Crystal structure of bis-[(oxalato-κ,)(1,4,8,11-tetra-aza-cyclo-tetra-decane-κ)chromium(III)] dichromate octa-hydrate from synchrotron X-ray data.

The asymmetric unit of the title compound, [Cr(CO)(CHN)][CrO]·8HO (CHN = 1,4,8,11-tetra-aza-cyclo-tetra-decane, cyclam; CO = oxalate, ox) contains one [Cr(ox)(cyclam)] cation, one half of a dichromate anion that lies about an inversion centre so that the bridging O atom is equally disordered over two positions, and four water mol-ecules. The terminal O atoms of the dichromate anion are also disordered over two positions with a refined occupancy ratio 0.586 (6):0.414 (6). The Cr ion is coordinated by the four N atoms of the cyclam ligand and one bidentate oxalato ligand in a arrangement, resulting in a distorted octa-hedral geometry. The Cr-N(cyclam) bond lengths are in the range 2.069 (2)-2.086 (2) Å, while the average Cr-O(ox) bond length is 1.936 Å. The macrocyclic cyclam moiety adopts the -V conformation. The dichromate anion has a staggered conformation. The crystal structure is stabilized by inter-molecular hydrogen bonds involving the cyclam N-H groups and water O-H groups as donors, and the O atoms of oxalate ligand, water mol-ecules and the CrO anion as acceptors, giving rise to a three-dimensional network.