Thallium centers

Long X-Tl (X = halogen) contacts between the thallium center and halogen atoms of the almost linear [AuR2] unit seem also to contribute to the stability of many of these systems. It is worth noting that theoretical studies revealed for the Au-Tl interaction in these systems a surprising calculated strength of about 276 kj mol-1, from which 80% is due to an ionic contribution and 20% to dispersion (van der Waals) [55]. 

Our first study of these systems was the synthesis in 1998 of the polymeric complex [ 1( 6 5)2( )2] through the reaction between triphenylphosphine oxide, thallium nitrate and lithium bis(pentafluorophenyl)aurate(I) [71]. This complex consisted of an extended unsupported linear chain of alternate gold and thallium centers. These atoms displayed Au-Tl interactions of 3.0358(8) and 3.0862(8) A, and the thallium atoms showed a distorted pseudo-trigonal-bipyramidal environment, taking into account the stereochemically active inert pair of this atom. As described below, the environment around thallium is one of the main factors that affects the optical properties of these mixed systems. 

The importance of the environment was also evident in the ID, 2D or 3D polymers [ TI(4,4 -bipy)THF Au(C6F5)2] , [Tl(l,10-phen) Au(C6F5)2] , [Tl(py)2] [Au(C6F5)2] and [ TI(2,2 -bipy) Au(C6F5)2] [76]. In all cases, the structures displayed an alternate arrangement of gold and thallium centers, which exhibited a wide range of metal-metal distances, even within the same complex. For instance, the... 

The previous reactions highlighted the role of the bis(perhalophenyl)aurates as donors of electronic density to the thallium atoms. These reactions can be considered to be Lewis neutralizations and lead to polymeric systems. In addition, the thallium centers incorporated in the reactions additional ligands (sometimes the solvent) into... 

A tetracobalt anionic complex, viz. [In Co(CO)4 4] (27) (37,37a), has been briefly described together with the thallium analogue (28) (37a), both formed by addition of [Co(CO)4] to either 25 or 26. No structural details have been reported although the indium and thallium centers are presumably tetrahe-drally coordinated by the four cobalt atoms. Mention is also made (37a) of the facile heterolytic bond dissociation (In—Co or Tl—Co) observed in polar solvents. Little has been reported about the reactivity of these complexes, although a discussion on the use of 25 as a catalyst in the dimerization of norbornadiene has appeared (58). 

FIGURE 16. Linear chains showing the different environments at the thallium centers. (a)L = OPPh3,R — C6F5 (b)L — OPPh3,L — acetone or tetrahydrofuran, R — C6C15. 

As commented above, different compositions lead to different emission energies, and these systems emit at 646, 609, 620, 606, and 683 nm, respectively, by excitation at 550 nm. Furthermore, there is no correspondence of the emissions with the gold-thallium lengths since all of them range from 2.9 to 3.1 A or with the environment around the thallium centers. As a plausible explanation it was reported that each 2D or 3D network could probably lead to different excited states, and the formation of such networks might be influenced by the presence or absence of coordinating solvents in their structures. 

The remaining structures for this group are organothallium(III) structures. The immediate coordination geometry about the thallium center in the structure of Me2Tl(S2COMe) (201) is shown in Fig. 122. The xanthate ligand chelates one... 

A detailed, multimethod study of hydrated Tl(III) cyanide species in aqueous solution reveals that Tl(III) forms very strong complexes with cyanide ions (even stronger than halide-Tl(III) interactions)." " Formation of a series of Tl(III) complexes T1(CN) n= -4t) has been established, and the solution structures and stability constants were reported. The mono- and dicyano complexes [Tl(CN)(OH2)5] and [Tl(CN)2(OH2)4] show six-coordinate thallium centers, whereas Tl(CN)3(OH2) and [T1(CN)4] have four-coordinate T1(III) ions. 

A tris(imidazolyl)borate (138) complex of thallium(I) has been synthesized.The solid-state structure of hydrotris(imidazolyl)boratothallium(I) consists of one-dimensional, twisted, ladderlike strands, and three-coordinate thallium centers. Due to the position of the nitrogen donors, the tris(imidazolyl)borate ligand is not capable of forming metal chelates as are observed in tris(pyrazolyl)borates. Poly(benzotriazolyl)borate ligands have some features of both tris(pyrazo-lyl)borate and tris(imidazolyl)borate systems. Thallium(I) complexes of bis-, tris-, and tetrakis (benzotriazolyl)borates are reported. These adducts have been synthesized by treating the corresponding potassium derivative with an equimolar quantity of thallium(I) formate. ... 

Tl(Bp4Bo)] exhibits Tl-Bpx units with pronounced Tl-jtazoiyi interaction between neighboring molecules, and extended 3D and ID structures through the bridging action of the poly(pyrazolyl)borate ligand between three symmetry related thallium centers.49... 

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