Tolis E J, Teberekidis V I, Raptopoulou C P, Terzis A, Sigalas M P, Deligiannakis Y, Kabanos T A
Department of Chemistry, University of Ioannina, Greece.
Chemistry. 2001 Jun 18;7(12):2698-710. doi: 10.1002/1521-3765(20010618)7:12<2698::aid-chem26980>3.0.co;2-2.
Two series of octahedral oxovanadium(IV) compounds, containing charged or neutral axial ligands, with the tetradentate amidate molecules Hcapca and H2capcah of the general formulae trans-[V(IV)OX(capca)]0/+ (where X = Cl- (1.CH2Cl2), SCN- (2), N3 (3), CH3COO- (4), PhCOO- (5), imidazole (6. CH3NO2), and eta-nBuNH2 (7)) and cis-[V(VI)OX(Hcapcah)]0/+ (where X = Cl- (8.0.5CH2Cl2), SCN (9), N3 (10.2CH3OH), and imidazole (11)), were synthesized and characterized by X-ray crystallography (1.CH3OH,8.CHCl3, 9.2CH3CN, 10.CH3CN and cis-[VO(imidazole)(Hcapcah)+) and continuous-wave electron paramagnetic resonance (cw EPR) spectroscopy. In addition to the synthesis, crystallographic and EPR studies, the optical, infrared and magnetic properties (room temperature) of these compounds are reported. Ab initio calculations were also carried out on compound 8 CHCl3 and revealed that this isomer is more stable than the trans isomer, in good agreement with the experimental data. The cw EPR studies of compounds 1-5, that is, the V(IV)O2+ species containing monoanionic axial ligands, revealed a novel phenomenon of the reduction of their A, components by about 10% relative to the N4 reference compounds ([V(IV)O-(imidazole)4]2+ and [V(IV)O(2,2-bipyridine)2]2+). In marked contrast, such a reduction is not observed in compounds 6. CH3NO2-11, which contain neutral axial ligands. Based on the spin-Hamiltonian formalism a theoretical explanation is put forward according to which the observed reduction of Az is due to a reduction of the electron - nuclear dipolar coupling (P). The present findings bear strong relevance to cw EPR studies of oxovanadium(IV) in vanadoproteins, V(IV)O2+-substituted proteins, and in V(IV)O2+ model compounds, since the hyperfine coupling constant, Az, has been extensively used as a benchmark for identification of equatorial-donor-atom sets in oxovanadium(IV) complexes.
合成了两个系列的八面体氧钒（IV）化合物，它们含有带电荷或中性的轴向配体，与通式为trans-[V(IV)OX(capca)]0/+（其中X = Cl- (1.CH2Cl2)、SCN- (2)、N3 (3)、CH3COO- (4)、PhCOO- (5)、咪唑 (6.CH3NO2) 和η-nBuNH2 (7)）以及cis-[V(VI)OX(Hcapcah)]0/+（其中X = Cl- (8.0.5CH2Cl2)、SCN (9)、N3 (10.2CH3OH) 和咪唑 (11)） 的四齿酰胺分子Hcapca和H2capcah，通过X射线晶体学（1.CH3OH、8.CHCl3、9.2CH3CN、10.CH3CN和顺式-[VO(咪唑)(Hcapcah)+）以及连续波电子顺磁共振（cw EPR）光谱对其进行了表征。除了合成、晶体学和EPR研究外，还报道了这些化合物的光学、红外和磁性性质（室温）。还对化合物8 CHCl3进行了从头算计算，结果表明该异构体比反式异构体更稳定，这与实验数据高度吻合。对化合物1-5（即含有单阴离子轴向配体的V(IV)O2+物种）的cw EPR研究揭示了一个新现象，即相对于N4参考化合物（[V(IV)O-(咪唑)4]2+和[V(IV)O(2,2-联吡啶)2]2+），它们的A,成分降低了约10%。与之形成鲜明对比的是，在含有中性轴向配体的化合物6.CH3NO2-11中未观察到这种降低。基于自旋哈密顿形式主义提出了一种理论解释，表示观察到的Az降低是由于电子 - 核偶极耦合（P）的降低。本研究结果与钒蛋白、V(IV)O2+取代蛋白以及V(IV)O2+模型化合物中氧钒（IV）的cw EPR研究密切相关，因为超精细耦合常数Az已被广泛用作识别氧钒（IV）配合物中赤道供体原子集的基准。
