Metal-Metalloligand Coordination Polymer Embedding Triangular Cobalt-Oxo Clusters: Solvent- and Temperature-Induced Crystal to Crystal Transformations and Associated Magnetism.

Reaction of the metalloligand Ir(ppy-COOH) and the anisotropic paramagnetic Co ion under solvothermal conditions resulted in a metal-metalloligand coordination polymer, [Co(μ-O)(μ-OH){Ir(ppy-COO)(ppy-COOH)}(HO)]·2DMF·HO (). It consists of trimeric CoO secondary building units (SBUs) bridged by pairs of Ir to form chains of alternate orthogonal squares. The compound undergoes two single-crystal to single-crystal transformations while retaining its general structural features. A chemical transformation occurs to give [Co(μ-O){Ir(ppy-COO)(ppy-COOH)}(HO)(DMF)]·DMF·HO () by soaking in acetone, where a bridging water molecule departs and the solvent DMF bonds to the vacant site of the Co center. Both and undergo a temperature-induced transformation to [Co(μ-O){Ir(ppy-COO)(ppy-COOH)}(HO)(DMF)]·DMF (), where one more coordinated water molecule is lost. The major difference in the three phases is in the Co coordination spheres, which have considerable consequences on the magnetism. Compound displays paramagnetism down to 2 K, whereas and show weak ferromagnetism with values of 14 and 17 K, respectively.