ARTICLE pubs.acs.org/crystal
Synthesis, Magnetic Properties, and Structural Investigation of Mixed-Ligand Cu(II) Helical Coordination Polymers with an Amino Acid Backbone and N-Donor Propping: 1-D Helical, 2-D Hexagonal Net (hcb), and 3-D ins Topologies Published as part of a virtual special issue on Structural Chemistry in India: Emerging Themes. Amal Cherian Kathalikkattil,† Kamal Kumar Bisht,† Nuria Aliaga-Alcalde,‡ and Eringathodi Suresh*,† †
Analytical Science Discipline, Central Salt and Marine Chemicals Research Institute, Council of Scientific and Industrial Research (CSIR), G.B.Marg, Bhavnagar-364002, Gujarat, India ‡ ICREA-Departament de Química Inorganica, Universitat de Barcelona (UB), Diagonal 647, 08028-Barcelona-Spain ABSTRACT: Three Cu(II) coordination polymers, {[Cu(L-cysteate)(1,4-Bix)(H2O)] 3 H2O}n (1), {[Cu(L-aspartate)(1,4-Bix)0.5] 3 H2O}n (2), and {[Cu(L-aspartate)(4,40 -Bpy)0.5] H2O}n (3), have been synthesized solvothermally, employing enantiopure L-amino acids and bidentate N-donor ligands, 1,4bis(imidazol-1-ylmethyl)benzene (1,4-Bix) and 4,40 -bipyridyl(4,40 -Bpy), to yield 1-D, 2-D, and 3-D helical coordination polymers, respectively. All the three neutral frameworks are well-characterized by various physicochemical methods (C,H,N analysis, IR, TGA) including the single crystal X-ray diffraction technique. The chiral nature of complexes 2 and 3 was established using solid state CD spectra. Structural investigation of complex 1 revealed 1-D helical chains, whereas that of complex 2 confirms a chiral and helical two-dimensional 63-hcb net, with helicity propagating in both the dimensions. Cu(II) nodes with the mixed ligands in complex 3 generate a three-dimensional framework by the pillaring of Cu(L-aspartate) 2-D helical layers by 4,40 -Bpy units, identified as a (3,4)-coordinated binodal net with (63)(65.8)-ins topology. The temperature-dependent magnetic properties of the L-aspartic acid derived for complexes 2 and 3 were studied in detail. Complex 2 showed weak antiferromagnetic behavior, which matches well with the crystallographic parameters (synanti conformation of carboxylate bridged Cu(II), with lowest CuCu distance 5.367 Å). Similarly, complex 3, with a shorter and rigid N-donor ligand, 4,40 -Bpy, and the carboxylate group of the amino acid moiety linking the adjacent metal centers in the synanti conformation, also displayed a weak antiferromagnetic behavior at lower temperatures, showing the weak exchange couplings between Cu(II) centers.
’ INTRODUCTION Research in metal organic framework (MOF) chemistry, including the crystal engineering of coordination polymers, over the past two decades was not merely due to the diverse network topology by the amalgamation of chemistry and geometry1 but mainly due to their enormous potentials to emerge as new generation materials which could cleverly meet specific applications.2 The internal surface functionality and topology of MOF materials could be crafted efficiently by choosing appropriate ligands and metal ions with diverse coordination geometry under optimum reaction conditions. Considering the exponential growth of research in this field, increasing attention is being paid to the design and synthesis of new multidimensional MOFs, not only due to their aesthetic structural beauty but also in view of their application.311 Hence, design, synthesis, and characterization of coordination polymers continue to be of growing relevance in the present scenario. Chiral coordination polymers could be synthesized mainly by three methods,12 with the most viable and convenient method r 2011 American Chemical Society
being the use of chiral spacers as building blocks. Among them the use of enantiopure amino acids is the most common strategy, owing to their easy availability, natural occurrence (L-amino acids), multiple metal binding sites, and versatile bonding modes provided by amino carboxylate groups. Introduction of an amino acid moiety in MOFs can induce the intrinsic chirality of the preferred starting amino acid in an extended structure via a versatile bridging mode of the oxygen atom from the amino carboxylate group. Rosseinsky et al. successfully demonstrated the pillaring of parent metalamino acid complexes in designing porous chiral coordination polymers with application in the area of enantioselectivity and asymmetric catalysis.13,14 Metal organic framework/coordination polymers can be good magnetic materials15 because the distances of the multiple metal centers Received: November 30, 2010 Revised: February 20, 2011 Published: March 16, 2011 1631
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Crystal Growth & Design (moment carriers) can be tuned within the suitable interacting range by the judicious choice of the ligand moiety. We have initiated some work with [M(AA)L] type metal complexes (where M = metal ion, AA = amino acid, L = N-donor ligand), due to their increasing biological significance and amino acid being the building block of proteins.16 The present work originated from our interest in synthesizing Cu(II) complexes involving multidentate N-donor ligands (4,40 -Bpy/1,4-Bix) and enantiopure amino acids (L-cysteic acid/L-aspartic acid), to study various noncovalent interactions, including the hydrogen bonding/stacking which influences the decisive network topologies in their supramolecular arrangements and their magnetic properties. The conformationally flexible ligand 4-bis(imidazol1-ylmethyl)benzene (1,4-Bix) has been proved as a suitable building block for designing coordination polymers of various network topology. Structural diversities ranging from low dimensional entities such as 1D helix to linear threads to high-dimensional supramolecular networks such as 3-D interpenetrated networks, R-polonium-type networks, metal organic polyrotaxanes, brick-wall type networks, and chiral and magnetic metalorganic frameworks are reported in the literature by the judicious choice of N-donor linkers such as 1,4-Bix or 4,40 -Bpy.17 Optically pure amino acids (L-cysteic acid/L-aspartic acid) can bridge the metal centers by virtue of the versatile coordination modes of the amino-carboxylate end and possibly through the terminal carboxylate/sulfonate moiety, in generating the multidimensional network topologies in conjunction with the N-donor linker. As part of our ongoing efforts in the synthesis of supramolecular crystalline materials with diverse topology involving an amino acid moiety, herein we report the synthesis, characterization, magnetic studies, and single crystal structural investigation, including the topology of three helical multidimensional (1-D to 3-D) coordination networks. Three coordination polymers exhibiting helical/chiral properties were synthesized solvothermally involving chiral precursor L-amino acids (L-Asp or L-Cys) with flexible/rigid N-donor ligands. {[Cu(L-cysteate)(1,4-Bix)(H2O)] 3 H2O}n (1) is a 1-D helical coordination polymer while {[Cu(L-aspartate)(1,4-Bix)0.5] 3 H2O}n (2) is a 2-D chiral coordination polymer possessing a 2-D helical network, and {[Cu2(L-aspartate)(4,4'-Bpy)0.5] 3 H2O}n (3) is a 3-D chiral framework. Even though compound 3 has been reported by Rosseinsky et al., demonstrating its relevance toward enantioselective catalysis, temperature dependent magnetic studies of complexes 2 and 3 and their detailed structural investigation, topology, and solid state CD to establish the chirality in both the complexes are the highlights of the present investigation.
