Some structural and electronic properties of MX₃(M = Ln, Sc, Y, Ti⁺, Zr⁺, Hf⁺; X = H, Me, Hal, NH₂) from DFT calculations

Abstract

The geometry of trivalent homoleptic d0 MX3 (X = H, Me, Hal, NH2) complexes for the entire lanthanide family, neutral group 3 and cationic group 4 metal center complexes have been studied with DFT(B3PW91) calculations. The geometrical parameters are in good agreement with the available experimental data. The degree of pyramidalization of the metal is discussed. The hydride and alkyl complexes are strongly pyramidal. In the case of the halide, a pyramidal structure is preferred for fluoride and the systems become increasingly planar with heavier halides. The geometrical trends with X are similar for group 3, group 4 and lanthanide complexes. However group 3 complexes are almost planar, group 4 strongly pyramidal and lanthanide intermediate. The lanthanide contraction is reproduced. A natural bond orbital (NBO) charge analysis is used to rationalize the results. This highlights the similarities and differences in the M-X bonding in the three families of complexes. In all cases, the pyramidalization is related to the participation of the valence d orbitals in the M-X bonds but the M-X bond is mostly ionic in lanthanide and considerably more covalent for the d transition metals. The hydride and alkyl complexes, which have more covalent character than the halide complexes are more pyramidal. In the case of the halide complexes, the fluoride complexes, in which there is the least population of the M d orbitals, are found to be more pyramidal because the increasing covalency with heavier halide stabilizes the planar structure through dpi-ppi interaction. The electronic metal d-p transition of the free ion is shown to be a good indicator of the pyramidalization at M although these values should only be used qualitatively. The strong ionic character of the Ln-X bond gives a rationale for the more important elongation of the beta Si-C bond in La(CH(SiMe3)2)3 than in La(N(SiMe3)2)3. The elongation is shown to be in part due to the negative hyperconjugation of the lone pair used for the Ln-ligand bonds in the beta bonds.

DFT modeling of the relative affinity of nitrogen ligands for trivalent f elements: an energetic point of view

“…Theoretical calculations can indeed help in interpreting experimental findings by providing tools for a detailed description of the metal-ligand bond. [26][27][28][29][30][31][32][33][34][35][36][37][38] However, they should not be analyzed without a direct comparison with experiments whereas experimental data are rather scarce, especially for heavy trivalent actinides. To date, theoretical studies dedicated to trivalent rare earth complexes have thus been mainly applied to structural data, with very satisfying agreements, but other computational analyses, and notably energetic analyses, have seldom been validated.…”

Lanthanide Complexes: Electronic Structure and H—H, C—H, and Si—H Bond Activation from a DFT Perspective

“…The traditional interpretation of the agostic interaction cannot be satisfactory. In a study of La{CH(SiMe 3 ) 2 } 3 and La{N(SiMe 3 ) 2 } 3 , we have suggested that the elongation of the β Si-C bond is due, in part, to a derealization of the lone pair used for Ln-R bonding for R = CH(SiMej) 2 and N(SiMe 3 ) 2 within the ligand (35,36). This interpretation is not new in the literature (48).…”

“…The nature of the Ln-X bonding has been the subject of several papers (15-17, 36). The lanthanide elements are electropositive centers resulting in ionic Ln-X bonding.…”

Selective α‐Metalation of THF by a Cationic Zirconium Complex Supported by an (NNNN)‐Type Macrocyclic Ligand

“…[16] Indeed, it implies at least one step with an activation barrier of approximately 45 kcal mol 2 + is facile at high dihydrogen pressures, suggesting direct hydrogenolysis of alkyl complexes. [7] In conclusion, the unexpected formation of a cationic zirconium a-tetrahydrofuranyl complex via a cationic silyl intermediate was suggested by kinetic studies and DFT calculations.…”

“…Because reactions of alkyls with dihydrogen are known to proceed with relatively low activation barriers between 15 and 20 kcal mol À1 , the formation of 2 appears to be a complicated process. [16] Indeed, it implies at least one step with an activation barrier of approximately 45 kcal mol À1 (C À H bond activation of THF by the alkyl ligand). The formation of [{(Me 3 TACD)ZrA C H T U N G T R E N N U N G (m-H) 2 } 2 ] 2 + is facile at high dihydrogen pressures, suggesting direct hydrogenolysis of alkyl complexes.…”