Controllable spontaneous resolution in ultrasmall Cu–Ag bimetallic cluster ion pairs from achiral components

Abstract

Bimetallic cluster ion pairs containing a quaternary phosphonium and an ultrasmall Cu₂Ag₃ anionic cluster protected by thiolates: (PPh₃R′′)[Cu₂Ag₃(SR′)₆] (R′SH = cyclohexylthiol (CySH), R′′ = Ph, 1; Me, 2; Et, 3; Pr, 4; R′SH = tert-butylthiol (^tBuSH) and R′′ = Ph, 5) were reported. Without any chiral source, 1 crystallizes as conglomerate crystals with homochiral packings and spontaneous resolution occurs, while four other clusters 2–5 crystallize as racemic crystals with heterochiral packings. These results indicate that racemic and homochiral crystallization in the cluster system could be controlled through fine-tuning internal achiral structural components.