A THEORETICAL INTERPRETATION OF THE ELECTRONIC SPECTRA OF $Cr(CO)_{6}$ AND $Cr(CO)_{5}NH_{3}$
Loading...
Date
1971
Journal Title
Journal ISSN
Volume Title
Publisher
Ohio State University
Abstract
Non-Empirical Molecular Orbital (NEMO) calculations of $Cr(CO)_{6}$ and $Cr(CO)_{5}NH_{3}$ have been undertaken in order to interpret the electronic spectra of a series of compounds $Cr(CO)_{5} L$ where L is either an amine or a phosphine. Parameters were obtained mostly from SCF minimum basis set calculations of $CrH_{6}$, $NH_{3}$ and CO, although alpha values for Cr 3d orbitals were semiempirically chosen to match the first two vertical ionization potentials of $Cr(CO)_{6}$. In terms of orbital transitions, the calculations show that the lowest energy transition in $Cr(CO)_{6}$ should be from the filled $t_{2g}$ orbital to the empty $e_{g}$ orbital. These orbitals have 95\% and 72\% d character respectively. This transition splits 4 ways with replacement of one CO by $NH_{3}$. These are a red shifted (2.4 kk) e-$b_{1}$, an unshifted $b_{2}-b_{1}$, and blue shifted e-$a_{1}$, and $b_{2}-a_{1}$ transitions. The observed red shift of the lowest energy transition in Cr (CO)$_{5}NH_{3}$ is about 8 kk relative to $Cr(CO)_{6}$. A group of compounds $Cr(CO)_{5}$ $PR_{3}$ show red shifts of about 3 kk for the lowest energy transition and no shift for the second transition relative to $Cr(CO)_{6}$. Intensities of these transitions are typical of symmetry allowed d-d transitions ($\epsilon$ 300 to 3000). The first four vertical ionization potentials of $Cr(CO)_{6}$ are well reproduced by the calculation.
Description
Author Institution: Department of Chemistry, Worcester Polytechnic Institute