Synthesis, structure and properties of mononuclear cobalt(II) and cobalt(III) pseudohalide complexes containing N-donor Schiff bases: Synthetic control of metal oxidation levels

摘要

Two different series of cobalt(II) and cobalt(III) complexes of types [Co(L-1)(X)(2)] (1a-1f) and [Co(L-2)(X)(3)] (2a-2f), respectively [L-1 = N,N'-(bis(pyridin-2-yl)formylidene)propane-1,3-diamine (pfpd) or N,N'-(bis(pyridin-2-yl)benzylidene)propane-1,3-diamine (pbpd); L-2 = (N,N-diethyl,N'-(pyridin-2-yl)formylidene)ethane-1,2-diamine (pfed) or (N,N-diethyl,N-(pyridin-2-yl)benzylidene)ethane- 1,2-diamine (pbed); X = N-3(-) NCS- or NCO-] have been prepared and characterized using microanalytical, spectroscopic, magnetic, electrochemical and other physicochemical results. Structures of one member in each series, viz., [Co(pfpd)(NCS)(2)] (1c) and [Co(pbed)(N-3)(3)] (2b) are solved by X-ray diffraction measurements for the exact definition of the coordination sphere. Structural analysis reveals cobalt(II) centre in 1c adopts a distorted octahedral environment with a CoN6 chromophore ligated by four N atoms of the tetradentate Schiff base and two N-coordinated NCS- ions in trans orientation. In 2b, the three N atoms of the tridentate Schiff base and three N atoms of three terminal azides are found in meridional arrangement. The organic blockers are folded in ethylenic/propylenic part. Electrochemimal electron transfer study in MeCN solutions shows cobalt(III)-cobalt(II) response as oxidative in 1 and reductive in 2. Available information shows that the structures 1a, 1b, 1d-1f are cognate with le, whereas 2a, 2c, 2d-2f are iso-structural with 2b. All the complexes display intraligand (1)(pi-pi*) fluorescence and intraligand (3)(pi-pi*) phosphorescence in glassy solutions (MeOH at 77 K). (c) 2005 Elsevier Ltd. All rights reserved.