One-dimensional Cadmium(II) Coordination Polymers:Syntheses and Crystal Structures of[Cd(H2O)3(C5H6O4)]·2H2O, Cd(H2O)2(C6H8O4), and Cd(H2O)2(C8H12O4)

Jie Sun and Yue-Qing Zheng*

Ningbo/P. R. China, Municipal Key Laboratory of Inorganic Materials Chemistry,Institute for Solid State Chemistry, Ningbo University

Received November 27th, 2002.

Abstract. [Cd(H2O)3(C5H6O4)]·2H2O (1) and Cd(H2O)2(C6H8O4)(2) were prepared from reactions of fresh CdCO3 precipitate withaqueous solutions of glutaric acid and adipic acid, respectively,while Cd(H2O)2(C8H12O4) (3) crystallized in a filtrate obtainedfrom the hydrothermal reaction of CdCl2·2.5H2O, suberic acid andH2O. Compound 1 consists of hydrogen bonded water moleculesand linear 1

�{[Cd(H2O)3](C5H6O4)2/2} chains, which result from thepentagonal bipyramidally coordinated Cd atoms bridged by bis-chelating glutarato ligands. In 2 and 3, the six-coordinate Cd atomsare bridged by bis-chelating adipato and suberato ligandsinto zigzag chains according to 1

�{[Cd(H2O)3](C5H6O4)2/2} and1�{[Cd(H2O)2](C8H12O4)2/2}, respectively. The hydrogen bonds be-

Eindimensionale Cadmium(II)-Koordinationspolymere: Synthesen undKristallstrukturen von [Cd(H2O)3(C5H6O4)]·2H2O, Cd(H2O)2(C6H8O4) undCd(H2O)2(C8H12O4)

Inhaltsübersicht. [Cd(H2O)3(C5H6O4)]·2H2O (1) und Cd(H2O)2-(C6H8O4) (2) wurden durch Reaktionen von frisch gefälltemCdCO3 mit wäßrigen Lösungen von Glutarsäure bzw. Adipinsäuredargestellt, während Cd(H2O)2(C8H12O4) (3) aus dem Filtrat einerhydrothermalen Reaktion von CdCl2·2.5H2O, Korksäure und H2Okristallisiert. Verbindung 1 setzt sich aus den über H-Brücken-bindungen gebundenen H2O-Molekülen und den linearen1�{[Cd(H2O)3](C5H6O4)2/2}-Ketten zusammen. Letztere ergebensich aus pentagonal-bipyramidal koordinierten Cadmiumatomen,die über bis-chelatierende Glutarato-Liganden verknüpft werden.In den Verbindungen 2 bzw. 3 sind die sechsfach koordinierten Cd-Atome über bis-chelatierende Adipato- bzw. Suberato-Liganden zu

Introduction

Utilization of saturated α,ϖ-dicarboxylate anions as flexiblespacer ligands to construct coordination polymers is of cur-rent interest in coordination chemistry and supramolecularchemistry and has been attracting enormous attention[1�7]. Up to now, two α,ϖ-dicarboxylates of cadmium,

* Prof. Dr. Yue-Qing ZhengInstitute for Solid State ChemistryNingbo University,Ningbo 315211 P. R. ChinaTelefax: Int. �574/87600747e-mail: zhengcm@nbu.edu.cn

Z. Anorg. Allg. Chem. 2003, 629, 1001�1006 DOI: 10.1002/zaac.200200397 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1001

tween water and the carboxylate oxygen atoms are responsible forthe supramolecular assemblies of the zigzag chains into 3D net-works. Crystallographic data: (1) P1 (no. 2), a � 8.012(1), b �

8.160(1), c � 8.939(1) A, α � 82.29(1)°, β � 76.69(1)°, γ �

81.68(1)°, U � 559.6(1) A3, Z � 2; (2) C2/c (no. 15), a � 16.495(1),b � 5.578(1), c � 11.073(1) A, ß � 95.48(1)°, U � 1014.2(1) A3,Z � 4; (3) P2/c (no. 13), a � 9.407(2), b � 5.491(1), c � 11.317(2)A, ß � 95.93(3)°, U � 581.4(2) A3, Z � 2.

