Crystal structure of an unusual corrosion deposit, bis(ethylammonium) tetrachloroiron(II)

An Fe-containing deposit isolated from a commercial plant was identified by indexing its powder diffraction pattern, using the NIST Crystal Data Ident ification File to locate an isostructural Mn compound, and carrying out a s uccessful Rietveld refinement. The principal phase in the deposit was confi rmed to be bis(ethylammonium) tetrachloroiron(II). This compound crystalliz es in the orthorhombic space group Pbca, with a=7.3291(6), b=7.2603(6), c=2 1.7544(8) Angstrom, V=1157.59(14) Angstrom, and Z=4. The structure consists of single perovskitelike layers of corner-sharing FeCl6 octahedra parallel to the nb plane, separated by bilayers of ethylammonium cations. The octah edra are tilted 4.4 degrees with respect to the c-axis, and the layers are ruffled. The compound was apparently formed by reaction of the ethylamine c orrosion inhibitor with Fe from the steel process vessel and chloride in th e process stream. (C) 1999 International Centre for Diffraction Data. [S088 5-7156(99)01302-0].