Atomic coordinates, thallium

A), while the second thallium ion is three-coordinate with an additional interaction with the pyridyl nitrogen atom (Tl—N distance is 2.468(15) A). The metal-metal interaction occurs between the three-coordinate thallium ion of one molecule and the two-coordinate thallium ion of a neighbouring dimer. 

The structures of four tri-t-butoxysilanthiolates 210-213 have been reported. Whereas 210 is tetrameric with a nearly planar eight-membered ring, 211 and 212 are dimeric. In addition to the two thiolate S atoms the thallium atoms in 211 are also coordinated, albeit more weakly, by one butoxy O atom at a distance of 2.799(4) A. A similar (2+1) coordination is found for the mercury atoms in the monomeric species 212 [d(Hg-O) = 2.878(4) A]. Remarkably short Si-S distances are found in 213 and, in particular, 211 [2.078(2) A], suggesting that the M-S bonds (M = Pb, Tl) may exhibit a marked degree of ionicity in these compounds. 

The discussion of the main group 3-5 and 3-6 compounds in the previous sections was limited to examples in which the group 3 element E is three-coordinate, so that an empty p-orbital on E is available for overlap with a lone pair on the group 5 or 6 atom. For the same reason, the discussion here will focus on those compounds with three-coordination at gallium, indium, or thallium. In the case of the transition metal derivatives, it is transition metal -electrons that are available to overlap with the empty p-orbital on E to form the potential ir-bond, as illustrated in Fig. 26. 

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. 

A traditional example of a Zintl phase is represented by NaTl which may be considered as a prototype of the Zintl rules. The structure of this compound (face centred cubic, cF16, a = 747.3 pm) can be described (see also 7.4.2.2.) as resulting from two interpenetrating diamond type lattices corresponding to the arrangements of the Na and T1 atoms respectively (Zintl and Dullenkopf 1932). Each T1 atom therefore is coordinated to other four T1 at a distance a)3/4 = 747.3)3/4 = 323.6pm which is shorter than that observed in elemental thallium (d = 341-346 pm in aTl, hP2-Mg type, CN = 6 + 6) and d = 336pm in /3 Tl, (cI2-W type, CN = 8). 

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