Thallium cluster

Another contribution is represented by an investigation of a cubic thallium cluster phase of the Bergmann type Na13(TlA.Cdi A.)27 (0.24 < x <0.33) (Li and Corbett 2004). For this phase too the body centred cubic structure (space group Im 3, a = 1587-1599 pm) may be described in terms of multiple endo-hedral concentric shells of atoms around the cell positions 0, 0, 0, and 14,14,14. The subsequent shells in every unit are an icosahedron (formed by mixed Cd-Tl atoms), a pentagonal dodecahedron (20 Na atoms), a larger icosahedron (12 Cd atoms) these are surrounded by a truncated icosahedron (60 mixed Cd-Tl atoms) and then by a 24 vertices Na polyhedron. Every atom in the last two shells is shared with those of like shells in adjacent units. A view of the unit cell is shown in Fig. 4.38. According to Li and Corbett (2004), it may be described as an electron-poor Zintl phase. A systematic description of condensed metal clusters was reported by Simon (1981). 

The most extensive series of compounds that fall within this section are the anionic iron carbonyl-thallium clusters recently described by Whitmire (30-30h). These are generally made by reactions between iron carbonylate anions and either T1(I) or Tl(III) salts. Thus treatment of K[HFe(CO)4] with a variety of thallium salts followed by addition of [Et4N]Cl or Br affords the hexanuclear complex [Et4N]2[ Fe(CO)4 2 //-TlFe(CO)4 2], 17... 

Studies have been continued by Glaser and his co-workers on platinum-thallium clusters. Very large 7ptxi couplings ranging from 48 to 66 kHz have been observed by them for [(NC)5PtTl(en) i] ( = 1-3) complexes where en denotes ethylenediamine. 

The extreme hypoelectronicity of the indium and thallium clusters can be relieved by d-orbital participation from some of the vertex metal atoms. In the case of a normal bare post-transition metal vertex in a metal cluster sucb as those discussed in Section 10.6.1, tbe 12 external electrons may be divided into two types, namely, tbe 10 nonbonding d electrons and tbe 2 electrons of an external lone pair analogous to tbe B-H bonding pair in the polyhedral boranes B H (6 < n < 12). In this way a normal post-transition metal vertex such as indium may be considered to use a four-orbital sp bonding manifold just like light vertex atoms such as boron or carbon. However,... 

The growth of thallium clusters has been also observed by time-resolved optical spectroscopy. The coalescence steps are comparable with those of silver and the final plasmon band of Tl is located at 300 nm. ... 

This alternation of properties suggests that clusters of group-IIIB elements could display an intriguing variety of structures and properties. Unfortunately, extensive experimental data is available only for clusters of the simplest of these elements, i.e. aluminum. Less systematic but nevertheless abundant data has also been reported for indium. Boron, gallium and thallium clusters, by contrast, have been only marginally investigated in experiments. 

Some platinum-thallium clusters were touched upon in Section 8.07.1.5.2, here we look at additional examples in more detail. A synthesis of 53 that relies on the reaction of a thallium / -diketonate with 20 has been reported (Scheme II). The simple procedure gives yields in the range 60-75%, and X-ray structures confirm the triply... 

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. 

Fig. 32. Schematic illustration of the thallium-iron cluster compounds (a) [TI2Fe4(CO)I6]2-, (b) Fe2(CO) (c) [Tl2Fe6(CO)Mr, (d) [Tl4Fe8(CO)3o]4-. (e) [TleFe COy6-.

The only new report of a group 7 complex with thallium is the reaction of [Re7C(CO)2i]3 ion with T1PF6 (Equation (92)).94 The thallium adds in a triply bridging fashion opposite to the capping Re(CO)3 unit 99.94 The complex is stable in dichloromethane but dissociates in coordinating solvents. In acetone, infrared data indicated that the complex would be 99% dissociated at concentrations of the cluster of about 10-4M. Addition of halide ions to dichloromethane solutions causes a precipitation of the thallium(i) halide. 

Apparently Hypoelectronic Deltahedra in Bare Clusters of Indium and Thallium Polyhedra with Flattened Vertices... 

This section will focus on homonuclear neutral or anionic clusters of the elements aluminum, gallium, indium, and thallium, which have an equal number of cluster atoms and substituents. Thus, they may clearly be distinguished from the metalloid clusters described below, which in some cases have structures closely related to the allotropes of the elements and in which the number of the cluster atoms exceeds the number of substituents. The compounds described here possess only a single non-centered shell of metal atoms. With few exceptions, their structures resemble those of the well-known deltahedral boron compounds such as B4(CMe3)4 [30], B9CI9 [31] or [B H ]2 [32]. The oxidation numbers of the elements in these... 

Organoelemental thallium(I) compounds were prepared by similar routes starting with thallium(I) cydopentadienide, for instance [Eq. (4)]. In contrast to the clusters described so far, the metal-metal interactions in the tetrahedral dusters of compound 19 [42] or of the related pyrazolato derivative 20 [43] (Figure 2.3-4) are quite weak their bonding situation and stability are discussed in Section 2.3.3.1.2. 

Homonuclear clusters of the heavier elements of the third main-group aluminum, gallium, indium and thallium having direct element-element interactions form a fascinating new class of compounds. As discussed in the previous Chapter 2.3, in some cases their structures resemble those known with the lightest element of that group, boron, while in other cases novel, metal-rich compounds were obtained which do not have any analogue in boron chemistry. 

Clusters of the elements aluminum to thallium containing only one or two carbon atoms and strong direct element-element interactions, similar to boron rich car-baboranes, have not yet been synthesized, and also the corresponding silicon derivatives are relatively rare. To the best of our knowledge only one aluminum-silicon and one gallium-silicon cluster (1 and 2) has been reported in the literature. The reaction of metastable aluminum(I) chloride with decamethylsilicocene or with a mixture of SiCl4 and (AlCp )4, respectively, afforded black crystals of... 

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. 

Al, Ga, In and T1 differ sharply from boron. They have greater chemical reactivity at lower temperatures, well-defined cationic chemistry in aqueous solutions they do not form numerous volatile hydrides and cluster compounds as boron. Aluminium readily oxidizes in air, but bulk samples of the metal form a coherent protective oxide film preventing appreciable reaction aluminium dissolves in dilute mineral acids, but it is passivated by concentrated HN03. It reacts with aqueous NaOH, while gallium, indium and thallium dissolve in most acids. 

Notes on cluster phases in triel alloys. Li and Corbett (2004) have shortly reviewed the systematic and extensive experimental and theoretical work carried out by Corbett and co-workers (see for instance Corbett 1996). Considering alkali metal-triel alloys, they underlined, particularly for Ga, In and Tl, the richness of their chemistry (see also 5.3.4.4). Gallium forms many anionic network structures (and only a few phases containing isolated cluster units), indium gives several examples of both network and discrete cluster structures, thallium forms especially discrete clusters (Tl , T157A Tl , Tl , Tl(f, Tl ). 

One of the most interesting bare Group 13 metal clusters is the first one to be discovered [66], namely the 11-atom cluster frin in the intermetallic Kglnn-Analogous 11-vertex clusters were subsequently synthesized containing gallium [67] and thallium [68]. The frin cluster has 11+7=18 skeletal electrons = 2 n - 4 for n = 11. It is thus a highly hypoelectronic system relative to the 2n + 2 skeletal electron deltahedral boranes B H . The polyhedron found in Inn is... 

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