Novel Cadmium(II) Phosphonatophenylsulfonate Cluster Compounds

Jun 19, 2007 - Lijuan Chen , Dongying Shi , Junwei Zhao , Yulong Wang , Pengtao Ma , Jingping .... Zi-Yi Du , Cui-Cui Zhao , Zhong-Gao Zhou , Ke-Jun W...
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CRYSTAL GROWTH & DESIGN

Novel Cadmium(II) Phosphonatophenylsulfonate Cluster Compounds: Syntheses, Structures, and Luminescent Properties Zi-Yi Du, Xiu-Ling Li, Qing-Yan Liu, and Jiang-Gao Mao* State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fuzhou 350002, P. R. China

2007 VOL. 7, NO. 8 1501-1507

ReceiVed March 23, 2007; ReVised Manuscript ReceiVed May 14, 2007

ABSTRACT: Hydrothermal reactions of cadmium(II) salt with m-phosphonophenylsulfonic acid (H3L) and 1,10-phenanthroline (phen) or 4,4′-bipyridine (bipy) led to three novel cadmium(II) phosphonatephenylsulfonates, namely, [Cd4(L)2(phen)6(Cl)2(H2O)2]‚ 14H2O (1), [Cd6(L)4(phen)8]‚14H2O (2), and [Cd3(L)2(bipy)3(H2O)6]‚4H2O (3). Compound 1 contains a tetranuclear cadmium(II) cluster in which four cadmium(II) ions are bridged by two tetradentate phosphonate groups. Compound 2 features a hexanuclear cadmium(II) cage in which six cadmium(II) ions are bridged by one tetradentate and three pentadentate phosphonate groups. The structure of compound 3 features a novel 3D network based on 1D chains of [Cd3(L)2] cross-linked by 4,4′-bipy ligands; its topological structure is similar to that of CdSO4. Compounds 1-3 exhibit broad blue fluorescence emission bands at 408, 410, and 396 nm, respectively. Introduction The chemistry of metal phosphonates has been a research field of rapid expansion in recent years, which is mainly due to their potential applications in the area of catalysis, ion exchange, proton conductivity, intercalation chemistry, photochemistry, and material chemistry.1 Most of the metal phosphonates show a layered structure in which the metal centers are bridged by the phosphonate groups, although a variety of 1D chains and porous 3D networks have also been reported.1 Recently, our increasing attention has been devoted to the metal coordination chemistry of m-phosphonophenylsulfonic acid, which can adopt a variety of coordination modes and form a variety of metal cluster compounds when a second ligand such as phen or 4,4′-bipy ligand was also applied.2 By using this method, our group has isolated three zinc(II) phosphonates based on tetranuclear or hexanuclear cluster units and four lanthanide(III) phosphonates based on tetranuclear cluster units.2 We deem that both the weak coordination ability of the sulfonate group and the bidentate chelating nature of the second ligand such as phen facilitate the formation of cage compounds with discrete cluster units. Similar to zinc phosphonates, most of the cadmium phosphonates display open framework structures, especially layered structures.3-4 Although a few examples of zinc phosphonate cluster compounds have been reported,6,2a reports on cadmium phosphonate clusters are rare.4a Very recently, a tetranuclear cadmium cluster was reported,5 which contains a inorganic core similar to that of the tetranuclear zinc cluster we reported previously.2a A layer cadmium phosphonate based on a [Cd7L6]4cage unit (L ) MeN(CH2CO2H)(CH2PO3H2)) was isolated by our group.4i The Cd2+ ion usually adopts a higher coordination number (6, 7, and 8) than those of the zinc(II) ion (4, 5, 6) because of its larger ionic radius compared with the Zn2+ ion. It is thus of interest to explore cadmium phosphonate cluster compounds by using the m-phosphonatophenylsulfonate ligand and a second metal linker such as phen. We deem that such clusters may display different structures and physical properties from those of the corresponding zinc(II) ones. Our research efforts afforded three novel cadmium m-phosphonatophenylsulfonates, namely, [Cd4(L)2(phen)6(Cl)2(H2O)2]‚14H2O (1), * Corresponding author. E-mail: [email protected].

