Experimental charge density study of two FeS2 structures
Experimental charge density studies of inorganic solids have proven to be a difficult task due to systematic errors related to data collection such as absorption and extinction; however, the use of synchrotron radiation has the potential to minimize these problems.  One of the pioneering experimental electron density studies of an inorganic solid containing a transition metal was presented by Stevens et al.  who investigated the effect of crystal-field splitting of the partially filled iron d-orbitals in the pyrite structure of FeS2. Other studies of various FeS2 structures, including pyrite, has been performed by Gibbs et al. , however, these are all based on theoretical calculations rather than experiment. In the current study we revisit FeS2 through an experimental charge density study of the two low-spin iron FeS2 structures, pyrite and marcasite. High-quality, low-temperature single crystal diffraction data were collected with synchrotron radiation on both compounds at the ChemMatCARS beamline at the Advanced Photon Source. Extinction and absorption effects were minimized using small crystals (10 μm) and high-energy (28 keV) radiation. The experimental charge density has been determined by multipole least squares modelling and analyzed by means of the Quantum Theory of Atoms in Molecules. The resulting topology has been compared to the results obtained by Gibbs et al. and to current periodic ab-initio DFT calculations and in general a good agreement between experiment and theory is found. References  P. Coppens, Synchrotron Radiation in Crystallography, Academic Press: New York, 1992.  E.D. Stevens, M.L. DeLucia, P. Coppens, Inorg. Chem. 19 (1980) 813-820.  G.V. Gibbs, D.F. Cox, K.M. Rosso, N.L. Ross, R.T. Downs, M.A. Spackman, J. Phys. Chem. B. 111 (2007) 1923-1931.  R.F.W. Bader, Atoms In Molecules, A Quantum Theory, Oxford Science Publications: Oxford, 1990.
Charge density; Crystallography, X-Ray; QTAIM; FeS2; iron sulfide; polymorphism