ELECTROCHEMICAL, SPECTROCHEMICAL CHARACTERIZATION AND CRYSTAL-STRUCTURE OF (1,4,8,11-TETRAZACYCLOTETRADECANE) (ACETYLACETONATE) COBALT(III)COMPLEXES

Two Co-III-cyclam-acac complexes have been synthesized and isolated (a cac (-) = acetylacetonate ion): [Com( cyclam) (acac) ] (acac),and [Co- III(cyclam) (acac)] (BF4)(2). Fast atom bombardment mass spectrometry has been used to characterize [Co-III(cyclam)(acac)] (BF4)(2). Electro chemistry, spectrophotometry and IR spectroscopy helped to clear-up th e role of acac(-). The acetylacetonato ligand is in the Co-III coordin ation sphere of [Co-III(cyclam)(acac)](BF4)(2). In [Co-III(cyclam)(aca c)] (acac)(2), acac(-) is a ligand for the metal ion and also a counte r-ion for the cationic complex, identical in both compounds. The vario us protons of [Co-III(cyclam) (acac) ] (BF4)(2)have been identified us ing H-1 NMR ( 1D, 2D, COSY-DQF). C-13 NMR reveals that a symmetry elem ent exists in the complex; the a carbons of cyclam have been identifie d using an inverse H-1-C-13 correlation (HMQC). An X-ray crystallograp hic study ascertained the probable structure deduced from these method s. Com is six coordinated, the octahedron being slightly distorted: tw o of the four N atoms of the tetraazamacrocycle occupy adjacent positi ons of the equatorial plane, the O atom of acacetylacetonate the two o thers. (C) 1998 Elsevier Science S.A. All rights reserved.