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Syntheses and characterization of two metal–water clusters
Inorganica Chimica Acta 360 (2007) 3771–3776 www.elsevier.com/locate/ica
Syntheses and characterization of two metal–water clusters Taohai Li a, Feng Li b, Yanqin Wang a, Wenhua Bi a, Xing Li a, Rong Cao a
a,*
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fujian, Fuzhou 350002, PR China b The College of Chemistry, Xiang Tan University, Xiangtan, HuNan 411105, China Received 10 May 2007; accepted 15 May 2007 Available online 31 May 2007
Abstract Complexes 1 and 2, formulated {[Co2(4,4 0 -bpy)2 Æ 8H2O] Æ (CCA)2 Æ 4H2O}n (1) and {[Co(TMG)(4,4 0 -bpy)(H2O)2] Æ 3H2O}n (2) (H2CCA = 2-carboxylatocinnamate, H2TMG = 3,3-tetramethyleneglutate, 4,4 0 -bpy = 4,4 0 -bpyridine) have been synthesized by the reaction of cobalt (II), 4,4 0 -bpy and carboxylate ligands, in which 2D metal–water layers and 1D metal–water chains have been observed, respectively. In the metal–water clusters, the water molecules are trapped by the cooperative association of coordination interactions as well as hydrogen bonds. 2007 Elsevier B.V. All rights reserved. Keywords: Syntheses; Metal–water cluster; Layer; Chain
1. Introduction Water is the most abundant and cheapest inartificial solvent, which plays fundamental roles in almost all branches of natural sciences. Thus, as perfect model connecting isolated molecules to bulk water, it is not surprising that water clusters have been the focus of intense research interests [1]. With the development of research, water clusters have been classified as three classes: discrete water clusters, polymeric water clusters and metal–water clusters [2]. The structural elucidation of discrete and polymeric water clusters provides detailed knowledge of hydrogen-bonding and their fluctuations determined the properties of bulk water. Thus, the study of discrete and polymeric water clusters will help us to understand the anomalous behavior of bulk water/ice [3]. From an experimental point of view, so far a significant progress has been made with respect to the structural characterization of discrete water clusters (H2O)n (n = 2–16) [4–6], as well as polymeric water clusters such as chains
*
Corresponding author. Tel./fax: +86 591 83796710. E-mail address: [email protected] (R. Cao).
0020-1693/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2007.05.028
[7], tapes and 2D layers [8]. However, only disperse information is available on metal–water clusters [9]. In biology, water clusters are important to the proton pathways in the cytochrome b6f complex of plant chloroplast thylakoid membrane, mitochondrial ATPase [10], carbonic anhydrase II [11], as well as in redox proteins [12,13]. In addition, water clusters play a crucial role in energy-transduction. However, the details of the water clusters in either energy-transduction or proton conduction in proteins and enzymes are largely unknown [12,14]. As well known, most active centers of proteins and enzymes in living systems contain metal atoms. The investigation of interactions between metal atoms and small water clusters may help us unravel the mechanism in energy-transduction or proton conduction. As known, metal–water clusters not only involved the hydrogen-bonding interactions between water molecules, but also the coordination bonds between metal atoms and water clusters. Thus, the structural study of metal–water clusters can provide valuable information for unraveling the mechanism in energytransduction or proton conduction. In this sense, the design and synthesis of metal–water clusters is more important than discrete or polymeric clusters.
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The lattices of crystal hosts offer environments for stabilizing water clusters, which play important roles in the formation of different water morphologies. To obtain metal– water clusters, it is important to construct suitable host frameworks. We have successfully designed and synthesized 1D polymeric water chain and tape [15,16]. As continuous research of synthesizing water clusters, we investigated the reactions of 4,4 0 -bpyridine, Co(NO3)2 Æ 6H2O with 2-carboxylatocinnamate (H2CCA) or 3,3tetramethyleneglutarate (H2TMG), respectively, and obtain two complexes, {[Co2(4,4 0 -bpy)2 Æ 8H2O] Æ (CCA)2 Æ 4H2O}n (1) and {[Co(TMG)(4,4 0 -bpy)(H2O)2] Æ 3H2O}n (2) (H2CCA = 2-carboxylatocinnamate, H2TMG = 3,3-tetramethyleneglutate, 4,4 0 -bpy = 4,4 0 -bpyridine). In the crystal lattice of complexes 1 and 2, two kinds of cobalt–water clusters have been observed. 2. Experimental All chemicals were obtained commercially and used without further purification. Elemental analyses were carried out on an Elementar Vario EL III analyzer. Infrared (IR) spectra were recorded with Perkin–Elmer Spectrum One as KBr pellets in the range 4000–400 cm1. Thermogravimetric analyses were carried out with a NETZSCH STA 449C unit at a heating rate of 10 C min1 under nitrogen. X-ray powder diffraction measurements for 1 and 2 were recorded on a RIGAKU DMAX2500PC diffractometer using Cu Ka radiation. 2.1. Synthesis of {[Co(4,4 0 -bp)(H2O)4] Æ (CCA) Æ 2H2O}n (1) 4,4 0 -bpy (0.016 g, 0.1 mmol), H2CCA (0.019 g, 0.1 mmol), KOH (0.012 g, 0.2 mmol) and Co(NO3)2 Æ 6H2O (0.03 mg, 0.1 mmol) were dissolved in a mixture of water (8 ml) and ethanol (8 ml). After stirring for 2 h, a clear yellow solution was produced, and two weeks later, yellow prism crystals were collected. Yield: 36%. Anal. Calc. for C20H26N2O10Co: C, 46.79; H, 5.10; N, 5.46. Found: C, 46.77; H, 5.12; N, 5.47%. IR (KBr, cm1): 3315(s), 1641(s), 1606(s), 1538(s), 1384(vs), 1286(w), 1218(w), 1068(m), 977(w), 813(s), 630(m). 2.2. Synthesis of {[Co(TMG)(4,4 0 -bpy)(H2O)] Æ 3H2O}n (2) 4,4 0 -bpy (0.016 g, 0.1 mmol), H2TMG (0.024 g, 0.1 mmol), KOH (0.012 g, 0.2 mmol) and Co(NO3)2 Æ 6H2O (0.03 mg, 0.1 mmol) were dissolved in a mixture of water (8 ml) and ethanol (8 ml). After stirring for 2 h, a clear pink solution was produced, and two weeks later, red needle crystals were collected. Yield: 47%. Anal. Calc. for C19H28N2O8Co: C, 48.41; N, 5.94; H, 5.99; Found: C, 48.43; N, 5.97; H, 6.01%. IR (KBr, cm1): 3411 (m), 2942 (w), 2861(w), 1558 (vs), 1413 (s), 1222(w), 1066 (w), 815 (m), 632(w).