Keywords: Cadmium; Dicarboxylato complexes; Polymeric chains;Supramolecular assembly

zick-zack-förmigen Ketten gemäß 1�{[Cd(H2O)3](C5H6O4)2/2} bzw.

1�{[Cd(H2O)2](C8H12O4)2/2} verbrückt. Wasserstoffbrückenbindun-gen zwischen H2O-Molekülen und den Sauerstoffatomen der Carb-oxylat-Gruppen sind für den Aufbau eines dreidimensionalensupramolekularen Netzwerkes aus diesen Ketten verantwortlich.Kristalldaten: (1) P1 (no. 2), a � 8,012(1), b � 8,160(1), c �

8,939(1) A, α � 82,29(1)°, β � 76,69(1)°, γ � 81,68(1)°, U �

559,6(1) A3, Z � 2; (2) C2/c (no. 15), a � 16,495(1), b � 5,578(1),c � 11,073(1) A, ß � 95,48(1)°, U � 1014,2(1) A3, Z � 4; (3)P2/c (no. 13), a � 9,407(2), b � 5,491(1), c � 11,317(2) A,ß � 95,93(3)°, U � 581,4(2) A3, Z � 2.

namely Cd(H2O)2(C4H4O4) and Cd2(H2O)4(C4H4O4)2·H2O,were described. Both are coordination polymers with suc-cinato ligands and both show the Cd atoms in pentagonalbipyramidal environments of oxygen atoms [8, 9]. In theformer, the seven-coordinate metal atoms are bridged bysuccinato ligands into grid-like layers [8]. In the latter, how-ever, two adjacent pentagonal bipyramids are condensed todimers, which are linked by succinato ligands to generateopen layers with rhomboidal “windows” [9]. Here, we re-port the syntheses and crystal structures of the threecoordination polymers [Cd(H2O)3(C5H6O4)]·2H2O (1),Cd(H2O)2(C6H8O4) (2), and Cd(H2O)2(C8H12O4) (3) withthe Cd atoms bridged by bis-chelating dicarboxylato li-gands into linear or zigzag polymeric chains.

J. Sun, Y.-Q. Zheng

Experimental Section

Preparation

All chemicals of p.a. grade were commercially available and usedwithout further purification. The FT-IR spectra were recordedfrom KBr pellets in the range from 4000 cm�1 to 400 cm�1 on aShimadzu FTIR-8900 spectrometer. The combined TG/DTA meas-urements were carried out between 25�900 °C on powderedsamples under flowing N2 using a Seiko Exstar6000 TG/DTA6300equipment with a heating rate of 10 °C/min.

[Cd(H2O)3(C5H6O4)] ·2H2O (1): The white precipitate, which wasprepared by dropwise addition of 2.5 ml (1 M) Na2CO3 to a stirredaqueous solution of 0.57 g (2.5 mmol) CdCl2 ·2.5H2O in 10 mlH2O, was added to a stirred aqueous solution of 0.33g (2.5 mmol)glutaric acid in 20 ml H2O. The resulting mixture was furtherstirred for ca. 30 minutes to give a white suspension, which wasallowed to stand at room temperature. Within ca. 12 hours color-less well-shaped crystals were grown. Yield: over 95% based on theinitial CdCl2 ·2.5H2O input. IR (cm�1): 3422s, 2964w, 1556s, 1410s,1348w, 1315w, 1223w, 1161w, 1053w, 910w, 648m.

Cd(H2O)2(C6H8O4) (2): The synthetic procedure is similar to 1 ex-cept that 0.73 g (5.0 mmol) adipic acid was employed in place ofglutaric acid. The resulting suspension was filtered out and the fil-trate was allowed to stand at room temperature. Colorless well-shaped crystals were grown by slow evaporation at room tempera-ture for 4 days. Yield: ca. 35% based on the initial CdCl2 ·2.5H2Oinput. IR (cm�1): 3421s, 2945w, 2862w, 1556s, 1418s, 1319m,1281w, 1177w, 1153w, 1070w, 943w, 923w, 881w, 714m.

