Vibrational spectra of PtCO and Pt(CO)(2) isolated in solid argon: Trends in unsaturated group 10 metal carbonyl molecules

The infrared spectrum of PtCO isolated in solid argon has been reinvestigat ed. Isotopic data on nu(1), nu(2), nu(3), 2 nu(1), and nu(1) + nu(3) have b een measured in the near- and far-infrared regions. This enables a complete harmonic force-field calculation based on a linear geometry, in agreement with all theoretical predictions. Comparisons of spectroscopic parameters f or the NiCO, PdCO, and PtCO series experimental and theoretical binding ene rgies are also presented. These results show that the perturbations of the CO ligand (CO bond force constants and nu(1) frequency shifts) are unreliab le indicators of the evolution of the metal-ligand interaction energies, co ntrary to the metal-carbon force constant. Comparison with theoretical pred ictions of the fundamental frequencies indicates a systematic underestimati on of the bending frequencies, especially sensitive for the heavy atom mono carbonyls. Similarly, the IR spectrum of Pt(CO)(2) has been studied, enabli ng the determination of the nu(1), nu(2), nu(3), nu(4), and nu(6) fundament als of this molecule and a discussion of the evolution of the Pt-C and C=O force constants with the coordination number. Complementary results concern ing Pt(CO)(n) (n = 3, 4) are also presented.