Structural, Magnetic, and Electronic Properties of a Pentacoordinated Intermediate-Spin (S = 3/2) Iron(III) Complex with a Macrocyclic [N4]2- Ligand

The complex (6,13-bis(ethoxycarbonyl)-5,14-dimethyl-1,4,8,11-tetraazacyclotetradeca-4,6,12,14-tetraenato(2−))iron(III) iodide, 3 (chemical formula C18H26O4N4FeI·0.5 C7H8), has been characterized by X-ray crystallography (a = 16.063(3) A, b = 15.895(3) A, c = 19.703(4) A, β = 107.11(3)°; monocline; I2/a; Z = 8), EPR and Mossbauer spectroscopy, and temperature-dependent magnetic susceptibility as well as by MO calculations. The pentacoordinated iron atom is 0.34 A outside of the [N4] plane. The equatorial Fe−N distances (1.92 A for the N's in neighborhood of the methylated C-atoms and 1.88 A for the others) are not significantly different from those found in octahedral low-spin iron(III) complexes with the same macrocyclic [N42-] ligand. The magnetic moment (μeff = 4.19 μB up to 20 K; ϑ = −7.37 K), the EPR measurements (gyeff = 5.38, gxeff = 2.70, and gzeff = 1.74), and the Mossbauer data (δ = 0.18 mm/s, ΔEQ = 3.56 mm/s, T = 120 K) indicate a pure intermediate-spin state of S = 3/2. The MO calculations yiel...