’ EXPERIMENTAL SECTION Materials. L-Cysteic acid monohydrate, L-aspartic acid, 4,40 -bipyridyl, imidazole, and R,R0 -dichloro-p-xylene were purchased from SigmaAldrich. Basic copper carbonate, K2CO3, and methanol were obtained from SD Fine Chemicals, Mumbai, India. Double distilled water and methanol were used as solvents for the syntheses of the complexes. All the reagents and solvents were used as received without further purification. Physical Measurements. IR spectra were recorded using KBr pellets on a PerkinElmer GX FT-IR spectrometer. CHNS analyses were done using a PerkinElmer 2400 CHNS/O analyzer. TGA analyses were carried out using METTLER TOLEDO STARe SW 8.10, and CD spectra and solid state UVvis spectra were recorded using a JASCO J-851-150 L CD spectrometer and a Shimadzu
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UV-3101PC spectrophotometer, respectively. X-ray powder diffraction data were collected using a Philips X-Pert MPD system with Cu KR radiation. Single crystal structures were determined using a BRUKER SMART APEX (CCD) diffractometer, and magnetic measurements were carried out with a Quantum Design SQUID MPMS-XL magnetometer working in the 2300 K range.
Synthesis of 1,4-Bis(imidazol-1-ylmethyl)benzene (1,4-Bix). 1,4-Bix was synthesized according to the procedure reported by B. F. Abrahams et al.18 Recrystallization of the crude product by dissolving in hot water and keeping at constant temperature of 23 C yielded needle type crystals within a couple of days. Synthetic procedure to prepare 1,4Bix is mentioned in Supporting Information as scheme S1. 1 H NMR Data: δ7.725 (s, 2H, NCH(a)), 7.240 (s, 2H, CdCH(d)), 7.084 (d, 2H, CdCH(e)), 6.969 (s, 4H, benzene ring(b)), 5.204 (4H, CH2(c)), 4.933(s, H2O). C, H, N Data: Calc (%): C = 61.29; H = 5.15; N = 20.45. Observed (%): C = 60.3; H = 6.21; N = 19.63. IR spectral data: (νmax/cm1) 3438(b), 3108(m), 2553(w), 2949(m), 1677(m), 1602(w), 1512(s), 1444(s), 1281(s), 1228(s), 1104(m), 1081(s), 1029(m), 919(s), 828(m), 767(m), 708 (m), 665(m). Synthesis of {[Cu(L-cysteate)(1,4-Bix)(H2O)] 3 H2O}n (1). To an aqueous dispersion (6 mL) of L-cysteic acid (84.58 mg, 0.50 mmol) and basic copper carbonate (110.50 mg, 0.50 mmol) was added slowly 1,4-Bix (136.00 mg, 0.50 mmol) in methanol (6 mL). The reaction mixture was stirred for 15 min in air and then transferred and sealed in a 25 mL Teflon-lined autoclave, which was heated at 398 K for 80 h. After slow cooling to room temperature, the product was washed with 10 mL of distilled water and filtered. Light blue colored crystals started appearing from the filtrate within a week by slow evaporation at room temperature. The crystals obtained were insoluble in common polar and nonpolar solvents. Elemental analysis for 1 (%), Calcd: C, 40.64; H, 4.01; N, 13.94; S, 6.39. Found: C, 40.52; H, 4.12; N, 13.60; S, 6.42. IR cm1 (KBr): 3440br, 3131s, 1630m, 1525m, 1385s, 1232s, 716m, 653m, 586m, 521m. CCDC Number: CCDC 784577. Synthesis of {[Cu(L-aspartate)(1,4-Bix)0.5] 3 H2O}n (2). A similar solvothermal method as in the case of complex 1 was adopted for the synthesis of 2, except that L-aspartic acid (66.50 mg, 0.50 mmol) was used instead of L-cysteic acid. Blue block crystals were obtained readily after cooling the solvothermal vessel to room temperature. The crystals obtained were insoluble in common polar and nonpolar solvents. Elemental analysis for 2 (%), Calcd: C, 40.02; H, 3.67; N, 12.74. Found: C, 39.94; H, 3.97; N, 12.45. IR (KBr): 34013273br, 3114s, 1630m, 1521m, 654m, 612m. CCDC Number: CCDC 784578. Synthesis of {[Cu2(L-aspartate)(4,40 -Bpy)0.5] 3 H2O}n (3). A similar 3-D Cu coordination framework was synthesized earlier by Rosseinsky et al.14 Synthesis of complex 3 under different reaction conditions using basic copper carbonate is illustrated as follows. To an aqueous dispersion (6 mL) of L-aspartic acid (66.50 mg, 0.50 mmol) and basic copper carbonate (110.50 mg, 0.50 mmol) was slowly added 4,40 bipyridyl (78.00 mg, 0.50 mmol) in methanol (6 mL). The reaction mixture was stirred for 15 min in air and then transferred and sealed in a 25 mL Teflon-lined autoclave, which was heated at 398 K for 80 h. After gradual cooling to room temperature at the rate of 10 C per hour, light blue crystals were deposited in the Teflon vessel suitable for single crystal diffraction studies along with the amorphous matter. The material was washed several times with a 1:1 methanol/water mixture to separate the crystals from the amorphous matter present. Crystals of 3 were found to be insoluble in common polar and nonpolar solvents. Elemental analysis for 3 (%), Calcd: C, 37.67; H, 2.46; N, 9.76. Found: C, 37.44; H, 2.87; N, 9.55. IR (KBr): 36433283br, 3152s, 1642m, 1604m, 2461m, 1971m, 646m, 617m, 566m, 538m. CCDC Number: CCDC 784579. X-ray Crystallography. X-ray data for 13 were collected at 110 K on a Bruker Smart Apex CCD equipped with graphite monochromatized Mo KR radiation (λ = 0.71073 Å). Data were processed through the 1632
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Table 1. Crystal Data and Refinement Parameters for Complexes 13 identification code
compound 1
compound 2
compound 3
chemical formula
C17H20CuN5O7S
C11H12CuN3O5
formula weight
501.98
329.78
270.71
crystal color
light blue
blue
light blue
C9H7CuN2O4
crystal size (mm)
0.50 0.10 0.05
0.30 0.12 0.04
0.31 0.09 0.07
temperature (K)
110(2)
110(2)
110(2)
crystal system
monoclinic
orthorhombic
orthorhombic
space group
P21/c
P2(1)2(1)2
P2(1)2(1)2
a (Å) b (Å)
10.3197(10) 19.6947(19)
23.234(6) 5.1735(12)
21.490(3) 6.8822(10)
c (Å)
11.0388(11)
11.294(3)
7.8075(11)
R (deg)
90
90
90
β (deg)
112.798(2)
90
90
γ (deg)
90
90
90
Z
4
4
4
V (Å3)
2068.3(3)
1357.6(6)
1154.7(3)
density (mg/m3) absorption coefficient (mm1)
1.612 1.208
1.613 1.631
1.557 1.890
F(000)
1032
672
544
reflections collected
12265
9396
5722
independent reflections
4783
2353
2643
R(int)
0.0405
0.0640
0.0336
number of parameters
320
182
117
S(goodness of fit) on F2
1.281
1.200
1.158
final R1/wR2 (I > 2σ(I)) weighted R1/wR2 (all data)
0.0831/0.1619 0.0956/0.1668
0.0842/0.1778 0.0888/0.1800
0.0630/0.1439 0.0678/0.1460