[Cd6(L)4(phen)8]‚14H2O (2), and [Cd3(L)2(bipy)3(H2O)6]‚4H2O (3). They feature a novel tetranuclear cluster, hexanuclear cluster, or 3D network, respectively. Herein, we report their syntheses, crystal structures, and characterizations. Experimental Section Materials and Methods. m-Phosphonophenylsulfonic acid (mHO3S-C6H4-PO3H2, H3L) was synthesized according to the procedures previously described by Montoneri.7 All other chemicals were obtained from commercial sources and used without further purification. Elemental analyses were performed on a German Elementary Vario EL III instrument. The FT-IR spectra were recorded on a Nicolet Magna 750 FT-IR spectrometer using KBr pellets in the range of 4000-400 cm-1. Thermogravimetric analyses were carried out on a NETZSCH STA 449C unit at a heating rate of 10 °C/min under an oxygen atmosphere. Photoluminescence analyses were performed on a Perkin Elemer LS55 fluorescence spectrometer. X-ray powder diffraction (XRD) patterns (Cu-KR) were collected on a XPERT-MPD θ-2θ diffractometer. [Cd4(L)2(phen)6(Cl)2(H2O)2]‚14H2O (1). A mixture of Cd(ac)2 (0.3 mmol), CdCl2 (0.1 mmol), and H3L (0.3 mmol) as well as phen (0.6 mmol) in 10 mL of distilled water was sealed into a Parr Teflon-lined autoclave (23 mL) and heated at 150 °C for 4 days. The initial and final pH values are about 3.5. Colorless prism-shaped crystals of 1 were collected in ca. 70% yield based on Cd. Its purity was confirmed by XRD powder diffraction (see the Supporting Information). Anal. Calcd for C84H88N12O28P2S2Cl2Cd4 (Mr ) 2360.22): C, 42.75; H, 3.76; N, 7.12. Found: C, 42.63; H, 3.59; N, 7.07. IR data (KBr, cm-1): 3436 (s), 3055 (m), 2967 (m), 2874 (m), 1622 (m), 1517 (m), 1427 (s), 1206 (s), 1116 (s), 1101 (vs), 1034 (vs), 997 (m), 970 (s), 848 (s), 727 (s), 700 (m), 617 (m), 578 (s). [Cd6(L)4(phen)8]‚14H2O (2). A mixture of Cd(ac)2 (0.36 mmol), H3L (0.3 mmol), and phen (0.5 mmol) in 10 mL of distilled water was sealed into a Parr Teflon-lined autoclave (23 mL) and heated at 150 °C for 4 days. The initial and final pH values did not show much change and are close to 4.0. Colorless prism-shaped crystals of 2 were collected in ca. 72% yield based on Cd. Its purity was confirmed by XRD powder diffraction (see the Supporting Information). Anal. Calcd for C120H108N16O38P4S4Cd6 (Mr ) 3308.74): C, 43.56; H, 3.29; N, 6.77. Found: C, 43.65; H, 3.18; N, 6.84. IR data (KBr, cm-1): 3434 (s), 3055 (m), 2918 (m), 2846 (m), 1623 (m), 1517 (m), 1427 (s), 1218 (m), 1191 (s), 1141 (s), 1101 (vs), 1032 (vs), 998 (m), 970 (s), 848 (m), 797 (m), 728 (s), 699 (m), 620 (m), 566 (m). Synthesis of [Cd3(L)2(bipy)3(H2O)6]‚4H2O (3). A mixture of Cd(ac)2 (0.4 mmol), H3L (0.3 mmol), and 4,4′-bipy (0.42 mmol) in 10 mL of distilled water was sealed into a Parr Teflon-lined autoclave (23 mL) and heated at 150 °C for 4 days. The initial and final pH

10.1021/cg070280v CCC: $37.00 © 2007 American Chemical Society Published on Web 06/19/2007

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Table 1. Summary of Crystal Data and Structural Refinements for 1-3

empirical formula fw space group a (Å) b (Å) c (Å) R (deg) β (deg) γ (deg) V (Å3) Z Dcalcd (g cm-3) µ (mm-1) GOF on F2 R1, wR2 [I>2σ(I)]a R1, wR2 (all data) a

