[(3-Carboxyphenyl)-sulfonyl]glycine Ligand as a Versatile Building

Chain, Pillar, Layer, and Different Pores: A N-[(3-Carboxyphenyl)-sulfonyl]glycine Ligand as a Versatile Building Block for the Construction of Coordination Polymers Lu-Fang Ma,† Li-Ya Wang,*,† Xian-Kuan Huo,†,‡ Yao-Yu Wang,§ Yao-Ting Fan,‡ Jian-Ge Wang,† and Shu-Hui Chen†,‡

CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 2 620–628

College of Chemistry and Chemical Engineering, Luoyang normal uniVersity, Luoyang 471022, P. R. China, Department of Chemistry, Zhengzhou UniVersity, Zhengzhou 450001 P. R. China, and Department of Chemistry, Shaanxi Key Laboratory of Physico-Inorganic Chemistry, Northwest UniVersity, Xi’an 710069, P. R. China ReceiVed August 22, 2007; ReVised Manuscript ReceiVed October 18, 2007

ABSTRACT: Five novel coordination polymers containing N-[(3-carboxyphenyl)-sulfonyl]glycine (H3L), namely [Co3L2(µ2bipy)2(H2O)6]n · 2nCH3OH · 8nH2O (1), [Mn(HL)(µ2-bipy)(H2O)2]n · nH2O (2), [Mn(HL)(µ2-bipy)(H2O)]n · 3nH2O (3), [Mn(HL)(bipy)(µ2bipy)0.5(H2O)]n · 4nH2O (4), [Ca(H2O)4Cu2(µ2-bipy)2L2]n · 4nH2O (5) (bipy ) 4,4′-bipyridine), were prepared under control by tuning the reaction conditions such as pH value, reaction temperature, and starting materials. X-ray structural analyses of 1–5 reveal their structural diversity ranging from one-dimensional (1D) (1), two-dimensional (2D) (2), and noninterpenetrating 3-D porous coordination polymers (3, 4) to a 2-fold 3D interpenetrating network (5). Compound 1 presents a 1D chain structure with alternating [CoL(H2O)]22binuclear and [Co(4,4′-bipy)2(H2O)4]2+ mononuclear units along the a-axis. Polymer 2, which was formed at a comparatively lower temperature, has a 2D structure extended by a HL2- ligand and a monopillar of bipy. A higher temperature was used in the preparation of 3 and 4. In addition, 3 was synthesized also at a higher pH value. In 3, HL2- ligands link the metal ions to form 2D wavelike rectangle-grid layers which are held together through µ2-bipy molecules in a double-pillar supporting fashion to give a 3D porous framework. A decrease of the pH value led to the formation of another 3D porous framework 4, in which each Mn center binds two trans-located bipy molecules. One bipy behaves as a terminal ligand, while the other one acts as a bridging ligand extending the 2D layers into a unique 3D porous framework. When calcium hydroxide was used, it led to the construction of a 2-fold 3D interpenetrating network of 5 where the Cu atoms are joined by bipy ligands to generate a 1D zigzag chain. The thermogravimetric (TG) and powder X-ray diffraction (PXRD) measurements reveal that both 3 and 4 are stable after dehydration. All of these suggest that the ligand of H3L is a versatile building block for the construction of metal organic frameworks (MOFs). Introduction The rational design and syntheses of novel coordination polymers have achieved considerable progress in the field of supramolecular chemistry and crystal engineering, owing to their potential applications in gas storage,1 sensor technology,2 separation processes,3 ion exchange,4 luminescene,5 magnetism,6 and catalysis,7 as well as due to their intriguing variety of architectures and topologies. It is well-known that organic ligands play crucial roles in the design and construction of desirable frameworks. The changes in flexibility, length, and symmetry of organic ligands can result in a remarkable class of materials bearing diverse architectures and functions. Thus, the construction of target molecules with properties mentioned above is a challenge for synthetic chemists. To achieve the desired networks, an important family of multidentate O-donor ligands, organic aromatic polycarboxylates, are often applied as bridging ligands to construct novel coordination polymers due to their versatile coordination modes.8 Meanwhile, there has been extensive interest in the porous metal-organic framework (PMOF), and one of the challenges in microporous coordination polymeric frameworks is their fragility. Crystal structures with large cavities are stabilized by inclusion of either suitable guests or interpenetrating lattices, and the absence of the guest molecules often results in low thermal stability of the host framework. Thus, the designed construction of extended * To whom correspondence should be addressed. E-mail: [email protected]. † Luoyang normal university. ‡ Zhengzhou University. § Northwest University.

