Pt2Tl Building Blocks for Two-Dimensional Extended Solids: Synthesis, Crystal Structures, and Luminescence

The beta-diketonate compounds of Pt(II), [Pt(R-C<^>C*)(acac)] (acacH = acetylacetone, R-CH<^>C* = 1-(4-cyanophenyl)-3-methyl-1H-imidazol-2-ylidene (NCCH<^>C*) 1A, 1-(4-(ethoxycarbonyl)phenyl)-3-methyl-1H-imidazol-2-ylidene (CO2Et-CH<^>C*) 1B, 1-(3,5-dichlorophenyl)-3-methyl-1H-imidazol-2-ylidene (Cl-CH<^>C*) 1C) containing cyclometalated N-heterocyclic carbenes were synthesized from compounds [{Pt(mu-Cl)(R-C<^>C*)}(2)] (R = CN A, CO2Et B, Cl C). Compound C was prepared for the first time following a step-by-step protocol used to synthesize A and B. The X-ray structures of complexes 1B and 1C show that only in 1B the molecules stack in pairs through intermolecular Pt...Pt (3.370 angstrom) and pi-pi (similar to 3.43 angstrom) interactions between the NHC ligand and the acac. The reaction of compounds 1A1C with TlPF6 (2:1 molar ratio) leads to the clusters [{Pt(R-C<^>C*)(acac)}(2)Tl](+) (R = CN 2A, CO2Et 2B, Cl 2C), which exhibit a Pt2Tl sandwich structure, where two slightly distorted square planar Pt(R-C<^>C*)(acac) subunits are bonded to a Tl(I) center through donoracceptor PtTl bonds. Compounds 2A and 2B show an extended two-dimensional lattice in the solid state through intermolecular Pt..Pt and TlE (E = N, O) interactions; meanwhile 2C forms discrete molecules without any kind of intermolecular interaction among them. The effects of the R substituent and the PtTl interactions on the crystal structures and the photophysical properties have been investigated.