3d–4d–4f Heterotrimetallic 3D Chiral Frameworks Based on Octahedral

Jan 15, 2013 - Octahedral {Ni6Ag8S12Cl} or Trigonal Dipyramidal {Co2Ag3S6} Clusters: ..... Crystal data of compounds 2, 3, and 6 were also collected...
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3d−4d−4f Heterotrimetallic 3D Chiral Frameworks Based on Octahedral {Ni6Ag8S12Cl} or Trigonal Dipyramidal {Co2Ag3S6} Clusters: Synthesis, Crystal Structures, and Characterization Zhong-Yi Li,†,‡ He-Qing Huang,† Long Xu,† Rui-Bin Liu,† Jian-Jun Zhang,*,† Shu-Qin Liu,† and Chun-Ying Duan*,†,‡ †

Chemistry College, Dalian University of Technology, Dalian 116024, China State Key Laboratory of Fine Chemicals, Dalian University of Technology, Dalian 116024, China

‡

S Supporting Information *

ABSTRACT: The self-assembly reactions of AgNO3, Ln(NO3)3 (Ln = La, Eu, and Tb), D-penicillamine (D-pen, H2L), and NiCl2 (or CoCl2) lead to the formation of six new compounds: (H3O)3[LnNi6Ag8L12Cl(Ac)(H2O)4](H2O)28 (Ln = La (1); Eu (2); and Tb (3)) and (H3O)2[LnCo2Ag3L6](H2O)3 (Ln = La (4); Eu (5); and Tb (6)). Single crystal X-ray analyses show that 1, 2, and 3 are isomorphous and have a 3D anionic framework in which the nodes are octahedral {Ni6Ag8S12Cl} clusters, and Ln3+ ions and the connectors are the CCHCOO chains of the D-pen ligands. Moreover, 4, 5, and 6 are also isomorphous, possessing a 3D anionic framework with trigonal dipyramidal {Co2Ag3S6} clusters, Ln3+ as nodes, and the CCHCOO chains of the D-pen ligands as connectors. Topology analysis indicates that the two series of 3d− 4d−4f heterotrimetallic frameworks have (3,3)-connected utg and (6,6)connected pcu networks, respectively. The frameworks are rigid and stable. The porosity is retained after the guest molecules are removed and can take back guest molecules again. Solid-state UV−vis spectroscopy experiments show that compounds 1−6 are all medium gap semiconductors with band gaps of 1.82, 1.80, 1.83, 1.68, 1.71, and 1.72 eV, respectively.

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INTRODUCTION Multifunctional open framework materials derived from the combination of components with inherent properties through self-assembly process have received much attention in recent years because of their fascinating structures and potential applications in many different areas, such as catalysis, sizeselective uptake, and separation, storage, and conductivity.1 Of these, the chalcogenides,2 especially 3D chalcogenide frameworks, occupy an important position as they represent a perfect combination of chalcogenide clusters and porous materials, and some even can act as porous semiconductors.3,4 The fascinating structures and interesting properties of these materials inspires chemists to develop new chalcogenide frameworks with either new cluster units or new framework topologies, which are the main factors affecting the properties of the products. Generally, the chalcogenide frameworks are based on metal ions from groups 12−14, and some also are based on or doped with transition metal ions.3−5 By contrast, Ln-doped frameworks are still quite rare due to the unstable Ln−S bond, although Ln3+ ions have higher coordination number and interesting photoluminescence properties. Thus, organic−inorganic hybrid method has been developed through the use of suitable organic ligands, which can hold Ln3+ ions and chalcogenide clusters together.6−8 Several low dimensional Ln-doped materials have been synthesized in this way.7,8 However, 3D © XXXX American Chemical Society

Ln-doped open frameworks are uncommon, and the synthesis of this special framework still remains a great challenge.6a In marked contrast to the extensive studies of heterobimetallic compounds, relatively few papers are devoted to the studies of heterotrimetallic compounds, especially of d−d′−f types, although interesting properties such as catalysis,9 photoactive materials,10 and molecular magnetism11−13 have been observed in many of them owning to the interactions among three types of metal ions locating in close proximity in one molecular system. Moreover, most of the heterotrimetallic compounds bear isolated structure and extended frameworks are rare.12,13 To our knowledge, only two reports focused on 3D d−d′−f heterotrimetallic compounds have been published up to now.13 α-Amino acids (AAs) are essential molecules to form peptides and proteins that serve important biological functions. Because of their various coordination modes and chiral nature, AAs can be used as ligands for the construction of a wide range of 3d−4f heterometallic clusters with interesting magnetic properties and chiral metal−organic frameworks (MOFs) with enantioselective recognition, separation, and catalytic properReceived: November 11, 2012 Revised: December 28, 2012

