Synthesis, spectroscopic and structural characterization of the high-spin Fe(II) cyanato-N and thiocyanato-N "picket fence" porphyrin complexes

Two new iron(II) five-coordinated porphyrin complexes [Na(2,2,2-crypt)] [Fe(II)(TpivPP)(NCO)] (1) (TpivP-P = alpha,alpha,alpha,alpha-tetrakis(o-pivalamidophenyl) porphyrin known as picket fence porphyrin and 2,2,2-crypt is the cryptand-222) and [K(2,2,2-crypt)][Fe(II)(TpivPP)(NCS)] (2) have been prepared and characterized. The UV-Vis and IR spectroscopic data are consistent with a cyanato-N and thiocyanato-N ferrous porphyrinates. The Mssbauer data and the X-ray structural analysis indicate that the Fe(II) cation in 1 and 2 is high-spin (S = 2) and has the (d(xy))(2) (d(xz))(1) (d(yz))(1) (d(z2))(1) (d(x2-y2))(1) ground state electronic configuration. For complex 1, the average equatorial iron-pyrrole N bond length (Fe-N(p) = 2.120(2) angstrom), the distance between the iron and the 24-atom mean plane of the porphyrin ring (Fe-P(C) = 0.6805(7) angstrom) and the distance between the iron and the plane made by the four pyrrole nitrogens (Fe-P(N) = 0.5923(12) angstrom) are longer than those of complex 2 and similar five-coordinated Fe(II) high-spin porphyrinates. This is probably due to the significant electronic repulsion of the d(x2-y2) and d(xy) orbitals by the negative charge of the pyrrole N atoms in case of 1. (C) 2010 Elsevier B.V. All rights reserved.