Crystal structure of bis[(oxalato-κ2O1,O2)(1,4,8,11-tetraazacyclotetradecane-κ4N)chromium(III)] dichromate octahydrate from synchrotron X-ray data

Abstract

The asymmetric unit of the title compound, [Cr(C2O4)(C10H24N4)]2[Cr2O7]·8H2O (C10H24N4= 1,4,8,11-tetraazacyclotetradecane, cyclam; C2O4= 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 molecules. 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 CrIIIion is coordinated by the four N atoms of the cyclam ligand and one bidentate oxalato ligand in acisarrangement, resulting in a distorted octahedral 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 thecis-V conformation. The dichromate anion has a staggered conformation. The crystal structure is stabilized by intermolecular hydrogen bonds involving the cyclam N—H groups and water O—H groups as donors, and the O atoms of oxalate ligand, water molecules and the Cr2O72−anion as acceptors, giving rise to a three-dimensional network.