A

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Table 1. Crystal Data and Structure Refinement for 1, 4, and 5a formula MW crystal system space group a (Å) b (Å) c (Å) α (deg) β (deg) γ (deg) V (Å3)/ Z dcalcd (g/cm3) F(000) θ range (deg) reflections collected/unique R(int) Goodness-of-fit on F2 R1b (I > 2σ(I)) wR2c (all data) max/mean shift in final cycle absolute structure parameter a

1

4

5

C62H184Ag8ClLaN12Ni6O61S12 3848.51 tetragonal P41212 24.3687(14) 24.3687(14) 47.322(6) 90 90 90 28101(4)/8 1.819 15504 1.87−25.00 135132/24729 0.0896 0.989 0.0489 0.1206 0.001/0.000 0.021(13)

C30H66Ag3Co2LaN6O17S6 1555.63 trigonal P3221 10.1695(9) 10.1695(9) 41.686(7) 90 90 120 3733.5(8)/3 2.076 2316 2.31−24.99 18436/4359 0.0969 1.051 0.0482 0.1092 0.002/0.000 0.01(3)

C30H66Ag3Co2EuN6O17S6 1568.68 trigonal P3221 10.1532(8) 10.1532(8) 41.538(6) 90 90 120 3708.3(7)/3 2.107 2334 2.32- 27.47 25940/5663 0.0969 1.039 0.0588 0.1595 0.001/0.000 0.02(3)

1, a = 0.0642, b = 0.0000; 4, a = 0.0488, b = 3.2922; 5, a = 0.0812, b = 2.3256. bR1 = ∑(||Fo| − |Fc||)/∑|Fo|. cwR2 = {∑w[(F2o − F2c )]/∑w[(F and w = [σ2(F2o) + (aP)2 + bP]−1, where P = (F2o + 2F2c )/3.

2 2 0.5 o) ]} ,

ties.14 However, among them, 3D frameworks based on heterometallic clusters are quite rare.15 Cysteine and penicillamine contain both hard (O and N) and soft (S) donors, which makes them good ligands for many heterometallic transition metal chalcogenide clusters (such as {Ni6Ag8S12}16 and {Ni2Au3S6}17), extended chalcogenide frameworks based on single metal node18 and even several 1D or 2D polymeric compounds based on the transition metal chalcogenide clusters.8 Our continued investigations of 3d−4f heterometallic clusters based on amino acids have resulted in the discovery of six new 3d−4d−4f heterotrimetallic 3D chiral frameworks: (H3O)3[LnNi6Ag8L12Cl(Ac)(H2O)4](H2O)28 (Ln = La (1); Eu (2); and Tb (3)) and (H3O)2[LnCo2Ag3L6](H2O)3 (Ln = La (4); Eu (5); and Tb (6)). In the two series of compounds, Dpenicillamine was first used as an S-donor provider for the preassembly of octahedral {Ni6Ag8S12Cl} or trigonal dipyramidal {Co2Ag3S6} clusters, then CCHCOO chains of the Dpen ligands were used as connectors to link the clusters and Ln3+ nodes into 3D frameworks with either (3,3)-connected utg or (6,6)-connected pcu topology. Here, their structures and properties were described.

