Coordination polymers of a bis-isophthalate bridging ligand with single molecule magnet behaviour of the CoII analogue

Abstract

A linear diamine-bisisophthalate bridging linker N,N′-bis(1,3-dicarboxyphenyl-5-methylene)-1,3-dimethylpropanediamine, designed to incorporate amine/ammonium functionalities in the core of the ligand, has been isolated as the pentahydrate of its dihydrochloride salt (H₆L)Cl₂·5H₂O. Using this compound, four new coordination polymers have been formed, namely poly-[M(H₂L)]·4.5H₂O (1M, where M = Co, Zn, Cd) and poly-[Cd(H₂L)(OH₂)]·DMF·7H₂O (2). Compounds 1M are isostructural 2D coordination polymers that contain 1D channels occupied by water molecules. In the case of 1Co these form a well ordered hydrogen-bonding network as determined by single crystal X-ray studies. Compound 2, synthesised under similar conditions, is a 1D coordination polymer in which the metal is partially solvated. DC and AC magnetic studies of 1Co, which posseses a mononuclear cobalt(II) node, revealed single molecule magnet behaviour (SMM) with an effective barrier height U_eff of 37.7 K and τ₀ = 1.02 × 10⁻⁹ s, among the highest reported for Co^II coordination polymers.