Square-Planar N₂S₂Ni^II Complexes with an Extended π-Conjugated System

The reaction of a mixture of 2-(1-naphthyl)benzothiazoline (HL1) and 2,6-diphenylbenzo[1,2-d:4,5-d‘]bisthiazoline (H3L2) with nickel(II) acetate tetrahydrate yielded three kinds of square-planar nickel(II) complexes: one nickel(II) complex with innocent ligands ([Ni(L1)2] (1c)) and two nickel(II) complexes with non-innocent ligands ([Ni(L1−L1)] (1a) and [Ni(L1−L2)] (1b)). The complex 1c has two bidentate-N,S ligands, which are formed via ring opening of HL1. On the other hand, the two complexes 1a and 1b contain a tetradentate-N2S2 ligand, which is created via ring opening of HL1 and H3L2, followed by bond formation between imino carbon atoms. Complexes 1a and 1b show very intense absorptions in the near-infrared (NIR) region, characteristic of square-planar complexes with non-innocent ligands. The third nickel(II) complex having a non-innocent tetradentate-N2S2 ligand ([Ni(L2−L2)] (2)) was prepared from H3L2 and nickel(II) acetate tetrahydrate. The electronic spectrum of 2 exhibits a very intense absorption at 981 nm (ε = 3.6 × 104 M-1 cm-1), which is significantly red-shifted compared with those of 1a (837 nm and 4.4 × 104 M-1 cm-1) and 1b (885 nm and 4.5 × 104 M-1 cm-1), indicating the presence of an extended π delocalization. The reaction of 2,6-bis(3,5-dichlorophenyl)benzo[1,2-d:4,5-d‘]bisthiazoline (H3L3) with nickel(II) acetate tetrahydrate also led to the formation of a nickel(II) complex with a non-innocent ligand ([Ni(L3−L3)] (3)). While complex 3 is analogous to 2, its electrical conductivity is much higher than that of 2. The molecular structures of 1b, 1c, 2, and 3 were determined by X-ray crystallography.将2-(1-萘基)苯并噻唑啉（HL1）与2,6-二苯基苯并[1,2-d:4,5-d']双噻唑啉（H3L2）的混合物与四水合乙酸镍(II)反应，得到三种平面正方形镍(II)配合物：一种含无辜配体（innocent ligand）的镍(II)配合物([Ni(L1)2] (1c))，以及两种含非无辜配体（non-innocent ligand）的镍(II)配合物([Ni(L1−L1)] (1a)和[Ni(L1−L2)] (1b))。配合物1c含有两个双齿N,S配体（bidentate-N,S ligand），该配体通过HL1的开环反应生成。与之相对，配合物1a和1b则含有一个四齿N2S2配体（tetradentate-N2S2 ligand），该配体由HL1与H3L2开环后，通过亚胺碳原子之间成键形成。配合物1a与1b在近红外（near-infrared, NIR）区域展现出极强吸收峰，这是含非无辜配体的平面正方形配合物的特征。第三种含非无辜配体四齿N2S2配体的镍(II)配合物([Ni(L2−L2)] (2))由H3L2与四水合乙酸镍(II)制备得到。配合物2的电子光谱在981 nm处呈现极强吸收（摩尔消光系数ε = 3.6 × 10^4 M-1 cm-1），相较于1a（837 nm，ε=4.4 × 10^4 M-1 cm-1）与1b（885 nm，ε=4.5 × 10^4 M-1 cm-1）发生了显著红移，表明体系中存在扩展π离域现象。2,6-双(3,5-二氯苯基)苯并[1,2-d:4,5-d']双噻唑啉（H3L3）与四水合乙酸镍(II)的反应，同样得到了一种含非无辜配体的镍(II)配合物([Ni(L3−L3)] (3))。尽管配合物3与2结构类似，但其电导率远高于2。配合物1b、1c、2与3的分子结构通过X射线晶体衍射（X-ray crystallography）得以确定。