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Microscope equipped with OXFRD EDAX. Metal analyses were carried out by inductive coupled plasma emission spectrometer (ICP) Optima 2000DV. Magnetic measurement was performed on a Quantum Design MPMS XL-7. The data was corrected for the sample holder and the diamagnetic contributions. General Synthesis of (H3O)3[LnNi6Ag8L12Cl(Ac)(H2O)4](H2O)28 (1−3). To 20 mL of the 0.2 M sodium acetate buffer solution (pH = 5.2) containing 150 mg (1 mmol) of ligand (D-penicillamine), 1 mL of NiCl2·6H2O (119 mg, 0.5 mol/L) aqueous solution was added. After stirring for ten minutes, 113 mg (0.67 mmol) of AgNO3 in 1 mL of water was added to the mixed solution. Red crystals were obtained by slow diffusion of 2 mL of the resulting solution and 2 mL of aqueous solution of Ln(NO3)3 (0.25 M) in an H tube with deionized water as a buffer layer between them. (H3O)3[LaNi6Ag8L12Cl(Ac)(H2O)4](H2O)28 (1). Yield: 94%, based on Ni. Anal. Calcd. for C62H184Ag8ClLaN12Ni6O61S12: C, 19.35; H, 4.82; N, 4.37%. Found: C, 19.27; H, 4.40; N, 4.02%. IR (KBr pellet, cm−1): 3416 s, 3218 s, 2961 m, 1597 s, 1454 m, 1366 s, 1208 w, 1162 w, 1114 m, 1051 w, 934 w, 785 m, 699 m, 599 m. (H3O)3[EuNi6Ag8L12Cl(Ac)(H2O)4](H2O)28 (2). Yield: 96%, based on Ni. Anal. Calcd. for C62H184Ag8ClEuN12Ni6O61S12: C, 19.28; H, 4.80; N, 4.35%. Found: C, 19.24; H, 4.58; N, 4.21%. IR (KBr pellet, cm−1): 3422 s, 3205 s, 2967 m, 1596 s, 1456 w, 1385 s, 1209 w, 1161 w, 1115 w, 1052 w, 936 w, 801 m, 680 m, 593 m. (H3O)3[TbNi6Ag8L12Cl(Ac)(H2O)4](H2O)28 (3). Yield: 91%, based on Ni. Anal. Calcd. for C62H184Ag8ClTbN12Ni6O61S12: C, 19.25; H, 4.79; N, 4.34%. Found: C, 19.11; H, 4.38; N, 4.16%. IR (KBr pellet, cm−1): 3417 s, 3220 s, 2965 m, 1594 s, 1455 m, 1384 s, 1208 w, 1162 w, 1115 m, 1053 w, 935 w, 785 m, 681 m, 599 m. General Synthesis of (H3O)2[LnCo2Ag3L6](H2O)3 (4−6). The above-mentioned synthesis procedure was repeated except CoCl2·6H2O was used to substitute for NiCl2·6H2O, and brownish black crystals were obtained. However, the best yield was obtained when the ratio of H2L/Co2+/Ag+/Ln was controlled to be 3:1:1:1. (H3O)2[LaCo2Ag3L6](H2O)3 (4). Yield: 92%, based on Ag. Anal. Calcd. for C30H66Ag3Co2LaN6O17S6: C, 23.16; H, 4.27; N, 5.40%. Found: C, 23.23; H, 4.36; N, 5.32%. IR (KBr pellet, cm−1): 3417 s, 3229 s, 2953 m, 1593 s, 1453 m, 1387 s, 1168 w, 1127 m, 1048 m, 941 w, 800 w, 709 w, 598 w.

EXPERIMENTAL SECTION

Materials and Instrumentation. All chemicals were obtained from commercial sources and used without further purification. X-ray powder diffraction (XRPD) measurements were carried out on a Riguku D/Max-2400 X-ray Diffractometer using Cu Kα (λ = 1.5418 Å) at room temperature. Elemental analyses were determined using a Vario EL III elemental analyzer. Thermogravimetric analyses were performed under a flow of nitrogen (40 mL/min) at a ramp rate of 10 °C/min, using a NETZSCH STA 449F3 instrument. FT-IR spectra were recorded in the range of 4000−400 cm−1 on a JASCO FT/IR430 spectrometer with KBr pellets. CD and UV−vis diffuse reflectance spectra were measured on a JASCO J-810 Spectropolarimeter and UV550 spectrophotometer, respectively. Energy-dispersive X-ray spectroscopy (EDS) was performed by FEI Quanta 450 Scanning Electron B

