Tellurium structure

Figure 16.1 Structures of various allotropes of selenium and the structure of crystalline tellurium (a) the Seg unit in a- fi- and y-red selenium (b) the helical Se chain along the c-axis in hexagonal grey selenium (c) the similar helical chain in crystalline tellurium shown in perspective and (d) projection of the tellurium structure on a plane perpendicular to the c-axis.

A comparison of 160 and 100 is also instructive. The former contains two more electrons than the latter (Te2 vs. Sb2) and this results in quite different structures being adopted, with the tellurium structure more open than the antimony structure (i.e., less M—E bonds). 

However, an X-ray crystal study of one of the derivatives of 21, 3-phenyl-5-(4-methoxyphenyl-1,2-oxatellurolyl-l-ium chloride 21 (R = Ph, Ar = C6H4OMe-4) justifies its T-shaped tricoordinate tellurium structure (83JA875), which is portrayed in Fig. 4. 

The subhalides of tellurium are an especially important class of solid state compounds, and they have been the subject of intensive studies, so that a rather complete picture of their chemistry and their properties has been obtained in recent years. Because of their high tellurium content they contain fragments of the homonuclear tellurium chains their modified tellurium structures are of great current interest with respect to possibly significant physical properties. Consequently, the results of various investigations on the synthesis of the compounds, on phase analysis by thermal methods, on crystal growth, on the structures, on spectroscopic, thermodynamic, optical, photoelectric, electrochemical properties have been reported in the last two decades. In a comprehensive review (237) all significant results are reported and discussed in detail so that the present chapter will be restricted to some selected and chemically important features. 

The tellurium subhalides represent a group of recently discovered compounds which have been investigated by the methods of solid-state and structural chemistry. Because of their high tellurium content and their crystal structures containing homonuclear tellurium connections they have attained significance as modified tellurium structures . As a consequence, tellurium subhalides have been the subject of various investigations in the fields of solid-state and chemical physics. 

Big. 19. Structural units of tellurium and telluriiun subhalides t modified tellurium structures . The upper numbers (bond lengths and bond angles) in Tc2X refer to X=Br, the numbers below toX=I... 

With respect to the homonuclear linkage of tellurium atoms, the tellurium subhalides may be described as modified tellurium structures . The 3i-chain of the element is modified by steps, going from a 2,-chain in Te3Cl2 to a ribbon of condensed planar zigzag chains in Te2X and a separated planar zigzag chain in 3-Tel down to a four-membered tellurium ring in a-Tel. 

Detailed optical investigations of tellurium subhalides have been carried out on Te3Cl2 and a-Tel which, from the point of view of, modified tellurium structures are the structural antipodes. 

Tellurium dioxide, Te02- Obtained by burning Te in air or heating tellurales(IV). Has rutile or brookile structures. Almost insoluble in water but gives tellurates(IV) with bases and, e g., TeCl4 with acids. 

This review is structured as follows. In the next section we present the theory for adsorbates that remain in quasi-equilibrium throughout the desorption process, in which case a few macroscopic variables, namely the partial coverages 0, and their rate equations are needed. We introduce the lattice gas model and discuss results ranging from non-interacting adsorbates to systems with multiple interactions, treated essentially exactly with the transfer matrix method, in Sec. II. Examples of the accuracy possible in the modehng of experimental data using this theory, from our own work, are presented for such diverse systems as multilayers of alkali metals on metals, competitive desorption of tellurium from tungsten, and dissociative... 

Tellurium nitride was first obtained by the reaction of TeBt4 with liquid ammonia more than 100 years ago. The empirical formula TeN was assigned to this yellow, highly insoluble and explosive substance. However, subsequent analytical data indicated the composition is Tc3N4 which, in contrast to 5.6a and 5.6b, would involve tetravalent tellurium. This conclusion is supported by the recent preparation and structural determination of Te6N8(TeCl4)4 from tellurium tetrachloride and tris(trimethylsilyl)amine (Eq. 5.5). The TceNs molecule (5.12), which is a dimer of Tc3N4, forms a rhombic dodecahedron in which the... 

There is no evidence for the tellurium analogues ArN=Te, but the cyclic trimers (EN Bu)3 (E = Se, Te) are stable crystalline solids that have been structurally characterized (Section 6.3). 

The selenium analogue [PhCNSeSeN] and cyano-functionalized diselenadiazolyl radicals adopt cofacial dimeric structures, e.g., 11.4 (E = Se), with unequal Se Se interactions of ca. 3.15 and 3.35 A. In the latter case the radical dimers are linked together by electrostatic CN Se contacts.Tellurium analogues of dithiadiazolyl radicals (or the corresponding cations) are unknown, but calculations predict that the radical dimers, e.g., 11.4 (E = Te), will be more strongly associated than the sulfur or selenium analogues. ... 

Intramolecular heteroatom coordination may also influence the stabilities or structures of catenated tellurium compounds. For example, a rare example of a tritelluride, bis[2-(2-pyridyl)phenyl]tritelluride, is stabilized by a Te N contact of 2.55 The ditelluride (2-MeOCelFtCOTe) has an unusual planar structure. Although the C=0 Te interaction is longer (3.11 A) than the Me 0 contact (2.76 A), ab initio molecular orbital calculations indicate that the planarity results predominantly from the former intramolecular connection. 

Figure 16.11 Structural relations between tellurium and its subhalides (a) tellurium, (b) Te3Cl2, (c) Te2Br and Te2l, (d) /3-TeI, and (e) a-Tel.

Se3Bri3- < > SeCls , TeClj-, TeCle ", etc.< > The anion structures are much as expected with the Se species featuring square planar (pseudo-octahedral) units, and the trinuclear Se " anions as in the tellurium analogue above. See also p. 776. There are, in addition, a fascinating series of bromoselenate(II) dianions based on fused planar SeBr4 units, e.g. Se3Brg ", Se4Bri4 ,... 

The two mixed tellurium(IV) halides listed in Table 16.5 were prepared by the action of liquid Br2 on TeCl2 to give the yellow solid TeBr2Cl2, and by the action of I2 on TeBr2 in ether solution to give the red crystalline TeBr2l2 their structures are as yet unknown. 

The similarity of the electronic structures of thiophene and tellurophene [72JCS (Pl)199] implies that their chemistry toward Fc3(CO)l2 should be the same. Thus, tellurophene produces [Fe3Fc2(CO)9], ferrole 83, and 114 [72JOM(42)C87,96JCS (D)1545]. The same trend is observed in the reactions of the derivatives of tellurium and selenium heterocycles [97JCS(D)1579, 98JCS(D)3947]. 

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