Zinc and Cobalt Complexes Derived from Tetradentate Tripodal Ligands with N2O2 Donorset as Model Compounds for Phosphatases

Schnieders D, Hammerschmidt A, Merkel M, Schweppe F, Krebs B

Abstract

Starting from the tripodal tetradentate ligands (3,5-dibromo-2-hydroxybenzyl)(2-hydroxybenzyl)(2-pyridyl)- methylamine (H(2)L1), (3,5-dibromo-2-hydroxybenzyl)(2-hydroxy-5-nitrobenzyl)(2-pyridyl)methylamine (H2L2), and (3,5-dichloro-2-hyd roxybenzyl)(2-hydroxy-5-nitrobenzyl)(2-pyridyl)methylamine (H2L3) the new isostructural dinuclear zinc compounds [Zn-2(L1)(2)]center dot N(CH2CH3)(3) (1), [Zn-2(L2)(2)]center dot 2CH(3)OH (2) and [Zn-2(L3)(2)]center dot C4H10O (3) were synthesized. Due to their enzyme-like trigonal bipyramidal N2O3 coordination environment of the zinc ions and the similar Zn center dot center dot center dot Zn distances the complexes can be considered to be structural models for the active sites in phospholipase C and nculease P1. With H2L3 also the dinuclear complex [Co-2(L2)(2)(CH3OH)]center dot 2CH(3)OH center dot 0.5C(4)H(10)O (4) could be prepared. The new compounds were isolated and characterized by single crystal X-ray crystallography as well as infrared spectroscopy. The cobalt compound 4 was additionally characterized by UV-Vis spectroscopy and magnetic measurements. 1 crystallizes in the monoclinic space group P2(1)/n with a = 11.2814(2), b = 28.6154(2), c =13.1866(3) angstrom, beta = 96.995(1)degrees, V = 4225.2(2) angstrom(3), Z = 4. 2 and 3 are monoclinic, space group C2/c with a = 23.084(5), b = 9.232(2), c = 21.849(4) angstrom, beta = 96.83(3)degrees, V = 4623(2) angstrom(3) , z = 4, and a = 22.7834(3), b = 9.2463(1), c = 21.6351(3) angstrom, beta = 97.592(1)degrees, V = 4517.7(2) angstrom(3), Z = 4, respectively. 4 crystallizes in the monochnic space group 12/a with a = 22.4680(4), b = 20.5517(4), c = 22.8910(6) angstrom, beta = 111.938(1)degrees, V = 9804.7(4) angstrom(3), Z = 8. 4 shows an effective magnetic moment of 6.72 mu(B) at 300 K which clearly indicates the presence of two cobalt(II) high spin ions with Curie-Weiss behaviour above 80 K. At lower temperatures a decrease of the effective magnetic moment was observed.