Cd(H2O)2(C8H12O4) (3): A 23 ml teflon-lined stainless steelautoclave charged with 0.57 g (2.5 mmol) CdCl2 ·2.5H2O, 0.87 g

Table 1 Crystallographic and experimental data of 1, 2 and 3

1 2 3

Formula C5H16CdO9 C6H12CdO6 C8H16CdO6

FW 332.58 292.56 320.61Crystal shape colorless block colorless block colorless needleCrystal size/mm 0.29 � 0.09 � 0.09 0.67 � 0.33 � 0.20 0.44 � 0.27 � 0.11Crystal system triclinic monoclinic monoclinicSpace group P1 C2/c P2/ca/A 8.012(1) 16.495(1) 9.407(2)b/A 8.160(1) 5.578(1) 5.491(1)c/A 8.939(1) 11.073(1) 11.317(2)α/° 82.29(1)ß/° 76.69(1) 95.48(1) 95.93(3)γ/° 81.68(1)U/A3 559.6(1) 1014.2(1) 581.4(2)Z 2 4 2Dx/g cm�3 1.974 1.916 1.831T/K 293 293 293µ/mm�1 1.980 2.150 1.884Transmission coefficient 0.481�0.541 0.086�0.154 0.141�0.172Measured reflections 3139 1557 1901Unique reflections (Rint) 2585 (0.0204) 1168 (0.0247) 1340 (0.0202)Obs. reflections [I � 2σ(I)] 2378 1150 1293R1, wR2 [I � 2σ(I)]a) 0.0221, 0.0524 0.0540, 0.1451 0.0218, 0.0539R1, wR2 (all data)a) 0.0260, 0.0540 0.0542, 0.1454 0.0228, 0.0548A, B valuesb) 0.0237, 0.0185 0.0883, 0.0000 0.0306, 0.0674Number of variables 201 62 70Extinction coefficient 0.042(2) 0.065(3) 0.022(2)Goodness of fit on F2 1.065 1.548 1.093δρmin; δρmax/e ·A�3 �0.428; 0.476 �2.916; 1.412 �0.567; 0.879

a) wR2 � [Σw(Fo2�Fc

2)2/Σw(Fo2)2]1/2

b) w � [σ2(Fo2) � (AP)2 � BP]�1 with P � (Fo

2 � 2Fc2)/3,

2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim zaac.wiley-vch.de Z. Anorg. Allg. Chem. 2003, 629, 1001�10061002

(5.0 mmol) suberic acid, 0.66 g (11.8 mmol) and 10 ml H2O washeated to 160 °C for 5 days and then cooled to room temperature.After filtration, the filtrate was maintained at room temperature.Colorless elongated crystals were grown within 3 days. Yield: lessthan 10% based on the initial CdCl2 ·2.5H2O input. IR (cm�1):3207m, 2945m, 2860w, 1533s, 1429s, 1406w, 1364w, 1296w, 1267w,1205w, 1196w, 1013w, 951w, 741m.

X-ray structural analyses

Suitable single crystals of 1, 2 and 3 were selected under a polariz-ing microscope and fixed with epoxy cement on fine glass fibreswhich were then mounted on a Bruker P4 single crystal dif-fractomerter (graphite-monochromated Mo-Kα radiation, λ �

0.71073 A) for cell determination and the subsequent data collec-tion. The lattice parameters were refined from the 2� values(10�25°) of 25 carefully centered reflections. The reflection inten-sities with 2�max � 55° were collected at 293 K using the �-2�

scan technique. On the basis of the monitored reflections, the em-ployed single crystals exhibit no detectable decay during the datacollection. The data were corrected for Lp effects and the empiricalabsorption correction has been applied on the basis of psi-scanof a few suitable reflections. The programs SHELXS-97 [10] andSHELXL-97 [11] were used for structure determination and refine-ment. The structures were solved by using direct methods. Sub-sequent difference Fourier syntheses led to the positions of the re-maining non-hydrogen atoms. All hydrogen atoms were derivedfrom the difference Fourier maps. All non-hydrogen atoms werefinally refined with anisotropic displacement parameters by full-matrix least-squares technique [11]. The hydrogen atoms weretreated isotropically. Detailed informations on the crystal data andthe structure determination are summarized in Table 1. Selected