1

2

3

C84H88N12O28P2S2Cl2Cd4 2360.22 P1h 11.6702(6) 13.9160(7) 16.0247(8) 69.041(1) 69.716(1) 84.264(1) 2278.7(2) 1 1.720 1.147 1.038 0.0383, 0.0861 0.0454, 0.0915

C120H108N16O38P4S4Cd6 3308.74 P1h 17.152(4) 21.120(5) 21.207(5) 84.590(9) 76.168(9) 67.475(6) 6890(3) 2 1.595 1.098 1.108 0.0810, 0.1828 0.1297, 0.2181

C42H52N6O22P2S2Cd3 1456.16 C2/c 20.4331(1) 11.7979(2) 23.9485(3) 90 112.723(1) 90 5325.1(1) 4 1.824 1.410 1.139 0.0409, 0.0925 0.0494, 0.0966

R1 ) ∑|Fo| - |Fc|/∑|Fo|, wR2 ) {∑w[(Fo)2 - (Fc)2]2/∑w[(Fo)2]2}1/2.

values are about 3.8 and 4.3, respectively. Colorless brick-shaped crystals of 3 were collected in ca. 65% yield based on Cd. Its purity was confirmed by XRD powder diffraction (see the Supporting Information). Anal. Calcd for C42H52N6O22P2S2Cd3 (Mr ) 1456.16): C, 34.64; H, 3.60; N, 5.77. Found: C, 34.59; H, 3.49; N, 5.68. IR data (KBr, cm-1): 3400 (s), 3076 (m), 3048 (m), 2919 (m), 2846 (m), 1604 (s), 1535 (m), 1491 (m), 1415 (m), 1221 (s), 1179 (s), 1101 (vs), 1071 (s), 1028 (vs), 996 (m), 950 (s), 860 (m), 808 (m), 699 (m), 630 (s), 552 (m). Single-Crystal Structure Determination. Data collections were performed on a Saturn 70 CCD diffractometer (for compounds 1 and 2) and a Siemens Smart CCD diffractometer (for compound 3). Both diffractometers are equipped with a graphite-monochromated Mo-KR radiation (λ ) 0.71073 Å). Intensity data for compound 1 were collected at 143 K, whereas those for compounds 2 and 3 were collected at 293 K. All three data sets were corrected for Lorentz and polarization factors as well as for absorption by the SADABS program or a multiscan method.8a, 8b All three structures were solved by direct methods and refined by full-matrix least-squares fitting on F2 by SHELX-97.8c All non-hydrogen atoms except O(13w)-O(24w) in compound 2 were refined with anisotropic thermal parameters. All hydrogen atoms were located at geometrically calculated positions and refined with isotropical thermal parameters. The hydrogen atoms for the water molecules are not included in the refinements. Lattice water molecules O(3w), O(4w), O(6w), O(7w), and O(8w) in compound 1 are severely disordered and each display two orientations with 50% occupancy for each site. One sulfonate group in compound 2 is also severely disordered with O(24) exhibiting two orientations with 50% occupancy each. The occupancy factors of lattice water molecules O(2w) and O(5w) in compound 1 and O(5w)-O(24w) in compound 2 were reduced to 50% because of their larger thermal parameters. Crystallographic data and structural refinements for compounds 1-3 are summarized in Table 1. Important bond lengths are listed in Table 2. More details on the crystallographic studies as well as atom displacement parameters are given in the Supporting Information.

Results and Discussion Structure of [Cd4(L)2(phen)6(Cl)2(H2O)2]‚14H2O (1). The structure of compound 1 features an isolated tetranuclear cadmium(II) phosphonatophenylsulfonate cluster unit. There are two independent cadmium(II) ions in the asymmetric unit of 1. Cd(1) ion has a distorted octahedral environment (Figure 1); three of the six coordination sites are filled by three phosphonate oxygen atoms from two L3- anions and the remaining three sites are occupied by two nitrogen atoms of a bidentate chelating phen ligand and one chlorine anion. Cd(2) ion is octahedrally coordinated by one phosphonate oxygen atom, two bidentate chelating phen ligands and an aqua ligand. The Cd-O (2.238(2)-2.607(2) Å), Cd-N (2.310(3)-2.430(3) Å), and Cd-Cl (2.467(1) Å) bond distances are comparable to those reported in other cadmium(II) phosphonates.3-5

