SPECTROSCOPY AND ELECTROCHEMISTRY OF COBALT(III) SCHIFF-BASE COMPLEXES

The structural, spectroscopic, and electrochemical properties of cobal t(III) derivatives of acacen (H(2)acacen = bis(acetylacetone) ethylene diimine) and related ligands have been investigated. Electronic struct ure calculations indicate that the absorption between 340 and 378 nm i n Co-III(acacen) spectra is attributable to the lowest pi-pi intralig and charge-transfer transition. Equatorial ligand substitutions affect reduction potentials less than axial ligand changes, consistent with an electronic structural model in which d(z)(2) is populated in formin g cobalt(II). The crystal structure of [Co(3-Cl-acacen)(NH3)(2)]BPh4 h as been determined: The compound crystallizes in the monoclinic space group P2(1)/m (No. 11) with a = 9.720(2) Angstrom, b = 18.142(4) Angst rom, c = 10.046(2) Angstrom, beta = 100.11(3)degrees, D-c = 1.339 g cm (-3), and Z = 2; the complex cation, [Co(3-Cl-acacen)(NH3)(2)](+), exh ibits a slightly distorted octahedral coordination geometry. The dista nces between the cobalt atom and the two axial nitrogen donor atoms di ffer only slightly (1.960(6) and 1.951(6) Angstrom) and are similar to Co-N distances found in cobalt-ammine complexes as well as the axial Co-N distances in [Co(acacen)(4-MeIm)(2)]Br.1.5H(2)O; the latter compo und crystallizes in the triclinic space group <P(1)over bar> (No. 2) w ith a = 18.466(9) Angstrom, b = 14.936(7) Angstrom, c = 10.111(5) Angs trom, alpha = 96.27(5)degrees, beta = 94.12(5)degrees, gamma = 112.78( 5)degrees, D-c = 1.447 g cm(-3), and Z = 4.