cis-octahedral nickel(II) complexes with symmetric and unsymmetric tripodal tetraamine ligands

Nickel(II) complexes with the aliphatic tripodal tetraamine Ligands N(CH2CH 2NH2)(3) (tren, 1), N[(CH2CH2-CH2NH2) (CH2CH2NH2)(2)] (baep, 2), N[(CH2CH2C H2NH2)(2-)(CH2CH2NH2)] (abap, 3), and N(CH2CH2CH2NH2)(3) (trpn, 4) are repo rted. The tripodal tetradentate N-4 ligands 1-4 react with Ni(NO3)(2). 6H(2 )O in acetonitrile or methanol to give the blue nickel(II) complexes [Ni(1) (eta (1)- NO3)(2)] (5a), [Ni(2)(eta (1)- NO3)(2)] (5b), [Ni(3)(eta (2)-NO3) ]NO3. CH3CN (5c . CH3CN), and [Ni(4)(eta (2)-NO3)]NO3. CH3OH (5d . CH3OH). With NiCl2. 6H(2)O, the complexes [Ni(l)Cl(H2O)]Cl .H2O (6a), [Ni(2)(mu -Cl )(2)Ni(2)]Cl-2 . 2CH(3)OH (6b . 2CH(3)OH), [Ni(3)Cl(H2O)]Cl (6c), and [Ni(4 )(H2O)(2)]Cl-2.H2O (6d .H2O) are obtained. The molecular structures of comp lexes 5a-d and 6b-d have been determined by X-ray diffraction analysis and they are compared with the molecular structure of the previously characteri zed complex 6a. Complexes 5a-d and 6b-d exhibit octahedrally coordinated ni ckel atoms. The tripodal Ligands occupy four of the six coordination sites in a pseudo-facial manner. Complexes of the unsymmetrical Ligands 2 and 3 p ossess both five- and six-membered chelate rings. The extension of the liga nd arms in 1-4 leads to a systematic variation in the geometric and UV/Vis spectroscopic properties of the complexes depending on the size of the chel ate rings formed by the ligands.