One-dimensional Cadmium(II) Coordination Polymers

interatomic distances and bond angles are given in Tables 2�4.Crystallographic data (excluding structure factors) for the com-pounds in this paper have been deposited with the CambridgeCrystallographic Data Centre as supplementary publication nos.CCDC 200349 (C5H16CdO9), 200350 (C6H12CdO6) and 200351(C8H16CdO6). Copies of the data can be obtained, free of charge,on application to CCDC, 12 Union Road, Cambridge CB2 1EZ,UK, (fax: �44 1223 336033 or e-mail: deposit@ccdc.cam.ac.uk).

Results and Discussion

Structure description

The principal building blocks in the title compounds 1, 2,and 3 are chains according to 1

�{[Cd(H2O)3](C5H6O4)2/2},1�{[Cd(H2O)2](C6H8O4)2/2}, and 1

�{[Cd(H2O)2](C8H12O4)2/2},respectively (Fig. 1). While the former chain is almostlinear, the latter two are zigzag shaped.

Compound 1 consists of linear 1�{[Cd(H2O)3](C5H6O4)2/2}

chains and hydrogen bonded H2O molecules (Fig. 2).Within the linear chains, the Cd atoms are in the consider-

Fig. 1 Fragments of the crystal structures of 1, 2, and 3. Linearchain 1

�[Cd(H2O)3(C6H6O4)2/2] in 1 (a); zigzag chain 1�[Cd(H2O)2-

(C6H8O4)2/2] in 2 (b); zigzag chain 1�[Cd(H2O)2(C8H12O4)2/2] in 3

(c). The thermal ellipsoids are shown at the 45% probability level.

Z. Anorg. Allg. Chem. 2003, 629, 1001�1006 zaac.wiley-vch.de 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1003

Fig. 2 Crystal structure of 1 viewed along [101] (small solidcircles: H atoms; gray balls: O atoms; dark balls: C atoms).

able distorted pentagonal bipyramidal [CdO7] coordinationdefined by three water oxygen atoms and four carboxylateoxygen atoms of two bis-chelating glutarato ligands. Two ofthe three H2O molecules occupy the apical positions of thepentagonal bipyramid. The Cd�O bond distances fall inthe region between 2.224(2) A and 2.719(2) A. Two longerbonds to oxygen atoms O(2) and O(4)#1 of the carboxylategroups located in the equatorial plane are observed. Theaxial O�Cd�O bond angle exhibits significant deviationfrom linearity (173.63(7)°) and the non-axial ones varyfrom 51.16(6)° to 160.57(6)° (Table 2). As far as the bis-chelating glutarate anion is concerned, all non-hydrogenatoms are coplanar. The Cd atoms are bridged by the gluta-rato ligands to generate linear chains extending along the[101] direction. The chains are further linked by interchainhydrogen bonds with the coordinated H2O molecules asdonors and both coordinated H2O molecules and oxygenatoms of the carboxylate group as acceptors. Bond dis-tances and angles within the hydrogen bonds are summar-ized in Table 2. Within the 3D network formed, two crystal-lographically distinct lattice H2O molecules are located. Thelattice water oxygen atoms act as acceptors in hydrogenbonds with the coordinating water molecules with distancesd(O�H···O) � 2.653�2.740 A, and angles �(O�H···O) �163�175° (Table 2). Furthermore, the H2O molecules aredonors in hydrogen bonds with the coordinating water mol-ecules (d(O�H···O) � 2.653�2.792 A, �(O�H···O) �156°) and carboxylate oxygen atoms (d(O�H···O) �2.734�2.996 A, �(O�H···O) � 153�177°) as acceptors.

