Structure, optical and magnetic behaviour of meso-tetraphenylporphyrinatoiron(III) tetracyanoethenide, [FeIII(TPP)]+[TCNE]˙− †

Abstract

The direct redox reaction between tetracyanoethylene (TCNE) and meso-tetraphenylporphyrinatoiron(II), [FeII(TPP)], formed the electron transfer salt (ETS) [FeIII(TPP)][TCNE], which has been structurally, spectroscopically, and magnetically characterized. It has an extended one-dimensional linear chain with coordination polymer motif comprised of [FeIII(TPP)]+ and bridging μ-[TCNE]˙− with Fe–NTCNE distance 1.889(2) Å. This coordination geometry is consistent with a low-spin iron(III) ion, i.e., one electron transfer from FeII to TCNE produces S = 1/2 [FeIII(TPP)]+ having a (dxy)2(dyz,dzx)3 configuration and S = 1/2 [TCNE]˙−. 57Fe Mössbauer data, δ = 0.28 mm s−1 and ΔE = 2.19 mm s−1 at 77 K, also support the low-spin state. The room temperature magnetic moment of the ETS, 1.20 μB, arises from two S = 1/2 systems having antiferromagnetic coupling, −190 cm−1 (H = −2Σ Ji jSiSj).