SAINT19 reduction and SADABS20 absorption software. The structures were solved by direct methods using SHELXTL21 and were refined on F2 by the full-matrix least-squares technique using the SHELXL-9722 package. The diagrams of the crystal structures are generated using the programs ORTEP,23 Mercury 2.3,24 or PLATON.25 Details of crystallographic data and structure refinement parameters for all three compounds are given in Table 1. In the case of 1, the C17 carbon possesses a positional disorder and the occupancy factor for the different positions of the carbon atom is obtained by the FVAR command of the SHELXL-97 program, and this atom is refined only isotropically in the final cycles of refinement. Similarly, in the case of 3, the pyridyl nitrogen N2 and carbon atoms C5, C6, and C7 of the symmetrically disposed 4,40 -Bpy moiety possess a positional disorder, as in the case of 1, and refined only isotropically. Hydrogen atoms attached to the disordered carbon of the 0 L-cysteate moiety in 1, disordered atoms of the 4,4 -Bpy for 3, and the lattice water hydrogens in the case of 2 are not located/included in the final refinement cycles. However, all other hydrogen atoms attached to the ligand moieties except the one mentioned above are either located from the difference Fourier map or stereochemically fixed. The disordered water molecule present in the lattice was removed from the structural data of 3 by PLATON SQUEEZ,25 because the residual peaks obtained from the difference Fourier map were diffused and it was difficult to model the disordered water molecule. Magnetic Measurements. Magnetic measurements were carried out at “Unitat de Mesures Magnetiques (Universitat de Barcelona)” on polycrystalline samples with a Quantum Design SQUID MPMS-XL magnetometer working in the 2.0300 K range. The magnetic fields were 0.05 and 1.0 T for 2 and 1.0 T for 3, respectively. The diamagnetic corrections were evaluated from Pascal0 s constants. The fit was performed by minimizing the function R (agreement factor defined as ∑[(χM)exptl (χM)calcd]2/∑[(χM)exptl]2).
’ RESULTS AND DISCUSSION IR, PXRD, and TGA Data. IR spectra of all the three complexes are given in the Supporting Information as Figures S2, S3, and S4, respectively. In the case of complex 1, the broad band centering near 3440 cm1 and a sharp signal at 3131 cm1 can be attributed to the OH and NH stretching frequencies of the water molecule and the amino group, respectively. The sharp bands at 1385 cm1 and 1232 cm1 indicate the presence of a sulfonate functionality. Moreover, the medium frequency bands at 1630 cm1 and 1525 cm1 for the asymmetric and symmetric CdO stretching modes of carboxylic acid suggest the presence of an amino acid moiety coordinated to the Cu(II) center in complex 1. The incorporation of an aromatic ligand is identified by several overtone bands in the 23921842 cm1 range. The weak bands at 716, 653, 586, and 521 cm1 may be attributed to the CuN and CuO vibrational modes. In the case of complex 2, broad bands in the region around 3401 cm1 and the sharp signal at 3114 cm1 are attributable to the OH and NH stretching frequencies, whereas the medium frequency bands at 1630 cm1 and 1521 cm1 are for the asymmetric and symmetric CdO stretching modes of the carboxylate group of the Laspartate ligand coordinated to the metal center. The weak bands at 654 and 612 cm1 can be assigned to the CuN and CuO vibrational modes. For complex 3, the broad band around 3417 cm1 and the sharp signal at 3152 cm1 correspond to the OH and NH stretching frequencies. The presence of the coordinated amino acid moiety is established via medium frequency bands at 1642 and 1604 cm1 belonging to the asymmetric CdO stretch and 1410 cm1 for the symmetric 1633
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Figure 1. (ac) ORTEP diagrams depicting the coordination sphere with the atom numbering scheme for complexes 13 (40% probability factor for the thermal ellipsoids; only the major occupancy site for disorder atoms C17 in 1 and N2, C5, and C6 in 3 is shown in the diagram, and H-atoms are omitted for clarity).
CdO stretching modes of the carboxylic acid. The incorporation of an aromatic ligand is identified by several overtone bands in the region between 2461 and 1971 cm1, and weak bands at 646, 617, 566, and 538 cm1 can be assigned to the CuN and CuO vibrational modes. In order to confirm the homogeneity of the solvothermally synthesized materials, we have analyzed the PXRD patterns of complexes 13 and correlated the results with the respective simulated powder patterns obtained from the single crystal data. As depicted in Figures S5, S6, and S7 of the Supporting Information, the basic features of the PXRD pattern for all three compounds corroborate with the simulated single crystal data, indicating that the phase purity of the bulk product was obtained. All three complexes were air-stable and retained their crystalline integrity under ambient conditions. Thermogravimetric analysis (TGA) was performed to gauge the thermal stability, desolvation, and decomposition of complexes 13, which contain lattice water molecules. The thermogravimetric curve of 1 indicates the loss of a lattice water molecule in the temperature range 50130 C, followed by a gradual decomposition, leading to the collapse of the coordination compound. An observed weight loss of 3.59% (calculated 3.52%) corresponds to the loss of a lattice water molecule in the range 40100 C which is followed by the loss of a coordinated water molecule in the region 100140 C (obsd 3.62%, calc 3.59%). The gradual decomposition of the hydrogen bonded helical network proceeds in the temperature range 160 C onward (Figure S8). Similarly, the thermogram for 2 (Figure S9) also confirms the loss of a lattice water molecule followed by the gradual decomposition of the 2-D network. The first step in the range 40160 C of the TGA data indicates the loss of lattice water molecules with an observed weight loss of 5.56% (calculated 5.50%). TGA for complex 3 (Figure S10) indicates mainly three decay processes in the temperature ranges 40100, 140280, and 290650 C. While the first decay step indicates the loss of a lattice water molecule, the second and third steps envelop the successive decomposition of the 3-D network. The first observed weight loss of 3.22% indicates the release of the lattice water (calculated weight loss 3.27%) in the region 40110 C (peak at 75 C), which was removed from the crystal data due to difficulty in modeling the disordered water molecule. The framework starts to decompose with the loss of residual components beyond 180 C. Thus, the TGA data for all three complexes corroborate well with the structural data.
