Effective core potential study of multiply bonded transition metal complexes of the heavier main group elements

Abstract

A computational study, using relativistic effective core potentials, is presented of transition metalmain group multiply bonded complexes, of interest in the context of catalysis and chemical vapor deposition of TM/MG materials. Model do transition metal complexes chosen are of the general form CI,ME where M = Zr (n = 2). Ta (n = 3), and W (n = 4). Main group elements of interest are the tetrels (E = C, Si, Ge, Sn), pnictogens (E = N, P, As, Sb), and chalcogens (E = 0, S, Se, Te). A comparison between calculated metric data and available experimental data for a wide range Of TM =MG complexes will help in further assessing efficient computational approaches to TM complexes, particularly of the heavier MG elements, as a function of metal, ligand and level of theory. In the present work restricted Hartree Fock (RHF) and Mdler-Plesset second order perturbation theory (MP2) wavefunctions were employed. In most cases there are small differences between RHF and MP2 calculated geometries, with both methods showing good agreement with experimental data, suggesting these approaches will be suitable for the study of larger, more experimentally relevant models. Changes in ZrE bond lengths for E = chalcogen (upon going from RHF to MP2) suggest a fundamentally different description between the Zr-0x0 bond and heavier chalcogens, a result supported by recent experimental data for a series of Zr-chalcogenidos. To date no examples have been reported of arsinidene and stibinidene complexes. Computational results show similar behavior among the heavier pnictogen complexes, i.e., /M=EH (E = P, As, Sb), suggesting that strategies used to synthesize phosphinidenes may be suitable in the search for the first L,M=AsR and L,M =SbR complexes. Additionally, calculations suggest that design of ligand sets which yield linearly coordinated phosphinidenes (and presumably As and Sb analogues) will lead to phosphinidenes with stronger metal-pnictogen bonds and increased thermodynamic stability versus nonlinearly coordinated examples. 0 I994 John Wiley & Sons, Inc.

Theoretical Estimation of Vibrational Frequencies Involving Transition Metal Compounds

“…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.…”

“…Previous research compared geometries calculated with RHF and Møller-Plesset secondorder perturbation theory (MP2) wave functions using the SBK(d) scheme. 20 This study of multiply bonded complexes, chalcogenides included, led to two important conclusions. First, both RHF/SBK(d) and MP2/SBK(d) geometries are close to experimental data.…”

“…To summarize, TMelement bonds differ by 1-3% with bond angles involving the TM being, on average, within 3-4% of each other at the RHF/ SBK(d) and MP2/SBK(d) levels of theory. 20 Correlation effects are generally more significant toward the right in a TM series, toward the left in a MG row, and for heavier elements in a main group column. 20 These results, along with the accuracy of structural prediction, strongly supports the suitability of RHF/ SBK(d) wave functions for these systems.…”

“…20 Correlation effects are generally more significant toward the right in a TM series, toward the left in a MG row, and for heavier elements in a main group column. 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.…”

“…If anything, MP2/SBK(d) tends to overcorrect differences between RHF/SBK(d) and experimental geometries. 20 Second and more importantly, there is only a small difference in calculated geometries despite the much greater expense of MP2 calculations. To summarize, TMelement bonds differ by 1-3% with bond angles involving the TM being, on average, within 3-4% of each other at the RHF/ SBK(d) and MP2/SBK(d) levels of theory.…”