Structure, optical and magnetic behaviour of meso-tetraphenylporphyrinatoiron(III) tetracyanoethenide, [Fe-III(TPP)](+)[TCNE](.-)

The direct redox reaction between tetracyanoethylene (TCNE) and meso-tetrap henylporphyrinatoiron(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 c hain with coordination polymer motif comprised of [Fe-III(TPP)](+) and brid ging mu-[TCNE](-) with Fe-N-TCNE distance 1.889(2) Angstrom. This coordinat ion geometry is consistent with a low-spin iron(III) ion, i.e., one electro n transfer from Fe-II to TCNE produces S=1/2 [Fe-III(TPP)](+) having a (d(x y))(2)(d(yz),d(zx))(3) configuration and S=1/2 [TCNE](-). Fe-57 Mossbauer d ata, delta =0.28 mm s(-1) and DeltaE epsilon=epsilon2.19 mm s(-1) at 77 K, also support the low-spin state. The room temperature magnetic moment of th e ETS, 1.20 mu (B), arises from two S=1/2 systems having antiferromagnetic coupling, -190 cm(-1) (H=-2 Sigma J(ij)S(i)S(j)).