The β-diketonate compounds of Pt(II), [Pt(R-C^C*)(acac)] (acacH = acetylacetone, R-CH^C* = 1-(4-cyanophenyl)-3-methyl-1H-imidazol-2-ylidene (NC-CH^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(μ-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 å) and π-π (~3.43 å) interactions between the NHC ligand and the acac. The reaction of compounds 1A-1C with TlPF₆ (2:1 molar ratio) leads to the clusters [{Pt(R-C^C*)(acac)}₂Tl]⁺ (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 donor-acceptor Pt-Tl bonds. Compounds 2A and 2B show an extended two-dimensional lattice in the solid state through intermolecular Pt^...Pt and Tl-E (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 Pt-Tl interactions on the crystal structures and the photophysical properties have been investigated.