Characterization of some high-spin iron(III) complexes with urea derivaties. Crystal structure of diaquatetrakis(perhydropyrimidin-2-one)iron trichloride dihydrate and of perhydrophyrimidin-2-one

Abstract

High-spin complexes of the type [FeL₆]X₃, where L = urea, 1,3-dimethylurea (dmu), 1,3-diethylurea (deu), perhydropyrimidin-2-one (1,3-trimethyleneurea, tu), imidazolidin-2-one (1,3-ethyleneurea, eu), and X = ClO₄ or Br, and [Fe(tu)₄(OH₂)₂]Cl₃·2H₂O have been prepared. A discrete octahedral geometry for all these complexes has been inferred from i.r., magnetic susceptibility, and Mössbauer measurements. The crystal structure of [Fe(tu)₄(OH₂)₂]Cl₃·2H₂O has been solved by a three-dimensional Patterson synthesis: the crystals are orthorhombic, space group P2₁2₁2₁, with a= 18.627(9), b= 15.555(7), c= 9.876(5)Å, Z= 4, refined to R 0.056 for 2567 observable reflections. The iron atom is co-ordinated to two cis-oxygen atoms of two water molecules [Fe–O 2.028(5) and 2.036(5)Å respectively] and to four oxygen atoms of the tu ligands [Fe–O 1.996(5), 1.940(5), 1.995(5), and 2.000(5)Å respectively] in approximately actahedral manner. For comparison, the crystal structure of perhydropyrimidin-2-one has also determined by direct methods: orthorhombic, space group Pnam(no. 62), with a= 10.282(3), b= 6.763(3), c= 7.171(2)Å, Z= 4, R 0.039, 392 observable reflections. Iterative extended-Hückel calculations have been performed.