On the covalence in coinage-metal halides M3X3 (M = Cu, Ag and Au, X = F - I)

Systematic theoretical investigations have been performed to understand the periodicity, structures and interactions of the coinage-metal halide series, M3X3(M = Cu, Ag and Au, X = F - I) at MP2 theoretical level with extended basis sets. Mechanisms of M-X and M-M interactions were investigated by natural bond orbital analyses, natural resonance theory, electron localisation function, electron density deformation, atoms in molecules and visualised by reduced density gradient analyses. Periodic trends are found in the bond length, stability and covalent nature of the M-X and M-M interactions. As expected, increased covalence when halogens become heavier and Au-Au and Au-X interactions contain enhanced covalence in comparison with lighter congeners Cu3X3 and Ag3X3.