Spectrophotometric Study of the Equilibria between Nickel(II) Schiff-Base Complexes and Alkaline Earth or Nickel(II) Cations in Acetonitrile Solution^†

Adduct formation between M(ClO4)2 and nickel(II) complexes of tetradentate Schiff-base ligands ([NiL]) have been investigated in acetonitrile by means of UV−vis spectrophotometric analysis (M2+= Mg2+, Ca2+, Sr2+, Ba2+, Ni2+; [NiL] = [Ni(salen)] = [N,N‘-ethylenebis(salicylideneiminato)]nickel(II), [Ni(salphen)] = [N,N‘-o-phenylenebis(salicylideneiminato)]nickel(II), [Ni(salpren)] = [N,N‘-propylenebis(salicylideneiminato)]nickel(II)). [NiL] complexes act as bidentate oxygen-donor ligands forming adducts of the type [(NiL)M]2+ and [(NiL)2M]2+ whose general order of increasing stability was correlated to the dimensions of the M2+ cations. Complexes of general composition 2[Ni(salen)]·M(ClO4)2 were isolated as powders in the solid state (M = Sr, Ca, Mg). X-ray structures of the crystalline complexes [{Ni(salen)}2Ba(ClO4)2(thf)] (1) (thf = tetrahydrofuran) and [{Ni(salen)}2Ni(H2O)2](ClO4)2 (2) are reported. 1 crystallizes in the space group P21/c (a = 10.995 Å; b = 20.830 Å; c = 19.567 Å, β = 116.94°) and 2 in C2/c (a = 10.3020 Å; b = 21.818 Å; c = 17.796 Å; β = 118.98°). Two [Ni(salen)] units act as oxygen bidentate ligands in both the compounds. The barium is coordinated to eight oxygen atoms in a distorted square antiprismatic geometry. An 8-fold coordination is completed by a molecule of tetrahydrofuran and two perchlorate anions acting as bi- and monodentate O-ligands, respectively. In 2, the nickel atom, coordinated to two [Ni(salen)] complexes, has a distorted octahedral geometry and completes its coordination by linking two molecules of water.本研究以乙腈为溶剂，采用紫外-可见（UV−vis）分光光度法，探究了高氯酸金属盐M(ClO₄)₂与四齿席夫碱配体合镍(II)配合物([NiL])之间的加合物形成行为，其中M²⁺包括Mg²⁺、Ca²⁺、Sr²⁺、Ba²⁺、Ni²⁺；[NiL]分别为[N,N'-乙撑双(水杨亚胺基)]合镍(II)([Ni(salen)])、[N,N'-邻亚苯基双(水杨亚胺基)]合镍(II)([Ni(salphen)])以及[N,N'-亚丙基双(水杨亚胺基)]合镍(II)([Ni(salpren)])。 [NiL]配合物可作为双齿氧供体配体，形成[(NiL)M]²⁺与[(NiL)₂M]²⁺型加合物，其稳定性递增的普遍规律与M²⁺阳离子的离子尺寸相关。 固态下，组成为2[Ni(salen)]·M(ClO₄)₂的配合物（M=Sr、Ca、Mg）以粉末形式被分离得到。本文报道了晶体配合物[{Ni(salen)}₂Ba(ClO₄)₂(thf)]（1，thf=四氢呋喃）与[{Ni(salen)}₂Ni(H₂O)₂](ClO₄)₂（2）的X射线晶体结构。 配合物1的晶体空间群为P2₁/c（晶胞参数：a=10.995 Å；b=20.830 Å；c=19.567 Å，β=116.94°），配合物2的晶体空间群为C2/c（a=10.3020 Å；b=21.818 Å；c=17.796 Å；β=118.98°）。两种化合物中，两个[Ni(salen)]单元均作为双齿氧配体参与配位。 钡原子以变形正方形反棱柱几何构型与八个氧原子配位，其中一个四氢呋喃分子与两个高氯酸根阴离子分别作为双齿、单齿氧配体，共同完成了该八配位环境。 在配合物2中，与两个[Ni(salen)]配合物配位的镍原子采取变形八面体几何构型，并通过结合两个水分子完成其配位环境。