Creation of Optically Pure Crystals from a Meso-Type Gold(I) Metalloligand with d- and l-Amino Acids: A Coordination Trick

Abstract

A unique example of a coordination system that creates optically pure crystals from a meso compound with d- and l-amino acids is reported. The 1:1 reaction of a newly prepared meso digold(I) complex, [Au₂ (dcpe)(d-Hpen)(l-Hpen)] ([H₂ 1]), with Co(OAc)₂ under aerobic conditions yielded a cationic Au^I₂ Co^III trinuclear complex, [Au₂ Co(dcpe)(d-pen)(l-pen)]⁺ [2]⁺ , in which [1]^2- acts as a hexadentate-N₂ ,O₂ ,S₂ metalloligand to a Co^III center. Similar reactions with M(OAc)₂ (M=Ni and Zn) produced analogous but neutral Au^I₂ M^II complexes, [Au₂ M(dcpe)(d-pen)(l-pen)] ([3_M ]). Complexes [2]⁺ and [3_M ] are chiral (C vs. A) at the octahedral Co^III and M^II centers due to the arrangement of the N₂ ,O₂ ,S₂ donor set. In addition, through spontaneous resolution, [3_M ] gave optically pure C-[3_M ] and A-[3_M ] crystals, showing the creation of homochirality from meso-[1]^2- and achiral M²⁺ through crystallization. Such a phenomenon was not observed for [2]⁺ , which gave a racemic compound containing both C-[2]⁺ and A-[2]⁺ .

Keywords: chiral resolution; crystal engineering; heterometallic complex; molecular recognition.