The performance of density-functional/Hartree–Fock hybrid methods: Cationic transition-metal methyl complexes MCH+3 (M=Sc–Cu,La,Hf–Au)

Abstract

Hybrid methods, including a mixture of Hartree–Fock exchange and density functional exchange-correlation treatment have been applied to the cationic methyl complexes MCH+3 of the first and third-row transition metals (M=Sc–Cu,La,Hf–Au). Bond dissociation energies and optimum geometries obtained with the ‘‘Becke-Half-and-Half-Lee–Yang–Parr’’ and ‘‘Becke-3-Lee–Yang–Parr’’ functionals and from calibration calculations employing quadratic configuration interaction with single and double excitations and with a perturbative estimate of triple excitations are reported. A comparison of the results for the 3d-block species to earlier high-level ab initio calculations and experimental data is carried out in order to assess the reliability of hybrid methods as a practical tool in organometallic chemistry. Furthermore, the bond dissociation energies of the cationic 5d-block transition-metal methyl complexes, many of which have not been investigated so far, are predicted.

Density functional localized orbital corrections for transition metals

“…First, it can be noticed that the errors for ScCH 3 , VCH 3 , and MnCH 3 are extremely large ͑ϳ15-20 kcal/ mol͒. The error for NiCH 3 is relatively small and the bond dissociation energy for CuCH 3 is significantly underestimated.…”

“…3,5 But the basis sets used for these calculations were relatively small and the results strongly depend on that. Very large basis sets are probably required for CCSD͑T͒ calculations to be able to recover most of the correlation energy.…”

“…This metric was only applied to single bonds since sigma and pi bonds have considerable differences in shapes and the interaction between multiple orbitals may be too complex to be captured by this simple metric. We will thus focus now on our molecular compounds having only sigma bonds between the metal and the ligand such as M u H, M u CH 3 , M + u H, and M + u CH 3 . The electronic structure of the compounds was discussed in paragraph III, and the values of the distances and the second moment of the localized orbitals are given in the Supplementary Materials.…”

“…Thus, for these cases we defined spin delocalization parameters. Since these parameters are expected to depend much more on the nature of the ligand than on the nature of the metal, one parameter was defined for CrH + and CuH + and another for CrCH 3 + and CuCH 3 + . Based on a survey of the experimental data, we also observed that generally Sc and Ti display irregular behaviors regarding spin delocalization.…”

“…1,2 DFT calculations on first-row transition metals attempting to assess accuracy have been carried out in the past but were generally limited to relatively small or medium sized test sets, [3][4][5][6][7][8][9][10] although a few papers with larger test sets have appeared in recent years. 2,11,12 Moreover, only few research groups have tried to improve DFT by including transition metals in their training sets.…”