Crystal and Molecular Structure of {[Cu(L-cysteate)(1,4Bix)(H2O)] 3 H2O}n (1). Crystallographic data and ORTEP dia-
grams depicting the coordination sphere for all the three complexes are given in Table 1 and Figure 1, respectively. Complex 1 extends as 1-D helical chains along [0 1 0] supplemented by extensive intra- and intermolecular hydrogen bonding, with the lattice water molecule present as solvent of crystallizations. Complex 1 crystallizes in a monoclinic system with the P21/c space group. The Cu(II) metal center possesses a distorted square pyramidal environment with a N3O2 coordination sphere in which the deprotonated L-cysteic acid is coordinated via the amino carboxylate end to form a five member chelated ring and 1,4-bis(imidazol-1-ylmethyl)benzene (1,4-Bix) is coordinated through the terminal nitrogen atoms N1 and N4 in extending the helical network with water oxygen O6 at the apical position, as depicted in Figure 1a. Thus, the basal plane of the Cu(II) center encompasses nitrogen atoms N1 and N4 from two different 1,4-Bix moieties, it encompasses amino nitrogen (N5) and carboxylate oxygen (O1) in chelated mode from L-cysteate, and the axial position of the square pyramid is satisfied by the coordinated water molecule (CuO6 = 2.328(4) Å), which is above the basal plane (by 0.13 Å) toward the axial water molecule in completing the pentacoordination. The CuN distances of the 1,4-Bix and the amino nitrogen of the L-cysteate ligand range from 1.986(4) to 2.004(5) Å, while the CuO1 distance of the carboxylate oxygen coordinated to the metal is 1.972(3) Å (Supporting Information S13), which is similar to the cases of amino-acidato Cu(II) complexes reported earlier.16ac The flexible exobidentate N-donor ligand 1,4-Bix is oriented in syn conformation, bridging the adjacent Cu(II) centers through the terminal nitrogens N1 and N4, giving rise to a polymeric helical chain along the b-axis, as depicted in Figure 2. The terminal imidazole rings (N1C to C3N2) and (N3C12 to C14N4) of the 1,4-Bix ligand are rotated by 64.41 and 87.35 with respect to the central phenyl ring to make effective coordination with Cu(II) by adopting the syn conformation in bridging the neighboring metal centers with a Cu 3 3 3 Cu separation distance within the helical chain 11.23 Å. In an attempt to understand the supramolecular arrangement of the helical network, the packing and hydrogen bonding interactions between the molecules were analyzed in detail. The free sulfonate end as well as the carboxylate oxygen O2 confines the role of the multidentate bridging ligand L-cysteate to a simple chelating ligand with a Cu(II) center, thereby limiting complex 1 to a 1-D helical
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Figure 2. (a and b) Helical net in the one-dimensional coordination polymer for complex 1 via bridging the metal centers by the flexible 1,4,-Bix moiety (ball and stick and space filling diagrams). (c) H-bonding interactions between the adjacent helicate nets with opposite helicity in the formation of hydrogen bonded bilayers in complex 1.
Figure 3. Packing diagram with hydrogen bonding interactions viewed down the c-axis in complex 1, depicting the two dimensional hydrogen bonded supramolecular assembly between the double stranded helical bilayered network through the lattice water molecule oriented between the bilayers.
coordination polymer via linking the metal atoms through the terminal nitrogen atoms of the 1,4-Bix ligand (Figure 2a). The noteworthy feature of this complex is the involvement of oxygen atoms of the lynching SO3 group and the coordinated carboxylate group acting as acceptors (O1 and SO3) along with the coordinated and lattice water molecule in the formation of a threedimensional supramolecular assembly via various intra- as well as intermolecular H-bonding interactions. Neighboring helical nets with left and right handed helicity exist as bilayers oriented along the b-axis via intermolecular NH 3 3 3 O, CH 3 3 3 O, and OH 3 3 3 O hydrogen bonding interactions in which the sulfonate oxygen acts as acceptors and amino and coordinated water hydrogens act as the donors in stabilizing the double stranded helical bilayers in the crystal lattice as depicted in Figure 2c. Hence, the sulfonate oxygen O3 is involved in a weak intermolecular CH 3 3 3 O interaction with methyl hydrogen H11A, whereas O4 is making two CH 3 3 3 O and one NH 3 3 3 O contact with the imidazole hydrogen H2, H3, and the amino hydrogen H2C, respectively. Further, sulfonate oxygen O5 is involved in CH 3 3 3 O interaction with the methyl hydrogen H11A and H11B attached C11; coordinated water O6 acts as a donor relating hydrogen H6 in OH 3 3 3 O intermolecular H-bonding with coordinated carboxylate oxygen O1 in the formation of bilayers between the single stranded helical nets with P and M helicity. As depicted in the packing diagram viewed down
the c-axis (Figure 3), the helices running down the b-axis are H-bonded laterally to give a thick layer running along the ab-plane; furthermore, the intralayer water molecule(O7) gives an overall 3-D hydrogen bonded network in which O7 acts as both donor and acceptor. Thus, the hydrogen atom attached to O7 (H7C and H7D) is making an OH 3 3 3 O contact with the sulphonate oxygen O5 and the noncoordinated carboxylate oxygen O2. O7 acts as an acceptor in making OH 3 3 3 O and CH 3 3 3 O contacts with the H6 of the coordinated water molecule and the methyl hydrogens H4A and H4B, respectively. Details of all these pertinent hydrogen bonding interactions with the symmetry codes in the formation of the two-dimensional hydrogen bonded sheetlike network in complex 1 are given in Table 2. Structural reports on mixed ligand metal complexes involving L-cysteic acid with N-donor ligands are scarce in the literature. The crystal structures of two coordination complexes, [Cu(Lcysteate)(2,20 -Bpy)(H2O)] (a) and {[Co(L-cysteate)(4,40 -Bpy) (H2O)] 3 H2O}n (b), synthesized under different reaction conditions have been reported by us recently.16a The complex (a) is a discrete monomer which is associated via OH 3 3 3 O and NH 3 3 3 O interactions into bilayers and exists as supramolecular hydrogen bonded racemic helicates connecting the screw related molecules. The Co complex (b) is a two-dimensional coordination network obtained by the hydrothermal method in which adjacent one-dimensional carboxylate bridged 1635
