Department of Chemistry, R. K. Mission Residential College, Narendrapur, Kolkata 700 103, India.
Dalton Trans. 2013 Apr 7;42(13):4586-601. doi: 10.1039/c2dt32693k.
o-Imino-p-R'-benzosemiquinone anion radical (L(R')(IS)(˙-)) complexes of oxidovanadium(IV) of type [(L(1)(R-))(VO(2+))(L(R')(IS)(˙-))] (R = H, R' = H, 1; R = H, R' = -CMe(3), 2; R = -CMe(3), R' = H, 3 and R = -CMe(3), R' = -CMe(3), 4) incorporating the redox-innocent tridentate NNO-donor L(1)(R-) ligands (L(1)(R)H = 2,4-di-R-6-{(2-(pyridin-2-yl)hydrazono)methyl}phenol) were isolated and substantiated by elemental analyses, IR, mass, NMR and UV-vis spectra including the single crystal X-ray structure determinations. The V-O(phenolato) (cis to the V=O) lengths spanning 1.905(3)-1.9355(15) Å in 1-4 are consistent with the coordination to the VO state. The V-O(IS) (trans to the V=O) lengths, 2.1505(17)-2.1869(15) Å, in 1-4 are longer due to the trans influence of the V=O bond. The V-N(IS) lengths, 1.906(3)-1.924(2) Å, in 1-4 are comparatively shorter due to the higher affinity of the paramagnetic VO ion towards the L(R')(IS)(˙-) anion radicals. Density functional theory (DFT) calculations using B3LYP, B3PW91 and PBE1PBE functionals on 1 and 2 authenticated that the closed shell singlet (CSS) solutions (dianionic o-amido-p-R'-phenolates (L(R')(AP)(2-)) coordinated to VO(3+), Type I) of 1-4 are unstable with respect to the open shell singlet (OSS) perturbations. Broken symmetry, BS (1,1) M(s) = 0 (L(R')(IS)(˙-) coordinated to the VO(2+) ion, Type III) solutions of 1-4 are stable and reproduce the experimental bond parameters. Frozen glasses EPR spectra of 1-4 ions (e.g. g(||) = 1.948, g(⊥) = 1.978, A(||) = 184 (22 G), A(⊥) = 62(15 G) for 2) and unrestricted DFT calculations on 1, 2, 1 and 2 ions using doublet spin state elucidated that the reversible anodic waves at [0.15-0.31] V of 1-4 complexes are due to the oxidation of L(R')(IS)(˙-) generating [(L(1)(R-))(VO(2+))(L(R')(IQ))]+ complexes (L(R')(IQ) = o-imino-p-R'-benzoquinone) coordinated to the VO ion (Type V) while the irreversible cathodic waves at -[1.08-1.49] V are due to the formation of unstable (L(1)(R-))(VO(2+))(L(R')(AP)(2-)) complexes (Type II). The second anodic waves at [0.76-0.89] V are assigned to a VO-VO couple affording diamagnetic (L(1)(R-))(VO(3+))(L(R')(IQ)), 1-4 complexes (Type VI) which are identified by UV-vis spectra, DFT and time dependent (TD) DFT calculations. Spectro-electrochemical measurements and TD DFT calculations on 1 and 2 disclosed that lower energy electronic absorption bands of 1-4 are due to the LMCT and CSS-OSS perturbation which disappear in 1-4 ions. 1-4 absorb at 600-650 nm due to d-d transitions and MLCT which are absent in VO(3+) complexes, 1-4.
o-亚氨基-p-R'-苯醌阴离子自由基（L(R')(IS)(˙-)) 与氧化钒 (IV) 的配合物，属于 [(L(1)(R-))(VO(2+))(L(R')(IS)(˙-))] 类型（R = H，R' = H，1；R = H，R' = -CMe(3)，2；R = -CMe(3)，R' = H，3 和 R = -CMe(3)，R' = -CMe(3)，4），其中包含氧化还原惰性的三齿 NNO-供体 L(1)(R-)配体（L(1)(R)H = 2,4-二-R-6-{(2-(吡啶-2-基)腙基)甲基}苯酚），通过元素分析、红外、质谱、核磁共振和紫外可见光谱（包括单晶 X 射线结构测定）进行了分离和证实。V-O（苯酚酯）（与 V=O 顺式）的长度在 1-4 中跨越 1.905(3)-1.9355(15) Å，与 VO 状态的配位一致。V-O（IS）（与 V=O 反式）的长度，在 1-4 中为 2.1505(17)-2.1869(15) Å，由于 V=O 键的反式影响而较长。V-N（IS）的长度，在 1-4 中为 1.906(3)-1.924(2) Å，由于顺磁 VO 离子对 L(R')(IS)(˙-)阴离子自由基的更高亲和力而较短。使用 B3LYP、B3PW91 和 PBE1PBE 函数对 1 和 2 进行密度泛函理论（DFT）计算证实，封闭壳层单重态（CSS）溶液（二阴离子 o-酰胺-p-R'-苯酚酯（L(R')(AP)(2-)）与 VO(3+)配位，类型 I）的 1-4 相对于开放壳层单重态（OSS）的扰动是不稳定的。打破对称，BS(1,1)M(s)=0（L(R')(IS)(˙-)与 VO(2+)离子配位，类型 III）的 1-4 溶液是稳定的，并再现了实验键参数。1-4离子的冷冻玻璃 EPR 光谱（例如 g(||)=1.948，g(⊥)=1.978，A(||)=184(22 G)，A(⊥)=62(15 G)对于2）和使用双重态自旋态对1、2、1和2离子进行的无限制 DFT 计算阐明了 1-4 配合物在 [0.15-0.31] V 处的可逆阳极波归因于 L(R')(IS)(˙-)的氧化生成[(L(1)(R-))(VO(2+))(L(R')(IQ))]+配合物（L(R')(IQ)=o-亚氨基-p-R'-苯醌）与 VO 离子配位（类型 V），而不可逆阴极波在- [1.08-1.49] V 处归因于不稳定的(L(1)(R-))(VO(2+))(L(R')(AP)(2-))配合物（类型 II）的形成。第二个在 [0.76-0.89] V 处的阳极波归因于 VO-VO 对，生成顺磁(L(1)(R-))(VO(3+))(L(R')(IQ))、1-4配合物（类型 VI），这通过 UV-vis 光谱、DFT 和时间相关（TD）DFT 计算得到证实。对 1 和 2 的光谱电化学测量和 TD DFT 计算表明，1-4 的较低能量电子吸收带归因于 LMCT 和 CSS-OSS 扰动，这些在 1-4 离子中消失。1-4在 600-650nm 处吸收归因于 d-d 跃迁和 MLCT，它们在 VO(3+) 配合物1-4中不存在。