porous organic or metal-organic frameworks with thermal stability is one of the most challenging issues in current synthetic chemistry.9 The combination of metal ions and bridging ligands containing different dicarboxylates or rigid and flexible pillars (pyridyl containing) or both can allow the formation of coordination networks possessing permanent porosity and high thermal stability. Thus, the search for this kind of versatile polycarboxylate ligand to construct porous frameworks rationally is necessary for systematic fine-tuning units of structural and chemical functionality. Recently, the remarkable, multidentate ligand, N-[(3-carboxyphenyl)-sulfonyl]glycine (H3L; Scheme 1) based on 3-(chlorosulfonyl)benzoic acid and glycine, seized our attention for the following reasons: (1) Glycine is a basic building unit in proteins for study in medical applications. N-Sulfonyl amino acids were found to reproduce the coordination behavior of peptides and their selectivity toward metal ions. (2) It can act not only as a hydrogen bond acceptor but also as a hydrogen bond donor, depending upon the degree of deprotonation. (3) It holds multipotential groups, i.e., the nitrogen atom and two oxygen atoms of the glycinato group, two oxygen atoms of the carboxylate group, and two oxygen atoms of sulfonate group which can afford interesting structures with tunable dimensionality. (4) It not only has one rigid carboxylate group affixed to the aromatic ring but also extends one flexible glycinato part. This asymmetric geometry may lead to acentric crystal structures. With the aim of understanding the coordination chemistry of this new versatile ligand and preparing new porous materials with interesting structural topologies and excellent physical properties, we chose H3L as a bridging ligand to react with the

10.1021/cg700797v CCC: $40.75  2008 American Chemical Society Published on Web 01/03/2008

Building Blocks for Coordination Polymers Scheme 1. N-[(3-Carboxyphenyl)-sulfonyl]glycine Ligand and Its Coordination Modes Observed in 1–5

d-block metal ions Cu(II), Co(II), and Mn(II). The neutral ligand bipy was introduced into the M(II)/H3L system, and five novel coordination polymers were obtained. The details of their syntheses, structures, and magnetic properties are reported below. Both 3 and 4 exhibit high stabilities and maintain their frameworks after removal of the guest molecules. Experimental Section Synthesis of N-[(3-Carboxyphenyl)-sulfonyl]glycine. To a solution of glycine (2.25 g, 0.03 mol) in NaOH 2 M (30 mL), 3-(chlorosulfonyl)benzoic acid (6.78 g, 0.03 mol) was added. The mixture was stirred at room temperature for 2 h, and then, the aqueous solution is acidified to pH ) 4 with 6 M hydrochloric acid; white solid derivative begins to crystallize at once. The crystals were collected on a filter and are recrystallized from 20 mL of 50% alcohol, yield about 65%. mp 188–190 °C. Anal. Calcd. for C9H11N O7S: C, 38.99; H, 4.00; N, 5.05. Found: C, 38.90; H, 3.92; N, 4.95%. IR. 3285s, 1709s, 1441s, 1171m, 753m, 1337s, 894m. Preparation of MOFs 1–5. [Co3L2(µ2-bipy)2(H2O)6]n · 2nCH3OH · 8nH2O (1). The mixture of Co(OAc)2 · 4H2O (125 mg, 0.5 mmol) and H3L (132 mg, 0.5 mmol) was stirred into a 15 mL aqueous solution, which was refluxed for about 1 h. Then, the pH was adjusted to 6 or so with 1 mol · L-1 NaOH. And then, a 3 mL methanol solution of bipy (40 mg, 0.25 mmol) was added. The reaction mixture was heated in a water bath for 10 h at 70 °C and then filtered. The red crystal was separated from the mother liquor by slow evaporation at room temperature after 2 weeks. Anal. Calcd. for C40H64Co3N6O28S2: C, 36.46; H, 4.89; N, 6.38. Found: C, 36.61; H, 4.97; N, 6.28%. IR. 3423s, 1594s, 1410s, 1102s, 1176m, 723m, 1386s, 847m. [Mn(HL)(µ2-bipy)(H2O)2]n · nH2O (2). A mixture of an aqueous methanol solution of Mn(OAc)2 · 4H2O (123 mg, 0.5 mmol), H3L (130 mg, 0.5 mmol), and bipy (40 mg, 0.25 mmol) was stirred for 6 h at room temperature and then filtered. The filtrate was allowed to stand for one week. The colorless crystals obtained were suitable for X-ray analysis. Anal. Calcd. for C19H21MnN3O9S: C, 43.69; H, 4.05; N, 8.04. Found: C, 43.58; H, 4.13; N, 8.10%. IR. 3413s, 1594s, 1423s, 1171m, 732m, 1387s, 863m. [Mn(HL)(µ2-bipy)(H2O)]n · 3nH2O (3). 3 was synthesized in a procedure analogous to that of 1 except that Mn(OAc)2 · 4H2O was used instead of Co(OAc)2 · 4H2O and the pH value was adjusted to 8 by NaOH solution until a small amount of precipitate formed. Yellow crystals were produced after two days. Anal. Calcd. for C19H23MnN3O10S: C, 42.23; H, 4.25; N, 7.77. Found: C, 42.31; H, 4.07; N, 7.75%. IR. 3409s, 1603s, 1386s, 1167m, 729m, 1337s, 811m.

