We report the synthesis, molecular structures and applications of bis(pyrazolylmethyl)pyridine Zn(II) and Cu(II) complexes in the ring-opening polymerization (ROP) of s-carprolactone (s-CL). Reactions of bis(3,5-dimethyl-pyrazol-1-ylmethyl)pyridine (L1) with the appropriate Zn(II) and Cu(II) carboxylates afforded the corresponding complexes; [Zn(L1)(C6H5COO)21 (1), [Zn(L1)(2-Br-C6H4COO)(2)] (2), [Cu(L1)(C6H5COO)(2)] (3) and [Cu(L1)(2-Br-C6H4COO)21 (4) in good yields. Solid state structures of complexes 1 and 2 reveal that the complexes are polymeric and monomeric respectively. EPR analyses of the paramagnetic Cu(II) complexes 3 and 4 were consistent with anisotropic coupling and confirm that the compounds are monomeric both in solution and solid states. Complexes 1-4 formed active catalysts for the polymerization of s-CL at 110 degrees C to give polymers with moderate molecular weight and molecular weight distributions. Kinetic analyses of the polymerization reactions indicate pseudo first-order dependency on both monomer and catalyst. (C) 2015 Elsevier B.V. All rights reserved.