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, C3H4N2) showing a wide spectrum of excellent antimicrobial activities against bacteria, yeast and mold, which has been obtained as non-crystalline, colorless powder, was successfully converted to molecular, crystalline complex [Ag(imd)(PPh3)(3)] 2 by a reaction of 1 with three equivalents of PPh3 in CH2Cl2. This novel complex 2 was not obtained from reactions in solutions of the precursors [AgCl(PPh3)(3)] and/or [AgCl(PPh3)(2)](2) with Himd in the presence of NaOH or with sodium salt of imd(-). On the contrary, the corresponding gold(I) complex [Au(imd)(PPh3)] 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, nucleic 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) spectroscopies. The complex 2 in solution was present in a rapid equilibrium with the dissociated species of two PPh3 ligands, i.e., [Ag(imd)(PPh3)]. The P-31 NMR measurements at low temperature showed that: (i) all PPh3 ligands in 2 in CHCl3 solution migrated at room temperature between the two isotopes Ag-109 and Ag-107, in addition to the dissociation of two PPh3 ligands, and (ii) there were present the 4-coordinate tetrahedral complex 2 and the dissociated complex [Ag(imd)(PPh3)] in solution. (C) 1998 Elsevier Science Inc. All rights reserved.