Au-Tl interactions

When [AuTl(C6F5)2]n reacts with DMSO the complex [Tl2 Au(C6F5)2 2 lt-DMSO 3]n [126] is obtained. The crystal structure of this complex shows unsupported Au - Tl interactions that range from 3.2225(6) to 3.5182(8) A but there are no Tl- - - Tl interactions. There are Au- - - Au interactions of3.733 A and the gold centers are almost linearly coordinated to two pentafluorophenyl groups. The complex is strongly luminescent both at room temperature (emits at 440 nm (exc.390 nm)) and at 77 K (emits at 460 nm (exc. 360 nm)). 

The number of compounds with Au-Tl interactions for which the structure has been investigated by single-crystal X-ray diffraction has increased considerably in the last years and some important molecular dimensions are collected in Table 4.3. 

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. 

These complexes present a different disposition of the metals in their striking crystal structures, which display very interesting features. In the acetone derivative the metals are held together through four unsupported Au- -Tl interactions and an additional Tl- -Tl contact resulting in a loosely bound butterfly cluster (Fig. 21), while in the second complex there are only two Au- Tl contacts and a bridging dioxane molecule between... 

Since the early example of Balch et al. [92] of solvent-induced luminescence of a trigold(I) complex, attributed to the presence of columnar Au -Au interactions, other examples have been proposed as efficient VOC detectors based on extended metal-metal contacts involving Au(I), as well as other metal ions. For example, Fernandez et al. described the vapochromic and vapoluminescent behaviour of [T1 [Au(C6Cl5)2] (lOd, Fig. 10), which exhibits a 3D network of Au-Tl interactions... 

AuCN has a similar structure to AgCN and likewise dissolves in excess cyanide to form Au(CN)J this is important in the extraction of gold. It has been characterized as various salts (Tl, K, Bu4N, Cs) with Au-C 1.964A (Bu4N salt [91]). The thallium salt has short Au-Au (3.10A) and Au-Tl (3.50 A) interactions extended-Huckel calculations indicate the importance of relativistic effects in these covalent interactions. Isocyanides form stable complexes ... 

Luminescent trigonal gold(I) metallocryptates have been obtained by reaction of 2,9-bis(diphenylphosphino)-l,8-naphthyridine or 2,9-bis(diphenylphosphino)-l,10-phananthroline PPh2(phen)PPh2 with [AuCl(tht)] (molar ratio 3 2) and in the presence of a cation Na+, Tl+ or Hg°, which is encapsulated in the cavity making Au-M interactions [207]. Similar mixed metal metallocryptands with Pd(0) or Pt(0) have been reported (Figure 1.29) [208]. 

Its absorption spectrum shows one band at 320 nm (e = 2900 M 1cm 1), assigned to the cti - ct2 transition localized in the Au-Tl moiety. The emission spectrum in the solid state at 77 K shows a band at 602 nm, which is attributable to a transition between orbitals that appear as a result of the metal-metal interaction. In this sense, Fenske-Hall molecular orbital calculations indicate that the ground state is the result of the mixing of the empty 6s and 6pz orbitals of gold(I) with the filled 6,v and the empty 6pz orbitals of thallium(I). In frozen solution, this derivative shows a shift of the emission to 536 nm, which has been explained by a higher aggregation of [AuT1(MTP)2] units in the solid state if compared to the situation in solution. 

C6C15) with dimethylsulfoxide (DMSO), which leads to the synthesis of [Tl2 Au(C6F5)2 2 p-DMSO 3] or [Tl2 Au(C6Cl5)2 2 h-DMSO 2]ra, respectively.62 The crystal structure of the complex with fluorine shows a monodimensional polymer formed by repetition of [Au--Tl(p-0 = SMe2)3Tl] units, with gold-thallium interactions of 3.2225(6)-3.5182(8), while the pentachlorophenyl derivative contains two bridging DMSO molecules and an additional [Au(C6Cl5)2] anion. In addition, a thallium-thallium interaction of 3.7562(6) A appears in the latter (Fig. 21). 

In both structures the gold atoms are linearly coordinated to two pentachlorophenyl rings with similar Au-C distances and C-Au-C angles (see Table XVIII). A remarkable difference is observed in Au- -Tl distances, which range from 3.0331(6) to 3.1887(6) A in the butterfly-type compound while the dioxane derivative displays the shortest Au- -Tl distance described to date (2.8935(3) A),149 151-157 being even shorter than the sum of Au and Tl covalent radii (3.08158 or 2.92 A159). The first complex also presents an intramolecular Tl- -Tl interaction of 3.6027(6) A, similar to the distances observed in dimeric [Tl(S2CNEt)2]2 (3.60 and 3.62 A).160... 

Finally, it is worth mentioning that both complexes luminesce in the solid state both at room temperature and at 77 K, showing different luminescent behavior, the dioxane derivative being one of the still scarce blue luminescent materials. In contrast, the acetone complex is also luminescent in solution and shows a solvent dependence on the emission. Luminescence and conductivity measurements suggest that the Tl- -Tl interaction also exists in solution (probably stabilized by solvent molecules) and TD-DFT calculations seem to indicate that this interaction is responsible for luminescence in this case. This contrasts with other pentahalophenyl Au/Tl complexes, in which the optical properties are associated with the Au- -Tl contacts.149,151-154... 

Its X-ray crystal structure consists of one-dimensional linear chains that run parallel to the crystallographic z-axis. Its polymeric nature is a consequence of unsupported Au- -T1 interactions of 3.0044(5) and 2.9726(5) A between [ Au(C6C15)2] and Tl+ ions as shown in Fig. 31. 

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