Table 1 Crystal data and structure refinement parameters for complexes 1 and 2
Formula Crystal size (mm) Molecular mass Crystal system Space group ˚) a (A ˚) b (A ˚) c (A a () b () c () ˚ 3) V (A Z T (K) Dcalc (g cm3) F(0 0 0) Reflections collected Independent reflections Data/restrain/ parameters Goodness-of-fit on F2 Final R indices [I > 2r(I)] R indices (all data)
1
2
C20H26CoN2O10 0.60 · 0.35 · 0.20 513.37 triclinic P 1 7.3854(15) 11.432(2) 13.625(3) 92.88(3) 98.04(3) 97.18(3) 1127.4(4) 2 173(2) 1.512 534 8640 6621
C19H26CoN2O7 0.30 · 0.04 · 0.04 453.35 monoclinic C2/c 19.896(8) 11.484(4) 20.429(8) 113.188(6) 4291(3) 8 173(2) 1.410 1848 16 021 4861
6621/3/798
4861/28/300
1.003 R1 = 0.0228, wR2 = 0.0455 R1 = 0.0215, wR2 = 0.0452
1.012 R1 = 0.0669, wR2 = 0.1946 R1 = 0.0780, wR2 = 0.2098
2.3. Crystal data collection and structure determination X-ray diffraction data for complexes 1 and 2 were collected on a Rigaku diffractometer with a Mercury CCD ˚ ) at 173(2) K. Empirarea detector (Mo Ka; k = 0.71073 A ical absorption corrections were applied to the data using the CRYSTALCLEAR program [17]. The structures were solved by the direct method and refined by the full-matrix leastsquares on F2 using the SHELXTL-97 program [18]. All non-hydrogen atoms were refined anisotropically. The organic hydrogen atoms were generated geometrically and hydrogen atoms of water molecules were located in a difference map and refined with the distance restraint O– ˚ . Crystallographic data for 1 and 2 are sumH = 0.85(1) A marized in Table 1. Bond lengths and bond angles are listed in Table 2. 3. Results and discussion For preparing metal–water clusters, there are two crucial conditions. One is the existence of two or more free water molecules, which provides the possibility of forming discrete or polymeric water clusters. Another is the coordination of water to metal centers. The coordination of water to metal atoms would not only provide hydrogen donor/ acceptor like free water, but also link the discrete or polymeric water clusters to central metal atoms. Low temperature may be available for the coordination of water to metal in the reaction systems. Thus, we give up the well known hydrothermal synthetic method for the construc-
T. Li et al. / Inorganica Chimica Acta 360 (2007) 3771–3776 Table 2 ˚ ), bond angles () for 1 and 2 Selected bond distances (A 1 Co(1)–O(1) Co(1)–O(3) Co(1)–N(1) Co(2)–O(5) Co(2)–O(7) Co(2)–N(3) N(1)–Co(1)–N(2) 2 Co(1)–O(3)#1 Co(1)–O(3) Co(1)–O(2)#1 Co(1)–O(2) Co(1)–N(2) Co(1)–N(3)#2 O(3)#1–Co(1)–O(3) O(3)#1–Co(1)– O(2)#1 O(3)–Co(1)–O(2)#1 O(3)#1–Co(1)–O(2) O(3)–Co(1)–O(2) O(2)#1–Co(1)–O(2) O(3)#1–Co(1)–N(2) O(3)–Co(1)–N(2) O(2)#1–Co(1)–N(2) O(2)–Co(1)–N(2) O(3)#1–Co(1)– N(3)#2 O(3)–Co(1)–N(3)#2 O(2)#1–Co(1)– N(3)#2 O(2)–Co(1)–N(3)#2 N(2)–Co(1)– N(3)#2
2.0490(19) 2.1127(19) 2.164(2) 2.0770(18) 2.0679(18) 2.169(2) 178.05(9)
Co(1)–O(2) Co(1)–O(4) Co(1)–N(2) Co(2)–O(6) Co(2)–O(8) Co(2)–N(4) N(3)–Co(2)–N(4)
2.1065(19) 2.0500(19) 2.180(2) 2.1526(18) 2.0428(18) 2.159(2) 178.89(9)
2.081(3) 2.081(3) 2.141(3) 2.141(3) 2.188(5) 2.194(5) 177.66(16) 96.69(12)
Co(2)–O(4)#3 Co(2)–O(4) Co(2)–O(4W) Co(2)–O(4W)#3 Co(2)–N(1) Co(2)–N(1)#3 O(4)#3–Co(2)–O(4) O(4)#3–Co(2)–N(1)
2.070(3) 2.070(3) 2.208(3) 2.208(3) 2.196(4) 2.196(4) 180.000(1) 93.15(13)
83.39(12) 83.39(12) 96.69(12) 176.30(17) 91.17(8) 91.17(8) 88.15(8) 88.15(8)
O(4)–Co(2)–N(1) O(4)#3–Co(2)–N(1)#3 O(4)–Co(2)–N(1)#3 N(1)–Co(2)–N(1)#3 O(4)#3–Co(2)–O(4W) O(4)–Co(2)–O(4W) N(1)–Co(2)–O(4W) N(1)#3–Co(2)– O(4W) O(4)#3–Co(2)– O(4W)#3 O(4)–Co(2)–O(4W)#3 N(1)–Co(2)– O(4W)#3 N(1)#3–Co(2)– O(4W)#3 O(4W)–Co(2)– O(4W)#3
86.85(13) 86.85(13) 93.15(13) 180.0 81.08(13) 98.92(13) 89.63(12) 90.37(12)
88.83(8) 88.83(8) 91.85(8) 91.85(8) 180.000(1)
98.92(13) 81.08(13) 90.37(12) 89.63(12) 180.000(1)
Symmetry codes: #1 x + 1, y, z + 1/2; #2 x, y + 1, z; #3 x + 1, y + 1, z + 1.
