Structure Reports Online

Volume 66, Part 8 (August 2010)

metal-organic compounds

pb2030 scheme

Acta Cryst. (2010). E66, m990-m991 [ doi:10.1107/S1600536810023986 ]

{[Na1(-H₂O)Na2]₂[(C₂O₄)₂Cr(-OH)₂Cr(C₂O₄)₂]·H₂O}_n, a novel hydrated form

M. M. Bélombé, J. Nenwa, J. Ngouné, E. Álvarez and A. Galindo

Abstract: The unit cell of the title compound, poly[[ [mu] -aqua- [mu] -hydroxido-di- [mu] -oxalato-chromium(III)disodium] monohydrate], {[CrNa₂(C₂O₄)₂(OH)(H₂O)]·H₂O}_n, contains four [Na1( [mu] -H₂O)Na2][(C₂O₄)₂Cr( [mu] -OH)·H₂O] formula units, each of which consists of two crystallographically independent Na⁺ sites (bridged by one aqua ligand), one half of a centrosymmetric di- [mu] -hydroxido-bis[cis-bis(oxalato)chromate(III)] dimer, [(C₂O₄)₂Cr( [mu] -OH)₂Cr(C₂O₄)₂]^4-, and one uncoordinated water molecule. The structure is best described as a coordination polymer in which the three-dimensional lattice framework is realized by the interconnection of the metallic atoms via the O atoms of the aqua, hydroxide and oxalate ligands. One Na atom is heptacoordinated by one water, one hydroxide and five oxalate O atoms, whilst the other is pentacoordinated by one water and four oxalate O atoms. The coordination around the Cr³⁺ sites is pseudo-octahedral, involving four aqua and two hydroxide O atoms. Adjacent Na atoms are separated by 3.593 (2) Å, whereas the intradimer CrCr spacing is 2.978 (1) Å. The crystal structure is consolidated by extended relatively weak O-HO hydrogen bonding with OO distances ranging from 2.808 (4) to 3.276 (5) Å.