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Figure 1. (a) Overall structure of 1 viewed along the b direction. (b) Coordination polyhedron of the La3+ ion. (c) Structure of the {Ag8Cl} unit. (d) Structure of the {Ni6Ag8S12Cl} cluster. (e) Coordination mode of the {Ni6Ag8L12Cl} MBB. (H3O)2[EuCo2Ag3L6](H2O)3 (5). Yield: 89%, based on Ag. Anal. Calcd. for C30H66Ag3Co2EuN6O17S6: C, 22.97; H, 4.24; N, 5.36%. Found: C, 23.18; H, 4.19; N, 5.27%. IR (KBr pellet, cm−1): 3422 s, 3226 s, 2953 s, 1595 s, 1453 m, 1388 s, 1168 w, 1171 w, 1128 m, 1050 w, 942 w, 801 w, 705 w, 602 w. (H3O)2[TbCo2Ag3L6](H2O)3 (6). Yield: 93%, based on Ag. Anal. Calcd. for C30H66Ag3Co2TbN6O17S6: C, 22.87; H, 4.22; N, 5.33%. Found: C, 22.96; H, 4.21; N, 5.19%. IR (KBr pellet, cm−1): 3422 s, 3227 s, 2954 s, 1586 s, 1452 m, 1388 s, 1172 w, 1128 m, 1050 w, 941 w, 803 w, 705 w, 601 w. X-ray Structure Determinations. Intensity data were measured at 293(2) K on a Bruker SMART APEX II CCD area detector system. Data reduction and unit cell refinement were performed with SmartCCD software.19 The structures were solved by direct methods using SHELXS-97 and were refined by full-matrix least-squares methods using SHELXL-97.20 For 1, all nonhydrogen atoms were refined anistropically except O25 (carboxylate oxygen atom from the coordinated Ac− group). Hydrogen atoms on the coordinated water molecules could not be located. The hydrogen atoms were included in the structural model as fixed atoms (using idealized sp2-hybridized geometry and C−H bond lengths of 0.95 Å) riding on their respective carbon atoms. Since the disordered water molecules and H3O+ cations could not be unambiguously modeled, the Platon Squeeze option was utilized based on the model that included the coordinated H2O only.21a Squeeze indicates 1 solvent regions in the cell corresponding to about 2484 electrons/cell or approximately three H3O+ cations and 28 water

molecules per formula, which is consistent with the results of EDS (no Na+ is detected), elemental analysis, and TGA. The maximum residual peak and hole on the final difference Fourier map corresponded to 1.299 e−/Å3 (2.74 Å from O3) and −0.571 e−/Å3 (0.76 Å from La1), respectively. For 4 and 5, the structural models incorporated anisotropic thermal parameters for all nonhydrogen atoms and isotropic thermal parameters for all hydrogen atoms. All the hydrogen atoms attached to carbon atoms were placed in calculated positions and refined using the riding model. Hydrogen atoms on the free water molecules could not be located. The maximum residual peak and hole on the final difference Fourier map, respectively, corresponded to 1.73 e−/Å3 (1.04 Å from Co1) and −0.55 e−/Å3 (0.73 Å from Co1) for 4, and 4.786 e−/ Å3 (1.09 Å from Co1) and −1.001 e−/Å3 (0.55 Å from Co1) for 5. Crystal data as well as details of data collection and refinement for 1, 4, and 5 are summarized in Table 1, and selected bond lengths and angles are given in Tables S1, S2, and S3, Supporting Information. Crystal data of compounds 2, 3, and 6 were also collected. Because of the weak intensities, only preliminary structures can be observed. Compounds 2 and 3 are isomorphous with 1, while 6 is isomorphous with 4 and 5, as also confirmed by powder XRD patterns and elemental analysis data. Their cell parameters are listed in Table S4, Supporting Information. C