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tion of organic–inorganic hybrid materials in crystalline form, and adopt solution method investigating the reaction of Co(NO3)2 Æ 6H2O, 4,4 0 -bpy with H2CCA or H2TMG at room temperature. 3.1. Crystal Structure of {[Co(4,4 0 bpy)(H2O)4] Æ (CCA) Æ 2H2O}n (1) From the reaction of H2CCA, 4,4 0 -bpy and Co(NO3)2 Æ 6H2O, complex 1 is obtained, whose crystal structure has been described in our previous work in Ref. [19]. Here details of the framework structure of 1 will not be discussed and only the description of water cluster in 1 will be made. In 1, there are eight crystallographically independent coordinated water molecules (O(1), O(2), O(3), O(4), O(5), O(6), O(7) and O(8)) and four free water molecules (O(1W), O(2W), O(3W) and O(4W)). Through hydrogenbonding (O(2)–H(2A) O(1W), O(2)–H(2B) O(3W) and O(5)–H(5B) O(3W)), O(2), O(5), O(1W) and O(3W) are associated to form discrete tetramer clusters. ˚ ) is The average O O distance of such tetramer (2.739 A ˚ in ice Ih at close to the corresponding value of 2.759 A 90 C [20]. O(3), O(6), O(2W), O(4W) form another kind of water tetramer by hydrogen-bonding of O(3)–H(3B) O(2W), O(6)–H(6A) O(2W) and O(6)–H(6B) O(4W), ˚) and the average O O distance of this tetramer (2.841 A ˚ in ice Ih [21], but similar is longer than the value of 2.759 A ˚ in liquid water [20]. This to the O O distance of 2.85 A kind of tetramer and their equivalents are connected into 1D polymeric water cluster by O(2W)–H2W2 O4W. Thus, O(6), O(2W), O(4W) and their equivalents form a polymeric water chain with O(3) dangling at one side, which looks like a tree with branch (Fig. 1). The geometric parameters of the water tetramers and chains are summarized in Table 3. Through the coordination of O(2), O(3)
Fig. 1. The 2D cobalt–water layer in 1.
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Table 3 ˚ and ) for 1 and 2 Hydrogen-bonding parameters (A O–H O
O–H
O O
H O
O–H O
1 O1–H1A O13 O1–H1B O11#1 O2–H2A O1W O2–H2B O3W#2 O3–H3B O2W O3–H3A O14#3 O4–H4B O12#2 O4–H4A O13#3 O5–H5A O10 O5–H5B O3W O6–H6B O4W O6–H6A O2W O7–H7B O15#3 O7–H7A O9 O8–H8B O15 O8–H8A O9#4 O1W–H1W1 O12#1 O1W–H1W2 O16#2 O2W–H2W2 O4W#4 O2W–H2W1 O15 O3W–H3W2 O16#3 O3W–H3W1 O12 O4W–H4W2 O14#3 O4W–H4W1 O11#2
0.834(16) 0.866(15) 0.829(16) 0.832(16) 0.817(16) 0.832(15) 0.845(16) 0.838(16) 0.846(15) 0.861(16) 0.823(16) 0.864(15) 0.843(16) 0.846(15) 0.841(15) 0.849(16) 0.836(16) 0.845(16) 0.838(16) 0.862(16) 0.848(16) 0.833(15) 0.856(16) 0.812(16)
2.751(3) 2.711(3) 2.662(3) 2.782(3) 2.727(3) 2.733(3) 2.737(3) 2.734(3) 2.582(2) 2.774(3) 2.825(3) 2.842(3) 2.791(3) 2.672(2) 2.732(3) 2.706(3) 2.755(3) 2.825(2) 2.968(3) 2.692(3) 2.731(3) 2.813(2) 2.773(3) 2.731(3)
1.926(16) 1.859(16) 1.836(16) 1.961(17) 1.933(16) 1.903(16) 1.910(16) 1.896(16) 1.744(16) 1.924(17) 2.002(16) 1.999(16) 1.953(17) 1.831(16) 1.926(16) 1.888(17) 1.931(16) 1.993(17) 2.19(2) 1.845(17) 1.883(16) 2.004(17) 1.948(17) 1.948(18)
170(3) 168(3) 174(3) 168(2) 164(3) 175(3) 166(2) 179(2) 170(2) 169(2) 178(3) 165(3) 172(2) 173(3) 160(2) 162(2) 169(3) 168(3) 154(3) 167(3) 176(3) 164(3) 162(3) 162(3)
2 O1W–H1W1 O2W O1W–H1W2 O3W#5 O2W–H2W1 O1W O4W–H4W2 O3W O4W–H4W1 O2#6 O4W–H4W1 O3
0.831 0.821 0.848 0.866 0.873 0.873
2.883 2.868 2.883 2.921 2.873 2.972
2.221 2.105 2.256 2.100 2.078 2.362
136(7) 154(6) 130(8) 158(1) 150(9) 127(2)
#1 x + 1, y, z 1; #2 x, y, z 1; #3 x 1, y, z; #4 x + 1, y, z; #5 x + 1/2, y + 1/2, z + 1/2; #6 x + 1, y, z + 1/2.
Fig. 2. The coordination environment of cobalt ions in 2 with the thermal ellipsoids at 30% probability level (all H atoms were omitted for clarity) #A x + 1, y, z + 1/2; #B x, y + 1, z; #C x + 1, y + 1, z + 1.
nation geometry, the coordination environments are different. As shown in Fig. 2, Co(1) is coordinated by four oxygen atoms from four carboxyl groups and two nitrogen atoms from two 4,4 0 -bpy, and Co(2) is coordinated by two oxygen atoms from two carboxyl groups, two oxygen atoms from two coordinated water molecules and two nitrogen atoms from two 4,4 0 -bpy. The carboxyl groups in 2 adopt monodentae and bidentae coordination modes, respectively. Each carboxyl group with bidentate mode bridges two cobalt atoms forming Co-TMG chains along [0 0 1] direction. The coordination of 4,4 0 -bpy connect adjacent Co-TMG chains into 2D layers in [0 1 1] plane (Fig. 3),
and O(5), O(6) to Co(1) and Co(2) atoms, the polymeric water chain and discrete water tetramer are linked into 2D metal–water layers at [1 0 1] plane. O(1), O(4), O(7) and O(8) do not participate in the formation of water clusters, and only provide hydrogen-bonding donor to the uncoordinated CCA2. Through the hydrogen-bonding (O(9)–O(7), O(10)–O(5), O(12)–O(3W), O(11)–O(4W), O(15)–O(8), O(15)–O(2W), O(16)–O(1W) and O(16)– O(3W)), the uncoordinated CCA2 are located above and below each 2D metal–water layer, respectively. The extending of Co-bpy linear chain along [0 1 0] direction connected adjacent 2D layers into 3D suprarchitecture. 3.2. Crystal Structure of {[Co(TMG)(4,4 0 bpy)(H2O)] Æ 3H2O}n (2) Inspired by the metal–water chain in 1, complex 2 was obtained under similar reaction conditions, except that H2CCA for 1 was replaced by H2TMG. X-ray diffraction study reveals that two crystallographically independent cobalt (II) atoms, two TMG2, two 4,4 0 -bpy and coordinated water molecules are present in 2. Though two cobalt atoms are six-coordinated with similar octahedral coordi-
Fig. 3. The 2D host layer in 2.