Different from 1, the Cd atoms in 2 and 3 are in similarsix-coordinate sites. Each of them is coordinated by twoH2O molecules and two chelating carboxylate groups of dif-ferent dicarboxylate anions to form severely distorted[CdO6] octahedra with the water molecules at cis positions.The Cd�O bond distances fall in the region from 2.222 Ato 2.347 A and 2.210 A to 2.349 A for 2 and 3, respectively(Tables 3 and 4). The Cd atoms are bridged by bis-chelatingadipato and suberato groups to zigzag chains according to1�{[Cd(H2O)2](C6H8O4)2/2} and 1

�{[Cd(H2O)2](C8H12O4)2/2},

J. Sun, Y.-Q. Zheng

Table 2 Selected bond lengths/A and angles/° of 1

Cd�O(1) 2.279(2) Cd�O(6) 2.345(2) C(2)�C(3) 1.517(3)Cd�O(2) 2.535(2) Cd�O(7) 2.313(2) C(3)�C(4) 1.514(3)Cd�O(3)#1 2.265(2) C(1)�O(1) 1.271(3) C(4)�C(5) 1.520(3)Cd�O(4)#1 2.719(2) C(1)�O(2) 1.251(3) C(5)�O(3) 1.262(3)Cd�O(5) 2.224(2) C(1)�C(2) 1.509(3) C(5)�O(4) 1.251(3)

O(1)�Cd�O(2) 53.75(6) O(2)�Cd�O(7) 88.56(7) O(6)�Cd�O(7) 173.63(7)O(1)�Cd�O(3)#1 94.15(6) O(3)#1�Cd�O(4)#1 51.16(6) O(1)�C(1)�O(2) 120.3(2)O(1)�Cd�O(4)#1 145.31(6) O(3)#1�Cd�O(5) 129.02(7) O(1)�C(1)�C(2) 116.9(2)O(1)�Cd�O(5) 136.67(7) O(3)#1�Cd�O(6) 90.43(7) O(2)�C(1)�C(2) 122.8(2)O(1)�Cd�O(6) 91.12(7) O(3)#1�Cd�O(7) 89.37(7) C(1)�C(2)�C(3) 117.4(2)O(1)�Cd�O(7) 95.24(7) O(4)#1�Cd�O(5) 77.93(7) C(2)�C(3)�C(4) 110.4(2)O(2)�Cd�O(3)#1 147.45(6) O(4)#1�Cd�O(6) 89.16(6) C(4)�C(4)�C(5) 117.1(2)O(2)�Cd�O(4)#1 160.57(6) O(4)#1�Cd�O(7) 85.76(7) O(3)�C(5)�C(4) 116.8(2)O(2)�Cd�O(5) 83.46(7) O(5)�Cd�O(6) 85.64(8) O(4)�C(5)�C(4) 121.9(2)O(2)�Cd�O(6) 95.00(7) O(5)�Cd�O(7) 89.54(8) O(3)�C(5)�O(4) 121.4(2)

Hydrogen bonding

D�H···A D�H H···A D···A D�H···AO(5)�H(5A)···O(9) 0.83 1.83 2.653 169O(5)�H(5B)···O(6)#2 0.78 2.01 2.778 167O(6)�H(6A)···O(1)#3 0.79 1.89 2.665 168O(6)�H(6B)···O(8)#2 0.88 1.88 2.740 163O(7)�H(7A)···O(8)#4 0.87 1.87 2.733 175O(7)�H(7B)···O(4)#4 0.72 2.00 2.715 173O(8)�H(8A)···O(2) 0.83 1.91 2.734 177O(8)�H(8B)···O(4)#5 0.80 2.26 2.996 153O(9)�H(9A)···O(7)#6 0.84 2.01 2.792 156O(9)�H(9B)···O(3)#7 0.83 1.98 2.785 165

Symmetry transformations used to generate equivalent atoms: #1 � x�1, y, z�1; #2 � �x�1, �y�2, �z�2; #3 � �x�1, �y�1, �z�2; #4 � �x, �y�2,�z�2; #5 � �x, �y�2, �z�3; #6 � �x�1, �y�2, �z�1; #7 � x�1, y�1, z�1