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Table 2. Hydrogen Bonding Parameters for Complexes 13 DH 3 3 3 A
d(D 3 3 3 A) (Å)
— DH 3 3 3 A (deg)
2.04(7)
2.881(8)
176(5)
2.21
2.937(6)
150
1.95
2.823(6)
168
1.94
2.807(7)
163
1.95
2.713(6)
172
2.55
3.414(8)
155
2.17
3.074(7)
163
2.60(5) 2.54(6)
3.467(7) 3.415(7)
159(6) 157(5)
2.55
3.337(7)
139
2.55
3.477(7)
159
2.45
3.321(8)
150
d(H 3 3 3 A) (Å) Compound 1
N(5)H(2C) 3 3 3 O(4)1 O(6)H(6C) 3 3 3 O(7)2 O(6)H(6D) 3 3 3 O(1)3 O(7)H(7C) 3 3 3 O(5)4 O(7)H(7D) 3 3 3 O(2)5 C(2)H(2) 3 3 3 O(4)4 C(3)H(3) 3 3 3 O(4)1 C(4)H(4A) 3 3 3 O(7)6 C(4)H(4B) 3 3 3 O(7)7
C(11)H(11A) 3 3 3 O(3)8 C(11)H(11A) 3 3 3 O(5)8 C(11)H(11B) 3 3 3 O(5)9
Symmetry code: (1) 2 x, y, 1 z; (2) 1 þ x, y, z; (3) x, 1/2 y, 1/2 þ z; (4) 2 x, 1/2 þ y, 3/2 z; (5) 1 þ x, 1/2 y, 1/2 þ z; (6) x, 1/2 y, 1/2 þ z; (7) x, y, z; (8) 2 x, y, 2 z; (9) 1 þ x, y, z Compound 2 N(1)H(1A) 3 3 3 O(4)1 N(1)H(1B) 3 3 3 O(1)1
2.36 2.48
3.093(12) 3.106(11)
139 127
C(6)H(6) 3 3 3 O(3)2 C(8)H(8A) 3 3 3 O(4)3
2.41
3.314(12)
165
2.59
3.513(14)
159
N(1)H(1A) 3 3 3 O(3)1 N(1)H(1B) 3 3 3 O(2)2 C(8)H(8) 3 3 3 O(1)3
2.13
2.902(6)
143
2.14
2.875(7)
138
2.53
3.281(7)
134
Symmetry code: (1) x, 1 þ y, z; (2) 3/2 x, 1/2 þ y, 2 z; (3) 3/2 x, 1/2 þ y, 2 z Compound 3
2.55 3.184(7) C(8)H(8) 3 3 3 O(4)4 Symmetry code: (1) 1/2 x, 1/2 þ y, 1 z; (2) 1/2 x, 1/2 þ y, z; (3) 1/2 x, 1/2 þ y, z; (4) 1/2 x, 1/2 þ y, 1 z
Co(L-cysteate) layers are pillared by the exobidentate 4,40 -Bpy ligand, forming a two-dimensional 44-sql network. In another set, mixed ligand chiral coordination compounds recently published by us, [{Cd(L-cysteate)(4,40 -Bpy)(H2O)} 3 3.5H2O]n (c) and [{Zn2(L-cysteate)2(4,40 -Bpy)2(H2O)4}(H2O)(4,40 -Bpy)] (d), showed 44-sql and 63-hcb type network topology, respectively.16d It is interesting to note that Jiang and co-workers also reported5e crystal structures of two interesting pillared supramolecular isomers, {[Co2(L-cysteate)2(4,40 -Bpy)2(H2O)2] 3 3H2O}n (e) and {[Co2 (L-cysteate)2(4,40 -Bpy)(H2O)4](4,40 -Bpy) 3 H2O}n (f), prepared by a variation of the reaction conditions with the same metal-toligand ratio of Co(NO3)2 3 6H2O with mixed ligands L-cysteic acid and 4,40 -bipyridine (4,40 -Bpy), giving rise to distinct solid phases. A comparison of the structural morphology of e and f revealed that two independent Co(II) centers are chelated and bridged by different L-cysteates, forming a one-dimensional (1D) chain, which is further pillared by 4,40 -Bpy into a novel three-dimensional (42 3 84)-lvt structure and a two-dimensional brick-wall structure for e and f, respectively. For the 3-D supramolecular network e, an additional coordination from the sulfonate oxygen compared to the two-dimensional brick-wall type net in f is observed. The crystal structure of the brick-wall type net in f with a Co metal center is comparable with the (63) brick-wall type net of Zn complex d. However, in the case of complex 1, the L-cysteate moiety is simply involved as a chelated ligand via an aminocarboxylate group, as observed for the discrete complex a. The helical one-dimensional network is fabricated by the coordination through the terminal
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nitrogen atoms of the 1,4-Bix moiety in the syn conformation, and the meso helical bilayer structure in complexes 1 and a can be attributed to the hydrogen bonding interactions. The comparative structural studies of the mixed ligand complexes involving L-cysteic acid and N-donor ligands with transition metals clearly indicate that the reaction conditions and versatile coordination geometries of the transition metals used play a crucial role in the structural diversity and the concomitant network topology. Crystal and Molecular Structures of {[Cu(L-aspartate)(1,4Bix)0.5] 3 H2O}n (2) and {[Cu(L-aspartate)(4,40 -Bpy)0.5] 3 H2O}n (3). Both complexes 2 and 3 are crystallized in the orthorhombic system with chiral space group P2(1)2(1)2 along with water molecules in the lattice as the solvent of crystallization. The crystal structure of complex 2 revealed a two-dimensional coordination arrangement, whereas 3 is a three-dimensional coordination net in which CuL-aspartate clusters are pillared by the N-donor ligands 1,4-Bix and 4,40 -Bpy, respectively. The ORTEP diagrams of the coordination spheres for 2 and 3 are depicted in Figure 1b and c, and the selected bond length and angles are shown in Table S13. Even though the structure for 3 is reported by Rosseinsky et al., in the context of enantioselective catalysis, we obtained the same product under different reaction conditions and explored the structural aspects with magnetic properties. In the case of complex 2, the coordination geometry about each metal center is distorted square pyramidal. As depicted in Figure 1b, two L-aspartate units are involved in coordination with the Cu(II). One of the L-aspartate molecules 1636
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Figure 4. (a) One dimensional CuL-aspartate chain propagating in helical fashion in complex 2 (green rod indicates the helical axis); (b) representation of CuL-aspartate helical backbone; (c) pillaring of CuL-aspartate helices by 1,4-Bix oriented in the anti conformation creating 2-D sheets in 2; (d and e) helical arrangement in the whole molecule involving both 1,4-Bix and L-aspartate viewed down the a-axis (ball and stick/space fill representation).
