Novel polynuclear architectures incorporating Co2+ and K+ ions bound by dimethylmalonate anions: Synthesis, structure, and magnetic properties

Abstract

The reaction of potassium dimethylmalonate (K2Me2Mal) and cobalt(II) pivalate [Co(Piv)2]n under various conditions resulted in {[K2Co(H2O-κO)(μ-H2O)(μ6-Me2Mal)(μ5-Me2Mal)]·2H2O}n (1) and {[K6Co36(H2O-κO)22(μ-H2O)6(μ3-OH)20(μ4-HMe2Mal-κ2O,O′)2(μ6-Me2Mal-κ2O,O′)2(μ5-Me2Mal-κ2O,O′)8(μ4-Me2Mal-κ2O,O′)12(μ4-Me2Mal)6]·58H2O}n (2) (where Me2Mal2− is the dimethylmalonate dianion). Coordination polymers 1 and 2 were characterized by X-ray diffraction and magnetochemical studies. Analysis of the magnetic behavior indicates that 1 is characterized by an extremely high anisotropy of magnetic susceptibility and very weak spin coupling between CoII centers through malonate groups; compound 2 contains a highly symmetric, spherical-like Co36 metal core that exhibits low magnetic anisotropy and antiferromagnetic interactions between CoII centers. Theoretical aspects of anisotropic magnetic properties of orbitally-degenerate CoII ions in polynuclear cobalt(II) complexes are discussed.