Synthesis, UV-visible and Mössbauer spectroscopic studies and molecular structure of the low-spin iron(II) Bis(tert-butyl isocyanide)(5, 10, 15, 20-[4-(benzoyloxy)phenyl]porphyrin) coordination compound

Abstract

The (tert-butyl isocyanide)(5,10,15,20-{tetrakis-[4-(benzoyloxy)phenyl]porphyrinato}iron(II) coordination compound with the formula [FeII(TPBP)(t-BuNC)2] (I) was prepared by the reduction of the triflato iron(III) starting material [FeIII(TPBP)(SO3CF3)] using a large excess of tert-butyl isocyanide. The UV-visible titration and IR spectra indicated that (I) is an iron(II) porphyrin derivative. A solid-state Mössbauer investigation of this species showed that the quadrupole splitting (ΔEQ) and the isomer shift (δFe) values are small [ΔEQ = 0.20 (1) mm.s−1 and δFe = 0.22 (1) mm.s−1 at 300 K]. These values are very close to those of the known bis(carbonyl) and the bis(cyano) iron(II) porphyrins. This indicates that (I) is a low-spin (S = 0) iron(II) metalloporphyrin where the t-BuNC is a good π-acceptor moiety comparable to the CN− and CO ligands. The X-ray molecular structure confirms the low-spin character of (I) where the average equatorial Fe(II)—N(pyrrole) bond length is 2.007 (2) Å. In the crystal, the [FeII(TPBP)(t-BuNC)2] molecules are linked together via weak C—H….O and C—H….Cg (Cg is the centroid of a pyrrole or a phenyl ring) intermolecular interactions forming two-dimensional chains parallel to the c axis.