Gold-thallium supramolecular complexes

The first descriptions of heteronuclear luminescent supramolecular complexes were given by Fackler et al. in 1988 and 1989. In these studies, one gold-thallium and one gold-lead complex were reported. As in the case of the gold-silver dinuclear systems, the extended systems appeared as a result of the unidirectional polymerization of dinuclear or trinuclear units through metal-metal interactions. These were prepared by reaction of the gold precursor [PPN][Au(MTP)2] (PPN = N(PPh3)2 ... 

As described above, among the several closed-shell metal ions that form luminescent supramolecular entities with gold, thallium(I) forms the most numerous examples. While aurophilic attractions can be considered the upper extreme of the metallophilic interactions (with values up to 46 kJ mol-1), intermetallic contacts involving T1(I) centers appear as the weakest ones (even <20 kJ mol-1),46 which is explained by the enhancement of the Au---Au interactions and the weakening of the Van der Waals attractions between the s2 metal atoms produced by the relativistic effects.47 Nevertheless, the complexes in which this interaction appears are surprisingly stable, with additional electrostatic, packing forces, or the ligand architecture, responsible for this fact. 

Reactions between basic gold(I) complexes and acid thalliumff) salts, which give rise to supramolecular networks formed via acid-base stacking containing unsupported gold-thallium interactions. 

A. Supramolecular Gold-Thallium Complexes with Bidentate Ligands... 

Of the metals that form luminescent supramolecular entities with gold, that for which most complexes are known is thallium in its +1 oxidation state. As described below, in recent years the contributions of several laboratories have been reported. Nevertheless, in some cases, the papers also report similar reactions with other metals, leading to similar structures. In order to maintain a congruent synthetic description, those examples will be discussed together as they appear in the original work. 

A particular case is that of d -d secondary interactions, first identified in gold compounds and described as aurophilic attraction [78-80], later generalized as metallophilic attraction [81]. This leads to supramolecular self-assembly in many gold compounds, especially when associated with three-center Au- -C Au bonds, and can be also found in other d metal compounds, such as silver, gold, and thallium complexes. Such supermolecules are illustrated by the quasi-cyclic pen-tamers Au5(Mes)5 and Cus(Mes)5, 33, and the tetramer Ag4(Mes)4, 34 [82]. 

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