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 supramolec

•The study prepares ten cobalt complexes of one triprotic, H3L, hexadentate ligand.•Structures of Co(III) and Co(II) complexes of H L are compared.•The structure of the Co(III) complexes of each of the four protonated states of the ligand are determined.•A number of supramolecular topologies, dimeric, 1D chain, tetrahedral cluster and 2D sheet, are described.•Two examples of chiral recognition are observed.

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.

Graphical abstractCobalt(III) complexes of a triprotic ligand, H3L, have been isolated and structurally characterized for each of the following protonation states of the ligand, H3L, H2L−, H1.5L1.5−, H1.45L1.55−, HL2− and L3−. A variety of topologies, dimeric, 1D zig-zag, tetrahedral and 2D sheets are observed in the structures.Figure optionsDownload full-size imageDownload as PowerPoint slide