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首页> 外文期刊>Chemistry: A European journal >The equilibrium between the octahedral and square pyramidal form and the influence of an axial ligand on the molecular properties of V~(IV)O complexes: A spectroscopic and DFT study
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The equilibrium between the octahedral and square pyramidal form and the influence of an axial ligand on the molecular properties of V~(IV)O complexes: A spectroscopic and DFT study

机译：八面体和方形锥体形状之间的平衡以及轴向配体对V〜（IV）O配合物分子性质的影响：光谱和DFT研究

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摘要

The previously unreported equilibrium in aqueous solution between the VIVO square pyramidal and trans octahedral form with an axial water molecule for a number of bidentate ligands with (N,O) and (O,O) donor sets (6-methylpicolinic (6mepicH) and 6-methyl-2,3-pyridinedicarboxylic (6-me-2,3-pdcH_2) acids, dipyridin-2-ylmethanol (Hdpmo) and 1,2dimethyl-3-hydroxy-4(1H)-pyridinone (Hdhp)) has been demonstrated by the combined application of EPR spectroscopy and DFT methods. The EPR spectra suggest that, with increasing ionic strength, the equilibrium is shifted towards the formation of the pentacoordinated species and values of K ≈ 4.0 and 7.0 for the systems containing 6-methyl-2,3-pyridinedicarboxylic acid and dipyridin-2-ylmethanol were measured. DFT calculations performed with Gaussian 03 and ORCA software predict the 51V anisotropic hyperfine coupling constant along the z axis (A_z), which can be used to demonstrate the presence of an axially bound ligand trans to the V=O bond. The results suggest that an axial donor (charged or not) can lower |Az|, in contrast to what was previously believed on the basis of the "additivity rule", and this explains the anomalous behaviour of the V~(IV)O complexes formed by N-{2-[(2-pyridylmethylene)amino]phenyl}pyridine-2-carboxamide (Hcapca) and several amidrazone derivatives. The decrease in |A_z| for the axial binding of a solvent molecule is mainly a result of the reduction of |Aiso| and this was also observed when the solid [VO(6methylpicolinato)2] was dissolved in DMSO or DMF. The variations in the structural (V=O, V-O and V-N distances, O-V-O and N-V-N angles, and the trigonality index r) and spectroscopic (|A_z|, |A_(iso)| and V(V=O)) properties as a function of the axial V-OH_2 distance (R) are also presented. Finally, the electronic structures of the pentaand hexacoordinated complexes are discussed.
机译：VIVO方形金字塔和反八面体形式与轴向水分子之间先前在水溶液中未报告的平衡，具有多个（N，O）和（O，O）供体组（6-甲基吡啶啉（6mepicH）和6）的双齿配体-甲基-2,3-吡啶二羧酸（6-me-2,3-pdcH_2）酸，吡啶2-2-基甲醇（Hdpmo）和1,2二甲基-3-羟基-4（1H）-吡啶酮（Hdhp））通过EPR光谱和DFT方法的组合应用得到了证明。 EPR谱表明，随着离子强度的增加，平衡朝着五配位物质的方向移动，对于含6-甲基-2,3-吡啶二甲酸和吡啶二-2-基甲醇的体系，K≈4.0和7.0被测量。使用高斯03和ORCA软件执行的DFT计算可预测沿z轴（A_z）的51V各向异性超精细偶合常数，可用于证明存在轴向键合的配体反式转换为V = O键。结果表明，轴向供体（带电或不带电）可以降低| Az |，这与以前基于“加性规则”的观点相反，这解释了V〜（IV）O配合物的异常行为。由N- {2-[（2-吡啶基亚甲基）氨基]苯基}吡啶-2-羧酰胺（Hcapca）和几种胺衍生物形成。 | A_z |的减少溶剂分子的轴向键合的主要原因是| Aiso |减少。当将固体[VO（6-methylpicolinatoato）2]溶于DMSO或DMF时，也观察到了这一点。结构（V = O，VO和VN距离，OVO和NVN角以及三角指数r）和光谱特性（| A_z |，| A_（iso）|和V（V = O））的变化如下：还介绍了轴向V-OH_2距离（R）的函数。最后，讨论了五和六配位配合物的电子结构。

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