Preparation and structure of silver complexes with 4-nitroimidazole

Abstract

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 13C 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) Å, β = 111.38(7)°, Z = 8, R = 0.021, 3443 observed reflections; [Ag(NO2ImH)2]BF4; monoclinic, P21/c, a = 9.543(4), b = 6.478(2), c = 20.869(9) Å, β = 90.84(3)°, 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 1H and 13C NMR spectra show that the cationic complexes dissociate in DMSO. The infrared and CP-MAS 13C NMR spectra are discussed in connection with the coordination patterns observed. Keywords: silver, imidazole, crystal structure, infrared spectroscopy, nuclear magnetic resonance.