Table 3 Selected bond lengths/A and angles/° of 2

Cd�O(1) 2� 2.323(3) C(1)�O(1) 1.259(6) C(2)�C(3) 1.489(8)Cd�O(2) 2� 2.346(3) C(1)�O(2) 1.259(6) C(3)�C(3)#2 1.52(1)Cd�O(3) 2� 2.222(2) C(1)�C(2) 1.508(6)

O(1)�Cd�O(1)#1 159.3(2) O(2)�Cd�O(2)#1 86.9(2) O(1)�C(1)�C(2) 118.6(4)O(1)�Cd�O(2) 55.8(1) O(2)�Cd�O(3) 146.15(8) O(2)�C(1)�C(2) 121.0(4)O(1)�Cd�O(2)#1 107.5(2) O(2)�Cd�O(3)#1 97.44(9) C(1)�C(2)�C(3) 115.8(5)O(1)�Cd�O(3) 91.26(9) O(3)�Cd�O(3)#1 97.2(1) C(2)�C(3)�C(3)#2 112.3(7)O(1)�Cd�O(3)#1 102.5(1) O(1)�C(1)�O(2) 120.4(4)

Hydrogen bonding

D�H···A D�H H···A D···A D�H···AO(3)�H(4A)···O(2)#3 0.92 1.82 2.741 174O(3)�H(4B)···O(1)#4 0.95 1.74 2.686 174

Symmetry transformations used to generate equivalent atoms: #1 � �x�1, y, �z�1/2; #2 � �x�1/2, �y�3/2, �z; #3 � �x�1, y�1, �z�1/2; #4 � �x�1,�y, �z

respectively (Fig. 1). The propagation vector of the chainsis orientated in the [101] direction in both compounds. Thechains are arranged in a way that the coordinated watermolecules donate hydrogen atoms to the chelating carb-oxylate atoms (O(2)) to form interchain hydrogen bonds(d(O�H···O) � 2.741 A, �(O�H···O) � 174° for 2,Table 3; d(O�H···O) � 2.693 A, �(O�H···O) � 168° for3, Table 4). This linkage of the chains leads to layers parallelto (101) and (102) in 2 and 3, respectively. As illustrated inFigures. 3 and 4, these layers are again held together byhydrogen bonds. Within these bonds, the coordinated waterO(3) molecules act as donors and the chelating carboxylateatoms (O(1)) as acceptors (d(O�H···O) � 2.686 A,�(O�H···O) � 174° for 2, Table 3; d(O�H···O) � 2.672 A,

2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim zaac.wiley-vch.de Z. Anorg. Allg. Chem. 2003, 629, 1001�10061004

�(O�H···O) � 178° for 3, Table 4). Similar to the glutaratoligands in 1, the non-hydrogen atoms in the adipto as wellas the suberato groups are nearly coplanar.

IR spectra

The i.r. spectra display broad bands centered at 3422, 3421,and 3207 cm�1 for 1, 2, and 3, respectively, in consistencewith the presence of water molecules. The symmetric andasymmetric COO stretching vibrations exhibit character-istic absorption bands at 1556, 1556 and 1533 and 1410,1418 and 1429 cm�1 for 1, 2 and 3, respectively. The∆ values (� (νasym(CO2)�νsym(CO2)) decrease from 146 cm�1

(1) through 138 cm�1 (2) to 104 cm�1 (3). The absorption

One-dimensional Cadmium(II) Coordination Polymers

Table 4 Selected bond lengths/A and angles/° of 3

Cd�O(1) 2� 2.323(2) C(1)�O(1) 1.259(3) C(2)�C(3) 1.515(3)Cd�O(2) 2� 2.349(2) C(1)�O(2) 1.255(2) C(3)�C(4) 1.519(3)Cd�O(3) 2� 2.210(2) C(1)�C(2) 1.505(3) C(4)�C(4)#2 1.525(5)