T. Li et al. / Inorganica Chimica Acta 360 (2007) 3771–3776
and the five-membered rings of TMG ligands locate at two sides of the 2D layer, respectively. In the crystal lattice of 2, three crystallographically independent water molecules (O1w, O2w and O3w) are observed, which are associated by hydrogen bonds (O2w O1w and O1w O3w) to form a water trimer. The water trimer is linked to its’ adjacent equivalents forming a (H2O)6 unit. In this water hexamer, O1w, O2w, O1wa, O2wa are connected into a four-membered ring through O1w O2wa and O1wa O2w, and O3w and O3wa are hanged at the up or down side of the four-membered ring by O1w O3w and O1wa O3wa, respectively. Thus, the water hexamer in complex 2 looks like a ‘‘chair’’ (Fig. 4). However, there are notable differences between such conformation looking like ‘‘chair’’ and the well known ‘‘chair conformation’’. In the hexamer with chair conformation, six water molecules are linked end to end by hydrogen bonds forming a close six-membered ring [22]. As mentioned above, the water hexamer in complex 2 are composed of one four-membered ring and two dangling water ˚ ) in the molecules. The average O O distance (2.855 A water hexamer of complex 2 is closer to the O O distance in liquid water than complex 1. Through the hydrogen bonds between O3w and the coordinated water (O4w), the guest water hexamer connect neighbor 2D host layers forming 3D supramolecular architecture. The hydrogen bonds of 2 are summarized in Table 3. 3.3. Thermal analysis and X-ray powder diffraction Thermogravimetric analysis has determined the thermal stability of complexes 1 and 2. TGA analyses of 1 show a 20.94% weight loss from 77 C to 122 C, which corresponds to the loss of all free water molecules and two coordinated water (calc: 21.04%). For 2, the weight loss of 15.21% from 72 C to 118 C is equivalent to the loss of three free water and one coordinated water (calc: 15.27%). After all water molecules are removed, the TGA curves of 1 and 2 exhibit some differences. For 1, the TGA data reveals two distinct weight loss of 37.04% (from 206 C to 319 C) and 30.42% (from 384 C to 420 C),
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which are equivalent to the loss of uncoordinated CCA ligand and coordinated bpy ligand, respectively. Different from 1, the TGA curve of 2 show continuous weight loss covering a temperature range from 263 C to 443 C, which corresponds to the decomposition of 2D host layer. The difference arises from the uncoordination or coordination of carboxylate ligand in 1 and 2. The weight loss of 1 and 2 ends at 14.61% and 15.91%, respectively, which indicates that only CoO is left. To support the TGA, the sample of 1 and 2 were characterized by X-ray powder diffraction (XRPD) at room temperature (Figs. S1 and S2). The patterns simulated from the single crystal X-ray data of 1 and 2 are in good agreement with the observed ones. 3.4. Vibrational spectra The FT-IR spectroscopy of 1 shows strong bands at 1540 cm1 and 1384 cm1 due to the tasym (CO2) and tsym (CO2). For 2, the tasym (CO2) and tsym (CO2) stretching vibrations appear at 1558 cm1 and 1413 cm1. The spectrum of 2 exhibits a broad band centered around 3411 cm1. The O–H stretching vibration for quasiplanar and puckered-boat water hexamer appears at 3400 and 3415 cm1, respectively [22,23], and the vibration for chair hexamer occur at 3495 and 2614 cm1 [24]. By comparison, the O–H stretching vibration of water hexamer in 2 is that of boat conformation. The spectrum of 1 shows a broad band around 3315 cm1. In comparison with the O–H stretching for water tetramer (3421 cm1) [25], it has some blue shifts. This may be due to the water tetramer in 2 are composed of both free and coordinated water molecules, which is different from those composed of free water molecules. After removing the water from the crystal lattices of 1 and 2 by heating, both of the bands centered around 3315 and 3411 cm1 disappear. Therefore, in the cases of 1 and 2, these bands are attributable to the O–H stretching frequency of the (H2O)4 and (H2O)6 core structure, respectively. Deliberate exposure to water vapor for 3 days does not lead to reabsorption of water into the lattice as monitored by FTIR spectroscopy.
Fig. 4. The 1D cobalt–water chain in 2.
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4. Conclusion Two complexes containing metal–water clusters have been synthesized from the reaction of cobalt (II), 4,4 0 bpy and carboxylate ligands (H2CCA or H2TMG) successfully. For complex 1, the host framework is 1D H2O–Co-bpy chain along [0 1 0] direction, and the discrete water tetramer as well as the polymeric water chain are linked into 2D Co–H2O layer at [1 0 1] plane. Different from complex 1, the host framework of 2 is 2D H2O– Co-caoboxylate/bpy layer at [0 1 1] plane, and the water hexamers as well as the coordinated water molecules to cobalt form 1D Co–H2O chain along [1 0 0] direction. Through sharing central cobalt atoms, the host chain (layer) and guest layer (chain) in 1 (2) are connected into 3D supramolecular architecture. The structural differences between 1 and 2 arise from the uncoordination or coordination of carboxylate ligands mainly. The successful synthesis of two metal–water clusters may be helpful in the rational design of metal–water morphologies and the study of mechanism in energy-transduction or proton conduction. Acknowledgements The authors are grateful to the financial support from the NNSF of China (90206040, 20325106, and 50472021). Appendix A. Supplementary material CCDC 289131 and 645608 contain the supplementary crystallographic data for 1 and 2. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ ccdc.cam.ac.uk. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica. 2007.05.028. References [1] (a) R. Ludwig, Angew. Chem., Int. Ed. 40 (2001) 1808; (b) R. Ludwig, Angew. Chem., Int. Ed. 42 (2003) 3458. [2] (a) L. Infantes, S. Motherwell, CrystEngComm. 4 (2002) 454; (b) L. Infantes, J. Chisholm, S. Motherwell, CrystEngComm. 5 (2003) 480.
