Spin-state equilibria in non-aqueous solution and quantum-mechanical investigations of iron(II) and nickel(II) complexes with 4-substituted 2,6-bis(benzimidazol-2-yl)pyridines
Spin-state equilibria in non-aqueous solution and quantum-mechanical investigations of iron(II) and nickel(II) complexes with 4-substituted 2,6-bis(benzimidazol-2-yl)pyridines
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非水溶液中的自旋态平衡以及铁(II)和镍(II)与4-取代2,6-双(苯并咪唑-2-基)吡啶配合物的量子力学研究
DOI：
10.1039/dt9940001523
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发表时间：
1994
期刊：
影响因子：
--
通讯作者：
F. Renz
中科院分区：
文献类型：
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作者：
W. Linert;M. Konečný;F. Renz
合成了一系列含三齿配体的阳离子配合物：L=4X-取代2，6-二(苯并咪唑-2-基)吡啶，[ML2][ClO4]2(M=Fe或Ni；X=H，OH或Cl)，并用元素分析、傅立叶变换红外光谱、核磁共振氢谱和紫外可见光谱对其结构进行了表征。通过邻苯二胺与4-取代吡啶-2，6-二元酸的缩合反应合成了4-取代吡啶-2，6-二甲酸。对镍配合物的配位场参数进行了估算。在甲醇、硝基甲烷和20%(v/v)二甲基甲酰胺的甲醇溶液中，[FeL~(2+)]~(2+)物种表现出热诱导自旋交叉行为(1A1→5T_2g)。这一行为因两个复杂的离解平衡而变得复杂，并对其平衡常数进行了估算。当M=Fe和X=H时，在甲醇溶液中(213-328K，µexptl=1.31-3.45µB)，配体取代反应在溶液中的自旋状态(µexptl=2.50，X=H；4.19，OH；和4.49µB，在295K时，在MeOH中)和金属-配体电荷转移带(500-557 nm)中的变化。当M=Fe和X=OH时，磁矩的微小变化(在220-332K时，µexptl=3.77-4.73uB)可能表明5Eg亚能级的布居温度可变或氢键的变化。计算结果与准相对论量子力学计算结果进行了比较，并对取代基为X=CHO、NH_2、CN、Me、NO_2、OH、CONH_2、CoCl、SH、F、Cl、Br或I的新配体L的自旋交叉行为进行了估算。[FeL_2]~(2+)的高自旋形式和低自旋形式与Δδ(苯中取代基X的~1H核磁共振参数增量)的计算生成热的差异表明在X=H附近有一个转折点，并在这个区域观察到了自旋交叉行为。在这个区域之外，几乎没有这样的行为，因此可以从Δδ值来预测其他取代基X的自旋交叉行为。
Cationic complexes with a series of tridentate ligands, L = 4X-substituted 2,6-bis(benzimidazol-2-yl)pyridines, [ML2][ClO4]2(M = Fe or Ni; X = H, OH or Cl), were isolated and characterized, together with the free pyridines, by elemental analysis, Fourier-transform IR, 1H NMR and UV/VIS spectroscopy. The syntheses were performed via condensation of o-phenylenediamine with 4-substituted pyridine-2,6-dicarboxylic acids. Ligand-field parameters were estimated for the nickel complexes. The [FeL2]2+ species show thermally induced spin-crossover behaviour (1A1→5T2g) which has been investigated in methanol, nitromethane and 20%(v/v) dimethylformamide in MeOH. The behaviour is complicated by two complex dissociation equilibria, for which equilibrium constants have been evaluated. Ligand substitution is reflected in a change of the spin state in solution (µexptl= 2.50, X = H; 4.19, OH; and 4.49 µB, Cl at 295 K, in MeOH) and in the metal-to-ligand charge-transfer band (500–557 nm); when M = Fe and X = H there is a pronounced spin-crossover equilibrium in methanolic solution (µexptl= 1.31–3.45 µB for 213–328 K). A small variation of the magnetic moments when M = Fe and X = OH (µexptl= 3.77–4.73 µB at 220–332 K) might indicate a temperature-variable population of the 5Eg sublevel or variation in hydrogen bonding. The results are compared with quasi-relativistic quantum-mechanical calculations, and the spin-crossover behaviour of the new ligands, L, with substituents X = CHO, NH2, CN, Me, NO2, OH, CONH2, COCl, SH, F, Cl, Br or I has been estimated. The differences in the calculated heats of formation between the high-and low-spin forms of [FeL2]2+ when plotted against Δδ(=1H NMR para increment for substituents X in benzene) show a turning point in the region around X = H and in this region spin-crossover behaviour is observed. Outside this region there is very little or no such behaviour and it is therefore possible to predict the spin-crossover behaviour for other substituents X from the Δδ value.