Valence shell charge concentrations at pentacoordinate d0 transition-metal centers: non-VSEPR structures of Me2NbCl3 and Me3NbCl2.
Valence shell charge concentrations at pentacoordinate d0 transition-metal centers: non-VSEPR structures of Me2NbCl3 and Me3NbCl2.
复制标题
五配位 d0 过渡金属中心的价壳电荷浓度：Me2NbCl3 和 Me3NbCl2 的非 VSEPR 结构。
作者：
G. Mcgrady;A. Haaland;H. Verne;H. V. Volden;A. J. Downs;D. Shorokhov;G. Eickerling;W. Scherer
单体，五配位甲基氯铌（IV）化合物Me 3 NbCl 2和Me 2NbCl 3的分子结构已确定的气体电子衍射（GED）和密度泛函理论（DFT）计算，并为Me 3 NbCl 2，通过单晶X-射线衍射。发现每个分子都有一个三角双锥（TBP）形式的重原子骨架，Cl原子位于轴向位置，与它们的振动光谱雅阁。TBP是有点扭曲的情况下，Me 2NbCl 3的两个轴向Nb-Cl键弯曲远离赤道，稍短的Nb-Cl键。此外，在Me 3 NbCl 2的情况下，X射线模型表明远离理想化的C3 h几何结构的结构扭曲，与量子化学计算的结果一致。通过DFT计算和对GED数据的最小二乘精化进行结构优化，得到以下结构参数（计算值/实验值; eq=赤道; ax=轴向;距离以A为单位，角度以度为单位;平均值在括号中）：Me 3 NbCl 2，C（3v）对称，Nb-Cl 2.370/2.319（3），Nb-C 2.173/2.152（4），C-H 1.096/1.124（5），角球NbCH 109.3/105.2（8），角球ClNbC 92.2/93.3（2），角球面CNbC119.9/119.7（1）; Me2NbCl 3，C（2v）对称，Nb-Cl（ax）2.361/2.304（5），Nb-Cl（eq）2.321/2.288（9），Nb-C 2.180/2.135（9），C-H 1.094/1.12（1），角球Cl（ax）NbCl（eq）98.5/96.5（6），角球CNbC 121.0/114（2），角球NbCH 108.9/109（2）。采用密度泛函理论（DFT）计算，通过严格分析电子密度的波函数和拓扑结构，探索了Me 2NbCl 3和Me 3 NbC（2）的电子结构。因此，这些化合物的结构被证明反映之间的排斥Nb-C和Nb-Cl键合的电子密度和电荷浓度引起的Nb原子的价层中的甲基配体，并产生主要从使用Nb（4d）功能的Nb-C键。
The molecular structures of the monomeric, pentacoordinated methylchloroniobium(IV) compounds Me3NbCl2 and Me2NbCl3 have 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 Me2NbCl3 with the two axial Nb--Cl bonds bent away from the equatorial, slightly shorter Nb--Cl bond. In the case of Me3NbCl2, moreover, the X-ray model suggests structural distortions away from the idealized C3h 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 A, angles in degrees; average values in brackets): Me3NbCl2, in C(3v) symmetry, Nb--Cl 2.370/2.319(3), Nb--C 2.173/2.152(4), C--H 1.096/1.124(5), angle-spherical NbCH 109.3/105.2(8), angle-spherical ClNbC 92.2/93.3(2), angle-spherical CNbC 119.9/119.7(1); Me2NbCl3, in C(2v) symmetry, Nb--Cl(ax) 2.361/2.304(5), Nb--Cl(eq) 2.321/2.288(9), Nb--C 2.180/2.135(9), C--H 1.094/1.12(1), angle-spherical Cl(ax)NbCl(eq) 98.5/96.5(6), angle-spherical CNbC 121.0/114(2), angle-spherical NbCH 108.9/109(2). The electronic structures of Me2NbCl3 and Me3NbC(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 Nb--C and Nb--Cl 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 Nb--C bonds.