Valence Shell Charge Concentrations at Pentacoordinate d0Transition‐Metal Centers: Non‐VSEPR Structures of Me2NbCl3and Me3NbCl2
- 9 August 2005
- journal article
- research article
- Published by Wiley in Chemistry – A European Journal
- Vol. 11 (17) , 4921-4934
Abstract
The molecular structures of the monomeric, pentacoordinated methylchloroniobium(IV) compounds Me3NbCl2and Me2NbCl3have been determined by gas electron diffraction (GED) and density functional theory (DFT) calculations, and, for Me3NbCl2, by single crystal X‐ray diffraction. Each of the molecules is found to have a heavy‐atom skeleton in the form of a trigonal bipyramid (TBP) with Cl atoms in the axial positions, in accord with their vibrational spectra. The TBP is somewhat distorted in the case of Me2NbCl3with the two axial NbCl bonds bentawayfrom the equatorial, slightly shorter NbCl bond. In the case of Me3NbCl2, moreover, the X‐ray model suggests structural distortions away from the idealizedC3hgeometry, in line with the results of quantum chemical calculations. Structure optimizations by DFT calculations and least‐squares refinement to the GED data yield the following structural parameters (calcd/exptl; eq=equatorial; ax=axial; distances in Å, angles in degrees; average values in 〈〉 brackets): Me3NbCl2, inC3vsymmetry, NbCl 〈2.370〉/〈2.319(3)〉, NbC 2.173/2.152(4), CH 〈1.096〉/1.124(5), ∢NbCH 〈109.3〉/105.2(8), ∢ClNbC 92.2/93.3(2), ∢CNbC 119.9/119.7(1); Me2NbCl3, inC2vsymmetry, NbClax2.361/2.304(5), NbCleq2.321/2.288(9), NbC 2.180/2.135(9), CH 〈1.094〉/1.12(1), ∢ClaxNbCleq98.5/96.5(6), ∢CNbC 121.0/114(2), ∢NbCH 〈108.9〉/109(2). The electronic structures of Me2NbCl3and Me3NbCl2have been explored by rigorous analysis of both the wavefunction and the topology of the electron density, employing DFT calculations. Hence the structures of these compounds are shown to reflect repulsion between the NbC and NbCl bonding electron density and charge concentrations induced by the methyl ligands in the valence shell of the Nb atom and arising mainly from use of Nb(4d) functions in the NbC bonds.Keywords
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