acts as a tridentate ligand, leading to the coordination of the amino nitrogen N1 and the oxygen atoms O1and O3 of the terminal carboxylate group. The remaining two coordination sites are occupied by carboxylate oxygen O2 from the 21 screw related similar CuL-aspartate cluster and the terminal nitrogen atom N2 of the symmetrically disposed 1,4-Bix moiety. The nitrogen atom N2 of the pillar ligand is positioned trans to the amino nitrogen N1 of the L-aspartate molecule in distorted square pyramidal coordination around Cu(II). The square base of the Cu(II) coordination environment is constituted by the chelated amino carboxylate group through N1, O3 of the first Laspartate, N2 from the 1,4-Bix moiety, and the O2 from the second L-aspartate, in which the CuN and CuO distances range from 1.981(7) Å to 1.994(9) Å, and 1.940(8) Å to 1.981(6) Å, respectively. The metal ion is above the square base plane by 0.18 Å toward the axially coordinated longer carboxylate oxygen O3 (CuO3 = 2.341(6) Å) in completing the distorted square pyramidal coordination geometry. The mode of orientation and linkage between the screw related Cu(II) metal centers by Laspartate ligand generates (CuL-aspartate)n clusters, leading to a helical corrugated layer along the b-axis (Figure 4a and b). Terminal carboxylate oxygens O1 and O2 from the L-aspartate ligand the synanti mode of coordination to bridge the adjacent metal centers with the Cu 3 3 3 Cu separation distance within the helical network 5.37 Å and the Cu 3 3 3 Cu 3 3 3 Cu angle 57.62. The (CuL-aspartate) helical clusters oriented along the b-axis are further pillared alternatively from either side via a 1,4-Bix ligand into a two-dimensional network, as depicted in Figure 4c. The Cu 3 3 3 Cu separation distance between the pillared Cu centers through the terminal nitrogens of the symmetrically disposed 1,4-Bix ligand in the anti mode is 13.16 Å, which is longer by 1.79 Å than that observed for complex 1. The difference in
Cu 3 3 3 Cu bridging distance can be attributed to the syn and anti conformation adopted by 1,4-Bix in 1 and 2, respectively, bridging the metal centers, which is evident from the mean plane angle of the symmetrically disposed imidazole rings making an angle 86.11 with the central phenyl ring in 1, whereas the imidzole rings espouse 64.41 and 87.35, respectively, for 2. Interestingly, two types of helical chains are observed along two different axes in complex 2. While the first helical chain involves Cu(II) centers bidged via L-aspartate (Figure 4a and b), the second helical motif comprises the whole molecule in which the (CuL-aspartate) chains are pillared by 1,4-Bix, with the metal on the alternate clusters imposing a helical twist in complex 2, viewed down the b-axis, as depicted in Figure 4d and e. TOPOS software26a was used to explore the topology of 2 in detail from the crystallographic data. The Cu(II) center generates a 3-coordinated hexagonal net (63-hcb), as depicted in Figure 5a. The identified network topology is evaluated on the basis of the Reticular Chemistry Structure Resource (RCSR) Database also.26b The packing diagram of complex 2 along with hydrogen bonding interactions is given in Supporting Information Figure S11. Amino hydrogens H1A and H1B from the L-aspartate are making a rather weak NH 3 3 3 O interaction with the carboxylate oxygens O1 and O4, while the methyl hydrogens H8A and H6 from the terminal imidaziole moiety are making good intermolecular CH 3 3 3 O hydrogen bonding with carboxylate oxygens O3 and O4, respectively. Even though hydrogens could not be located on lattice water molecule O5, it is making good short contact with the carboxylate oxygen O4 with O4 3 3 3 O5 distance 2.70 Å. Details of all these pertinent intermolecular H-bonding interactions with symmetry codes are given in Table 2. The crystal structure of the complex [Cu(L-aspartate)(4,40 Bpy)0.5]n 3 H2O (3) revealed that the Cu(II) possesses N2O4 1637
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Figure 5. (a) Simplified topological presentation of the 2-D hexagonal network (hcb) in 2 and the (b) 3-D ins topology for complex 3.
Figure 6. (a) Two dimensional (CuL-aspartate)n square grid type network in the bc-plane for 3; (b) pillaring of two-dimensional (CuL-aspartate)n grids by 4,40 -Bpy, generating a 3-D architecture in 3.
coordination with a distorted octahedral geometry (Figure 1c). A brief description of the crystal structure is presented here in an attempt to understand the structural topology and the magnetic behavior for complex 3. Cu(II) is coordinated with three different amino acid moieties, in which one is wrapped around the metal involving the amino carboxylate end (involving N1 and O3) and the terminal carboxylate oxygen O2, while the other two amino acid moieties coordinated to the metal via O1 and O4. Thus, all the carboxylate oxygens from the L-aspartate moiety are involved in coordination with the screw related metal centers along b- and c-axes in synanti fashion, generating a two-dimensional (CuL-aspartate)n grid type network along the bc-plane (Figure 6a). The Cu 3 3 3 Cu separation distance within the rectangular grid, with the Cu atom occupying the corners of the rectangle, is 5.34 and 5.76 Å, respectively. The two-dimensional rectangular grids are pillared by 4,40 -Bpy ligand (with a Cu 3 3 3 Cu distance 11.05 Å), generating a three-dimensional network, as depicted in Figure 6c. The CuO distance involving the carboxylate oxygens ranges from 1.956(4) to 2.437(5), and the CuN distance involving the amino nitrogen and terminal nitrogen from the 1,4-Bix is 1.984(4) to 2.037(6), respectively. In an attempt to understand the topology of the three-dimensional architecture, we have analyzed the structural data using the program TOPOS. In 3, the threedimensional framework obtained by the pillaring of Cu(L-aspartate) 2-D helical layers with 4,40 -Bpy units was identified as a (3,4)-coordinated binodal net with (63)(65.8)-ins topology (Figure 5b). A closer structural analysis of 3 reveals the cage type
structure as shown in Supporting Information Figure S12, and the 3-D grids are formed with the dimensions 11.0531 7.8075 6.8822 Å3 based on dCu 3 3 3 Cu 3 3 3 Cu distances, which opens up the possibility of the material to be microporous. Rosseinsky and coworkers reported some pioneering work in the area of porous chiral coordination polymers involving a chiral amino acid backbone and various exocyclic N-donor ligands toward enantioselective sorption of small chiral molecules, gas adsorption studies, and catalysis.13,14 In addition to the above-mentioned Cu complex, an almost identical Ni complex with a three-dimensional network is also reported by him incorporating 4,40 -Bpy and 1,2-bis(4-pyridyl)ethylene (4,40 -Bpe) N-donor pillar ligands in altering the cavity size of these chiral microporous materials.13a,14 As observed in complex 2, intermolecular NH 3 3 3 O interaction involving an amino nitrogen with the carboxylate oxygen and additional CH 3 3 3 O interactions involving the carboxylate oxygen with the phenyl hydrogen are observed in 3, which are given in Table 2, along with the symmetry codes. Circular Dichroism (CD) Analysis for 2 and 3. The chiral nature of the 2-D and 3-D coordination polymers (2 and 3) was confirmed by solid state CD spectroscopy using powdered bulk crystals in a KBr matrix. Compounds 2 and 3 display similar dichroic signals in CD spectra parallel to the respective absorption frequencies observed in solid state UV experiments, as shown in Figure 7. Both compounds 2 and 3 exhibit a negative Cotton effect at frequencies 464 and 394 nm, respectively, with sensible matching 1638
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Figure 7. Solid state CD spectra of complexes 2 and 3 in the KBr matrix (red). Inset (blue) spectra represent the solid state UV in the corresponding wavelength range.
