Mononuclear nickel(II) and zinc(II) complexes with deprotonated forms of the tripodal hexadentate ligand 1,3-bis-(2-hydroxybenzylidene)-2-(2- hydroxybenzylideneaminometh-yl)-2-methyl-propane-1,3-diamine

In the crystal structures of both title compounds, [1,3-bis-(2-hydroxy- benzyl-idene)-2-methyl-2-(2-oxido-benzyl-idene-amino-methyl)-propane-1, 3-diamine]-nickel(II) [2-(2-hydroxy-benzyl-idene-amino-methyl)-2-methyl-1,3-bis- (2-oxido-benzyl-idene)-propane-1,3-diamine]-nickel(II) chloride methanol disolvate, [Ni(C26H25.5N3O3)]2Cl·2CH4O, and [1,3-bis-(2-hydroxy-benzyl- idene)-2-methyl-2-(2-oxido-benzyl-idene-amino-methyl)-propane-1,3-diamine] -zinc(II) perchlorate [2-(2-hydroxy-benzyl-ideneamino-methyl)-2-methyl-1,3-bis- (2-oxido-benzyl-idene)-propane-1,3-diamine]-zinc(II) methanol tri-solvate, [Zn(C26H25N3O3)]ClO4·[Zn(C26H26N3O3)]·3CH4O, the 3d metal ion is in an approximately octa-hedral environment composed of three facially coordinated imine N atoms and three phenol O atoms. The two mononuclear units are linked by three phenol-phenolate O - H⋯O hydrogen bonds to form a dimeric structure. In the Ni compound, the asymmetric unit consists of one mononuclear unit, one-half of a chloride anion and a methanol solvent mol-ecule. In the O - H⋯O hydrogen bonds, two H atoms are located near the centre of O⋯O and one H atom is disordered over two positions. The Ni ^II compound is thus formulated as [Ni(H1.5 L)]2Cl·2CH3OH [H3 L is 1,3-bis(2 - hy-droxybenzyl-idene)-2-(2-hydroxy-benzyl-idene-amino-methyl)-2- methyl-propane-1,3-diamine]. In the analogous Zn^II com-pound, the asymmetric unit consists of two crystallographically independent mononuclear units, one perchlorate anion and three methanol solvent mol-ecules. The mode of hydrogen bonding connecting the two mononuclear units is slightly different, and the formula can be written as [Zn(H2 L)]ClO4·[Zn(HL)]·3CH3OH. In both compounds, each mononuclear unit is chiral with either a or a configuration because of the screw coordination arrangement of the achiral tripodal ligand around the 3d metal ion. In the dimeric structure, mol-ecules with - and - pairs co-exist in the crystal structure to form a racemic crystal. A notable difference is observed between the M - O(phenol) and M - O(phenolate) bond lengths, the former being longer than the latter. In addition, as the ionic radius of the metal ion decreases, the M - O and M - N bond distances decrease.