Spontaneous Resolution Induced by a Chiral Ni(II) Complex with an Achiral Tripodal Ligand

A chiral nickel(II) complex, [Ni(II)H₃L](ClO4)₂ (1), with an achiral ligand H₃L (=tris{2-(4-imidazolyl)methyliminoethyl}amine) was synthesized by in situ reaction between nickel(II) perchlorate hexahydrate and a condensation mixture of 4-imidazolecarboxaldehyde and tris(2-aminoethyl)amine. Single crystal X-ray analysis revealed that the H₃L ligand hexadentately binds to Ni(II) ion through three Schiff-base imine N atoms and three imidazole N atoms with distorted octahedral geometry. Both single-crystal X-ray diffraction and circular dichroism investigations found that the crystal of complex 1 was an enantiopure conglomerate. The hydrogen-bond network of N_imidazoleH⋯O_ClO4⋯HN_imidazole induced spontaneous resolution to form the conglomerate. The capped tripod-shaped [Ni(II)H₃L]²⁺ complex ions are hydrogen-bonded in a tail-to-tail mode and array in an up-and-down manner repeatedly to honeycomb an extended two-dimensional homochiral network with trigonal voids.