The L3- anion serves as a tetradentate ligand. It chelates bidentately with a Cd2+ ion and bridges with two other Cd2+ ions (Scheme 1). Both of the phosphonate oxygen atoms (O(1), O(2)) act as µ2-metal linkers, whereas the third phosphonate oxygen and the sulfonate group remain noncoordinated. The sulfonate group is usually a much weaker ligand compared with that of a phosphonate ligand, on the basis of our previous studies on metal compounds containing both types of groups.2 In this compound, the steric effects around the Cd2+ ions also play an important role. The interconnection of two Cd(1) ions by a pair of phosphonate groups resulted in Cd2O2 dimeric unit (Figure 2). The dimeric unit is further bridged to two additional Cd(2) ions to form a flatted tetranuclear cluster (Figure 2). Such a flatted tetranuclear cluster unit is different from the “cagelike” tetranuclear cluster units in zinc(II) phosphonatophenylsulfonates and lanthanide(III) phosphonatophenylsulfonates (Scheme 2),2 which is due to the different coordination modes of the phosphonatophenylsulfonate ligands. In the [Zn4(L)4(phen)4]4anion, the four metal ions are bridged by two bidentate and two tetradentate L3- ligands, whereas in [Ln4(L)4(phen)4(H2O)10]‚6H2O (Ln ) Nd, Eu, or Er), the four lanthanide(III) ions are bridged by two tridentate and two tetradentate L3ligands with each ligand connecting with three Ln(III) ions (Scheme 2). These discrete tetranuclear clusters in compound 1 are assembled into a 3D supramolecular network via hydrogen bonds among noncoordinating phosphonate, sulfonate oxygens, and the lattice water molecular (O‚‚‚O 2.59(1)-2.848(8) Å), as well as the π···π packing interaction between phenyl rings of phen ligands (Table 2 and the Supporting Information). Structure of [Cd6(L)4(phen)8]‚14H2O (2). The structure of compound 2 features an isolated hexanuclear cadmium(II) cluster unit. There are six independent cadmium(II) ions in the asymmetric unit in compound 2. Cd(1), Cd(4), and Cd(6) have a similar coordination geometry, and each is octahedrally coordinated by four phosphonate oxygen atoms from three L3anions and two nitrogen atoms from a bidentate chelating phen ligand. Cd(2) is five-coordinate with three phosphonate oxygen atoms from three L3- anions as well as one bidentate chelating phen ligand. Cd(3) and Cd(5) have a similar distorted octahedral environment, and each is coordinated by two phosphonate oxygen atoms from two L3- anions and four nitrogen atoms from two bidentate chelating phen ligands. The Cd-O (2.194(5)-2.558(5) Å) and Cd-N (2.307(6)-2.445(6) Å) bond distances are comparable to those in compound 1 and other cadmium(II) phosphonates reported.3-5

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Crystal Growth & Design, Vol. 7, No. 8, 2007 1503

Table 2. Selected Bond Lengths (Å) for Compounds 1-3a 1 Cd(1)-O(2)#1 Cd(1)-O(2) Cd(1)-Cl(1) Cd(2)-O(1) Cd(2)-N(3) Cd(2)-N(5)

2.256(2) 2.363(2) 2.467(1) 2.238(2) 2.364(3) 2.378(3)

Cd(1)-N(2) Cd(1)-N(1) Cd(1)-O(1) Cd(2)-O(1W) Cd(2)-N(6) Cd(2)-N(4)

O(3)‚‚‚O(8W)#2 O(5)‚‚‚O(6W')#2 O(2W)‚‚‚O(5W)#4 O(2W)‚‚‚O(5W)#5

Hydrogen Bonds 2.745(6) O(3)‚‚‚O(9W) 2.848(8) O(6)‚‚‚O(7W')#3 2.59(1) O(2W)‚‚‚O(3W)#4 2.76(1) O(5W)‚‚‚O(6W)#5

