Luminescent One- And Two-Dimensional Extended Structures and a Loosely Associated Dimer Based on Platinum(II)–Thallium(I) Backbones

Neutralization reactions between (NBu4)2[trans-Pt(C6F5)2(CN)2] 1 and (NBu4)2[cis-Pt(C6F5)2(CN)2] 2 with TlPF6 have been carried out, and the resulting structures of [trans,trans,trans-Tl2{Pt(C6F5)2(CN)2}·(CH3COCH3)2]n [4·(CH3COCH3)2]n and {Tl[Tl{cis-Pt(C6F5)2(CN)2}]·(H2O)}n [5·(H2O)]n have been determined by X-ray crystallography. Remarkably, the change from trans to cis geometry on the platinum substrate causes a significant decrease in the PtII···TlI metallophilic interaction. Thus, the platinum center in the trans fragment easily connects with two TlI ions forming a distorted pseudo-octahedron PtTl2, which generates a final two-dimensional layered structure by secondary additional intermolecular TlI···N(CN) interactions. However, the [cis-Pt(C6F5)2(CN)2]2− fragment interacts strongly with just one Tl center leading to an extended helical [−Pt−Tl−Pt−Tl−]nn− chain. In this case, the second thallium center neutralizes the anionic chain mainly through Tl···N(CN) (intra) and Tl···F(C6F5) (intra and inter)teractions. The reaction of TlPF6 with the monoanionic fragment (NBu4)[cis-Pt(C6F5)2(CN)(PPh2CCPh)] 3 yields the discrete associated dimer [Tl{cis-Pt(C6F5)2(CN)(PPh2CCPh)}]2 [6]2. Dimer [6]2 could be described as two square pyramids with the thallium atoms in the apical positions, connected through Tl···N(cyano) interactions. The final heteropolynuclear Pt−Tl complexes, except 4 at room temperature, show bright emission in the solid state when irradiated with UV–vis radiation, in contrast to the precursors 1 and 3, which are not luminescent. This difference indicates that the emissions in 4−6 are presumably related to the interaction between the metal centers. The Pt−Tl bonding interactions and, consequently, the emissive properties are lost in solution at room temperature, as shown by the conductivity and NMR measurements. However, variable-concentration luminescence measurements in glassy acetonitrile solutions indicate the formation of different aggregates with different degrees of Pt···Tl interactions for 4 and 5 and a dimeric structure similar to that observed in solid state for 6.