An Effective Core Potential Study of Transition-Metal Chalcogenides. 1. Molecular Structure

Abstract

A structural analysis is reported of roughly 150 transition-metal (TM)-chalcogenido complexes in a variety of chemical environments. With few exceptions, agreement between calculated and experimental geometries is excellent. The research provides convincing evidence that computational methods employed are adequately describing the bonding in these diverse T M complexes. Interesting trends in relative TMCh (RMc~J-RMc~) bond lengths are found. Experimental and computational data show that other than the zirconocene-and hafnocene-oxos there is similar behavior in relative bond lengths for widely varying TM-chalcogenido complexes. Relative bond lengths versus oxo (S-0, Se-0, and Te-0) in group IVB metallocenes tend to be larger than for other families of complexes and show less variation among the heavier chalcogens (Se-S, Te-S, and T e S e ) . Analysis of localized wave functions for CpZZrCh point to a greater contribution from a singly-bonded Zr-Ch structure (relative to Z1-Ch) when Ch is 0 compared to heavier chalcogens.Taken together, the data suggest that there is a fundamental difference in the Zr-oxo (and Hf-oxo) bond in relation to heavier chalcogens, consistent with recent experimental data. In previous studies of multiply bonded T M complexes we have focused on the ability of ECPs to make computations feasible for complexes incorporating even the heaviest transition metals. The present work also evaluates ECP methods for heavier main group (MG) elements. Thechalcogens (Ch) 0, S, Se, and Te are included in this study.

Theoretical Estimation of Vibrational Frequencies Involving Transition Metal Compounds

“…We have focused on TMdCh stretching frequencies since experimental assignment of these modes is the most accurate and least ambiguous. Also, TMdCh stretching frequencies are of greatest interest in connection with coupling vibrational data with electronic and molecular structural data 17,24 for probing the nature of the TM-chalcogen bond. 2.…”

“…[1][2][3][4][5][6][7] The SBK(d) scheme 19 was used in this research since a previous study showed it to be highly accurate for prediction of metric data of TMdCh complexes. 17 Other ECP implementations with similar valence basis sets will most likely do as well. 8,10,27 Linearly fitted SBK(d) calculations for the entire TM-chalcogenide data set gave an overall absolute difference of 38 cm -1 (theory versus experiment), whereas a linear fit of main group data 2 gave an absolute difference of 34 cm -1 .…”

“…20 These results, along with the accuracy of structural prediction, strongly supports the suitability of RHF/ SBK(d) wave functions for these systems. 17,20 Vibrational frequencies are calculated by numerical differentiation (single differencing) of analytical gradients for optimized geometries and are based on the harmonic approximation. The capability to calculate ECP analytic second derivatives does not yet exist in GAMESS, although previous studies suggest that the differences between analytic and numerical differentiation 3,4 are well within the experimental uncertainties of vibrational frequencies of most TM complexes.…”

“…A previous study showed the computational methods outlined below to be able to accurately predict the geometry of over 150 chalcogenides. 17 This predictive capability for a large series of diverse complexes strongly suggests that the computational model is accurately describing the electronic structure of these complexes. Hence, it is reasonable to inquire whether the methods can be used to predict vibrational frequencies.…”

Modeling Nonlinear Optical Properties of Transition Metal Complexes. Basis Set, Effective Core Potential, and Geometry Effects

“…Reported experimental R for inorganic complexes are rare since unlike organometallics, few form stable, molecular species under ambient conditions. Indeed, we were only able to find two for transition metal complexes: TiCl 4 and OsO 4 . 13 Although the latter is an oxo complex, we chose the former for this comparison given the extreme difficulties in doing allelectron calculations on an element as heavy as osmium.…”