Cd(1)-O(3) Cd(1)-O(8) Cd(1)-N(9) Cd(2)-O(15) Cd(2)-O(19) Cd(2)-N(15) Cd(3)-O(1) Cd(3)-N(13) Cd(3)-N(4) Cd(4)-O(13) Cd(4)-N(2) Cd(4)-O(3) Cd(5)-O(8) Cd(5)-N(8) Cd(5)-N(6) Cd(6)-O(7) Cd(6)-N(12) Cd(6)-O(14)

2.218(5) 2.330(5) 2.353(6) 2.194(5) 2.261(5) 2.344(7) 2.323(5) 2.364(7) 2.445(6) 2.240(5) 2.346(6) 2.500(5) 2.313(5) 2.370(7) 2.390(7) 2.245(5) 2.355(7) 2.455(5)

O(4)‚‚‚O(6W)#1 O(11)‚‚‚O(2W) O(16)‚‚‚O(2W)#2 O(18)‚‚‚O(8W) O(24')‚‚‚O(5W) O(4W)‚‚‚O(7W)#4

Hydrogen Bonds 2.77(2) O(10)‚‚‚O(1W) 2.80(2) O(12)‚‚‚O(6W) 2.84(1) O(17)‚‚‚O(4W) 2.68(2) O(24)‚‚‚O(9W)#3 2.60(2) O(3W)‚‚‚O(11W) 2.85(3)

Cd(1)-O(2) Cd(1)-O(3W)#1 Cd(1)-N(3) Cd(2)-O(1)#3 Cd(2)-O(2W) Cd(2)-N(2)#4

2.293(3) 2.333(4) 2.337(5) 2.306(3) 2.338(4) 2.368(4)

O(3)‚‚‚O(5W)#3 O(5)‚‚‚O(1W)#5 O(2W)‚‚‚O(5W) O(5W)‚‚‚O(5W)#7

Hydrogen Bonds 2.636(7) O(4)‚‚‚O(4W)#5 2.792(6) O(6)‚‚‚O(3W)#6 2.765(10) O(2W)‚‚‚O(4W) 2.84(2)

2.310(3) 2.383(3) 2.607(2) 2.347(2) 2.374(3) 2.430(3) 2.798(5) 2.64(1) 2.757(9) 2.74(1)

2 Cd(1)-O(20) Cd(1)-N(10) Cd(1)-O(7) Cd(2)-O(9) Cd(2)-N(16) Cd(3)-O(14) Cd(3)-N(3) Cd(3)-N(14) Cd(4)-O(21) Cd(4)-N(1) Cd(4)-O(1) Cd(5)-O(19) Cd(5)-N(5) Cd(5)-N(7) Cd(6)-O(2) Cd(6)-N(11) Cd(6)-O(15)

2.239(5) 2.332(7) 2.558(5) 2.260(5) 2.323(7) 2.284(5) 2.358(7) 2.431(7) 2.215(5) 2.336(6) 2.385(5) 2.286(5) 2.363(7) 2.384(7) 2.203(5) 2.307(6) 2.382(5)

Figure 1. ORTEP representation of the selected unit of 1. The thermal ellipsoids are drawn at the 50% probability level. Lattice water molecules and the carbon atoms of the phen ligands have been omitted for clarity. Symmetry codes for the generated atoms: (a) -x, 2 - y, 1 - z.

2.71 (1) 2.70(2) 2.77(1) 2.56(3) 2.75(4)

3 Cd(1)-O(2)#1 Cd(1)-O(3W) Cd(1)-N(4)#2 Cd(2)-O(1W) Cd(2)-N(1) Cd(2)-O(1)

2.293(3) 2.333(4) 2.361(5) 2.311(3) 2.342(4) 2.394(3) 2.923(8) 2.709(6) 2.824(7)

a Symmetry codes. For 1: #1 -x, -y + 2, -z + 1; #2 x, y + 1, z; #3 -x + 1, -y + 3, -z; #4 x + 1, y, z; #5 -x, -y + 2, -z. For 2: #1 -x + 1, -y + 1, -z; #2 -x + 2, -y, -z; #3 -x + 1, -y + 1, -z + 1; #4 -x + 2, -y, -z + 1. For 3: #1 -x, y, -z + 1/2; #2 x, y - 1, z; #3 -x, -y, -z; #4 x - 1/2, y - 1/2, z; #5 -x + 1/2, y + 1/2, -z + 1/2; #6 x + 1/2, y + 1/2, z; #7 -x + 1/2, -y - 1/2, -z.

