BIS(1,2,6,7-TETRACYANO-3,5-DIHYDRO-3,5-DIIMINOPYRROLIZINIDO) COMPLEXES OF IRON AND COBALT - PROPERTIES, CRYSTAL-STRUCTURES AND INTERACTION WITH DIOXYGEN

The synthesis and characterization of complexes of the ligand 1,2,6,7-tetracyano-3,5-dihydro-3,5-diiminopyrrolizinide, [ML2].nA (M = Fe 1 or Co 2; A = crystallization solvent) are described. For A = 1,2-dimethoxyethane (dme), n = 2, the compounds are isomorphous and isostructural as shown by crystal structure determinations. The central metal atom, which lies on a symmetry centre, co-ordinates four imino groups in a square-planar arrangement within the ligand equatorial plane, and completes its octahedral, tetragonally distorted MN(eq)4N(ax)2 co-ordination geometry with two axial cyano groups from two crystallographically equivalent complex molecules. The only significant difference between the two structures is confined to the M-N bond distances [Fe-N(eq) 2.090(5); Fe-N(ax) 2.295(5); Co-N(eq) 2.017(5); Co-N(ax) 2.369(5) angstrom]. Variable-temperature magnetic measurements on these two complexes reveal that they are both high-spin species (S = 2 and 3/2, respectively) with antiferromagnetic superexchange interactions, which are stronger when M = Co. The optical spectra of both sets of complexes are very similar to those of corresponding metal phthalocyanines. Also, both can be chemically oxidized by using O2 as oxidant in MeCN solution to give insoluble polymeric species, corresponding analytically to the formulae [FeL3(O2)].6MeCN and [CoL2(O2)].4MeCN. These complexes are shown to be superoxo adducts in which the dioxygen is centrosymmetrically bridged between the metal atoms in the formal oxidation state Fe(IV) and Co(III) respectively.