UCL Discovery

Abstract

Nickel K-edge EXAFS spectroscopy has been used to investigate, at 295 K and ca. 120 K, local structural properties of the inclusion compounds containing halogenoalkane guest molecules (2-chlorobutane, 2,3-dichlorobutane, 1,2-dichloroethane, 2-bromobutane, 2,3-dibromobutane and 1,2-dibromoethane) within the catena-[(1,2-diaminopropane)cadmium(II) tetra-mu-cyanonickelate(II)] host structure. For these inclusion compounds there are ambiguities in the interpretation of atomic positions 'located' for the guest molecules by diffraction-based approaches, and the work reported here has allowed an assessment of the scope of EXAFS spectroscopy for probing host-guest interaction in such situations. The optimum approach for handling the host structure within the EXAFS data analysis has also been assessed.The only atoms of the host structure that make a significant contribution to the nickel K-edge EXAFS spectrum are the carbon and nitrogen atoms of the Ni(CN)(4) unit and the cadmium atoms, with the C-N-Cd angle refined in multiple scattering calculations. Carbon and nitrogen atoms in the host structure corresponding to Ni ... C and Ni ... N distances in the range 3.5-5.0 Angstrom do not contribute significantly to the nickel K-edge EXAFS spectrum. For all the guest molecules studied (with the exception of 1,2-dibromoethane), the halogen atoms contribute significantly to the EXAFS spectrum, with physically sensible Ni ... Cl and Ni ... Br distances refined; this supports the suggestion that there is some degree of ordering of the guest molecules relative to the host structure in these inclusion compounds.