Poly[di-μ9-citrato-cobalt(II)tetrasodium]

Abstract

The title compound, [CoNa4(C6H5O7)2]n, was obtained under hydrothermal conditions as a minor product. The Co2+ cation is located on a crystallographic inversion center and is coordinated by six O atoms from two different citrate units, forming a [Co(C6H5O7)2]4− building unit with Co—O bond lengths between 2.0578 (17) and 2.0813 (16) Å. The structure features two crystallographically independent Na+ ions. The first Na+ cation is five-coordinated by O atoms of five carboxylate groups from four different citrate anions. The second Na+ cation is surrounded by six O atoms of five carboxylate groups from five different citrate anions. The carboxylate groups of the citrate are completely deprononated, the hydroxyl group, however, is not. It is coordinated to the Co2+ cation, and through an O—H...O hydrogen bond connected to a neighboring [Co(C6H5O7)2]4− building unit. The coordination modes of the carboxylate O atoms vary, with one O atom being coordinated to three different Na+ cations, three are bridging O atoms bound to two Na+ cations and two are connected to a Co2+ cation and a Na+ cation, respectively. Through these interconnections, the basic [Co(C6H5O7)2]4− building units are linked with each other through coordination of their carboxylate groups to the Na+ cations, forming a three-dimensional framework.