Polymeric coordination complexes based on cobalt, nickel, and ruthenium that exhibit synergistic thermal properties

Abstract

d-Block transition-metal-containing polymer blends which form coordination complexes are the focus of this research. The model compounds are Co chloride hexahydrate, Ni acetate tetrahydrate, and the dimer of dichlorotricarbonylruthenium (II). The ligand is poly (4-vinylpyridine), P4VP, or copolymers that contain 4-vinylpyridine repeat units. Differential scanning calorimetry suggests that the glass transition temperature (gtt) of the polymeric ligand(s) is enhanced by these d-block metal salts in binary and ternary blends. Co and Ni salts function as transition-metal compatibilizers for two immiscible copolymers of styrene with 4-vinylpyridine and butyl methacrylate with 4-vinylpyridine. At the molecular level, FTIR of P4VP-Ru precipitates reveals that the pyridine nitrogen lone pair coordinates to the metal center and strengthens Ru-carbonyl bonds in the polymeric complex. IR absorption frequencies of the CO ligands are consistent with {pi}-backbonding between the t{sub 2g} molecular orbitals of the metal in the octahedral point group and the {pi}* antibonding orbitals of CO. High-resolution C-13 solid-state NMR spectroscopy identifies at least two, and possibly three, carbonyl signals in the undiluted pseudooctahedral Ru dimer via the Bloch-decay pulse sequence. In the polymeric complex, carbonyl C-13 magnetization unique to the Ru salt is generated via intermolecular polarization transfer from the proton spin manifold of poly(4-vinylpyridine)more » using a cross-polarization thermal mixing time of 2 ms. Since there are no protons in the Ru dimer, the observation of energy-conserving H-1/C-13 spin diffusion between dissimilar molecules under matched Hartmann-Hahn spin-lock conditions argues convincingly that heteronuclear dipolar distances are small enough for the proposed polymeric complex to form. Thermodynamic interpretation of ligand field stabilization energies appropriate to tetrahedral Co complexes is employed to estimate the synergistic enhancement of the gtt.« less