Correlation among crystal shape, absolute configuration, and circular dichroism spectrum of enantiomorphs of tris[2-(((2-phenylimidazol-4-yl)methylidene)amino)ethyl]-aminemetal(II) nitrate-methanol (1/1)

A series of metal(III) complexes of a tripod-type ligand with the chemical formulas [M(H3L)](NO3)(2). MeOH (M = Mn (1), Fe (2), Co (3), Ni (4), Zn (6)) and [Cu(H3L)](NO3)(2). CH3CN .H2O (5) were synthesized and characterized (H3L = tris [2-(((2-phenylimidazol-4-yl)methylidene)amino)ethyl]amine). The crystal structures were determined, in which those of 1-4 and 6 are isomorphous and conglomerates, because they crystallize into the acentric space group P2(1)2(1)2(1). Each metal(II) ion of 1-4 and 6 assumes an octahedral coordination environment with the N-6 donor atoms of the tripod ligand and becomes either a C (clockwise) or an A (anticlockwise) enantiomorph because of the screw arrangement of the tripod-type ligand around the metal(II) ion. The crystals were divided into two groups, where their crystal shapes are mirror images and their CD spectra show enantiomeric patterns. The circular dichroism (CD) spectrum of the crystal used for the X-ray analysis was measured. The absolute configuration of the enantiomorph of the crystal used for the X-ray analysis was determined by the Flack parameter. The correlation among the crystal shape, the absolute configuration, and the CD spectral pattern was thus confirmed for 1-4 and 6. On the other hand, 5 assumes a square pyramidal coordination geometry with the Ns donor atoms, and hence, there are no optical isomers.