Synthesis and Structure of a Water-Soluble Hexanuclear Silver(I) Nicotinate Cluster Comprised of a “Cyclohexane-Chair”-Type of Framework, Showing Effective Antibacterial and Antifungal Activities: Use of “Sparse Matrix” Techniques for Growing Crystals of Water-Soluble Inorganic Complexes

The synthesis of a water-soluble anionic silver 2-mercaptonicotinate complex having effective antibacterial and antifungal properties is described. Its structure has been confirmed to be a hexameric cluster by an X-ray diffraction analysis of a mixed Na+/Tris+ salt (Tris+ = tris(hydroxymethyl)methylammonium cation). The [Ag(mna)]66- cluster has a Ag6S6 core and an overall shape of twisted hexagonal cylinder with six sulfur atoms and six silver atoms alternating on a puckered drum-like surface. Each Ag atom is trigonally coordinated by one N and two S ligands. The overall [Ag(mna)]66-·4Na+·2[(HOCH2)3CNH3]+·10H2O complex has a layered appearance in the crystal packing diagram, with a [Ag(mna)]6- cluster layer alternating with a solvent layer consisting of sodium atoms, Tris buffer cations, and water molecules. The structure is almost identical to that of a neutral [Ag(Hmna)]6 complex reported earlier. The neutral and charged complexes are both known to possess antimicrobial activities, and some biological properties of these and related compounds are briefly discussed in this paper.