Coordination properties of a dicompartmental ligand with tetra- and hexadentate coordination sites towards copper (II) and nickel (II) ions

摘要

A new dicompartmental ligand, N,N'-bis[2-iminomethyl-4-methyl-6-(4-methylpiperazin-1-ylmethyl)1-hydroxybenzene]1,8,naphthalene (H2L) possessing contiguous tetra- and hexadentate coordination sites has been synthesized in simple route by the Schiff's base condensation of the precursor compound (PC) 2-formyl-4-methyl-6[4-methyl-6-(4-methylpiperazin-1-yl)methyl]phenol with 1,8-diaminonaphthalene. The mononuclear and binuclear Cu(II) and Ni(II) complexes of this ligand have been prepared and characterized by elemental analysis, IR, NMR and UV-Vis spectra. The electronic spectra of the mono- and binuclear Cu(II) complexes and mononuclear Ni(II) complex revealed one d-d transition in the region 570-600 run. whereas the binuclear Ni(H) complex showed three d-d transitions at 800 nm (epsilon similar to 95 M-1 cm(-1)), 620 nm (epsilon similar to 140 M-1 cm(-1)) and 560 nm (epsilon similar to 250 M-1 cm(-1)), which were assigned to (3)A(2g) --> T-3(2g), (3)A(2g) --> T-3(1g), (3)A(2g) --> T-3(1g)(P), and these spin allowed electronic transitions are characteristic of an octahedral Ni2+ centre. The electrochemical studies evidenced for the mononuclear Cu(II) complex shows a single quasireversible one electron wave at -0.83 V (E-pc).The binuclear Cu(II) complex shows two quasireversible one electron reduction waves at -0.68 V (E-pc(1)) and -1.35 V (E-pc(2)) in the cathodic region. The mononuclear Ni(II) complex shows one quasireversible reduction potential at -0.80 V (E-pc) and the binuclear Ni(II) complex shows two irreversible reduction potentials at -1.10 V (E-pc(1)) and -1.40 V (E-pc(2)) in the cathodic region. The room-temperature magnetic moment value for the mononuclear Cu(II) complex is 1.72mu(B)(u(eff)) and for the binuclear Cu(II), 2.05mu(B)(mu(eff)). The mononuclear Ni(II) complex is square planar and diamagnetic whereas the binuclear Ni(H) complex has a magnetic moment value of 3.05 mu(B) (mu(eff)). Kinetic studies on the oxidation of pyrocatechol to o-quinone using the copper (II) complexes and hydrolysis of 4-nitrophenyl phosphate using the nickel (11) complexes as catalysts showed that the binuclear complexes have higher rate constant values than that of the corresponding mononuclear complexes. (C) 2004 Elsevier Ltd. All rights reserved.