In compound 2, there are four unique L3- ligands that feature two types of coordination modes (Scheme 1). One is pentadentate. It chelates bidentately with a cadmium(II) ion and bridges with three other Cd(II) ions. Two oxygen atoms act as a µ2metal linkers and the third one is unidentate. The other type of L3- ligand is tetradentate and bridges with four Cd(II) ions via its three phosphonate oxygen atoms. One phosphonate oxygen atom acts as a µ2-metal linker and the other two are unidentate. The interconnection of the six Cd(II) ions by four bridging L3- anions resulted in an elliptical hexanuclear cluster unit (Figure 5). Such an elliptical hexanuclear cluster unit differs significantly from the hexanuclear zinc(II) phosphonatophenylsulfonate cluster units we reported previously (Scheme 2)2a because of the different coordination modes of the phospho-

Figure 2. Cluster structure of compound 1. Cd, Cl, S, P, O, and N atoms are drawn as cyan, green, yellow, pink, red, and blue circles, respectively.

Scheme 1. Coordination Modes of m-Sulfophenylphosphonate Ligands in Compounds 1-3

natophenylsulfonate ligands. In [Zn6(L)4(phen)8]‚11H2O, there are two pair of tridentate and tetradentate L3- ligands that connect with three and four Zn(II) ions, respectively. Furthermore, the hexanuclear zinc(II) phosphonatophenylsulfonate cluster has a much smaller cavity than that of the hexanuclear cadmium(II) cluster. These discrete tetranuclear clusters in compound 2 are also assembled into a 3D supramolecular network via hydrogen bonds and weak π···π packing interactions (Figure 6, Table 2, and the Supporting Information).

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Figure 3. View of the structure of compound 1 down the a-axis. The cadmium polyhedra are shaded in cyan and the CPO3 and CSO3 groups are shaded in pink and yellow, respectively. O and C atoms are drawn as red and black circles, respectively. Hydrogen bonds are represented by dashed lines.

Scheme 2.

Tetranuclear and Hexanuclear Metal Cluster Units in the M-L-phen Systems (M ) Zn, Cd, Ln)

Structure of [Cd3(L)2(bipy)3(H2O)6]‚4H2O (3). The structure of compound 3 features a novel 3D network with a topology similar to that of CdSO4. Compound 3 contains three cadmium(II) ions, two L3- anions, three 4,4′-bipy ligands, and six aqua ligands as well as four lattice water molecules per formula unit. There are two independent cadmium(II) ions in the asymmetric unit of compound 2 (Figure 7). Cd(1) lying on a 2-fold axis is octahedrally coordinated by two phosphonate oxygen atoms from two L3- anions and two nitrogen atoms from two 4,4′bipy ligands as well as two aqua ligands, and Cd(2) occupying a general position has the same coordination environment as Cd(1). Different from Cd(1), a pair of Cd(2)N2O4 octahedra forms a Cd2O2 dimeric unit by edge-sharing (O(1)‚‚‚O(1)). The Cd-O (2.293(3)-2.394(3) Å) and Cd-N (2.337(5)-2.368(4) Å) bond distances are comparable to those in compounds 1 and 2 as well as other cadmium(II) phosphonates reported.3-5 The L3- anion serves as a tridentate ligand and bridges with three Cd(II) ions through two of its phosphonate oxygen atoms (Scheme 1). One of the phosphonate oxygen atoms (O(1)) acts as a µ2-metal linker and bridges a pair of Cd(2) ions. The third