Crystal Growth & Design, Vol. 8, No. 2, 2008 621 [Mn(HL)(bipy)(µ2-bipy)0.5(H2O)]n · 4nH2O (4). 4 was synthesized in a procedure analogous to that of 2 except that the reaction mixture was heated in a water bath for 7 h at 70 °C. The yellow crystals obtained were suitable for X-ray analysis in three days. Anal. Calcd. for C24H29MnN4O11S: C, 45.29; H, 4.59; N, 8.80. Found: C, 45.32; H, 4.69; N, 8.70%. IR. 3412s, 1590s, 1387s, 1222s, 732m, 1169s, 850m. [Ca(H2O)4Cu2(µ2-bipy)2L2]n · 4nH2O (5). 5 was synthesized in a procedure analogous to that of 1 except that Cu(OAc)2 · H2O was used instead of Co(OAc)2 · 4H2O and 1.2 mmol Ca(OH)2 was added. Blue crystals were produced after three weeks. Anal. Calcd. for C38H44CaCu2N6 O20 S2: C, 40. 18; H, 3.90; N, 7.40. Found: C, 40.48; H, 4.06; N, 7.29%. IR. 3419s, 1618s, 1397s, 1172m, 721m, 1331s, 804m. Materials and Physical Measurements. All reagents used in the syntheses were of analytical grade. Elemental analyses for carbon, hydrogen, and nitrogen atoms were performed on a Vario EL III elemental analyzer. The infrared spectra (4000-600 cm-1) were recorded by using KBr pellets on an Avatar 360 E.S.P. IR spectrometer. The crystal determination was performed on a Bruker SMART APEX II CCD diffractometer equipped with graphite-monochromatized Mo KR radiation (λ ) 0.71073 Å). Variable-temperature magnetic susceptibilities were measured using a MPMS-7 SQUID magnetometer. Diamagnetic corrections were made with Pascal’s constants for all constituent atoms. Thermogravimetric (TG) analyses were carried out on a STA449C integration thermal analyzer. The powder X-ray diffraction (PXRD) patterns were recorded with a Rigaku D/Max 3III diffractometer with a scanning rate of 4 °/min. X-ray Crystallography. Single crystal X-ray diffraction analyses of the five compounds were carried out on a Bruker SMART APEX II CCD diffractometer equipped with graphite-monochromated Mo KR radiation (λ ) 0.71073 Å) by using the φ/ω scan technique at room temperature. The structures were solved by direct methods with SHELXS-97. The hydrogen atoms were assigned with common isotropic displacement factors and included in the final refinement by use of geometrical restraints. A full-matrix least-squares refinement on F2 was carried out using SHELXL-97. The crystallographic data and selected bond lengths and angles for 1–5 are listed in Tables 1 and S1 of the Supporting Information. Hydrogen-bonding parameters in 1 are listed in Table S2 of the Supporting Information. Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Center. CCDC reference numbers: 632641 (1), 632587 (2), 632643 (3), 632642, and (4) 657013 (5).

