36-Nuclear CoII and NiII dimethylmalonate complexes with the [K(18-crown-6)]+ cationic fragments: synthesis and structure

A reaction of potassium dimethylmalonate (K2Me2Mal) with cobalt(II) or nickel(II) trimethylacetate in the presence of 18-crown-6 leads to the formation of 36-nuclear complexes {[K(18-crown-6)]2[K(H2O)(18-crown-6)]2[K6Co36(H2O)20(OH)18(Me2Mal)30(18-crown6)2(O)2]•xH2O}n (2) and {[K(H2O)2(18-crown-6)]6[K5Ni36(H2O)20(OH)18(18-crown-6)2(Me2Mal)28(HMe2Mal)2]4[K5Ni36(H2O)20(OH)20(18-crown-6)2(Me2Mal)29(HMe2Mal)]• •80H2O}n (3) (Me2Mal2– is the dianion of dimethylmalonic acid), respectively. The single crystal X-ray diffraction studies showed that the spherical 36-nuclear polyanions [Co36(H2O)12(OH)18(Me2Mal)30(O)2]10– (in compound 2) and [Ni36(H2O)12(OH)20(Me2Mal)30–x(HMe2Mal)x]y– (in compound 3; x = 1, y = 7; x = 2, y = 6) have similar structures, with their metal cores being formed of two layers: an internal one comprising 24 metal atoms and an external containing 12 metal centers. The inner cavity of the {MII36} anions was found to include one K+ aqua cation bonded to the oxygen atoms of the carboxylate or oxo ligands.