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RESULTS AND DISCUSSION

Scheme 1. Four Coordination Modes of the D-Pen Ligand

Crystal Structures of 1−3. Compounds 1, 2, and 3 are isomorphous, and only the structure of 1 is described in detail. The structure of 1 can be described as a heterotrimetallic 3D framework based on 3-connected La3+ and {Ni6Ag8S12Cl} nodes, and the connectors are CCHCOO chains of the D-pen ligands (Figure 1). In the structure, each La3+ ion has a {O9} donor set. As shown in Figure 1b, the upper face is formed by two terminal water molecules and two carboxylate oxygen atoms from two D-pen ligands, while the lower face is occupied by one water molecule, two carboxylate oxygen atoms from the chelating acetate anion, and one carboxylate oxygen atom from the third D-pen ligand. A distorted monocapped square antiprism configuration around the La3+ ion is completed by the additional binding of one water molecule from the cap position. The bond lengths of La−O are in the range of 2.471(6)−2.713(7) Å and the bond angles around La3+ ion range from 51.0(3) to 153.1(3)°. The 14-nuclear {Ni6Ag8S12Cl} cluster shows approximate Td symmetry with six Ni2+ ions arranged to form a Ni6 octahedron, eight Ag ions distributed at the centers of triangular faces, and one Cl− anion located at the center. The Ni···Ni and Ag···Ni separations are in the range of 6.90−7.26 and 3.96−4.20 Å, respectively. Each of the 12 thiolate atoms acts as a μ3-bridge to coordinate to one Ni2+ and two Ag+ ions. The corresponding ∠Ag−S−Ni are in the range of 116.32(11)−127.54(10)°. Although many {M6} or {LnM6 } compounds bearing octahedral metal skeleton have been reported, similar but larger octahedral structure is rare, and a close example is the {Ln6Cu12} octahedral cluster.15,22 Inside the octahedron, the eight Ag ions can also be treated as a distorted cube with Ag···Ag separations falling in the range of 3.24−3.72 Å. A Cl template is located in the center of the cube and plays an essential role in the formation of the compound. The Cl anion acts as a tetrahedral μ4-bridge and weakly coordinates to four neighboring Ag ions within the distances of 2.807(2)−2.859(2) Å. Its separations to the other four Ag+ ions are in the range of 3.154(2)−3.434(2) Å. Each Ni2+ ion has a distorted square coordination geometry formed by two nitrogen atoms and two thiolate atoms from two D-pen ligands arranged in cis-configuration. The bond angles around the Ni2+ ion range from 87.5(2) to 176.9(2)°. The Ni−N and Ni−S bond distances are in the range of 1.913(6)−1.944(7) Å and 2.156(2)−2.171(2) Å, respectively. Among the eight Ag ions, four are three-coordinated with three thiolate atoms from three D-pen ligands, and the coordination geometry may be described as a triangle. The other four have a trigonal pyramidal {S3Cl} donor set and are coordinated by three thiolate atoms and one central Cl anion. The Ag−S bond distances and ∠Ag− S−Ag fall in the range of 2.486(2)−2.544(2) Å and 80.25(6)− 95.77(7)°, respectively. The D-pen ligands in 1 are all deprotoned, as confirmed by IR spectrum (no peak in 1700−1650 cm−1 region is observed). Depending on whether the La3+ ion is involved in coordination, the ligand can adopts two coordination modes. In the first case, the ligand uses the S atom to bridge two Ag+ ions, one carboxylate oxygen atom to coordinate to an La3+ ion, and N, Sdonor set to chelate an Ni2+ ion. The corresponding coordination mode of the ligand can be described as μ4ηS1:ηS1:ηS1N1:ηO1 (Scheme 1a). The second coordination mode is μ3-ηS1:ηS1:ηS1N1 (Scheme 1b) where the ligand only coordinates to two Ag+ ions and one Ni2+ ion.

The linking of the 3-connected {Ni6Ag8S12Cl} and La3+ nodes in 1:1 ratio through the CCHCOO connectors leads to an anionic 3D framework. Free water molecules and hydronium ions are encapsulated in the pores. The number of H3O+ ions was determined by charge balance. The solvent accessible volume of 1 is about 10201 Å3, comprising 36.3% of the crystal volume, as calculated by the program PLATON.21b This data is comparable with that observed in the 3D frameworks based on {Ln6Cu24} nodes and amino acid linkers.16 Better insight of this 3D framework can be achieved by topology analysis using TOPOS software.23 The result indicates 1 has a 3-connected utg network with Schläfli symbol of (82.12) (Figure 2) and vertex symbol of (8.8.127) for both 3connected nodes. This type of topology is rare and only a couple of examples have been reported.24

Figure 2. Schematic diagram showing the connection mode of the utg net in 1. Blue spheres represent La3+ centers; green spheres represent the {Ni6Ag8S12Cl} clusters.

