Nickel(II) N2X2 Schiff-base complexes incorporating pyrazole (X = NH, O or S): syntheses and characterization †
作者:Bibhutosh Adhikhari、Oren P. Anderson、Agnete la Cour、Rita Hazell、Susie M. Miller、Carl E. Olsen、Hans Toftlund
DOI:10.1039/a703258g
日期:——
A series of four-co-ordinate nickel(II) N2X2 complexes (X = NH, O or S) with tetradentate Schiff-base ligands incorporating pyrazole has been prepared in order to compare the influence on the nickel(II) centre of the donor atoms in N2(NH)2 and N2S2 complexes versus N2O2 complexes. In each case, two identical parts of the ligand are linked by a two- or three-carbon aliphatic chain (n = 2 or 3). Crystal structures have been determined for a n = 3 N2(NH)2 complex, for two n = 3 N2S2 complexes and for a n = 2 N2O2 complex. All of the complexes have been investigated in solution by spectroscopic methods (UV/VIS/NIR, 1H NMR). The n = 2 and 3 N2(NH)2 complexes and the n = 2 N2S2 complexes are fully diamagnetic. An extension of the chain linking the two halves of the ligand from two to three carbon atoms induces a spin-equilibrium process (S = 0 â S = 1) for the resulting N2S2 complex (ÎG = 19â26 kJ molâ1 at 50 °C). Ligand-field parameters have been derived from the electronic spectra and the electrochemical properties of the N2S2 complexes have been investigated by cyclic voltammetry. From these results it is clear that low-spin character is emphasized in N2(NH)2 and N2S2 complexes of nickel(II) when compared with the corresponding N2O2 complexes.
制备了一系列含有吡唑的四齿席夫碱配体的四配位镍(II)N2X2配合物(X=NH、O或S),以比较对镍(II)中心的影响。 N2(NH)2 和 N2S2 配合物与 N2O2 配合物中的供体原子。在每种情况下,配体的两个相同部分通过二碳或三碳脂肪链连接(n=2或3)。已确定 n=3 N2(NH)2 络合物、两个 n=3 N2S2 络合物和 n=2 N2O2 络合物的晶体结构。所有配合物均已在溶液中通过光谱方法(UV/VIS/NIR、1H NMR)进行了研究。 n=2 和 3 N2(NH)2 配合物以及 n=2 N2S2 配合物是完全抗磁性的。连接配体两半的链从 2 到 3 个碳原子延伸,引发自旋平衡过程 (S = 0 – S = 1),生成 N2S2 络合物 (ΔG = 19 – 26 kJ mol-1 (50°C)。配体场参数由电子光谱得出,并且 N2S2 配合物的电化学性质已通过循环伏安法进行了研究。从这些结果可以清楚地看出,与相应的 N2O2 配合物相比,镍 (II) 的 N2(NH)2 和 N2S2 配合物强调了低自旋特性。