Redetermination of poly[aquadi-μ3-oxydiacetato-dicopper(II)]

The title complex, [Cu2(C4H4O5)2(H2O)]n, has a two-dimensional layer structure. The Cu atom has a distorted octahedral (CuO6) environment and is coordinated by four carboxylate group O atoms from three different oxydiacetate ligands in a planar arrangement and one half-occupancy water molecule and an ether O atom in the axial positions. In the crystal structure, weak intra- and intermolecular O—H⋯O hydrogen bonds help to stabilize the crystal packing. The structure has already been published [Whitlow & Davey (1975 ▶). J. Chem. Soc. Dalton. Trans. pp. 1228–1232]; this redetermination reports the structure with higher precision.

The title complex, [Cu 2 (C 4 H 4 O 5 ) 2 (H 2 O)] n , has a two-dimensional layer structure. The Cu atom has a distorted octahedral (CuO 6 ) environment and is coordinated by four carboxylate group O atoms from three different oxydiacetate ligands in a planar arrangement and one half-occupancy water molecule and an ether O atom in the axial positions. In the crystal structure, weak intra-and intermolecular O-HÁ Á ÁO hydrogen bonds help to stabilize the crystal packing. The structure has already been published [Whitlow & Davey (1975). J. Chem. Soc. Dalton. Trans. pp. 1228-1232; this redetermination reports the structure with higher precision.

Redetermination of poly[aquadi-µ 3 -oxydiacetato-dicopper(II)]
Ming-Lin Guo S1. Comment The structure of the title complex, (I), was determined some years ago [Whitlow & Davey, 1975)] using diffraction data collected at ambient temperature, the determination gave higher R values (R =0.088) and Z=8. The information of the structure was not found at the database of CCDC. Complex, (I), has been obtained as a by-product of study of heterobimetallic complexes involving Ba(NO 3 ) 2 , Cu(NO 3 ) 2 and oxydiacetic acid, using Na 2 CO 3 as base. We have taken this opportunity to redetermine the structure of (I) at 294 (2) K, leading to significantly improved precision.
The asymmetric unit in the structure of (I) comprises one Cu atom, one complete oxydiacetate dianion and half a water molecule, and is shown in Fig. 1 in a symmetry-expanded view, which displays the full coordination of the Cu atom.
Selected geometric parameters are given in Table 1. The Cu atom has octahedral coordination, with O1, O5, O2 ii and O4 i of three nonequivalent oxydiacetate dianions in a planar arrangement, and O3 and O6 atoms from one ether oxygen and half a water molecules in a trans conformation. Thus, the coordination octahedra of the Cu atoms can be visualized as having an elongated axial distortion.
In the structure of (I), each Cu atom is bonded to an oxydiacetate ligand via the O1 and O5 atoms of carboxylate groups and the ether oxygen O3 atom, each oxydiacetate ligand connect with other two Cu atoms via the O2 and O4 atom as a monodentate bonding mode and a bridging bonding mode, respectively. These result in the Cu1···Cu1 separations are 4.8666 (9)Å and 4.8501 (10) Å, respectively, and complete a two-dimensional layer connectivity of the structure parallel to ac plane. A number of weak intra-and intermolecular O-H···O hydrogen bonds interactions (see Table 2) further stabilize the two-dimensional framework within this layer. A packing diagram for the structure of (I) is shown in Fig. 2.

S2. Experimental
A mixture of 20 ml aqueous solution of sodium carbonate anhydrous (0.43 g, 4 mmol) and oxydiacetic acid (0.54 g, 4.0 mmol) was added dropwise into a solution of cupric nitrate (0.49 g, 2 mmol) and barium nitrate (0.52 g, 2 mmol) in 20 ml of distillated water under stirring at the room temperature for 20 min. After filtration, slow evaporation the filtrate over a period of two week at room temperature provided the crystals of (I).

S3. Refinement
The H atoms of the water molecule were found in difference Fourier maps and during refinement were fixed at an O-H distance of 0.85 Å, and with U iso (H) = 1.2 U eq (O). The H atoms of C-H groups were placed geometrically and during refinement were treated using a riding model, with C-H = 0.97 Å, and with U iso (H) = 1.2 U eq (C).  A view of the structure of (I), showing the atom-numbering Scheme; displacement ellipsoids were drawn at the 30% probability level. Symmetry codes (i) -x + 3/2, -y + 1/2, z + 1/2; (ii) x + 1/2, -y + 1/2, -z + 1.

poly[aquadi-µ 3 -oxydiacetato-dicopper(II)]
Crystal data Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.