Complex formation of monomeric thallium(III) species with 2,2'-bipyridine (bipy) in dimethyl sulfoxide (dmso) and acetonitrile solutions was studied by means of multinuclear (H-1, C-13, and (TI)-T-205) NMR spectroscopy. For the first time, NMR signals of the individual species [TI(bipy)(m)(SoIV)](3+) (M = 1-3) were observed despite intensive ligand and solvent exchange processes. The tris(bipy) complex was crystallized as [TI(biPY)(3)(dmso)](ClO4)(3)(dMSO)(2) (1), and its crystal structure determined. In this compound, thallium is seven-coordinated; it is bonded to six nitrogen atoms of the three bipy molecules and to an oxygen atom of dmso. Metal-metal bonded binuclear complexes [(NC)(5)Pt-TI(CN)(n)(SoIV)](n-) (n = 0-3) have been modified by attaching bipy molecules to the thallium atom. A reaction between [(NC)(5)Pt-TI(dMSO)(4)](s) and 2,2'-bipyridine in dimethyl sulfoxide solution results in the formation of a new complex, [(NC)(5)Pt-TI(bipy)(solv)]. The presence of a direct Pt-TI bond in the complex is convincingly confirmed by a very strong one-bond Pt-195-(TI)-T-205 spin-spin coupling ((1)J((195)pt-(TI)-T-205) = 64.9 kHz) detected in both Pt-195 and (TI)-T-205 NMR spectra. In solutions containing free cyanide, coordination of CN- to the thallium atom occurs, and the complex [(NC)(5)Pt-TI(bipy)(CN)(solv)](-) ((1)J(Pt-195-(TI)-T-205) = 50.1 kHz) is formed as well. Two metal-metal bonded compounds containing bipy as a ligand were crystallized and their structures determined by X-ray diffractometry: [(NC)(5)Pt-TI(bipy)(dMSO)(3)] (2) and [(NC)(5)Pt-TI(biPY)(2)] (3). The Pt-TI bonding distances in the compounds, 2.6187(7) and 2.6117(5) Angstrom, respectively, are among the shortest reported separations between these two metals. The corresponding force constants in the molecules, 1.38 and 1.68 N/cm, respectively, were calculated using Raman stretching frequencies of the Pt-TI vibrations and are characteristic for a single metal-metal bond. Electronic absorption spectra were recorded for the [(NC)(5)Pt-TI(bipy)(m)(solv)] compounds, and the optical transition was attributed to the metal-metal bond assigned.