phosphonate oxygen and the sulfonate group remain noncoordinated. All 4,4′-bipy ligands serve as bidentate bridging ligands. The interconnection of Cd(1) ions or Cd(2) ions by 4,4′-bipy ligands leads to two types of 1D chains along the a- and b-axes, respectively (Figure 8a). The cross-linking of the above two kind of chains via L3- anions leads to a complicated 3D network. The interconnection of the cadmium(II) ions by bridging L3- anions resulted in the formation of a 1D chain along c-axis. Each L3- ligand connects with one Cd(1) ion and a Cd(2)2O2 dimeric unit. Hence the 3D network structure of compound 3 can also be described as 1D cadmium(II) phosphonatophenylsulfonate chains being further connected by 4,4′bipy ligands (Figure 8a). To further understand the topological structure of the 3D framework in compound 3, we examined the connection mode of the metal centers and organic ligands. Cd(1) ion connects with two L3- and two 4,4′-bipy ligands, hence it is reasonable to consider it a four-connected node (T1) (see the Supporting Information, Figure S1). Likewise, each Cd(2)2O2 dimer unit can also be considered as an inorganic fourconnected node (T2) (see the Supporting Information, Figure

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Figure 4. ORTEP representation of the selected unit of 2. The thermal ellipsoids are drawn at the 50% probability level. Lattice water molecules and the non-coordinated sulfonate groups as well as the carbon atoms of phen and L3- ligands have been omitted for clarity. Figure 6. View of the structure of compound 2 down the a-axis. The CPO3 and CSO3 groups are shaded in pink and yellow, respectively. Cd, O, N, and C atoms are drawn as cyan, red, blue, and black circles, respectively. Hydrogen bonds are represented by dashed lines.

Figure 5. Cluster structure of compound 2. Cd, P, S, N, and O atoms are drawn as cyan, pink, yellow, blue, and red circles, respectively.

S1). The L3- anions and 4,4′-bipy ligands cannot be regarded as organic nodes, because both ligands connect only with two inorganic nodes. The interconnection of above two kinds of fourconnected nodes give a complex 3D topological structure (Figure 8b); such a structure is somehow similar to that of CdSO4.9 A number of hydrogen bonds formed among the noncoordinated phosphonate oxygen atoms (O(3)) and sulfonate oxygen atoms, aqua ligands, and lattice water molecules (Table 2, Figure 9). The O‚‚‚O contacts range from 2.636(7) to 2.84(2) Å. Luminescence Properties. The solid-state luminescence properties of compounds 1-3 as well as the phosphonatophenylsulfonate ligand were investigated at room temperature. The free m-sulfo-phenylphosphonate ligand exhibits only a fluorescence emission band at λmax ) 370 nm under 308 nm excitation. The phen ligand displays a fluorescence emission band at λmax ) 381 nm with a shoulder at 364 nm upon excitation at 339 nm. The bipy ligand shows a broad fluorescence emission band at λmax ) 423 nm (λex) 345 nm). Upon complexion of both

Figure 7. ORTEP representation of the selected unit of 3. The thermal ellipsoids are drawn at the 50% probability level. Lattice water molecules have been omitted for clarity. Symmetry codes for the generated atoms: (a) x, -1 + y, z; (b) -x, y, 1/2 - z; (c) -1/2 + x, -1/2 + y, z; (d) -x, -y, -z; (e) 1/2 + x, 1/2 + y, z; (f) x, 1 + y, z.

phosphonatophenylsulfonate and phen ligands with the Cd(II) ions, compound 1 displays a strong fluorescence emission band at λmax ) 408 nm (λex ) 311 nm) and compound 2 displays a strong fluorescence emission band at λmax ) 410 nm (λex ) 297 nm) (Figure 10). Upon complexion of both L3- and bipy ligands with the Cd(II) ions, compound 3 displays a fluorescence emission band at λmax ) 396 nm (λex) 308 nm). These emission bands are neither metal-to-ligand charge transfer (MLCT) nor ligand-to-metal charge transfer (LMCT) in nature, but rather can be attributed to an intraligand emission state, which is similar to our previously reported zinc(II) phosphonates in the Zn-L-phen and Zn-L-4,4′-bipy systems.2a TGA Studies. TGA curves of compound 1 exhibit three main steps of weight losses (Figure 11). The first step started at 42 and completed at 176 °C, which corresponds to the release of 16 water molecules. The observed weight loss of 11.0% is somehow smaller than the calculated value (12.2%); however,

1506 Crystal Growth & Design, Vol. 7, No. 8, 2007

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Figure 10. Solid-state emission spectra of compounds 1 (black), 2 (red), and 3 (green).

