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

The title compound, [CoNa(4)(C(6)H(5)O(7))(2)](n), was obtained under hydro-thermal conditions as a minor product. The Co(2+) cation is located on a crystallographic inversion center and is coordinated by six O atoms from two different citrate units, forming a [Co(C(6)H(5)O(7))(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 depronona-ted, the hydroxyl group, however, is not. It is coordinated to the Co(2+) cation, and through an O-H⋯O hydrogen bond connected to a neighboring [Co(C(6)H(5)O(7))(2)](4-) building unit. The coordination modes of the carboxyl-ate 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 Co(2+) cation and a Na(+) cation, respectively. Through these inter-connections, the basic [Co(C(6)H(5)O(7))(2)](4-) building units are linked with each other through coordination of their carboxyl-ate groups to the Na(+) cations, forming a three-dimensional framework.