Results and Discussion Syntheses. The syntheses were summarized in Scheme 2. The first attempts to react M(II) salts with H3L directly by conventional solution methods or by hydrothermal methods gave only some precipitates or microcrystalline products unsuitable for single crystal X-ray diffraction analysis. Considering that the introduction of a N-containing auxiliary ligand might tune the structure of the thus formed metal-organic complexes, we chose bipy as an ancillary ligand in this system. By varying the reaction parameters such as temperature, pH value, and the identity of the base, five compounds were successfully isolated in their crystalline forms with good yield. The results show that the auxiliary ligand (bipy) plays a crucial role in the formation of acentric MOFs. This “mix-ligands” method is a new idea to construct MOFs and has aroused attractive attention in the design of open porous MOFs.10 Crystal Structure of [Co3L2(µ2-bipy)2(H2O)6]n · 2nCH3OH · 8nH2O (1). Single X-ray crystal analysis reveals that 1 consists of 1D chains with alternating [CoL(H2O)]22- binuclear and [Co(4,4′-bipy)2(H2O)4]2+ mononuclear units along the a-direction. The crystal structure of 1 contains two independent cobalt ions (Figure 1a): The Co(1) ion has a distorted octahedral geometry with four water molecules in the equatorial sites and two nitrogen atoms from two different bipy molecules in the axial positions. The Co(2) ion is also coordinated in an octahedral geometry by two chelating oxygen atoms from the C6H5COO- motif, one nitrogen atom and one carboxylate

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Table 1. Crystallographic Data for Complexes 1–5 1 formula Mr temperature crystal system space group unit cell dimensions

V (Å3) Z F (g cm-3) F(000) GOF crystal size (mm3) R1, wR2 [I > 2σ(I)] R1, wR2 (all data) largest diff. peak and hole (e Å-3)

C40H64Co3N6O28S2 1317.88 293(2) K triclinic P1j a ) 9.5288(15) Å b ) 11.3655(19) Å c ) 13.732(2) Å R ) 69.107(2)° β ) 76.724(5)° γ ) 81.010(4)° 1347.7(4) 1 1.624 683 1.012 0.04 × 0.02 × 0.02 0.0498, 0.1256 0.0815, 0.1474 0.860 and –0.469

2

3

4

5

C19H21MnN3O9S 522.39 291(2) K orthorhombic P212121

C19H23MnN3O10S 540.40 291(2) K monoclinic P21/n

C24H29MnN4O11S 636.51 291(2) K monoclinic C2/c

C38H44CaCu2N6O20S2 1136.07 291(2) K monoclinic P21/n

a ) 10.912(2) Å b ) 11.683(3) Å c ) 17.184(4) Å

a ) 11.663(3) Å b ) 8.708(2) Å c ) 27.218(7)Å β ) 101.485(4) °

a ) 25.232(2) Å b ) 8.672(5) Å c ) 27.441(2) Å β ) 94.0970(10)°

a ) 10.855(4) Å b ) 15.576(6) Å C ) 13.577(5) Å β ) 96.017(5) °

2190.9(8) 4 1.584 1076 1.037 0.38 × 0.25 × 0.16 0.0440, 0.1030 0.0512, 0.1084 0.628 and –0.523

2708.9(11) 4 1.325 1116 1.038 0.16 × 0.10 × 0.07 0.0756, 0.2138 0.1469, 0.2673 0.943 and –0.760

5988.8(6) 8 1.412 2640 1.074 0.38 × 0.19 × 0.11 0.0708, 0.2235 0.0904, 0.2440 1.089 and –0.590

2282.8(15) 2 1.653 1168 1.095 0.37 × 0.16 × 0.11 0.0635, 0.1493 0.1040, 0.1730 1.161 and –1.176

Scheme 2. Progressive Change of Network from 1 to 5

oxygen atom from the coordinated glycinato part, one nitrogen atom from bipy, and one oxygen atom from water. The Co-O(L3-) and Co-Nbipy bond lengths are in agreement with those reported for carboxylate and bipy-containing Co(II) complexes.11 Each bipy acts as a bidentate bridging ligand to connect two cobalt atoms to form an alternating chain. The two carboxylate groups of the L3- ligand display different coordination modes. The carboxylate group of the glycinato part coordinates to the Co(II) ion in a monodentate mode while it coordinates to the carboxylate group of C6H5COO- motif in a chelating mode. Thus, each trivalent anion of L3- adopts a bisbidentate coordination mode (O, O and N, O) and bridges two cobalt atoms. This results in the formation of a dinuclear building block [CoL(H2O)]22-, in which two Co(II) ions are bridged by two L3- ligands. Every two of this kind of dinuclear building blocks are further connected by a mononuclear unit [Co(H2O)4]2+ via the coordination of bipy. Thus, 1 forms a novel 1D single-single-double-stranded chain (Figure 1a) different from those of the known 1D polymers, which are linear

