Slow magnetic relaxation in mixed-valence coordination polymer, containing Co(III) cluster and Co(II) nodes

Single-molecule magnets in cobalt clusters is much less well known than it is in manganese(II)/(III)/(IV) clusters. To explore new types of cobalt clusters and their potential applications, a new mixed valence coordination polymer ([Co(III)3Co(II)2(mba)6(Hdtba) (H2O)4]n, H2dtba=2,2’-dithiodibenzoic acid, H2mba=2-mercaptobenzoic acid) (1) is constructed by employing cobalt chloride hexahydrate and H2mba as starting reactants under hydrothermal conditions. Single-crystal XRD studies indicate that 1 consists of a trinuclear cobalt(III)-sulfur cluster moiety and two discrete cobalt(II) nodes, which result in the formation of a covalent three-dimensional complex network. Similarly, the cobalt(III) cluster moiety acts as a building unit in this infinite coordination polymer 1 instead of the discrete and tiara-like clusters previously reported in the literature. Magnetic studies show its slow magnetic relaxation in the absence of an applied dc field, which is characteristic behavior of single-ion magnets, caused by the individual Co(II) ions.