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), [Fe^II(TPP)], formed the electron transfer salt (ETS) [Fe^III(TPP)][TCNE], which has been structurally, spectroscopically, and magnetically characterized. It has an extended one-dimensional linear chain with coordination polymer motif comprised of [Fe^III(TPP)]⁺ and bridging μ-[TCNE]˙⁻ with Fe–N^TCNE distance 1.889(2) Å. This coordination geometry is consistent with a low-spin iron(III) ion, i.e., one electron transfer from Fe^II to TCNE produces S = 1/2 [Fe^III(TPP)]⁺ having a (d_xy)²(d_yz,d_zx)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 μ_B, arises from two S = 1/2 systems having antiferromagnetic coupling, −190 cm⁻¹ (H = −2Σ J_i jS_iS_j).