chain,12 zigzag chain,13 helical chain,14 ladder chain,15 doublestranded chain,16 and triple-stranded chain.17 Interestingly, the lattice-water, coordinated water, methanol, and sulfonamide oxygens are associated by hydrogen bonds to form a puckered 14-membered ring (Figure 1b). In the 14membered ring, the O(w) · · · O(w) distances range from 2.726 to 3.005 Å with an average distance of 2.891 Å which is very similar to the corresponding value observed in liquid water (2.85 Å).18 Meanwhile, the average O(w) · · · O(methanol) distance is 2.75 Å which is shorter than those observed in water–methanol clusters in a phosphorus functionalized trimeric amino acid host (2.857 Å).19 This might be attributed to its different modes of connectivity with the surrounding water molecules and the interaction with the host. Every puckered 14-membered ring consolidates four one-dimensional chains by hydrogen bonding and further extends it into a three-dimensional supramolecular structure. It is well-known that water and methanol constitute important prototypes of hydrogen-bonded liquids and more complex phenomenon that ensue upon mixing H2O and MeOH

Building Blocks for Coordination Polymers

Crystal Growth & Design, Vol. 8, No. 2, 2008 623

Figure 1. (a) 1D alternating polymeric chain architecture in 1. (b) Perspective view of the puckered 14-membered ring formed by hydrogen bonding of water, sulfonamide oxygen, and methanol molecules. The colors are as follows: red, oxygen (free water); blue, oxygen (coordinated water); purple, oxygen (methanol); green, oxygen (sulfonamide group).

has been at the focus of attention for a number of decades.20 Here, studies involved in the formation of mixed methanol– water clusters within the N-protected amino acid host will increase our understanding hydrogen-bonding patterns that exist within the individual liquids. Crystal Structure of [Mn(HL)(µ2-bipy)(H2O)2]n · nH2O (2). The asymmetric unit of 2 contains one Mn2+ cation, one bipy ligand, two water molecules, and one HL2- anion. As shown in Figure 2a, all Mn atoms are each octahedrally coordinated by two N atoms of different bipy ligands, two oxygen atoms of two water molecules, and two different glycinato parts with their oxygen atoms in the trans positions. The Mn-O(carboxylate) and Mn-N(bipy) bond lengths are in agreement with those in carboxylate- and bipy-containing manganese(II) complexes.21 Each HL2- group acts as a bismonodentate ligand to bridge two Mn(II) ions by the two oxygen atoms of the glycinato part affording a uniform chain. These chains are cross-linked by bridging bipy ligands along the b axis to generate a 2D rectangular grid layer with a 10.13 Å × 11.72 Å window (Figure 2b). The deprotonated carboxylate group of the C6H5COO- motif remains uncoordinated but contributes to the stabilization of the structure through extensive hydrogen bonds with water molecules and the sulfonamide nitrogen atom. Additional hydrogen bonds involve the coordinated carboxylate oxygen atoms, coordinated water molecules and free water molecules. Crystal Structure of [Mn(HL)(µ2-bipy)(H2O)]n · 3nH2O (3). The asymmetric unit of 3 comprises one Mn2+ cation, two half-bipy molecules, one HL2- anion, one coordinated water molecule, and three lattice-water molecules (Figure 3a). The geometry environment around the Mn (II) is octahedral. The four oxygen atoms were three oxygen atoms from three different HL2- and one oxygen atom from a water molecule which define the equatorial positions, whereas two nitrogen atoms of bipy molecules occupy the axial ones. The Mn-O bond distances fall in the range of 2.150(4)-2.210(4) Å, and the Mn-N bond distances are 2.283 (4) and 2.296 (5) Å, respectively. The coordination modes of the two carboxylate groups of the HL2ligand are different: (1) the carboxylate group of the C6H5COOmotif adopts a monodentate ligand to bind a metal ion; (2) the carboxylate group of the glycinato part acts as a bis-monodentate ligand to bridge two Mn centers. Two HL2- ligands bridge two

Figure 2. (a) Coordination environment of Mn (II) ion in 2. (b) 2D sheets bridged by bipy molecules.