Figure 8. (a) Three-dimensional framework of compound 3. Phenyl and SO3 groups have been omitted for clarity. (b) Topological structure of compound 3.

Figure 11. TGA curves for compounds 1-3.

Figure 9. View of the structure of compound 3 down the b-axis. The CPO3 and CSO3 groups are shaded in pink and yellow, respectively. Cd, O, N, and C atoms are drawn as green, red, blue, and black circles, respectively. Hydrogen bonds are represented by dashed lines.

we deem that this is within the experimental error because the results of TGA may have larger errors, especially when the compound contains a larger number of lattice water molecules, such as in compound 1. The second and third steps are overlapping and started at 254 °C and completed at 867 °C, which correspond to the combustion of the organic ligands. The total observed weight loss at 900 °C is 71.7% and the final residuals were not characterized. TGA curves of compound 2

also exhibit three main steps of weight losses. The first step started at 42 °C and completed at 97 °C, which corresponds to the release of the lattice water molecule. The observed weight loss of 8.0% is close to the calculated value (7.6%). The second and third steps are overlapping and started at 260 °C and completed at 821 °C, which corresponds to the combustion of the organic ligands. The total weight loss at 900 °C is 63.6%, and the final residuals were not characterized. TGA curves of compound 3 exhibit three main steps of weight losses. The first step started at 45 °C and completed at 186 °C, which corresponds to the release of 10 water molecules. The observed weight loss of 11.8% is close to the calculated value (12.4%). The second and third steps are overlapping and started at 280 °C and completed at 575 °C, which corresponds to the combustion of the organic ligands. The total observed weight loss at 900 °C is 65.8%, and the final residuals were not characterized. On the basis of XRD diffraction studies (see the Supporting Information), only compound 3 retains crystallinity after the release of lattice water molecules. This is reasonable, because hydrogen bonds in compounds 1 and 2 are very important to sustaining their 3D supramolecular structures, hence the removal of lattice water molecules will result in the collapse of their 3D structures. For compound 3, the skeleton of the structure can be retained after the loss of water molecules, because the lattice waters are located at the cavities of its 3D framework.

Novel Cadmium(II) Sulfonate-Phosphonate Cluster Compounds

Conclusion In summary, the hydrothermal syntheses, crystal structures, and characterizations of three new cadmium(II) phosphonatophenylsulfonates, namely, [Cd4(L)2(phen)6(Cl)2(H2O)2]‚ 14H2O (1), [Cd6(L)4(phen)8]‚14H2O (2), and [Cd3(L)2(bipy)3(H2O)6]‚4H2O (3) (H3L ) m-HO3S-Ph-PO3H2), have been reported. When the bidentate chelating phen was applied as the second metal linker, two types of discrete clusters (compounds 1 and 2) were obtained. The formation of these two different types of clusters is related to the different coordination modes of the phosphonatophenylsulfonate ligands, different counteranion of the cadmium(II) sources, and the different M/L/phen molar ratios. When the bidentate bridging 4,4′-bipy was used as the second metal linker, compound 3 with three-dimensional structure was obtained. It should be noted that the structures of the tetranuclear and hexanuclear cadmium(II) phosphonatophenylsulfonate clusters differ significantly from those of the corresponding zinc(II) ones because of the different coordination modes of the phosphonatophenylsulfonate ligands as well as higher coordination numbers for the cadmium(II) ions (5 and 6) compared to those for the zinc(II) ions (4 and 5) in their clusters we reported previously.2a We are currently exploring the possible cluster compounds of post-transition main group elements such as Ga(III), In(III), Sn(II), etc., by applying this synthetic route. Acknowledgment. This work was supported by the National Natural Science Foundation of China (20371047, 20521101), the Key Project of CAS (KJCX2-YW-H01), and the NSF of Fujian Province (E0420003, E0610034). Supporting Information Available: X-ray crystallographic files in CIF format, inter-ring distances and dihedral angles for compounds 1 and 2, topology connectors in compound 3, and XRD patterns for all three compounds (PDF). This material is available free of charge via the Internet at http://pubs.acs.org.

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