PREPARATION AND STRUCTURE OF SILVER COMPLEXES WITH 4-NITROIMIDAZOLE

The reaction of 4-nitroimidazole (NO2ImH) with AgNO3 and AgBF4 in neutral or weakly acidic aqueous media yielded the insoluble [Ag(NO2Im)] compound, whose infrared and C-13 NMR spectra are consistent with a polymeric chain of deprotonated ligands bridging silver atoms via the endocyclic nitrogen atoms. In strongly acidic solution, [Ag(NO2ImH)2]X salts (X = NO3, BF4) were obtained and their crystal structures were determined. [Ag(NO2ImH)2]NO3: monoclinic, P2/n, a = 14.214(1), b = 12.571(2), c = 14.222(1) angstrom, beta = 111.38(7)-degrees, Z = 8, R = 0.021, 3443 observed reflections; [Ag(NO2ImH)2]BF4: monoclinic, P2(1)/c, a = 9.543(4), b = 6.47892), c = 20.869(9) angstrom, beta = 90.84(3)-degrees, Z = 4, R = 0.027, 1646 observed reflections. In both compounds, the two-coordinated metal forms roughly collinear bonds to two neutral ligands via the endocyclic nitrogen atom adjacent to the nitro group. One oxygen of each nitro group makes a secondary Ag-O bond near the equatorial plane. The anions are hydrogen bonded to the ligand N-H groups and do not directly interact with the metal. Solution H-1 and C-13 NMR spectra show that the cationic complexes dissociate in DMSO. The infrared and CP-MAS C-13 NMR spectra are discussed in connection with the coordination patterns observed.