M(TEIM) complexes with M as Co and Fe: Analogues of classic M(TIM)

Abstract

The syntheses and characterization of Fe and Co complexes supported by a new tetra-imine macrocycle, TEIM (2,3,9,10-tetraethyl-1,4,8,11-tetraazacyclotetradeca-1,3,8,10-tetraene), are reported. Templating with Co(OAc)2·4H2O yielded trans-[Co(TEIM)Cl2][PF6] (1a), which was converted to trans-[Co(TEIM)X2][PF6] (X = N3 (2a) and NO2 (3a)) through reactions with NaX (X = N3 or NO2). Templating with Fe generated trans-[Fe(TEIM)(NCCH3)2][PF6]2, which was oxidized to trans-[Fe(TEIM)Cl2][PF6] (1b). The reaction of 1b with NaN3 formed [Fe(TEIM)(N3)2][PF6] (2b) while the reaction with [Fe(TEIM)(NCCH3)2][PF6]2 and NaNO2 yielded trans-[Fe(TEIM)(NO2)2] (3b). Single crystal X-ray diffraction studies revealed a pseudo-octahedral geometry around the Co / Fe centers with the ethyl groups oriented above or below the plane of the TEIM ring. The absorption spectra of 1b displays weak charge transfer bands near the UV to visible region, while 2b and 3b displayed intense charge transfer bands within the visible region. Cyclic voltammograms of 1a revealed four 1 e− reductions while those of 2a and 3a display only three cathodically shifted reductions. Analogous studies of 1b and 2b revealed two 1 e- reductions while 3b displays only an oxidation event. EPR studies of ferric complexes 1b and 2b indicated a low spin d5 electronic figuration with S = ½ ground state.