Syntheses, crystal structures, and spectroscopic properties of mixed-ligand cobalt(III) complexes with optically active penicillaminates: Stereospecific interactions and spontaneous crystallizations depending on counter anions

Abstract

The optically active mixed-ligand complex, [Co(d-pen)(bpma)]+ {pen=penicillaminate; bpma=bis(2-pyridylmethyl)amine}, and its enantiomer, [Co(l-pen)(bpma)]+, were prepared by the reactions of CoCl2·6H2O, bpma, and d-pen2− (or l-pen2−) under aerobic condition. The racemates, [Co(d-pen)(bpma)]0.5[Co(l-pen)(bpma)]0.5X·nH2O (dlCl: X=Cl, n=0; dlNO3: X=NO3, n=0; dlClO4·H2O: X=ClO4, n=1) were also obtained by using dl-pen2− (1:1 mixture of d- and l-pen2−) instead of optically active d- or l-pen2− in the coexistences of the corresponding counter anions. In the presence of PF6− as a counter anion, contrary to the cases of Cl−, NO3−, and ClO4−, a similar reaction results in not racemate but mixture of chiral crystals accompanied by spontaneous crystallizations as chiral single crystals of [Co(d-pen)(bpma)]PF6·H2O (dPF6·H2O) or [Co(l-pen)(bpma)]PF6·H2O (lPF6·H2O). The crystal structures of racemates, dlCl, dlNO3, and dlClO4·H2O, were determined by X-ray crystallography, and compared with those of optically active dPF6·H2O and lPF6·H2O. In the racemic crystals of dlCl, dlNO3, and dlClO4·H2O, characteristic networks are built up by stereospecific π–π stacking and/or hydrogen bonding interactions between two enantiomeric complex cations attendant on auxiliary hydrogen bonds with counter anions. Contrary to dlCl, dlNO3, and dlClO4·H2O, the crystal structures of dPF6·H2O and lPF6·H2O are stabilized by the direct hydrogen-bonding networks between homochiral complex cations.