Synthesis, structure and supramolecular features of cobalt(III) and cobalt(II) complexes, [CoHxL](ClO4)y (x = y = 3, 2, 1.50, 1.45, 1 and 0 and x = 3, y = 2) of a triprotic imidazole containing Schiff base ligand. Effect of protonation state on supramolecular structure

Abstract

Aerial reaction of cobalt(II) perchlorate with H3(1) {H3(1) is the tripodal ligand derived from the condensation of tris(2-aminoethyl)amine with three equivalents of 4-methyl-5-imidazolecarboxaldehyde} in acidic methanol results in isolation of both the orange [CoH3(1)](ClO4)2 (trace) and red [CoH3(1)](ClO4)3 (2 pseudopolymorphs). An analogous reaction in methanol gives [CoH2(1)](ClO4)2. Reaction of [CoH2(1)](ClO4)2 (generated in situ) with aqueous sodium hydroxide gives [CoH(1)](ClO4) (two pseudopolymorphs) and a trace amount of [CoH1.45(1)](ClO4)1.45. Reaction of [CoH3(1)](ClO4)3 with 1.5 equivalents of hydroxide gives [CoH1.5(1)](ClO4)1.5. Reaction of [CoH(1)](ClO4) with methanolic potassium hydroxide in acetonitrile gave [Co(1)] (two pseudopolymorphs). Complexes were characterized by EA and IR if available in sufficient amounts. All ten complexes were structurally characterized and their metrical parameters are consistent with a high spin cobalt(II) for [CoH3(1)](ClO4)2 and low spin cobalt(III) for all of the cobalt(III) complexes. [CoH3(1)](ClO4)2 and one polymorph of [CoH3(1)](ClO4)3 dimerize by hydrogen bonding through three perchlorate anions. [CoH2(1)](ClO4)2 and one of the pseudopolymorphs of [CoH(1)](ClO4) form intermolecular imidazole-H…imidazolate hydrogen bonds resulting in hetero and homochiral 1D zig-zag chains, respectively. [CoH1.5(1)](ClO4)1.5 forms a tetrahedral array of octahedral cobalt complexes held together by intermolecular imidazole-H…imidazolate hydrogen bonds. [CoH1.45(1)](ClO4)1.45 forms a hexameric structure with a large central channel containing solvent and perchlorate anions. [CoH(1)](ClO4) and both polymorphs of [Co(1)] form no intermolecular imidazole-H…imidazolate hydrogen bonds but do exhibit extensive hydrogen bond formation with water.