Mn(II) ions to form a 22-membered ring, and another four Mn(II) ions and four HL2- ligands also form a 30-membered


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Figure 3. (a) Local coordination environment of the Mn(II) ion with the atomic name scheme in 3. H atoms are omitted. (b) Perspective view of the Mn-HL2- sheet.

ring. Therefore, a [Mn(HL)(H2O)]∝ layer is formed by an alternative arrangement of 22-membered rings and 30-membered rings (Figure 3b). Within the 22-membered ring, the Mn · · · Mn separation is 11.396 Å. And, the closest Mn · · · Mn distance within the 30-membered ring is 5.244 Å. An interesting aspect of the structure is that the 2D sheets are connected by bipy ligands through the axial positions of both Mn centers in subunits to form a 3D double pillared-layer structure, as shown in model III in Scheme 2. The whole structure can alternatively be described as a 3D porous framework with the open channels possessing approximate dimensionalities of 8.64 Å × 9.00 Å along the b axis, and guest water molecules occupy the channels (Figure 4a and b). The effective free volume of 3 was calculated by PLATON analysis as 33% of the crystal volume (894.9 out of the 2708.9 Å3 unit cell volume). Crystal Structure of [Mn(HL)(bipy)(µ2-bipy)0.5(H2O)]n · 4nH2O (4). The asymmetric unit of 4 comprises one Mn(II) cation, one monodentate bipy molecule, one-half µ2-bipy molecule, one HL2- anion, one coordinated water molecule, and four lattice-water molecules (Figure 5a). Each Mn(II) ion is six-coordinated by two bipy nitrogen atoms and four carboxylate oxygen atoms from three different HL2- ligands. The Mn-O bond lengths are in the range of 2.132(3)-2.206(3) Å,andtheMn-Nbondlengthsareintherangeof2.298(3)-2.302(4) Å, respectively. The two pyridine rings of each bipy molecule twist with dihedral angles of 25.6° and 11.43° for bridging and monodentate bipy ligands, respectively. The coordination modes of the HL2- anion are similar to those in 3. The dimeric Mn2 units are interconnected to form 22-membered rings and 30-

Figure 4. (a) View of the channel formed by the 3D network (latticewater molecules are omitted for clarity). (b) Space-filling model of 3 as viewed down the b axis: C gray; O red; S yellow; N blue.

membered rings. The 22-membered ring is enclosed by two Mn(II) ions and two carboxylate groups with the Mn · · · Mn separation being 11.438 Å, larger than that in 3. The resulting 2D sheets are pillared by bipy to generate a 3D framework, which contains large 1D channels (9.64 Å × 7.27 Å) along the b axis (Figure 5b and c). The void space accounts for 22.5% of the crystal volume and is occupied by guest water molecules (1345.7 out of the 5988 Å3 unit cell volume). The arrangements of bipy between two different layers in 4 are significantly



Figure 5. (a) Crystallographic environment around the Mn(II) center in 4 (H atoms are ommitted). (b) X-ray crystal structure of 4 showing channels along the b axis. Guest molecules are ommitted. (c) Space-filling model of the channel structures along the b axis. Guest molecules are ommitted.

different from those in 3 (Figure 6). In 3, two Mn(II) ion subunits are connected by bipy ligands to produce doubly straight chains, which are linked by HL2- to give a 2D sheet motif. This arrangement phenomenon of bipy has been reported in some 3D porous frameworks constructed from 2D layers and pillared by bipy ligands.22 It is very interesting that in 4 each Mn center binds two trans-located bipy molecules. One is a terminal bipy molecule which stands vertically in the interlayer by coordinating to an Mn ion. And, the other is bridging bipy which is situated alternatively above and below the 2D planes to link the 2D layers into a 3D open framework, as shown in model IV Scheme 2. To the best of our knowledge, such a unique arrangement of bipy molecules in porous MOFs is unprecedented. We have investigated the reactions of H3L, bipy, and Mn(II) salts under different conditions including variations of the Mn(II)

salts, molar ratios, reaction temperatures, and pH values. Different molar ratios and different counteranions (such as nitrate, perchlorate, or acetate) of the starting materials under the same reaction conditions result in the same compound but with different yields. The formation of complexes containing asymmetric carboxylic acid ligands is very sensitive to the pH of the reaction system,23 so different structures can be constructed via changing only the pH values while using the same reagents. It was observed that complexes 3 and 4 were synthesized at pH values of 8 and 5, respectively. To the best of our knowledge, It is rare to obtain different porous metal organic frameworks from the same starting materials under different pH values. Analyses of the synthetic conditions and structures of complexes 2 and 3 or 4 show that temperature has a very important influence on the formation and structure of the


