PREPARATION AND CHARACTERIZATION OF NEW TRANSITION-METAL COMPLEXES OF NITROIMIDAZOLES - X-RAY CRYSTAL-STRUCTURES OF 2 COPPER-COMPLEXES - BIS-[MU-CHLORO)CHLORO-BIS-(1-(2-HYDROXYETHYL)-2-METHYL-5-NITROIMIDAZOLE)COPPER(II)] AND DICHLORO-BIS-(2-METHYL-5-NITROIMIDAZOLE)COPPER(II) - 1ST OBSERVATION OF NITRO-GROUP COORDINATION TO THE METAL-ION IN THESE HETEROCYCLES

2-Methyl-5-nitroimidazole [MNIH, (1)] forms the complexes Cu(MNIH)2X2 [X = Cl (1a), Br (1b), NO3 (1c), OH (1d)] and Co(MNIH)2X2 [X = Cl (1e), OAc (1f)]. X-ray crystal structure of 1a shows a distorted octahedral geometry for the copper(II) ion bonded to two chlorine atoms and two nitroimidazole molecules through N(1) and with a trans diaxial coordination to one of the oxygen atoms of the nitro groups. This is the first example of nitroimidazole derivatives in which the nitro group occupies a coordination site. Spectroscopic evidence suggests that for compounds 1b-1f the preferred coordination site for the metal ion is N(1), with interaction of the nitro group adjacent to it, giving extra stability to the complexes. The copper complexes, 1b and 1c, contain six coordinated metal atoms, while 1e is tetrahedral and 1f is a carboxylate-bridged dimer. The other ligand, 1-(2-hydroxyethyl)-2-methyl-5-nitroimidazole[metronidazole, HEMNI (2)] forms the complexes Cu(HEMNI)2X2 [X = Cl (2a, 2b), Br (2c), OAc (2d)] and Co(HEMNI)2Cl2 (2e). An X-ray crystal structure determination on Cu(HEMNI)2Cl2 (2a) shows a centrosymmetric chlorobridged dimer. The coordination geometry around each copper atom is trigonal bipyramidal with three equatorial chlorine atoms and two axial imidazole molecules. The rest of the metronidazole complexes obtained were shown to be a dimeric compound with bridging acetates, 2d, two monomeric octahedral (X = Cl, Br) copper compounds, 2b and 2c, and a tetrahedral cobalt compound, 2e.