units in the lanthanide frameworks constructed by H4TCPP, H6HCPP and H8OCPP.

Lanthanoid MPF derivatives based on H4TCPP and H8OCPP scaffolds, prepared via different synthetic methodologies, have been reported previously by our group.50,23,24 In most of these MPFs the Ln(III) ions form polynuclear metal aggregates as connecting units. The frameworks associated with H4TCPP feature e.g. 1D Ln(COO)3(H2O)2 binding synthons, while those involving H8OCPP showed 1D {NaLn(H2O)2(COO)4}n helical chains at the connecting nodes (Figure 11). Due to the helical geometry of the lanthanoid pillars the interporphyrin channel voids are zig-zag in nature and the porphyrin molecules are stacked in a face-to-face manner. Frameworks 6-7 (Ln-hcMPFs) built with H6HCPP also possess 1D helical chains {Ln(COO)5Na2(H2O)2(µ2-H2O)2}n. as building units. Here, the helical structure 24 ACS Paragon Plus Environment

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as well as the stacking between the porphyrin frameworks is affected, however, by the direct coordination between neighboring porphyrin entities (see above; Figure 11). PXRD and thermogravimetric analysis To ensure the phase purity of the compounds presented in this study, X-ray diffraction patterns of powder samples have been recorded. The diffraction patterns for the simulated data (calculated from single crystal data) are well matched with the observed data, which proves the bulk homogeneity of the crystalline solids (see Section 2 in the ESI). The experimental patterns have a few un-indexed diffraction peaks, and some peaks are slightly broadened and shifted in comparison to those simulated patterns probably due to effects of the unidentified and disordered solvent. The frameworks do not show any measurable PXRD pattern after removal of solvent molecules at elevated temperatures. TGA curves for representative samples were recorded under flowing N2 for crystalline samples in the temperature range 40−1000 °C (Section-2 in ESI). From crystallographic analysis the compounds contain nearly 50 to 60 % void volumes which are occupied by the solvent species. Hence, the initial weight losses in the TGA curves are related to the solvent molecules present in the intra-lattice voids. The TGA curves of Mn-hcMPF (1) represent nearly 38 % weight loss (calculated weight loss is 48%) in three intervals till 380°C out of which initial weight loss can be attributed to volatile H2O molecules and the remaining weight loss to DMF molecules. The excess calculated weight percentage observed may be due to retention of some solvent molecules in the lattice even at elevated temperatures. In compound 2, an initial weight loss of 6.5 % was observed in the region 50-130°C which can be attributed to 2 lattice water molecules and 4 coordinated water molecules/molecular formula (Calculated Wt % of H2O molecules is 6.24 %). The plot is followed by weight loss of 42 % in two intervals till 330°C, in which DMF molecules were desolvated (calculated weight loss of DMF molecules is 30%). The second weight loss i.e desolvation of DMF molecules is also accompanied by decomposition of MOF framework, as a result the observed weight loss is more than the calculated weight loss. For compound 3 a weight loss of 24% was recorded in the region 50-390°C whereas the calculated weight loss of coordinated, lattice H2O molecules, and DMF molecules according to the molecular formula is 33.2%. The calculated weight loss is more than observed weight which can be assumed that some of the DMF molecules were retained in the framework and were desolvated during the decomposition of the framework above 400 °C. In the TGA curve of compound 4 a weight loss of nearly 17 % was observed till 380°C. The calculated weight loss 25 ACS Paragon Plus Environment


corresponding to H2O and DMF molecules according to the molecular formula is 14.5 %. This plot is followed by the decomposition of the desolvated framework in two intervals. A gradual weight loss of 28 % was observed in the TGA curve of compound Gd-hcMPF (7) in the region 50-400°C. The calculated weight loss from molecular formula is nearly 36% which includes contribution from lattice, coordinated water molecules and lattice DMF molecules. It is assumed that the solvent molecules responsible for excess weight loss start desolvation along with the framework decomposition. The desolvated framework of all the compounds does not show any characteristic PXRD patterns, which indicates that the frameworks are collapsing after removal of solvent molecules.

Concluding Remarks Combining coordination abilities of different linkers and achieving the new linker with versatile coordination ability opens new pathways for constructing open framework materials.

We have demonstrated such strategy in this article by modeling hexatopic

porphyrin linker (H6HCPP) with carboxylate coordination groups, on the basis of octatopic and tetratopic carboxy-porphyrin analogs. Synthesis of the H6HCPP linker was achieved in higher yields from the corresponding dipyrromethane and aldehyde reactants by utilizing the catalyst (TFA) concentration in excess ratio. The octahedral geometry of hexatopic linker was well integrated with the 6-connected inorganic building units like Mn/Zn paddlewheels and Co3 trigonal prisms to form 6-connected wxyl network topology in case of Mn/ZnhcMPF and nia topological network in Co-hcMPfs. Modulator synthetic approaches were utilized to obtain crystalline framework materials (hcMPFs) with p-block elements and lanthanides. This approach induces the formation of 5-connected InNa2 cluster which drives the formation of In-hcMPF of tcj/hc topological network. The formation of Pb-hcMPF, sustained by 6-connected Pb2 dimers in pcu alpha-Po primitive cubic topological type, is the cumulative outcome of the modulator approach and coordination geometry of the linker employed. The Ln-hcMPfs (Ln=Pr, Gd) reported in this article also belong to 6,7-connected tcj/hc topological networks featuring helical 1D heterometallic chains as building block connecters. Whereas, the late lanthanoid element Yb-hcMPF forms 6-connected framework stabilized by the dinuclear Yb2 cluster. The coordination behavior expressed by the ZnH6HCPP linker in its frameworks derives a distinctive coordination network topologies characterized by well defined pore channels with large solvent accessible voids. The present article steers the new horizons of MMPFs in two ways as follows: (a) designing porphyrin linkers having different coordination behaviors on same porphyrin skeleton, and (b) obtaining


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the crystalline frameworks through the modulator approaches from multifunctional porphyrin linkers. Similar modeling strategies are under way to construct open framework materials with novel linkers of different coordination abilities and to extend the framework's variety by utilizing the NaOH modulator approach.

ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.cgd.0000000. Reaction conditions, structural parameters, TGA and PXRD curves, additional illustrations of the crystal structures and their topologies, summary of the SHAPE and topological analysis Accession codes CCDC 1565825-1565832 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Center, 12 Union Road, Cambridge CB2 1EZ, UK, fax:+44 1223 336033.

AUTHOR INFORMATION Corresponding Authors *E-mail: [email protected] *E-mail: [email protected]

Notes The authors declare no competing financial interest.

ACKNOWLEDGMENTS This research was supported by the Israel Science Foundation (grant no. 108/12)

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"For Table of Contents Use Only"

Open MOFs with the unique hexatopic zinc-5,15-bis(4'carboxyphenyl)-10,20-bis(3',5'-dicarboxyphenyl)porphyrin linker Bharat Kumar Tripuramallu,* Soumyabrata Goswami, Israel Goldberg*

We synthesized novel hexatopic porphyrin linker (H6HCPP) by using an excess concentration of TFA. The supramolecular reactions of zinc metallated linker (Zn-H6HCPP) with different metal centers through ameliorated modulator approaches afforded various open hexacarboxymetalloporphyrin frameworks (hcMPFs) perforated by wide intra-lattice voids.


Open MOFs with Unique Hexatopic Zinc-5,15-bis(4â²-carboxyphenyl

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Open MOFs with Unique Hexatopic Zinc-5,15-bis(4â²-carboxyphenyl