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Figure 6. Schematic representation of the repeat units in 3 (a) and 4 (b) showing different arrangement of bipy. The yellow sphere represents the large pore defined within the frameworks.

complexes. Complex 2 was synthesized under similar conditions except for the lower temperature. This is consistent with the fact that higher reaction temperature leads to an increase in condensation of the MOFs. Crystal Structure of [Ca(H2O)4Cu(µ2-bipy)2L2]n · 4nH2O (5). As shown in Figure 7a, the asymmetric unit of [Ca(H2O)4Cu2(bipy)2L2] · 4H2O contains one [Ca(H2O)4]2+ moiety, two Cu(II) ions, two L3- ligands, and four water molecules. The Cu(II) ion is five-coordinated by two bipy and two L3ligands with pyramidal CuN3O2 geometry. The Ca ion is sixcoordinated in a distorted octahedral geometry by the coordination of four water molecules and two oxygen atoms from different L3- ligands. The Ca-O bond lengths range from 2.285(5) to 2.335(4) Å. Every L3- ligand adopts a tetradentate bridging mode to link one Ca and two Cu atoms in the Cu(bipy)2-L3--Cu(bipy)2 and Cu(bipy)2-O-C-O-Ca fashions. This means that it uses the nitrogen atom and one carboxylate oxygen atom from the glycinato part to chelate to one Cu atom and one carboxylate oxygen atom from the other carboxylate group to coordinate to another Cu atom. At the same time, the remaining carboxylate oxygen atom from the glycinato part coordinates to a Ca atom. The Cu atoms from different binuclear units are joined by crystallographically independent bipy spacers to generate a 1D zigzag chain with a period of 11.407 Å. The adjacent chains are further bridged by L3- ligands to form a corrugated 2D structure. (Figure 7b) The two pyridine rings of each coordinated bipy molecule twist with a dihedral angle of 27°. The interesting feature of the structure is that the Ca ions link the 2D structure into a porous coordination polymer with large channels of 15.80 Å × 8.88 Å2 via its coordination to oxygen atoms from the adjacent layers (Figure 7c). The large cavities in the structure allow two of this kind of 3D network to weave into a 2-fold interpenetrating topological structure as depicted in Figure 8. The volume of the effective void calculated by PLATON is about 10.3% of the unit-cell volume in the selfinclusion structure. Thermal Analyses and PXRD Patterns. The thermogravimetric analysis (TGA) study of 3 shows that the first weight loss of 13.43% (calcd: 13.38%) observed from 30 to 200 °C corresponding to the loss of three free water molecules and one coordinated water per formula unit. The second process might include two steps from 200 to 650 °C. It is the decomposition of the material. The final residue of 12.98% is close to the calculated 13.15% based on MnO. Correspondingly, the TGA of 4 is similar to that of 3 (Figure S1 in the Supporting Information). In principle, TGA measurements alone cannot be

