Ni(II) complexes with pyrazole-derived ligands.: Crystal structures of [Ni(HL0)2ClH2O][Ni(HL0)2(H2O)2]Cl3•CH3OH•H2O and [Ni(HL1)2(H2O)2]Br2•2.5DMF (HL0=3-phenyl-5-(2-pyridyl)pyrazole and HL1=3-phenyl-5-(6-methyl-(2-pyridyl))pyrazole)

The reaction of 3-phenyl-5-(2-pyridyl)pyrazole (HL0) and 3-phenyl-5-(6-methyl-(2-pyridyl))pyrazol (HL1) with nickel(II) salts produces mononuclear coordination compounds. The new complexes have been characterised by elemental analyses, conductivity measurements and infrared and electronic spectroscopies. Two different forms of mononuclear nickel(II) complexes have been prepared and structurally characterised by X-ray crystallography: [Ni(HL0)(2)Cl(H2O)][Ni(HL0)(2)(H2O)(2)]Cl-3. CH3OH .H2O [Ni(HL1)(2)(H2O)(2)]Br-2.2.5DMF. In the cationic com plexes, the coordination of the Ni(II) is octahedral with two bidentate HL0 or HL1 neutral ligands in a cis disposition. The degree of distortion from regular octahedral geometry is compared to closely related structures. In the solid state, cations and anions are bonded by hydrogen bonding. (C) 2001 Elsevier Science Ltd. All rights reserved.