Modification of Binuclear Pt−Tl Bonded Complexes by Attaching Bipyridine Ligands to the Thallium Site

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 (1H, 13C, and 205Tl) NMR spectroscopy. For the first
time, NMR signals of the individual species [Tl(bipy)m(solv)]3+ (m = 1−3) were observed despite intensive ligand
and solvent exchange processes. The tris(bipy) complex was crystallized as [Tl(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)5Pt−Tl(CN)n(solv)]n- (n = 0−3) have been modified by attaching bipy molecules to the thallium atom. A
reaction between [(NC)5Pt−Tl(dmso)4](s) and 2,2‘-bipyridine in dimethyl sulfoxide solution results in the formation
of a new complex, [(NC)5Pt−Tl(bipy)(solv)]. The presence of a direct Pt−Tl bond in the complex is convincingly
confirmed by a very strong one-bond 195Pt−205Tl spin−spin coupling (1J(195Pt−205Tl) = 64.9 kHz) detected in both
195Pt and 205Tl NMR spectra. In solutions containing free cyanide, coordination of CN- to the thallium atom occurs,
and the complex [(NC)5Pt−Tl(bipy)(CN)(solv)]- (1J(195Pt−205Tl) = 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)5Pt−Tl(bipy)(dmso)3] (2) and [(NC)5Pt−Tl(bipy)2] (3). The Pt−Tl bonding distances in the
compounds, 2.6187(7) and 2.6117(5) Å, 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−Tl vibrations and are characteristic for a single metal−metal bond.
Electronic absorption spectra were recorded for the [(NC)5Pt−Tl(bipy)m(solv)] compounds, and the optical transition
was attributed to the metal−metal bond assigned.