Electronic Influences on Metallophilic Interactions in [Pt(tpy)X][Au(C6F5)2] Double Salts

Four double salt compounds of the type [Pt(tpy)X][Au(C6F5)(2)], where tpy =2,2':6',2 ''-terpyridine and X = Cl, 3, Br, 4, I, 5, and CCPh, 6, and their platinum starting materials, [Pt(tpy)Br]Br center dot 2H(2)O, 1, and [Pt(tpy)(CCPh)]PF6 center dot DMF center dot H2O, 2, have been synthesized and characterized. Complex 2 is a solvated form of the known and structurally characterized [Pt(tpy)(CCPh)]PF6 species. All compounds were characterized by single-crystal X-ray diffraction, elemental analyses, and solution electronic spectra. Structural characterization shows that compounds 3 and 4 are similar in the solid state and form cation-anion stacking patterns while compounds 5 and 6 form chains of cations supported by metallophilic interactions with anion partners on either side of the chains. Solution studies (UV-vis and fluorescence) strongly suggest that there are no Pt center dot center dot center dot Au interactions in solution state. Electronic structure calculations with density functional theory (DFT) elucidate the subtle changes in the electronic scaffolding of the ions in these compounds and show that predictions of metallophilic interactions are not straightforward but can be understood in terms of orbital symmetry and the relative energies of the frontier orbitals.