From another point of view, the framework can also be treated as the combination of La3+ nodes and octahedral {Ni6Ag8L12Cl} molecular building blocks (MBBs) (Figure 1e) whose surface is decorated by 12 carboxylate groups that point to six directions. However, only three of the carboxylate groups are used to coordinate to three La3+ ions in meridional-mode. Crystal Structures of 4−6. Compounds 4, 5, and 6 are also isomorphous. Only the structure of 4 is described in detail. Compound 4 crystallizes in chiral trigonal P3221 space group and possesses a 3D anion framework structure with trigonal dipyramidal {Co2Ag3S6} clusters, La3+ ion as nodes, and the D

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Figure 3. (a) Overall structure of 4. CH3 groups and water molecules are omitted for clarity. (b) Coordination polyhedron of the La3+ ion. Symmetry code: A, y, x, −z. (c) Structure of the {Co2Ag3S6} cluster. (d) Coordination mode of the {Co2Ag3L6} MBB.

Figure 4. Packing diagram of 4 viewed along the c direction. Free water molecules and hydronium ions are represented as a space filling mode, while atoms in the framework are represented as wires or sticks mode.

E

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CCHCOO chains of the D-pen ligands as connectors (Figure 3). Each La3+ ion presents a distorted square antiprismatic geometry and coordinates to four carboxylate oxygen atoms from two monobidentate coordinated carboxylate groups (La− O bond distances are in the range of 2.538(7)−2.677(8) Å) and four carboxylate oxygen atoms from four monomonodentate coordinated carboxylate groups (La−O bond distances are in the range of 2.398(8)−2.429(6) Å). The bond angles around La3+ metal ion ranges from 71.8(3) to 157.1(2)°, and the La−O bond distances are in the expected range for such complexes.8 The structure of the {Co2Ag3S6} cluster can be described as a trigonal dipyramid. Three Ag+ ions are arranged into a triangle with ∠Ag···Ag···Ag close to 60°. Compared with 1, the absence of a central Cl− anion allows shorter Ag···Ag separations (2.949(1) and 2.909(2) Å). Two Co2+ ions act as apexes of the bipyramid. The Co2+ and Ag+ ions are bridged by a thiolate atom, and the corresponding ∠Co−S−Ag angles are in the range of 111.88(11)−113.27(11)°. The Co···Co and average Co···Ag separations are 6.94 and 3.86 Å, respectively. Each Ag+ ion adopts a 2-coordinated linear {S2} donor set with two S atoms from two D-pen ligands. The average Ag−S bond distance is 2.376(8) Å, and the S−Ag−S angles are close to 180°. Each Co2+ ion has a {S3N3} donor set. Three N atoms and three S atoms from three D-pen ligands are used to coordinate to the metal ion and a slightly distorted octahedral polyhedron is formed. The average Co−N and Co−S bond distances are 1.99(2) and 2.265(4) Å, respectively. The bond angles around Co2+ ion range from 84.3(2) to 174.6(2)°. The D-pen ligands in 4 have two types of coordination modes: μ3-ηS1:ηS1N1: ηO1 and μ3-ηS1: ηS1N1:ηO1O1 (Scheme 1c,d). In both modes, the ligand is used to coordinate to three metal ions, and the difference is that the carboxylate group bears a monomonodentate coordination mode in the former, while monobidentate in the latter. Compared with that in 1, the S atom in 4 is only used to coordinate to one Ag+ ion. The overall 3D anion framework was formed through the linking of the 6-connected {Co2Ag3S6} and La3+ nodes by CCHCOO connectors. Free water molecules and hydronium ions are encapsulated in the pores, as shown in Figure 4. The number of H3O+ ions was determined by charge balance. The solvent accessible volume of 4 is about 301.8 Å3, comprising 8.1% of the crystal volume, as calculated by the program PLATON.21b Topology analysis using TOPOS software indicates it has a 6-connected pcu network with Schläfli symbol of (412.63) (Figure 5).23 From another point of view, the framework can also be treated as the combination of La3+ nodes and {Co2Ag3L6} MBBs (Figure 3d) bearing six carboxylate groups that point to six directions. Each MBB uses six carboxylate groups to coordinate to six La3+ nodes, and each La3+ node is also connected by six neighboring MBBs to provide the framework. Synthesis and Characterization of the Compounds. Previously, Birker et al.16 have reported the preparation and structures of [M6M′8L12Cl]5− (M = Ni and Pd; M′ = Cu and Ag) clusters featured by 12 deprotonated carboxylate groups pointing along the center-vertice (octahedron) direction. The deprotonated carboxylate groups with O,O-donor set can be treated as active sites for further assembled reaction with the third metal ion. Ag2S is an important semiconductor (band gap = ∼1 eV) and near-infrared luminescent material, while Ln3+ ions prefer to coordinate to carboxylate groups.25 Thus, the self-assembly reactions of [Ni6Ag8L12Cl]5− cluster with Ln3+ ions were investigated.

