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)](6)(6-) cluster has a Ag(6)S(6) 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)](6)(6-).4Na(+).2(HOCH(2))(3)CNH(3)](+).10H(2)O 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.