Spectroscopic analysis of transition-metal coordination complexes based on poly(4-vinylpyridine) and dichlorotricarbonylruthenium(II)

The formation of coordination complexes between the nitrogen lone pair on poly(4-vinylpyridine) and the metal center in dichlorotricarbonylruthenium(II) is described in this research contribution. {RuCl2(CO)(3)}(2) was chosen because octahedral d(6) heavy-metal centers with a-acid carbonyl ligands exhibit very large ligand held stabilization energies which enhance the glass transition temperatures of polymeric coordination complexes. Relative to undiluted poly(4-vinylpyridine), which exhibits a glass transition at 145 degrees C, T-g increases by 27 degrees C at 3 mol% Ru2+. When the concentration of Ru2+ is greater than 5 mol%, detection of a diffuse T-g above 200 degrees C is difficult via calorimetry because the discontinuity in specific heat decreases considerably. Ambient-temperature infrared spectroscopic data for the pyridine side-group in the polymer suggest that the pyridine nitrogen coordinates to ruthenium. Symmetry considerations and high-temperature infrared data for the carbonyl stretching vibrations are consistent with structural models which contain two CO ligands and two pyridine sidegroups or three CO ligands and I pyridine sidegroup in the coordination sphere of ruthenium. Hence, it is possible that the transition-metal salt bridges two different chains via the pyridine nitrogen lone pair, forming coordination crosslinks. Hindered mobility of this nature provides a reasonable explanation for the enhancement in T-g by 9 degrees C/mol% Ru2+, up to 3 mol% Ru2+. Ambient temperature infrared signals in the carbonyl region suggest that as many as five different ligand arrangements of the following pseudo-octahedral complex, RuCl2(CO)(2)(Py)(2), exist simultaneously at low Ru2+ concentrations and could be responsible for coordination crosslinks. Upon heating, the highly symmetric isomers with trans-CO ligands transform irreversibly to pseudo-octahedral structures with lower symmetry (i.e., cis-CO ligands). Octahedral ruthenium d6 salts are attractive physical property modifiers when polymeric ligands coordinate to the metal center. (C) 1999 Elsevier Science Ltd. All rights reserved.