Figure 5. Schematic diagram showing the connection mode of the pcu net in 4. Blue spheres represent La3+ centers; green spheres represent the {Co2Ag3S6} clusters.

Compounds 1, 2, and 3 were synthesized by slow diffusion reaction in H tubes with [Ni6Ag8L12Cl]5− species in one side and Ln3+ ions (Ln3+ = La3+, Eu3+, and Tb3+) in the other. This preparation method is different from that for the preparation of series of low dimensional compounds based on [M6M′8L12Cl]5− building blocks.8 In the structure of 1, among the 12 active sites (deprotonated carboxylate groups) of the {Ni6Ag8L12Cl} MBB, only three were used to coordinate to the lanthanide ions. EDS, ICP, and CHN analysis are in agreement with the crystal structure formula. Similar synthesis reaction but using CoCl2 led to the formation of brownish black crystals of compounds 4, 5, and 6. The increase of the metallic coordination number from 4 (Ni2+, for 1, 2, and 3) to 6 (Co2+, for 4, 5, and 6) leads to an entirely different MBB, {Co2Ag3L6}, featured by six deprotonated carboxylate groups pointing along the center-thiolate direction. The preparation of a similar [Ni2Au3L6]5− cluster has been reported, but it has never been used as building blocks to build extended structure.17 So, 4, 5, and 6 are the first 3D polymeric compounds based on the {M2M′3L6} building blocks. In 4, the six active sites (deprotonated carboxylate groups) of the {Co2Ag3L6} MBB were all used to coordinate to the lanthanide ions. Both EDS and ICP experiments indicated that the ratio of Co/Ag/La is 2:3:1, which is consistent with the formula. The magnetic susceptibility measurement was performed on microcrystalline samples of 4 at 300 K. The effective magnetic moment is 5.48μB, close to the value 5.36μB expected for two independent Co2+ ions, which confirms that the Co ions remain at +2 state during the reaction. The solid-state luminescent spectra of the six compounds were measured at room temperature; unfortunately, no emission peaks were observed, which can be explained as the quenching effect due to the presence of transition-metal ion (Ni2+ or Co2+) with unpaired electrons.26 To analyze their chirality, solid-state circular dichroism (CD) spectra for 1 and 4 were recorded on bulk samples with a KBr pellet between 200 and 550 nm at room temperature (Figure S2, Supporting Information). The CD spectrum of 1 displays positive cotton effects at about 312 and 463 nm and negative cotton effects at about 256 and 392 nm. The CD spectrum of 4 shows clear cotton effects with positive signals at about 314 and 389 nm and negative signals at about 257 and 450 nm. These results suggest that the bulk samples (1 and 4) are the same F

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and 1.72 eV, respectively, indicating all the compounds are medium gap semiconductors. Besides, all the Eg are in the energy range suitable for visible-light photocatalytic applications.27 Compared with the bulk Ag2S (1 eV),28 there is a noticeable blue shift of the absorption edges, which is consistent with other M−Ag heterometallic chalcogenides.29 Previously, two 3D compounds [Cd(L-cysteinate)] and [Zn(L-cysteinate)] bearing 1D Cd−S ladder chain or zigzag Zn−S skeleton were reported.18b Solid-state optical experiments show huge blue shifts of the band gap up to 2.59 and 1.37 eV with respect to the bulk MS structures for the two compounds, respectively. Compared with the two compounds, less blue shift of the band gaps in 1−6 might be partially ascribed to the presence of polynuclear MS clusters in the frameworks.

