Low-temperature redetermination of hexa­kis(μ-chloro­acetato-κ2 O:O′)-μ3-oxido-tris[aquachromium(III)] nitrate 3.5-hydrate

A low-temperature redetermination of the trinuclear cluster compound described as [Cr(3)(C(2)H(2)ClO(2))(6)O(H(2)O)(3)]NO(3)·3H(2)O [Glowiak, Kubiak & Jezowska-Trzebiatowska (1977 ▶). Bull. Acad. Pol. Sci. Ser. Sci. Chim.25, 359-371] shows that the salt is a 3.5-hydrate, [Cr(3)(C(2)H(2)ClO(2))(6)O(H(2)O)(3)]NO(3)·3.5H(2)O. The trinuclear cluster cation is disordered in four of the six monochloro-acetate groups. One is disordered over two positions in respect of the chloro-methyl atoms (occupancy ratio 0.50:0.50); another is disordered over three positions in respect of the chloro-methyl atoms (occupancy ratio 0.50:0.37:0.13) whereas two are disordered over two positions in respect of the Cl atoms only (occupancy ratios 0.84:0.16 and 0.60:0.40). Of the four independent uncoordinated water mol-ecules, one has an occupancy factor of 0.5. The trinuclear cation has an oxido O atom that is connected to three water-coordinated Cr(III) atoms, the three metal atoms forming the points of an equilateral triangle. Six carboxyl-ate groups each chelate a Cr-O-Cr fragment. The cations, anions and uncoordinated water mol-ecules are linked by hydrogen bonds.