Synthesis and crystal structure of protonated sodium potassium dimeric(citrate) dioxovanadium(V)

The titled complex NaK3 [VO2 (Hcit)]2. 7H2O (H4cit=citric acid) has been pre-pared and characterized by X-ray diffraction. It crystallizes in monoclinic space group P21/n with unit cell parameters:a = 1.125 8(2) nm, b=1. 577 4(3) nm, c=1. 655 9(1) nm, β=98. 568 (9)°and Dc = 1.851 g. cm-3, Z=4. Each dimer contains a quasi-centrosymmetric planar four-member V2O2 ring with two exocyclic citrate entities coordinated by the oxygen atoms of the hydroxy- and a-carboxylate ligand, while the other two β-carboxylate groups remain uncomplexed as its deprotonated and protonated citratovanadate(V).