Figure 8. Fittings of the χM vs T (left) and χMT vs T (right) of complex 2 and χMT vs T of complex 3 between 2.0 and 300.0 K. The experimental data for 2 and 3 is shown as black and hollow squares, respectively, whereas the solid red line presents the theoretical data for 2.
corresponding to the UV absorption plots, which apparently designate the chiral nature in the framework materials. However, the inflection points associated with the mentioned negative maximum signals can be attributed to the contribution of the framework geometry/rigidity to the resultant chirality of respective bulk crystals. Magnetic Data. Solid-state, variable-temperature (2300 K) magnetic susceptibility data using 0.05 T (from 2 to 25 K) and 1.0 T (from 30 to 300 K) fields were collected on polycrystalline samples of complex 2. The resulting data is plotted in Figure 8 as χM vs T (left) and χMT vs T (right), respectively. The χMT data for compound 2 shows a behavior characteristic of very weak coupled CuII systems, comparable to isolated mononuclear species containing such a metal center. This way, the magnetic susceptibility value at 300 K is 0.40 cm3 mol1 K, very similar to that expected for a magnetically isolated S = 1/2 system (χMT = 0.375 cm3 mol1 K, assuming g = 2.0); this value is maintained upon cooling until approximately 20 K (0.39 cm3 mol1 K) and slightly drops to 0.38 cm3 mol1 K at 2 K (Figure 8). This drop at the lowest temperatures is due to the sum of different factors, such as field saturation, zero-field splitting, and antiferromagnetic intermolecular interactions. On the other hand, the crystallographic data of 2 depict a complex 2-D system formed by 1D helical frameworks connected
with each other through L-cysteate ligands. This could be simplified from a magnetic point of view, where interactions among chains could be neglected due to the nature and length of ligand. 1D arrays are formed by CuII ions connected to two other screw related neighbors at identical distances (Cu 3 3 3 Cu distances of 5.367 Å) and with the same type of arrangements. Hence, correlation of the magnetic data was performed using an expression for the case of chains of equally spaced CuII ions.27 The final equation was derived from the Hamiltonian H = J∑SAi 3 SAiþ1.28 The best fit parameters were found for J = 0.11 ( 0.01 cm1, g = 2.04 ( 0.01, TIP = 60 106 cm3 mol1, and R = 2 105. These values were already anticipated in the description of the experimental data above and match well with other 1D CuII systems in the literature.29 To evaluate the results, we should stress two parts: (i) first, the value of the exchange coupling indicates a very weak (almost inexistent) interaction among CuII ions. This compound shows a unique distance among the copper centers (5.367 Å) longer than other examples in the literature30 which directly correlates to the strength of the coupling. Also, weak interactions are typical in carboxylate-bridge CuII arrays where the carboxylate groups adopt synanti conformations. On the other hand, all CuII ions are pentacoordinated, exhibiting square pyramidal arrangements, where each carboxylate group bounds the apex of one Cu unit with the base of a neighbor. Taking into account the metallic orbitals involved in such coordinations, these motives could also be classified as perpendicular (the dz2 orbital of a Cu ion is in the same plane as the dx2y2 orbitals of the neighbor; equatorialaxial),31 where the exchange between centers is expected to be weak. All the factors described above agree with the lower value found for J. (ii) In connection with the negative sign and, therefore, the antiferromagnetic nature of the exchange within the polymeric units, previous works in the literature have shown the possibility of both ferro- and antiferromagnetic interactions in carboxylate-bridge Cu(II) systems exhibiting synanti conformations.2729,31 In general, the planarity of the CuOCOCu skeleton indicates antiferromagnetic coupling, but also the distribution of the magnetic orbitals (perpendicular) as well as the dihedral angle between the plane formed by the O1C1O2 atoms of the carboxylate and the equatorial Cu1 center (not orthogonal for this compound) should be taken into account.29 Small variations concerning these aspects may facilitate a type of exchange versus the other. Here, the weak and antiferromagnetic nature of 2 matches well with the magnetic description of the orbitals and crystallographic parameters. 1639
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Crystal Growth & Design Temperature-dependent magnetic susceptibility measurements of 3 display a quasi constant value of 0.43 cm3 mol1 K at 300 K that barely decreases until 5 K (0.41 cm3 mol1 K) and then slightly drops to a value close to 0.40 cm3 mol1 K at 2 K. The decrease of the χMT depicts, as before, a weak antiferromagnetic behavior of the system at the lowest temperatures. Figure 8 (white squares) shows the magnetic behavior of this compound. As explained above, weak ferro- or antiferromagnetic behavior would be expected for synanti carboxylate bounded CuII systems.2729,31 In principle, the composition of this compound is very similar to the previous; however, now the system presents a 3-D arrangement, where each CuII center coordinates through the ligand to four other CuII ions building the final framework. Owing to the JahnTeller effect, the coordination sphere of each CuII ion could be better described as a distorted, elongated octahedron, where the magnetic orbital is the dx2y2 orbital. The magnetic orbitals are displayed in an equatorial-axial manner among each other, explaining the weak strength of the exchange coupling. Considering the complexity of the structure, the rigorous treatment of the experimental magnetic data would only be possible by performing theoretical calculations. Therefore, the overall system could only be described as weak and antiferromagnetic and the exchange couplings among CuII centers are expected to be very small.
