Intramolecular hydrogen bonding between 2-cyanoguanidine and 3-chloro-6-(pyrazol-1-yl)pyridazines in copper(II) complexes

Abstract

Treatment of copper(II) salts with 3-chloro-6-(pyrazol-1-yl)pyridazine (cppd)–2-cyanoguanidine (cnge) mixtures yielded [Cu(cppd)2(H2O)2][NO3]2, [Cu(cppd)(cnge)2(H2O)(FBF3)][BF4], Cu(cppd)2Cl2·2H2O and Cu(cppd)2Br2· 2H2O. The corresponding 3-chloro-6-(3,5-dimethylpyrazol-1-yl)pyridazine (cmppd) systems gave Cu(cmppd)(cnge)2(NO3)2·6H2O, [Cu(cmppd)2(cnge)][BF4]2, [Cu(cmppd)(cnge)Cl2]·H2O and Cu(cmppd)(cnge)Br2·H2O. Four of the complexes have been structurally characterised. Whereas the copper atoms in [Cu(cppd)2(H2O)2][NO3]2 and [Cu(cppd)(cnge)2(H2O)(FBF3)][BF4] have tetragonally elongated distorted octahedral geometry, those in [Cu(cmppd)2(cnge)][BF4]2 and [Cu(cmppd)(cnge)Cl2]·H2O adopt trigonal-bipyramidal geometries. The centrosymmetric [Cu(cppd)2(H2O)2]2+ cation comprises two equatorial bidentate chelating cppd ligands and two axial water molecules while [Cu(cppd)(cnge)2(H2O)(FBF3)]+ comprises one cppd and two monodentate cnge molecules as equatorial ligands and one water molecule and one BF4– anion as axial ligands. In the [Cu(cmppd)(cnge)Cl2] molecule the chlorine atoms occupy equatorial sites, the cnge an axial position and the cmppd ligand straddles equatorial and axial sites, while in the [Cu(cmppd)2(cnge)]2+ cation the cnge ligand is located equatorially and the two cmppd ligands straddle equatorial and axial sites. Preliminary structural data for Cu(cppd)2Br2·2H2O are consistent with a centrosymmetric tetragonally elongated octahedral copper atom similar to that in [Cu(cppd)2(H2O)2][NO3]2. Comparable IR and UV/VIS data were obtained for Cu(cmppd)(cnge)2(NO3)2·6H2O and [Cu(cppd)(cnge)2(H2O)(FBF3)][BF4] and for Cu(cmppd)(cnge)Br2·H2O and [Cu(cmppd)(cnge)Cl2]·H2O, suggesting similar molecular structures. Intramolecular N–H· · ·N hydrogen bonds occur between cnge amino groups and pyridazine non-ligating nitrogens in the mixed-ligand complexes [Cu(cppd)(cnge)2(H2O)(FBF3)][BF4] and [Cu(cmppd)(cnge)Cl2]·H2O but not [Cu(cmppd)2(cnge)][BF4]2. That in [Cu(cppd)(cnge)2(H2O)(FBF3)][BF4] differentiates between the two cnge ligands, their different roles being confirmed by the presence of two diagnostic νasym(NCN) doublets in its IR spectrum.