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

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)(2)Cl-2 . 2H(2)O and Cu(cppd)(2)Br-2 . 2H(2)O. The corresponding 3-chloro-6-(3,5-dimethylpyrazol-1-yl)pyridazine (cmppd) systems gave Cu(cmppd)-(cnge)(2)(NO3)(2) . 6H(2)O, [Cu(cmppd)(2)(cnge)][BF4](2), [Cu(cmppd)(cnge)Cl-2]. H2O and Cu(cmppd)(cnge)Br-2 . 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)Cl-2]. 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)Cl-2] 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)(2)Br-2 . 2H(2)O 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) . 2H(2)O and [Cu-(cppd)(cnge)(2)(H2O)(FBF3)][BF4] and for Cu(cmppd)(cnge)Br-2 . H2O and [Cu(cmppd)(cnge)Cl-2]. 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)Cl-2]. 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 v(asym)(NCN) doublets in its IR spectrum.