A Dynamic Combinatorial Library of Cyclic AuI2NiII Complexes with Cysteine/Penicillamine Showing Solvent-Controlled Crystallization.

A dynamic combinatorial library (DCL) is a set of molecular species existing in equilibrium in solution that can undergo self-assembly via reversible chemical bonds. Here, we report a unique DCL system that shows the independent crystallization of products from solvents with slightly different polarities. The reaction of a 1:1 mixture of [Au2(dppm)(dl-cys)2]2- and [Au2(dppm)(dl-pen)2]2- with Ni2+ in solution gave a DCL containing 10 cyclic AuI2NiII molecules of [Au2Ni(dppm)(dl-cys/dl-pen)2]. Upon crystallization, three kinds of enantiomeric pairs, homoleptic-heterochiral C/A-[Au2Ni(dppm)(d-cys)(l-cys)], homoleptic-homochiral [Au2Ni(dppm)(d-pen)2]/[Au2Ni(dppm)(l-pen)2], and heteroleptic-homochiral [Au2Ni(dppm)(d-cys)(d-pen)]/[Au2Ni(dppm)(l-cys)(l-pen)], were produced from the reaction solutions of MeOH, MeOH/H2O, and EtOH/H2O, respectively. The independent crystallization was explained by a combination of the different hydrogen-bonding interactions of the AuI2NiII molecules in the crystal and the different thermodynamic stabilities of the molecules in solution.