1,2-dibromo- and 1,2-diiodotetrafluorobenzene as precursors of anionic homo- and heterometallic gold complexes

By reaction of LiR and [AuCl(tht)] the new organometallic compounds NBu4[AuR2] (R = 2-C6BrF4 (1), 2-C6F4I (2)) have been prepared. They react with TlPF6 in different molar ratios yielding anionic extended chains with the stoichiometries {NBu4[Tl-2(AuR2)(3)]}(n), (R = 2-C6BrF4 (3), 2-C6F4I (4)) and {NBu4[Tl(AuR2)(2)]}(n) (R = 2-C6BrF4 (5), 2-C6F4I (6)). The crystal structures of 3 and 4 consist of anionic chains formed by association of loosely bound Au2Tl2 clusters interconnected by [AuR2](-) anions via unsupported Au center dot center dot center dot Tl interactions, while 5 shows infinite polymetallic Au/Tl chains with an additional [AuR2](-) fragment bonded to each Tl-1 via unsupported Au center dot center dot center dot Tl contacts. The heterometallic bromotetrafluorophenyl complexes 3 and 5 display luminescence in the solid state, which is assigned to excited states that appear as result of the interactions between the metal centers. At 77 K different emissions appear in glassy solutions, which are assigned to the presence of oligomers of different length. In the case of the iodotetrafluorophenyl derivatives, in spite of presenting similar structures, complex 4 is weakly luminescent and complex 6 is nonluminescent both in the solid state at room temperature and at 77 K and in glassy solutions. This result is probably a consequence of the heavy-atom effect (HAE) due to the presence of iodine instead of bromine, which in the case of complex 4 provokes a reduction of the intensity if compared with its homologous compound 3 and which in 6 leads to the total quenching of the emission.