Force Constants of Nickel Carbonyl from Vibrational Spectra of Isotopic Species

Abstract

The infrared spectra of gaseous Ni(13CO). and Ni(C180)4 and the infrared and Raman spectra of CC4 solutions of these isotopic molecules were recorded. General quadratic valence force constants have been calculated from the frequencies of the normal species and the two isotopic species. The resulting force constant solution is similar to that obtained previously assuming a pi electron interaction potential function. These results put the force constants of metal carbonyls on a firmer basis.1

VIBRATIONAL SCALING FACTORS FOR Rh(I) CARBONYL COMPOUNDS IN HOMOGENEOUS CATALYSIS

“…For small molecules, the calculation of accurate anharmonic force fields is a practical option, see for example [42], but this becomes not feasible for larger molecules. For Ni(CO) 4 , for example, the estimated anharmonicity constants from isotope experiments are between -3 and -11 cm -1 [43] and would bring calculated frequencies in even closer agreement with experiments. The use of a simple vibrational scaling factor aims to correct for (i) inherent deficiencies of the electronic structure methods, and (ii) the potential energy surface to be not harmonic.…”

The electronic structure of transition metal carbonyl complexes

“…For Cr(CO)n, for instance, kco from a CO energy factored calculation, including anharmonicity corrections, is 16.95 mdyn/A, to be compared with the accurate value 17.04 [33]. For Ni(CO)4 17-74 is obtained in the same way, to be compared with 17.68 [31]. Assuming the anharmonicity corrections for Co(CO)4-and Fe(CO)4= to be equal to those for Ni(CO)4, we have calculated the force constants for these complexes using the CO energy factoring.…”

“…In recent years very careful and detailed investigations of the IR and Raman spectra of the carbonylcomplexes Ni(CO)4 [31], Fe(CO)5 [32] and Cr(CO)6 [33] have been published. For these systems, anharmonicity corrections have been determined, and force constants calculated from a general quadratic valence force field.…”

Calculation of equilibrium geometries and harmonic frequencies by theLCGTO-MCP-local spin density method

“…We however agree with the conclusions supported by the HF calculation [25], i.e., that the latter assignment [28] for v3 is correct. If we look at the two modes for which experimental harmonized frequencies are available ( ul = 2 154 cm-' and v5 = 2092 cm-') [27], agreement with theory is improved for both modes and for both theories, and in the case of the LCGTO-MCP-LSD method, agreement with experiment is remarkable (13 cm-' for u1 and 4 cm-' for v5). As for the other modes, the observed frequencies should only be slightly lower than the harmonic frequencies since the anharmonic effects are thought to be small [ 271.…”