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Syntheses and characterization of two metal–water clusters Taohai Li a, Feng Li b, Yanqin Wang a, Wenhua Bi a, Xing Li a, Rong Cao a
a,*
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences, Fujian, Fuzhou 350002, PR China b The College of Chemistry, Xiang Tan University, Xiangtan, HuNan 411105, China Received 10 May 2007; accepted 15 May 2007 Available online 31 May 2007
Abstract Complexes 1 and 2, formulated {[Co2(4,4 0 -bpy)2 Æ 8H2O] Æ (CCA)2 Æ 4H2O}n (1) and {[Co(TMG)(4,4 0 -bpy)(H2O)2] Æ 3H2O}n (2) (H2CCA = 2-carboxylatocinnamate, H2TMG = 3,3-tetramethyleneglutate, 4,4 0 -bpy = 4,4 0 -bpyridine) have been synthesized by the reaction of cobalt (II), 4,4 0 -bpy and carboxylate ligands, in which 2D metal–water layers and 1D metal–water chains have been observed, respectively. In the metal–water clusters, the water molecules are trapped by the cooperative association of coordination interactions as well as hydrogen bonds. 2007 Elsevier B.V. All rights reserved. Keywords: Syntheses; Metal–water cluster; Layer; Chain
1. Introduction Water is the most abundant and cheapest inartificial solvent, which plays fundamental roles in almost all branches of natural sciences. Thus, as perfect model connecting isolated molecules to bulk water, it is not surprising that water clusters have been the focus of intense research interests [1]. With the development of research, water clusters have been classified as three classes: discrete water clusters, polymeric water clusters and metal–water clusters [2]. The structural elucidation of discrete and polymeric water clusters provides detailed knowledge of hydrogen-bonding and their fluctuations determined the properties of bulk water. Thus, the study of discrete and polymeric water clusters will help us to understand the anomalous behavior of bulk water/ice [3]. From an experimental point of view, so far a significant progress has been made with respect to the structural characterization of discrete water clusters (H2O)n (n = 2–16) [4–6], as well as polymeric water clusters such as chains
*
Corresponding author. Tel./fax: +86 591 83796710. E-mail address: [email protected] (R. Cao).
0020-1693/$ - see front matter 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.ica.2007.05.028
[7], tapes and 2D layers [8]. However, only disperse information is available on metal–water clusters [9]. In biology, water clusters are important to the proton pathways in the cytochrome b6f complex of plant chloroplast thylakoid membrane, mitochondrial ATPase [10], carbonic anhydrase II [11], as well as in redox proteins [12,13]. In addition, water clusters play a crucial role in energy-transduction. However, the details of the water clusters in either energy-transduction or proton conduction in proteins and enzymes are largely unknown [12,14]. As well known, most active centers of proteins and enzymes in living systems contain metal atoms. The investigation of interactions between metal atoms and small water clusters may help us unravel the mechanism in energy-transduction or proton conduction. As known, metal–water clusters not only involved the hydrogen-bonding interactions between water molecules, but also the coordination bonds between metal atoms and water clusters. Thus, the structural study of metal–water clusters can provide valuable information for unraveling the mechanism in energytransduction or proton conduction. In this sense, the design and synthesis of metal–water clusters is more important than discrete or polymeric clusters.
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The lattices of crystal hosts offer environments for stabilizing water clusters, which play important roles in the formation of different water morphologies. To obtain metal– water clusters, it is important to construct suitable host frameworks. We have successfully designed and synthesized 1D polymeric water chain and tape [15,16]. As continuous research of synthesizing water clusters, we investigated the reactions of 4,4 0 -bpyridine, Co(NO3)2 Æ 6H2O with 2-carboxylatocinnamate (H2CCA) or 3,3tetramethyleneglutarate (H2TMG), respectively, and obtain two complexes, {[Co2(4,4 0 -bpy)2 Æ 8H2O] Æ (CCA)2 Æ 4H2O}n (1) and {[Co(TMG)(4,4 0 -bpy)(H2O)2] Æ 3H2O}n (2) (H2CCA = 2-carboxylatocinnamate, H2TMG = 3,3-tetramethyleneglutate, 4,4 0 -bpy = 4,4 0 -bpyridine). In the crystal lattice of complexes 1 and 2, two kinds of cobalt–water clusters have been observed. 2. Experimental All chemicals were obtained commercially and used without further purification. Elemental analyses were carried out on an Elementar Vario EL III analyzer. Infrared (IR) spectra were recorded with Perkin–Elmer Spectrum One as KBr pellets in the range 4000–400 cm1. Thermogravimetric analyses were carried out with a NETZSCH STA 449C unit at a heating rate of 10 C min1 under nitrogen. X-ray powder diffraction measurements for 1 and 2 were recorded on a RIGAKU DMAX2500PC diffractometer using Cu Ka radiation. 2.1. Synthesis of {[Co(4,4 0 -bp)(H2O)4] Æ (CCA) Æ 2H2O}n (1) 4,4 0 -bpy (0.016 g, 0.1 mmol), H2CCA (0.019 g, 0.1 mmol), KOH (0.012 g, 0.2 mmol) and Co(NO3)2 Æ 6H2O (0.03 mg, 0.1 mmol) were dissolved in a mixture of water (8 ml) and ethanol (8 ml). After stirring for 2 h, a clear yellow solution was produced, and two weeks later, yellow prism crystals were collected. Yield: 36%. Anal. Calc. for C20H26N2O10Co: C, 46.79; H, 5.10; N, 5.46. Found: C, 46.77; H, 5.12; N, 5.47%. IR (KBr, cm1): 3315(s), 1641(s), 1606(s), 1538(s), 1384(vs), 1286(w), 1218(w), 1068(m), 977(w), 813(s), 630(m). 2.2. Synthesis of {[Co(TMG)(4,4 0 -bpy)(H2O)] Æ 3H2O}n (2) 4,4 0 -bpy (0.016 g, 0.1 mmol), H2TMG (0.024 g, 0.1 mmol), KOH (0.012 g, 0.2 mmol) and Co(NO3)2 Æ 6H2O (0.03 mg, 0.1 mmol) were dissolved in a mixture of water (8 ml) and ethanol (8 ml). After stirring for 2 h, a clear pink solution was produced, and two weeks later, red needle crystals were collected. Yield: 47%. Anal. Calc. for C19H28N2O8Co: C, 48.41; N, 5.94; H, 5.99; Found: C, 48.43; N, 5.97; H, 6.01%. IR (KBr, cm1): 3411 (m), 2942 (w), 2861(w), 1558 (vs), 1413 (s), 1222(w), 1066 (w), 815 (m), 632(w).
