TRANSFORMATION OF POLYMERIC SILVER(I) IMIDAZOLATE TO MONOMERIC IMIDAZOLATOTRIS(TRIPHENYLPHOSPHINE) SILVER(I) COMPLEX - SYNTHESIS OF [AG(IMD)(PPH3)(3)] (HIMD = IMIDAZOLE) AND ITS CHARACTERIZATION IN THE SOLID-STATE AND IN SOLUTION

Polymeric silver(I) imidazolate [Ag(imd)](n) (1; Himd = imidazole, C3H 4N2) showing a wide spectrum of excellent antimicrobial activities aga inst bacteria, yeast and mold, which has been obtained as non-crystall ine, colorless powder, was successfully converted to molecular, crysta lline complex [Ag(imd)(PPh3)(3)] 2 by a reaction of 1 with three equiv alents of PPh3 in CH2Cl2. This novel complex 2 was not obtained from r eactions in solutions of the precursors [AgCl(PPh3)(3)] and/or [AgCl(P Ph3)(2)](2) with Himd in the presence of NaOH or with sodium salt of i md(-). On the contrary, the corresponding gold(I) complex [Au(imd)(PPh 3)] 3 was formed by a reaction of the precursor [AuCl(PPh3)] and Himd in the presence of NaOH. From a synthetic viewpoint, these facts show the ordering of ligand replacement in these complexes to be Ag-P much greater than Ag-Cl > Ag-N, while Au-P much greater than Au-N > Au-Cl. This ordering also exhibits the different reactivity of silver(I) and gold(I) complexes with biological ligands such as proteins, enzymes, n ucleic acids and amino acids. The complex 2 was fully characterized by complete elemental analyses, TG/DTA, FT-IR, solution molecular weight measurement and various solution NMR (H-1, C-13, P-31 and Ag-109) spe ctroscopies. The complex 2 in solution was present in a rapid equilibr ium with the dissociated species of two PPh3 ligands, i.e., [Ag(imd)(P Ph3)]. The P-31 NMR measurements at low temperature showed that: (i) a ll PPh3 ligands in 2 in CHCl3 solution migrated at room temperature be tween the two isotopes Ag-109 and Ag-107, in addition to the dissociat ion of two PPh3 ligands, and (ii) there were present the 4-coordinate tetrahedral complex 2 and the dissociated complex [Ag(imd)(PPh3)] in s olution. (C) 1998 Elsevier Science Inc. All rights reserved.