Mononuclear nickel(II) and zinc(II) complexes with deprotonated forms of the tripodal hexadentate ligand 1,3-bis(2-hydroxybenzylidene)-2-(2-hydroxybenzylideneaminomethyl)-2-methylpropane-1,3-diamine.

In the crystal structures of both title compounds, [1,3-bis(2-hydroxybenzylidene)-2-methyl-2-(2-oxidobenzylideneaminomethyl)propane-1,3-diamine]nickel(II) [2-(2-hydroxybenzylideneaminomethyl)-2-methyl-1,3-bis(2-oxidobenzylidene)propane-1,3-diamine]nickel(II) chloride methanol disolvate, Ni(C(26)H(25.5)N(3)O(3))Cl x 2 CH(4)O, and [1,3-bis(2-hydroxybenzylidene)-2-methyl-2-(2-oxidobenzylideneaminomethyl)propane-1,3-diamine]zinc(II) perchlorate [2-(2-hydroxybenzylideneaminomethyl)-2-methyl-1,3-bis(2-oxidobenzylidene)propane-1,3-diamine]zinc(II) methanol trisolvate, [Zn(C(26)H(25)N(3)O(3))]ClO(4) x [Zn(C(26)H(26)N(3)O(3))] x 3 CH(4)O, the 3d metal ion is in an approximately octahedral 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 molecule. 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(H(1.5)L)Cl x 2 CH(3)OH [H(3)L is 1,3-bis(2-hydroxybenzylidene)-2-(2-hydroxybenzylideneaminomethyl)-2-methylpropane-1,3-diamine]. In the analogous Zn(II) compound, the asymmetric unit consists of two crystallographically independent mononuclear units, one perchlorate anion and three methanol solvent molecules. The mode of hydrogen bonding connecting the two mononuclear units is slightly different, and the formula can be written as [Zn(H(2)L)]ClO(4) x [Zn(HL)] x 3 CH(3)OH. In both compounds, each mononuclear unit is chiral with either a Delta or a Lambda configuration because of the screw coordination arrangement of the achiral tripodal ligand around the 3d metal ion. In the dimeric structure, molecules with Delta-Delta and Lambda-Lambda 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.