Valence Shell Charge Concentrations at Pentacoordinate d0 Transition-Metal Centers: Non-VSEPR Structures of Me2NbCl3 and Me3NbCl2
✍ Scribed by G. Sean McGrady; Arne Haaland; Hans Peter Verne; Hans Vidar Volden; Anthony J. Downs; Dmitry Shorokhov; Georg Eickerling; Wolfgang Scherer
- Publisher
- John Wiley and Sons
- Year
- 2005
- Tongue
- English
- Weight
- 411 KB
- Volume
- 11
- Category
- Article
- ISSN
- 0947-6539
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✦ Synopsis
Abstract
The molecular structures of the monomeric, pentacoordinated methylchloroniobium(IV) compounds Me~3~NbCl~2~ and Me~2~NbCl~3~ have been determined by gas electron diffraction (GED) and density functional theory (DFT) calculations, and, for Me~3~NbCl~2~, 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 Me~2~NbCl~3~ with the two axial NbCl bonds bent away from the equatorial, slightly shorter NbCl bond. In the case of Me~3~NbCl~2~, moreover, the X‐ray model suggests structural distortions away from the idealized C~3__h__~ geometry, 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): Me~3~NbCl~2~, in C~3__v__~ symmetry, 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); Me~2~NbCl~3~, in C~2__v__~ symmetry, NbCl~ax~ 2.361/2.304(5), NbCl~eq~ 2.321/2.288(9), NbC 2.180/2.135(9), CH 〈1.094〉/1.12(1), ∢Cl~ax~NbCl~eq~ 98.5/96.5(6), ∢CNbC 121.0/114(2), ∢NbCH 〈108.9〉/109(2). The electronic structures of Me~2~NbCl~3~ and Me~3~NbCl~2~ have 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.