Rare Silver-Histidine Cluster Complex and Its Single-Crystal-to-Single-Crystal Phase-Transition Behavior.

Silver complexes with proteinogenic amino acid ligands are of interest for biomedical and antimicrobial applications. In this work, we obtained {[Ag 7 (l-his) 4 ](NO 3 ) 3 ·3H 2 O} 0.2 {[Ag 8 (l-his) 4 (H 2 O) 2 ](NO 3 ) 4 ·3H 2 O} 0.8 ( 1 ) and {[Ag 7 (d-his) 4 ](NO 3 ) 3 ·3H 2 O} 0.2 {[Ag 8 (d-his) 4 (H 2 O) 2 ](NO 3 ) 4 ·3H 2 O} 0.8 ( 2 ), which represent the first example of any Ag-exclusive complex featuring a cluster-type core motif and with only proteinogenic amino acid ligands. Upon immersion into acetonitrile, an interesting single-crystal-to-single-crystal transformation occurred to produce a new cluster complex of the formula [Ag 8 (l-his) 4 (NO 3 )(H 2 O)](NO 3 ) 3 ( 3 ). Using a racemic mixture of histidine, the reaction under otherwise identical conditions led to the production of the second example of a three-dimensional (3D) network structured Ag-exclusive complex with only a proteinogenic amino acid ligand. Compared with other Ag-histidine complexes in the literature, the significance of reaction conditions, particularly the Ag/histidine ratio and pH of the reaction mixture, is revealed. Temperature-dependent emission of 1 and 2 at 440 nm characteristic of silver-philophilic interactions was also observed.