Geometry and orientation of molecules in a graphite fluoride matrix

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Polarization dependences of the EXAFS and XANES spectra of graphite fluoride intercalation compounds C2Fx·yA (x ≈ 1, A=Br2, Fe(AA)3, FeCl3, SnCl4; AA=acetylacetonate) synthesized by diffusion from solution were measured. The measurements were carried out in the FeK-, BrK-, and SnK-edge of absorption spectral regions using synchrotron radiation of the VEPP-3 storage ring (Institute of Nuclear Physics, Siberian Branch, Russian Academy of Sciences). The polarization dependences of effective coordination numbers and edge σ-resonance intensity are analyzed, and parameters of the local surroundings of atoms (coordination numbers, interatomic distances, Debye-Waller factors σ2) are determined. For the Br2 intercalates, the orientation angle with respect to the matrix layers is 64±1.5°, and the interatomic distances are close to those in the gas phase. The FeCl3 molecule forms dimers in the matrix as it does in the gas phase, and the iron atoms have tetrahedral surroundings. For the Fe(AA)3 molecules intercalated into the matrix, the iron atoms have significantly distorted octahedral environments. For the SnCl4 intercalates, the lowering of temperature does not cause additional coordination of Sn atoms, and structural disorder of SnCl4 makes the major contribution to σ2.