Partial and Gradual Hydrolysis of 2,2′-Biimidazoline upon Coordination to Metal Ions,yielding New Chelating Ligands - Synthesis,Characterization and X-ray Structure of two Examples with Cobalt(III) and Copper(II)

The synthesis, a full structural characterization of two transition-metal compounds obtained by in-situ hydrolysis and partly hydrolysis of the ligand 2, 2′-biimidazoline (abbreviated as biz) is reported. When the biz ligand is completely hydrolysed the compound, N, N′-bis(2-aminoethyl)oxamide (abbreviated as H₂oxen) is obtained, while the partial hydrolysis results in the ligand N-(2-aminoethyl)imidazoline-2-carboxamide (abbreviated as Hoxim). The Co^III ion in the mononuclear Co^III compound, Co(biz)(oxim)(NCS)](ClO₄)(C₂H₅OH)_1/6(H₂O)_1/6 ( 1 ), has an octahedral coordination consisting of 6 nitrogen atoms with a distance varying from 1.889(6) to 1.950(5) Å. Two nitrogen atoms originating from a biz molecule, 3 nitrogen atoms are from the oxim ligand and one nitrogen is from the thiocyanate anion. Each Cu^II ion in the dinuclear Cu^II compound, Cu₂(H₂oxen)(oxim)₂(C₂H₅OH)₂] (ClO₄)₂ ( 2 ), has a slightly distorted square-pyramidal structure of which the basal plain consists of3 nitrogen atoms of the oxim ligand and one nitrogen atom of the H₂oxen ligand, which is used as a “spacer” connecting the second Cu^II atom, with Cu-N distances which vary from 1.944(2) to 2.037(2) Å. The apical position is formed by the oxygen atom of a semi-coordinating ethanol molecule with a Cu-O distance of 2.446(2) Å. The compounds are characterized by elemental analysis, ligand field, infrared and, for the Cu^II ion, also by EPR spectroscopy.