Ni(II) complexes with pyrazole-derived ligands. Crystal structures of [Ni(HL0)(2)ClH2O][Ni(HL0)(2)(H2O)(2)]Cl-3 center dot CH3OH center dot H2O and [Ni(HL1)(2)(H2O)(2)]Br-2 center dot 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-meth yl-(2-pyridyl))pyrazol (HL1) with nickel(II) salts produces mononuclear coo rdination compounds. The new complexes have been characterised by elemental analyses, conductivity measurements and infrared and electronic spectrosco pies. 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 t he cationic com plexes, the coordination of the Ni(II) is octahedral with t wo 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.