Thallium atom

Alloys of lead and thallium have a structure based upon cubic closest packing from 0 to about 87-5 atomic percent thallium. The variation of the lattice constant with composition gives strong indication that ordered structures PbTl, and PbTl, exist. In the intermediate ranges, solid solutions of the types Pb(Pb,Tl)a and Pb(Pb,Tl)TlB exist. Interpretation of interatomic distances indicates that thallium atoms present in low concentration in lead assume the same valence as lead, about 2-14, and that the valence of thallium increases with increase in the mole fraction of thallium present, having the same value, about 2-50, in PbTls and PbTl, as in pure thallium. A theory of the structure of the alloys is presented which explains the observed phase diagram,... 

A very simple treatment can be carried out by assuming that the liquid phase is a series of ideal solutions of lead and thallium, and that in the solid phase isomorphous replacement of thallium atoms in the PbTl3 structure by lead atoms occurs in the way corresponding to the formation of an ideal solution. For the liquid phase the free energy would then be represented by the expression... 

TpAnt]Tl, and that the composition of the crystal studied was approximately [TpAnt](CoNCS)0.94TI0.06. As a consequence of the cocrystallization, the crystallographic site occupied by the CoNCS moiety was disordered with a thallium atom (Fig. 57). The ability of [TpAnt]CoNCS and [TpAnt]Tl, which differ substantially in the number of atoms at the disordered site, to cocrystallize is presumably due to the fact that the disordered site is enclosed within the pocket that is provided by the tris(pyrazolyl)hydroborato ligand. 

KT1 does not have the NaTl structure because the K+ ions are too large to fit into the interstices of the diamond-like Tl- framework. It is a cluster compound K6T16 with distorted octahedral Tig- ions. A Tig- ion could be formulated as an electron precise octahedral cluster, with 24 skeleton electrons and four 2c2e bonds per octahedron vertex. The thallium atoms then would have no lone electron pairs, the outside of the octahedron would have nearly no valence electron density, and there would be no reason for the distortion of the octahedron. Taken as a closo cluster with one lone electron pair per T1 atom, it should have two more electrons. If we assume bonding as in the B6Hg- ion (Fig. 13.11), but occupy the t2g orbitals with only four instead of six electrons, we can understand the observed compression of the octahedra as a Jahn-Teller distortion. Clusters of this kind, that have less electrons than expected according to the Wade rules, are known with gallium, indium and thallium. They are called hypoelectronic clusters their skeleton electron numbers often are 2n or 2n — 4. 

From an analysis of their data, Materlik and co-workers were able to determine that for the ex situ case and in the absence of oxygen, the thallium atoms are located at twofold sites at a mean distance of 2.67 0.02 A. For the in situ case and again in the... 

When dioxane is added to [Au(C6C1s)2T1]00 (Equation (108)),120 a simple dimer results in which the Au-Tl groups are connected via a dioxane bridge between the two thallium atoms 132.120 The thallium atom is coordinated in a 7r-fashion to the toluene which served as the solvent of the reaction. The Tl(i) ion does not exhibit a stereochemically active lone pair, and the blue luminescence was attributed to an Au Tl charge transfer transition. 

The only thallium compound to be discussed here is the Tlf,Cl2[Si(CMe3)3]6 cluster 61. This remarkable compound was formed by the reaction of thallium) 111) chloride with NaSi(CMe3)3 [Eq. (28)] and precipitated in the form of black crystals in 21% yield, when a solution in toluene was stored at —25 °C for six months [92], Solutions of 61 in benzene decompose slowly at room temperature by the formation of ClSi(CMe3)3 and a black, not identified precipitate. The structure of 61 consists of two four-membered T13C1 heterocycles, which are connected by one Tl-Tl and two Tl-Cl bonds. A monomeric TI3CI heterocycle was isolated as a byproduct in which one thallium atom was bonded to two Si(CMe3)3 substituents. 

Figure 5 Structures of TIjBa Ca jCu Oj,. (n = 1,2,3). Thallium atoms are shown on ideal (octahedral-type) sites for clarity (see text). Metal atoms are shaded and Cu-O bonds are shown.

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 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... 

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