handed conformation, which is consistent with the single crystal structural analyses. To examine the thermal stabilities of 1 and 4, thermogravimetric analysis (TGA) experiments were performed by heating the crystalline sample under nitrogen atmosphere in the temperature range of 20−800 °C (Figure S3, Supporting Information). The TGA curve of 1 reveals that the first weight loss of 16.38% in the temperature region of 20−250 °C corresponds to the loss of all the water molecules (ca. 16.46%) and might be accompanied by a process of proton transfer to the framework.13a After 250 °C, the material shows a striking weight loss, indicating complete decomposition of the framework. Compound 4 exhibits two distinct weight losses. The first step (5.88%) involves loss of noncoordinating water molecules at temperature below 230 °C (ca. 5.92%) and is also accompanied by a process of proton transfer to the framework. Then, 4 continues to lose its weight until 800 °C. The reversible water adsorption studies of 1 and 4 were also carried out before 150 °C (Figures S4 and S5, Supporting Information). Compound 1 loses its weight of 16.86%, 11.56%, 11.27%, and 11.03% in the first, second, third, and fourth cycles, respectively, suggesting that 1 can reversibly absorb 24 water molecules back from air (ca. 11.24%) after the loss of original solvent molecules. Compound 4 loses its weight of 6.08% in the first cycle, corresponding to the loss of three water molecules and two hydronium ions (ca. 5.92%). However, a little larger weight loss was observed in the second, third, and fourth cycles (6.61%, 6.48%, and 6.55%, respectively), indicating that 4 can reversibly absorb 5.6 water molecules back from air (ca. 6.49%) after the loss of original solvent molecules. Moreover, the PXRD patterns (Figures S6 and S7, Supporting Information) of 1 and 4 heated at 150 °C for 30 min are almost the same as those of the original phases. All the results indicate, the guest-free frameworks of 1 and 4 are rigid and stable. The porosity is retained for both compounds and can take back guest molecules again. The optical properties of the six compounds were investigated with solid-state UV−vis spectroscopy at room temperature, and the results are plotted in Figures 6, S10, and S11, Supporting Information, respectively. The band gap energies (Eg) were calculated from formula Eg = 1240/λg (eV), where λg stands for the wavelength in the minima of the second derivatives of the optical absorption curve. As a result, the band gaps for 1−6 are 1.82, 1.80, 1.83, 1.68, 1.71,

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CONCLUSIONS With the help of an S-, N-, and O-donor amino acid derivative (D-penicillamine), the simultaneous incorporation of 3d−4d transition metal chalcogenide clusters (either octahedral {Ni6Ag8S12Cl} or trigonal dipyramidal {Co2Ag3S6}) and 4f metal ions into a 3D framework has been achieved successfully, and two series of chiral heterotrimetallic framework with utg or pcu topology were obtained. Optical measurements show that the six compounds are all medium gap semiconductors. Consequently, this work proves that the S-containing amino acid is a good candidate for the construction of transition metal chalcogenide clusters, which can be further connected into 3D frameworks with the help of 4f metal ions. However, the active sites of the molecular building blocks ({Ni6Ag8L12Cl} and {Co2Ag3L6}) in the six compounds were only partly (for 1−3) or fully (for 4−6) used when being coordinated by 4f metal ions. This suggests that new compounds with structural diversity may be obtained by reasonable utilization of the active sites of the molecular building blocks. Furthermore, the quenching of luminescence due to the use of Ni2+ or Co2+ ions also suggest that other 3d transition-metal ions without unpaired electrons need to be tried. Further studies on the ideas are in progress.

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ASSOCIATED CONTENT

* Supporting Information S

Crystallographic data (CIF format) and crystallographic tables for 1−6; Figure S1−S12. This material is available free of charge via the Internet at http://pubs.acs.org.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. (J.-J.Z.); [email protected] (C.-Y.D.). Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS

This material is based upon work supported by the National Science Foundation of China (21071025 and 91122031), the Fundamental Research Funds for the Central Universities (DUT12YQ04 and DUT11LK22), and fund of Ministry of Education of China (20100041120021 and ROCS).

Figure 6. UV−vis diffuse reflectance spectra for 1 and 4. G

dx.doi.org/10.1021/cg301649p | Cryst. Growth Des. XXXX, XXX, XXX−XXX

Crystal Growth & Design

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Article

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dx.doi.org/10.1021/cg301649p | Cryst. Growth Des. XXXX, XXX, XXX−XXX