Table 1 Crystal data and structure refinement parameters for complexes 1 and 2
Formula Crystal size (mm) Molecular mass Crystal system Space group ˚) a (A ˚) b (A ˚) c (A a () b () c () ˚ 3) V (A Z T (K) Dcalc (g cm3) F(0 0 0) Reflections collected Independent reflections Data/restrain/ parameters Goodness-of-fit on F2 Final R indices [I > 2r(I)] R indices (all data)
1
2
C20H26CoN2O10 0.60 · 0.35 · 0.20 513.37 triclinic P 1 7.3854(15) 11.432(2) 13.625(3) 92.88(3) 98.04(3) 97.18(3) 1127.4(4) 2 173(2) 1.512 534 8640 6621
C19H26CoN2O7 0.30 · 0.04 · 0.04 453.35 monoclinic C2/c 19.896(8) 11.484(4) 20.429(8) 113.188(6) 4291(3) 8 173(2) 1.410 1848 16 021 4861
6621/3/798
4861/28/300
1.003 R1 = 0.0228, wR2 = 0.0455 R1 = 0.0215, wR2 = 0.0452
1.012 R1 = 0.0669, wR2 = 0.1946 R1 = 0.0780, wR2 = 0.2098
2.3. Crystal data collection and structure determination X-ray diffraction data for complexes 1 and 2 were collected on a Rigaku diffractometer with a Mercury CCD ˚ ) at 173(2) K. Empirarea detector (Mo Ka; k = 0.71073 A ical absorption corrections were applied to the data using the CRYSTALCLEAR program [17]. The structures were solved by the direct method and refined by the full-matrix leastsquares on F2 using the SHELXTL-97 program [18]. All non-hydrogen atoms were refined anisotropically. The organic hydrogen atoms were generated geometrically and hydrogen atoms of water molecules were located in a difference map and refined with the distance restraint O– ˚ . Crystallographic data for 1 and 2 are sumH = 0.85(1) A marized in Table 1. Bond lengths and bond angles are listed in Table 2. 3. Results and discussion For preparing metal–water clusters, there are two crucial conditions. One is the existence of two or more free water molecules, which provides the possibility of forming discrete or polymeric water clusters. Another is the coordination of water to metal centers. The coordination of water to metal atoms would not only provide hydrogen donor/ acceptor like free water, but also link the discrete or polymeric water clusters to central metal atoms. Low temperature may be available for the coordination of water to metal in the reaction systems. Thus, we give up the well known hydrothermal synthetic method for the construc-
T. Li et al. / Inorganica Chimica Acta 360 (2007) 3771–3776 Table 2 ˚ ), bond angles () for 1 and 2 Selected bond distances (A 1 Co(1)–O(1) Co(1)–O(3) Co(1)–N(1) Co(2)–O(5) Co(2)–O(7) Co(2)–N(3) N(1)–Co(1)–N(2) 2 Co(1)–O(3)#1 Co(1)–O(3) Co(1)–O(2)#1 Co(1)–O(2) Co(1)–N(2) Co(1)–N(3)#2 O(3)#1–Co(1)–O(3) O(3)#1–Co(1)– O(2)#1 O(3)–Co(1)–O(2)#1 O(3)#1–Co(1)–O(2) O(3)–Co(1)–O(2) O(2)#1–Co(1)–O(2) O(3)#1–Co(1)–N(2) O(3)–Co(1)–N(2) O(2)#1–Co(1)–N(2) O(2)–Co(1)–N(2) O(3)#1–Co(1)– N(3)#2 O(3)–Co(1)–N(3)#2 O(2)#1–Co(1)– N(3)#2 O(2)–Co(1)–N(3)#2 N(2)–Co(1)– N(3)#2
2.0490(19) 2.1127(19) 2.164(2) 2.0770(18) 2.0679(18) 2.169(2) 178.05(9)
Co(1)–O(2) Co(1)–O(4) Co(1)–N(2) Co(2)–O(6) Co(2)–O(8) Co(2)–N(4) N(3)–Co(2)–N(4)
2.1065(19) 2.0500(19) 2.180(2) 2.1526(18) 2.0428(18) 2.159(2) 178.89(9)
2.081(3) 2.081(3) 2.141(3) 2.141(3) 2.188(5) 2.194(5) 177.66(16) 96.69(12)
Co(2)–O(4)#3 Co(2)–O(4) Co(2)–O(4W) Co(2)–O(4W)#3 Co(2)–N(1) Co(2)–N(1)#3 O(4)#3–Co(2)–O(4) O(4)#3–Co(2)–N(1)
2.070(3) 2.070(3) 2.208(3) 2.208(3) 2.196(4) 2.196(4) 180.000(1) 93.15(13)
83.39(12) 83.39(12) 96.69(12) 176.30(17) 91.17(8) 91.17(8) 88.15(8) 88.15(8)
O(4)–Co(2)–N(1) O(4)#3–Co(2)–N(1)#3 O(4)–Co(2)–N(1)#3 N(1)–Co(2)–N(1)#3 O(4)#3–Co(2)–O(4W) O(4)–Co(2)–O(4W) N(1)–Co(2)–O(4W) N(1)#3–Co(2)– O(4W) O(4)#3–Co(2)– O(4W)#3 O(4)–Co(2)–O(4W)#3 N(1)–Co(2)– O(4W)#3 N(1)#3–Co(2)– O(4W)#3 O(4W)–Co(2)– O(4W)#3
86.85(13) 86.85(13) 93.15(13) 180.0 81.08(13) 98.92(13) 89.63(12) 90.37(12)
88.83(8) 88.83(8) 91.85(8) 91.85(8) 180.000(1)
98.92(13) 81.08(13) 90.37(12) 89.63(12) 180.000(1)
Symmetry codes: #1 x + 1, y, z + 1/2; #2 x, y + 1, z; #3 x + 1, y + 1, z + 1.
