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

[Image: see text] 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.