Applied field Moessbauer spectra of low-spin mononuclear and binuclear iron(III)-phthalocyanines

Well characterized low-spin Fe(III)phthalocyanine complexes have recently been synthesized. Two six-coordinate examples, a binuclear μ-oxo bridged complex [((γ-picoline)FePc)20], 1, and a mononuclear bis-azido complex (PNP)[FePc(N3)2], 2, display typical S = 1/2 Fe(III) parameters (1, δ = -0.20 mm/s, ΔEQ = 1.79 mm/s; 2, δ = 0.22 mm/s, ΔEQ = 2.47 mm/s at 4.2 K). As an applied longitudinal magnetic field is increased to 32 kOe the corresponding splittings in 1 and 2 indicate very small effective fields at the Fe nuclei. This is due to an S=0 ground state in the weakly antiferromagnetically coupled complex 1. The small hyperfine splitting in 2 contrasts with the well resolved hyperfine splitting reported for various S = 1/2 Fe(IIIporphyrins and Fe(III)heme proteins. (orig.)