POLYMERIC COORDINATION-COMPLEXES BASED ON COBALT, NICKEL, AND RUTHENIUM THAT EXHIBIT SYNERGISTIC THERMAL-PROPERTIES

d-Block transition-metal-containing polymer blends which form coordination complexes are the focus of this research. The model compounds are cobalt chloride hexahydrate, nickel acetate tetrahydrate, and the dimer of dichlorotricarbonylruthenium(II). The ligand is poly(4-vinylpyridine), P4VP, or copolymers that contain 4-vinylpyridine repeat units. Thermal analysis via differential scanning calorimetry suggests that the glass transition temperature of the polymeric ligand(s) is enhanced by these d-block metal salts in binary and ternary blends. Cobalt and nickel 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, Fourier transform infrared spectroscopy of P4VP-ruthenium precipitates reveals that the pyridine nitrogen lone pair coordinates to the metal center and strengthens ruthenium-carbonyl bonds in the polymeric complex. Infrared absorption frequencies of the CO ligands are consistent with pi-backbonding between the t2g molecular orbitals of the metal in the octahedral point group and the pi* antibonding orbitals of carbon monoxide. High-resolution carbon-13 solid-state NMR spectroscopy identifies at least two, and possibly three, carbonyl signals in the undiluted pseudooctahedral ruthenium dimer via the Bloch-decay pulse sequence. In the polymeric complex, carbonyl C-13 magnetization unique to the ruthenium salt is generated via intermolecular polarization transfer from the proton spin manifold of poly(4-vinylpyridine) using a cross-polarization thermal mixing time of 2 ms. Since there are no protons in the ruthenium 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. A thermodynamic interpretation of ligand field stabilization energies appropriate to tetrahedral cobalt complexes is employed to estimate the synergistic enhancement of the glass transition temperature, particularly when coordination cross-links are present.