Preparation, characterization, and crystal structures of tetraiodoferrates(III)

The extremely air and moisture sensitive tetraiodoferrates MFeI(4) with M = K, Rb and Cs have been synthesized by reaction of Fe, MI and I-2 at 300 degrees C in closed quartz ampoules. The essentially more stable alkylammonium tetraiodoferrates NR(4)FeI(4) with R = H, C2H5, n-C3H7, n-C4H9 and n-C5H11 can be obtained by reaction of Fe, NR(4)I and I-2 in nitromethane. The Raman and UV/Vis-spectra of the black compounds show the existence of tetrahedral [FeI4](-) ions in the structures. The crystal structure of the monoclinic CsFeI4 (CsTlI4 type, spgr P2(1)/c; a = 7.281(1) Angstrom; b = 17.960(3) Angstrom; c = 8.248(2) Angstrom; beta = 107.35(15)degrees) is built up by tetrahedral [FeI4](-) ions and CsI11 polyhedra. The crystal structure of the orthorhombic (n-C5H11)(4)NFeI4 (spgr Pnna; a = 20.143(4) Angstrom; b = 12.683(3) Angstrom; c = 12.577(3) Angstrom) contains tetrahedral [(n-C5H11)(4)N](+) ions and [FeI4](-) ions, respectively.