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tion of organic–inorganic hybrid materials in crystalline form, and adopt solution method investigating the reaction of Co(NO3)2 Æ 6H2O, 4,4 0 -bpy with H2CCA or H2TMG at room temperature. 3.1. Crystal Structure of {[Co(4,4 0 bpy)(H2O)4] Æ (CCA) Æ 2H2O}n (1) From the reaction of H2CCA, 4,4 0 -bpy and Co(NO3)2 Æ 6H2O, complex 1 is obtained, whose crystal structure has been described in our previous work in Ref. [19]. Here details of the framework structure of 1 will not be discussed and only the description of water cluster in 1 will be made. In 1, there are eight crystallographically independent coordinated water molecules (O(1), O(2), O(3), O(4), O(5), O(6), O(7) and O(8)) and four free water molecules (O(1W), O(2W), O(3W) and O(4W)). Through hydrogenbonding (O(2)–H(2A) O(1W), O(2)–H(2B) O(3W) and O(5)–H(5B) O(3W)), O(2), O(5), O(1W) and O(3W) are associated to form discrete tetramer clusters. ˚ ) is The average O O distance of such tetramer (2.739 A ˚ in ice Ih at close to the corresponding value of 2.759 A 90 C [20]. O(3), O(6), O(2W), O(4W) form another kind of water tetramer by hydrogen-bonding of O(3)–H(3B) O(2W), O(6)–H(6A) O(2W) and O(6)–H(6B) O(4W), ˚) and the average O O distance of this tetramer (2.841 A ˚ in ice Ih [21], but similar is longer than the value of 2.759 A ˚ in liquid water [20]. This to the O O distance of 2.85 A kind of tetramer and their equivalents are connected into 1D polymeric water cluster by O(2W)–H2W2 O4W. Thus, O(6), O(2W), O(4W) and their equivalents form a polymeric water chain with O(3) dangling at one side, which looks like a tree with branch (Fig. 1). The geometric parameters of the water tetramers and chains are summarized in Table 3. Through the coordination of O(2), O(3)
Fig. 1. The 2D cobalt–water layer in 1.
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Table 3 ˚ and ) for 1 and 2 Hydrogen-bonding parameters (A O–H O
O–H
O O
H O
O–H O
1 O1–H1A O13 O1–H1B O11#1 O2–H2A O1W O2–H2B O3W#2 O3–H3B O2W O3–H3A O14#3 O4–H4B O12#2 O4–H4A O13#3 O5–H5A O10 O5–H5B O3W O6–H6B O4W O6–H6A O2W O7–H7B O15#3 O7–H7A O9 O8–H8B O15 O8–H8A O9#4 O1W–H1W1 O12#1 O1W–H1W2 O16#2 O2W–H2W2 O4W#4 O2W–H2W1 O15 O3W–H3W2 O16#3 O3W–H3W1 O12 O4W–H4W2 O14#3 O4W–H4W1 O11#2
0.834(16) 0.866(15) 0.829(16) 0.832(16) 0.817(16) 0.832(15) 0.845(16) 0.838(16) 0.846(15) 0.861(16) 0.823(16) 0.864(15) 0.843(16) 0.846(15) 0.841(15) 0.849(16) 0.836(16) 0.845(16) 0.838(16) 0.862(16) 0.848(16) 0.833(15) 0.856(16) 0.812(16)
2.751(3) 2.711(3) 2.662(3) 2.782(3) 2.727(3) 2.733(3) 2.737(3) 2.734(3) 2.582(2) 2.774(3) 2.825(3) 2.842(3) 2.791(3) 2.672(2) 2.732(3) 2.706(3) 2.755(3) 2.825(2) 2.968(3) 2.692(3) 2.731(3) 2.813(2) 2.773(3) 2.731(3)
1.926(16) 1.859(16) 1.836(16) 1.961(17) 1.933(16) 1.903(16) 1.910(16) 1.896(16) 1.744(16) 1.924(17) 2.002(16) 1.999(16) 1.953(17) 1.831(16) 1.926(16) 1.888(17) 1.931(16) 1.993(17) 2.19(2) 1.845(17) 1.883(16) 2.004(17) 1.948(17) 1.948(18)
170(3) 168(3) 174(3) 168(2) 164(3) 175(3) 166(2) 179(2) 170(2) 169(2) 178(3) 165(3) 172(2) 173(3) 160(2) 162(2) 169(3) 168(3) 154(3) 167(3) 176(3) 164(3) 162(3) 162(3)
2 O1W–H1W1 O2W O1W–H1W2 O3W#5 O2W–H2W1 O1W O4W–H4W2 O3W O4W–H4W1 O2#6 O4W–H4W1 O3
0.831 0.821 0.848 0.866 0.873 0.873
2.883 2.868 2.883 2.921 2.873 2.972
2.221 2.105 2.256 2.100 2.078 2.362
136(7) 154(6) 130(8) 158(1) 150(9) 127(2)
#1 x + 1, y, z 1; #2 x, y, z 1; #3 x 1, y, z; #4 x + 1, y, z; #5 x + 1/2, y + 1/2, z + 1/2; #6 x + 1, y, z + 1/2.
Fig. 2. The coordination environment of cobalt ions in 2 with the thermal ellipsoids at 30% probability level (all H atoms were omitted for clarity) #A x + 1, y, z + 1/2; #B x, y + 1, z; #C x + 1, y + 1, z + 1.
nation geometry, the coordination environments are different. As shown in Fig. 2, Co(1) is coordinated by four oxygen atoms from four carboxyl groups and two nitrogen atoms from two 4,4 0 -bpy, and Co(2) is coordinated by two oxygen atoms from two carboxyl groups, two oxygen atoms from two coordinated water molecules and two nitrogen atoms from two 4,4 0 -bpy. The carboxyl groups in 2 adopt monodentae and bidentae coordination modes, respectively. Each carboxyl group with bidentate mode bridges two cobalt atoms forming Co-TMG chains along [0 0 1] direction. The coordination of 4,4 0 -bpy connect adjacent Co-TMG chains into 2D layers in [0 1 1] plane (Fig. 3),
and O(5), O(6) to Co(1) and Co(2) atoms, the polymeric water chain and discrete water tetramer are linked into 2D metal–water layers at [1 0 1] plane. O(1), O(4), O(7) and O(8) do not participate in the formation of water clusters, and only provide hydrogen-bonding donor to the uncoordinated CCA2. Through the hydrogen-bonding (O(9)–O(7), O(10)–O(5), O(12)–O(3W), O(11)–O(4W), O(15)–O(8), O(15)–O(2W), O(16)–O(1W) and O(16)– O(3W)), the uncoordinated CCA2 are located above and below each 2D metal–water layer, respectively. The extending of Co-bpy linear chain along [0 1 0] direction connected adjacent 2D layers into 3D suprarchitecture. 3.2. Crystal Structure of {[Co(TMG)(4,4 0 bpy)(H2O)] Æ 3H2O}n (2) Inspired by the metal–water chain in 1, complex 2 was obtained under similar reaction conditions, except that H2CCA for 1 was replaced by H2TMG. X-ray diffraction study reveals that two crystallographically independent cobalt (II) atoms, two TMG2, two 4,4 0 -bpy and coordinated water molecules are present in 2. Though two cobalt atoms are six-coordinated with similar octahedral coordi-
Fig. 3. The 2D host layer in 2.
