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

Bimetallic cluster ion pairs containing a quaternary phosphonium and an ultrasmall CuAg anionic cluster protected by thiolates: (PPhR'')[CuAg(SR')] (R'SH = cyclohexylthiol (CySH), R'' = Ph, 1; Me, 2; Et, 3; Pr, 4; R'SH = -butylthiol (BuSH) 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.