Reaction of the metalloligand Ir-III(ppy-COOH)(3) and the anisotropic paramagnetic Co-II ion under solvothermal conditions resulted in a metal-metalloligand coordination polymer, [Co-3(II)(mu(3)-O)(mu-OH2){Ir-III(ppy-COO)(2)(ppy-COOH)}(2)(H2O)(4)]center dot 2DMF center dot xH(2)O (I). It consists of trimeric Co3O 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-3(II)(mu(3)-O)(mu-OH2){Ir-III(ppy-COO)(2)(ppy-COOH)}(2)(H2O)(4)]center dot DMF center dot xH(2)O (II) by soaking in acetone, where a bridging water molecule departs and the solvent DMF bonds to the vacant site of the Co center. Both I and II undergo a temperature-induced transformation to [Co-3(II)(mu(3)-O)(mu-OH2){Ir-III(ppy-COO)(2)(ppy-COOH)}(2)(H2O)(4)]center dot DMF (III), 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 I displays paramagnetism down to 2 K, whereas II and III show weak ferromagnetism with T-C values of 14 and 17 K, respectively.