’ CONCLUSIONS Three Cu(II) helical coordination polymers, {[Cu(L-cysteate) (1,4-Bix)(H2O)] 3 H2O}n (1), {[Cu(L-aspartate)(1,4-Bix)0.5] 3 H2O}n (2), and {[Cu2(L-aspartate)(4,4'-Bpy)0.5] 3 H2O}n (3), have been synthesized and characterized well using various physicochemical techniques, including single crystal X-ray diffraction. Complex 1 is a one-dimensional helical coordination net, while 2 and 3 showed 2-D and 3-D networks, respectively. The temperature dependent magnetic properties of the L-aspartic acid based 2-D and 3-D network (2 and 3) showed weak antiferromagnetic interaction and exchange couplings among CuII centers, which is in agreement with the structural data. The chiral nature of both these compounds in the solid state is also established using circular dichroism data. In the case of complex 1, a helical network is assembled by the coordination of the terminal nitrogen atoms of the 1,4-Bix moiety, whereas in the case of 2 and 3, the coordination of the amino carboxylate end/free terminal carboxylate of the L-aspartate is involved in bridging screw related metal ions .The helical chains of 2 and 3 are pillared by the exobidentate N-donor ligands 1,4-Bix and 4,40 -Bpy, generating 2-D hexagonal net (hcb) and 3-D (ins) type topologies, respectively. The versatile coordination geometry around the Cu(II) center and the conformational flexibility of the L-aspartate ligand are responsible for the diversity in the network topology in these complexes. A systematic synthetic approach is required to establish the desired species in the solvothermal synthesis of coordination polymers involving a ligand system with an inbuilt chiral backbone to achieve the appropriate structural topology. We are currently exploring the design of novel multidimensional coordination networks with mixed bridging ligands involving the chiral components, and efforts are underway to investigate the inclusion properties, the guest exchange phenomenon gas adsorption properties, and their magnetic properties. ’ ASSOCIATED CONTENT
bS
Supporting Information. Synthesis of 1,4-Bix, IR spectra, TGA plots, and powder X-ray diffraction patterns for
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complexes 13, packing diagrams and additional crystallographic figures, selected bond angles, bond lengths table, and crystallographic information files (CIF) for structures 13. This material is available free of charge via the Internet at http://pubs. acs.org.
’ AUTHOR INFORMATION Corresponding Author
*Fax: þ91 278 2567562. Telephone: þ91 278-2567760. E-mail: sureshe123@rediffmail.com;
[email protected].
’ ACKNOWLEDGMENT The authors gratefully acknowledge the Department of Science and Technology (DST), New Delhi, India (Grant No. SR/S1/IC-37/2006), and CSIR, India (Grant No.NWP-0010), for financial support. A.C.K. and K.K.B. acknowledge DST (India) and CSIR (India) for S.R.F. and J.R.F., respectively. Dr. Aliaga-Alcalde acknowledges Ministerio de Educacion y Ciencia (CTQ2009-06959/BQU) for financial support and ICREA (Institucio Catalana de Recerca i Estudis Avanc-ats) for supporting the work. The authors are grateful to Mrs. Sheetal N. Patel for TGA data, Mr. Viral Vakani for microanalysis, Mr. Vinod Kumar Agrawal for IR data, Dr. Prgya Bhatt for PXRD analysis, and Dr. P. Paul for all-round analytical support. The authors are thankful to the reviewers for their critical comments, useful tips and suggestions for the assignment of topology in the case of complexes 2 and 3, and the relevant literature related to deducing the topology. ’ REFERENCES (1) Long, J. R.; Yaghi, O. M. Chem. Soc. Rev. 2009, 38, 1213. (2) Kuppler, R. J.; Timmons, D. J.; Fang, Q. R.; Li, J. R.; Makal, T. A.; Young, M. D.; Yuan, D.; Zhao, D.; Zhuang, W.; Zhou, H. C. Coord. Chem. Rev. 2009, 253, 3042. (3) Hong, D. Y.; Hwang, Y. K.; Serre, C.; Ferey, G.; Chang, J. S. Adv. Funct. Mater. 2009, 19, 1537. (4) (a) Wu, C.; Hu, A.; Zhang, L.; Lin, W. J. Am. Chem. Soc. 2005, 127, 8940. (b) Dybtsev, D. N.; Nuzhdin, A. L.; Chun, H.; Bryliakov, K. P.; Talsi, E. P.; Fedin, V. P.; Kim, K. Angew. Chem., Int. Ed. 2006, 45, 916. (5) (a) Rosi, N. L.; Eckert, J.; Eddaoudi, M.; Vodak, D. T.; Kim, J.; O’Keeffe, M.; Yaghi, O. M. Science 2003, 300, 1127. (b) Kesanli, B.; Cui, Y.; Smith, M. R.; Bittner, E. W.; Bockrath, B. C.; Lin, W. Angew. Chem., Int. Ed. 2005, 44, 72. (c) Pan, L.; Parker, B.; Huang, X.; Olson, D. H.; Lee, J. Y.; Li, J. J. Am. Chem. Soc. 2006, 128, 4180. (d) Chen, B.; Zhao, X.; Putkham, A.; Hong, K.; Lobkovsky, E. B.; Hurtado, E. J.; Fletcher, A. J.; Thomas, K. M. J. Am. Chem. Soc. 2008, 130, 6411. (e) Huang, F. P.; Li, H. Y.; Tian, J. L.; Gu, W.; Jiang, Y. M.; Yan, S. P.; Liao, D. Z. Cryst. Growth Des. 2009, 9, 3191. (6) (a) Horcajada, P.; Serre, C.; Vallet-Regí, M.; Sebban, M.; Taulelle, F.; Ferey, G. Angew. Chem., Int. Ed. 2006, 45, 5974. (b) Horcajada, P.; Serre, C.; Maurin, G.; Ramsahye, N. A.; Balas, F.; Regí, M. V.; Sebban, M.; Taulelle, F.; Ferey, G. J. Am. Chem. Soc. 2008, 130, 6774. (7) (a) Uemura, T.; Yanai, N.; Kitagawa, S. Chem. Soc. Rev. 2009, 38, 1228. (b) Uemura, T.; Horike, S.; Kitagawa, S. Chem. Asian J. 2006, 1, 36. (8) (a) Lill, D. T. D.; Gunning, N. S.; Cahill, C. L. Inorg. Chem. 2005, 44, 258. (b) Pelle, F.; Surble, S.; Serre, C.; Millange, F.; Ferey, G. J. Lumin. 2007, 492, 122. (9) Harbuzaru, B. V.; Corma, A.; Rey, F.; Atienzar, P.; Jorda, J. L.; García, H.; Ananias, D.; Carlos, L. D.; Rocha, J. Angew. Chem., Int. Ed. 2008, 47, 1080. 1640
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