used to determine the stability of an open structure since it may collapse without a notable change in the weight. To further test the stability of the porous frameworks, we examined the powder samples by X-ray diffraction analysis. The fully evacuated open structures have been found to be stable at least up to 200 °C (Figure S2 in the Supporting Information), which indicates that the two porous frameworks can stably exist even at the loss of both guest and coordinated water molecules. Magnetic Properties. The magnetic susceptibilities of 3 and 4 were measured in the 2-300 K temperature range and shown as χMT and χM versus T plots in Figure S3 (Supporting Information). The experimental χMT values of 3 and 4 at room temperature are 4.06 and 4.56 cm3 K mol-1 per Mn(II) ion, respectively, close to the spin value expected for an uncoupled high-spin Mn(II) ion (4.38 cm3 K mol-1). The temperature dependence of the reciprocal susceptibilities (1/χM) obeys the Curie–Weiss law above 5 K with θ ) -1.4 K, C ) 3.96 cm3 K mol-1, R ) 3.9 × 10-5 for 3 and θ ) -1.8 K, C ) 4.48 cm3 K mol-1, R ) 1.44 × 10-4 for 4, which indicates that antiferromagnetic interactions are operative in the two complexes. According to the structures of 3 and 4, it could be presumed that the main magnetic interactions between the metal centers might happen between two carboxylate bridged Mn(II) ions, whereas the superchange interactions between Mn(II) ions through the HL2- and bipy bridge can be ignored because of the long length of HL2- and bipy ligands. The magnetic susceptibility data were fitted assuming that the carboxylate bridges of Mn(II) ions form a uniform chain with exchange constant J and then bipy and HL2- connect the chains to form a 3D structure with an exchange constant zJ′. To simulate the experimental magnetic behavior, for 1D Mn(II) complexes, the ˆ ) following eq 1 is induced from the Hamiltonian H -2JΣi*jSˆiSˆj.24,25 XM )

( )

Ng2β2 [A + Bx2][1 + Cx + Dx3]-1 KT

(1)

where A ) 2.9167, B ) 208.04, C ) 15.543, D ) 2707.2, and x ) |J|/KT. χM (2) 2zJ′ 1 - 2 2 χM Nβ g The least-squares analysis of magnetic susceptibilities data led to J ) -0.11 cm-1, g ) 1.93, zJ′ ) -0.015 cm-1, and R ) 3.41 × 10-4 for 3 and J ) -0.089 cm-1, g ) 2.06, zJ′ ) χT )



Figure 8. Structure topology of 5 displaying 2-fold interpenetration.

Figure 7. (a) Coordination environments of the Cu(II) and Ca(II) ions with atom labeling in 5. (b) Schematic representation of corrugated 2D layer structure. (The longer and shorter rods represent the bipy and L3ligands, respectively.) (c) Perspective view of the 3D network of 5.

-0.011 cm-1, and R ) 1.09 × 10-5 for 4. As we know, the exchange coupling through the carboxylate bridge is highly dependent on the conformation modes of the bridge between the metal centers. The syn-anti mode induces much smaller J values than those of the syn-syn mode because of the expanded metal center and a mismatch in the orientation of magnetic orbitals.26 In 3 and 4, coupling J arises from the syn-anti carboxylate bridge and gives a weak antiferromagnetic coupling in this case. It is comparable to those reported for other Mn(II) species with similar carboxylate bridges.27 The results presented above confirm that the carboxylate bridges generally favor weak interactions. Conclusion By the use of an unexplored amino acid derivative ligand, N-[(3-carboxyphenyl)-sulfonyl]glycine, five novel 1D, 2D, and 3D coordination networks have been synthesized and structurally characterized. It is worth noting that the ligand H3L can be used

as a polydentate to coordinate transition metal ions into coordination polymers in different modes. Furthermore, the auxiliary ligand bipy adopts different functions in the assembly of complexes 1-5: bridging binuclear units in 1, monopillar in 2, double-pillar supporting fashion in 3, rare monocoordinated and bis-coordinated modes arrangement in porous 4, and 1D zigzag chain in 5. The PXRD studies confirm that the pore frameworks of 3 and 4 exhibit high stabilities against the removal of the free water and the coordinated water molecules. The pH values played an important role in the formation of 3 and 4. In summary, our research demonstrates for the first time that the new flexible ligand N-[(3-carboxyphenyl)-sulfonyl]glycine could be a potential building block to construct novel coordination polymers with unusual architectures and interesting physical properties. Subsequent works will be focused on the construction of novel polymers by reacting this and other related ligands (including another isomeric ligand, N-[(4-carboxyphenyl)-sulfonyl]glycine) with more metal ions under different conditions. Acknowledgment. This work was supported by the Natural Science Foundation of China (Nos. 20471046 and 20771054), Henan tackle key problem of science and technology (No. 072102270030), and the Foundation of Education Committee of Henan province (2006150017). Supporting Information Available: X-ray crystallographic files in CIF format, selected bond distances and bond angles for 1-5, hydrogen bonding parameters for 1, and thermal analyses, PXRD patterns, and magnetic properties of 3 and 4. This material is available free of charge via the Internet at http://pubs.acs.org.

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CG700797V

[(3-Carboxyphenyl)-sulfonyl]glycine Ligand as a Versatile Building

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