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and the five-membered rings of TMG ligands locate at two sides of the 2D layer, respectively. In the crystal lattice of 2, three crystallographically independent water molecules (O1w, O2w and O3w) are observed, which are associated by hydrogen bonds (O2w O1w and O1w O3w) to form a water trimer. The water trimer is linked to its’ adjacent equivalents forming a (H2O)6 unit. In this water hexamer, O1w, O2w, O1wa, O2wa are connected into a four-membered ring through O1w O2wa and O1wa O2w, and O3w and O3wa are hanged at the up or down side of the four-membered ring by O1w O3w and O1wa O3wa, respectively. Thus, the water hexamer in complex 2 looks like a ‘‘chair’’ (Fig. 4). However, there are notable differences between such conformation looking like ‘‘chair’’ and the well known ‘‘chair conformation’’. In the hexamer with chair conformation, six water molecules are linked end to end by hydrogen bonds forming a close six-membered ring [22]. As mentioned above, the water hexamer in complex 2 are composed of one four-membered ring and two dangling water ˚ ) in the molecules. The average O O distance (2.855 A water hexamer of complex 2 is closer to the O O distance in liquid water than complex 1. Through the hydrogen bonds between O3w and the coordinated water (O4w), the guest water hexamer connect neighbor 2D host layers forming 3D supramolecular architecture. The hydrogen bonds of 2 are summarized in Table 3. 3.3. Thermal analysis and X-ray powder diffraction Thermogravimetric analysis has determined the thermal stability of complexes 1 and 2. TGA analyses of 1 show a 20.94% weight loss from 77 C to 122 C, which corresponds to the loss of all free water molecules and two coordinated water (calc: 21.04%). For 2, the weight loss of 15.21% from 72 C to 118 C is equivalent to the loss of three free water and one coordinated water (calc: 15.27%). After all water molecules are removed, the TGA curves of 1 and 2 exhibit some differences. For 1, the TGA data reveals two distinct weight loss of 37.04% (from 206 C to 319 C) and 30.42% (from 384 C to 420 C),
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which are equivalent to the loss of uncoordinated CCA ligand and coordinated bpy ligand, respectively. Different from 1, the TGA curve of 2 show continuous weight loss covering a temperature range from 263 C to 443 C, which corresponds to the decomposition of 2D host layer. The difference arises from the uncoordination or coordination of carboxylate ligand in 1 and 2. The weight loss of 1 and 2 ends at 14.61% and 15.91%, respectively, which indicates that only CoO is left. To support the TGA, the sample of 1 and 2 were characterized by X-ray powder diffraction (XRPD) at room temperature (Figs. S1 and S2). The patterns simulated from the single crystal X-ray data of 1 and 2 are in good agreement with the observed ones. 3.4. Vibrational spectra The FT-IR spectroscopy of 1 shows strong bands at 1540 cm1 and 1384 cm1 due to the tasym (CO2) and tsym (CO2). For 2, the tasym (CO2) and tsym (CO2) stretching vibrations appear at 1558 cm1 and 1413 cm1. The spectrum of 2 exhibits a broad band centered around 3411 cm1. The O–H stretching vibration for quasiplanar and puckered-boat water hexamer appears at 3400 and 3415 cm1, respectively [22,23], and the vibration for chair hexamer occur at 3495 and 2614 cm1 [24]. By comparison, the O–H stretching vibration of water hexamer in 2 is that of boat conformation. The spectrum of 1 shows a broad band around 3315 cm1. In comparison with the O–H stretching for water tetramer (3421 cm1) [25], it has some blue shifts. This may be due to the water tetramer in 2 are composed of both free and coordinated water molecules, which is different from those composed of free water molecules. After removing the water from the crystal lattices of 1 and 2 by heating, both of the bands centered around 3315 and 3411 cm1 disappear. Therefore, in the cases of 1 and 2, these bands are attributable to the O–H stretching frequency of the (H2O)4 and (H2O)6 core structure, respectively. Deliberate exposure to water vapor for 3 days does not lead to reabsorption of water into the lattice as monitored by FTIR spectroscopy.
Fig. 4. The 1D cobalt–water chain in 2.
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4. Conclusion Two complexes containing metal–water clusters have been synthesized from the reaction of cobalt (II), 4,4 0 bpy and carboxylate ligands (H2CCA or H2TMG) successfully. For complex 1, the host framework is 1D H2O–Co-bpy chain along [0 1 0] direction, and the discrete water tetramer as well as the polymeric water chain are linked into 2D Co–H2O layer at [1 0 1] plane. Different from complex 1, the host framework of 2 is 2D H2O– Co-caoboxylate/bpy layer at [0 1 1] plane, and the water hexamers as well as the coordinated water molecules to cobalt form 1D Co–H2O chain along [1 0 0] direction. Through sharing central cobalt atoms, the host chain (layer) and guest layer (chain) in 1 (2) are connected into 3D supramolecular architecture. The structural differences between 1 and 2 arise from the uncoordination or coordination of carboxylate ligands mainly. The successful synthesis of two metal–water clusters may be helpful in the rational design of metal–water morphologies and the study of mechanism in energy-transduction or proton conduction. Acknowledgements The authors are grateful to the financial support from the NNSF of China (90206040, 20325106, and 50472021). Appendix A. Supplementary material CCDC 289131 and 645608 contain the supplementary crystallographic data for 1 and 2. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: deposit@ ccdc.cam.ac.uk. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.ica. 2007.05.028. References [1] (a) R. Ludwig, Angew. Chem., Int. Ed. 40 (2001) 1808; (b) R. Ludwig, Angew. Chem., Int. Ed. 42 (2003) 3458. [2] (a) L. Infantes, S. Motherwell, CrystEngComm. 4 (2002) 454; (b) L. Infantes, J. Chisholm, S. Motherwell, CrystEngComm. 5 (2003) 480.
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