O(1)�Cd�O(1)#1 151.06(9) O(2)�Cd�O(2)#1 88.30(8) O(1)�C(1)�C(2) 119.2(2)O(1)�Cd�O(2) 55.43(5) O(2)�Cd�O(3) 144.21(6) O(2)�C(1)�C(2) 121.2(2)O(1)�Cd�O(2)#1 102.06(6) O(2)�Cd�O(3)#1 99.45(7) C(1)�C(2)�C(3) 115.7(2)O(1)�Cd�O(3) 88.80(6) O(3)�Cd�O(3)#1 94.4(1) C(2)�C(3)�C(4) 112.4(2)O(1)�Cd�O(3)#1 111.14(7) O(1)�C(1)�O(2) 119.7(2) C(3)�C(4)�C(4)#2 112.8(2)

Hydrogen bonding

D�H···A D�H H···A D···A D�H···AO(3)�H(5A)···O(1)#3 0.78 1.89 2.672 178O(3)�H(5B)···O(2)#4 0.72 1.98 2.693 168

Symmetry transformations used to generate equivalent atoms: #1 � �x�1, y, �z�1/2; #2 � �x�2, �y�1, �z�1; #3 � �x�1, �y�1, �z�1; #4 � �x�1,y�1, �z�1/2

Fig. 3 Layers of zigzag chains 1�[Cd(H2O)2(C6H8O4)2/2] in the

crystal structure of 2 (on top); Perspective view of the crystal struc-ture of 2 along [010] (small solid circles: H atoms; gray balls:O atoms; dark balls: C atoms)

bands at 2964, 2945 and 2945 cm�1 for 1, 2 and 3, respec-tively, could be assigned to the C�H stretching vibrations.

Z. Anorg. Allg. Chem. 2003, 629, 1001�1006 zaac.wiley-vch.de 2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim 1005

Fig. 4 Layers of zigzag chains 1�[Cd(H2O)2(C8H12O4)2/2] in the

crystal structure of 3 (on top); Perspective view of the crystal struc-ture of 3 along [010] (small solid circles: H atoms; gray balls:O atoms; dark balls: C atoms)

Thermal analyses

Figure 5 shows the TG-DTA curves of the three cadmiumcarboxylates. When heated under flowing nitrogen atmos-

J. Sun, Y.-Q. Zheng

Fig. 5 TG (solid line) �DTA (dotted line) curves of 1, 2, and 3

phere, an endothermic dehydration starts at 35 °C, 60 °Cand 70 °C, respectively, which is completed at 150 °C, 120 °Cand 145 °C, respectively. The observed weight losses of26.3%, 12.2% and 11.2% correspond well to the calculatedvalues of 27.08%, 12.32% and 11.24%. The dehydrationtemperature increases from 1 to 3. The lower value for 1 isexpected because it contains non-bonded H2O molecules.The dehydrated product of 1 undergoes an exothermicphase transition at 245 °C and decomposes above 357 °C inthree continuous steps. The first step shows a sharp DTApeak and the following are quite broad. It remains a darkresidue of 6.4% at 900 °C. The dehydrated intermediates of2 and 3 decompose at nearly the same temperature (290 °Cand 285 °C), exhibiting one well resolved weight loss fol-

2003 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim zaac.wiley-vch.de Z. Anorg. Allg. Chem. 2003, 629, 1001�10061006

lowed by two gradual weight losses. At 900 °C, the darkresidue for 2 is 2.7%, but no residue is observed for 3, prob-ably because the initially-formed anhydrous product of 3 iscompletely sublimed at higher temperature. Obviously, thedecompositions of the dehydrated intermediates of 1 and 2are difficult to interpreted at present. Further investigationsare necessary for gaining a clear picture of the thermal de-compositions of the title compounds.

Acknowledgement: The project was financially supported by theNational Natural Science Foundation (20072022), the Excellentyoung Teachers Program of Moe, P. R. China (C982302), the Zheji-ang Provincial Natural Science Foundation (RC99034), NingboMinicipal Key Doctor’s Funds (0011002), Ningbo Municipal Natu-ral Science Foundation (01J20130-1) and Scientific Research Fundof Ningbo University (0208035). The authors also thank Mr. J.-L.Lin for his X-ray data collection.

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