Metallophilicity

A transmetallation reaction was used to synthesize the complex [Au(C6F5)2][Bi (C6H4CH2NMe2-2)2j [119] and the crystal structure of the complex was studied by X-ray diffraction. This is the first example of metallophilic interactions of the Bi(111) atom and this is the most interesting characteristic of this complex, the presence of Au Bi distances of 3.7284(5) A. 

Hermann, H.L., Boche, G. and Schwerdtfeger, P. (2001) Metallophilic Interactions between Closed-Shell Copper(I) Molecules - A Theoretical Study. Chemistry A European Journal, 7, 5333-5342. 

O Grady, F. and Kaltsoyannis, N. (2004) Does metallophilicity increase or decrease down group 11 Computational investigations of [Cl-M-PHj]2 (M=Cu, Ag, Au, [111]). Physical Chemistry Chemical Physics, 6, 680-687. 

Catalano et al. reported the synthesis and characterization of a new series of Pd°-based metallocrypates that bind Tl1 ion in the absence of attractive ligand interactions through metal-lophilic connections. The cationic species have been characterized by a variety of methods and have considerable stability. From the solid-state structural data it is apparent that interaction of the metal atoms with one another is the dominant bonding interaction within the metallocryptate cavity. The characterization of complexes supports the concept of metallophilic behavior as a fundamental component of bonding in closed-shell systems. These materials may ultimately serve as prototypical systems for detection of closed-shell ions 946... 

Scheme 5 shows a group of alkynylgold(i) complexes for which the studies focused on the UV-VIS electronic absorption and emission properties. Most of these compounds are of the type [(L)AuC=CR], for which the methods of synthesis have been summarized above. The products were found to show phosphorescence in various polymorphs and crystal forms of solvates. Although there are no metallophilic interactions discernible in the crystal between most of the monomers due to the steric effect of the large tertiary phosphines, there is nevertheless strong excitonic coupling based on other weak interactions, which depend on the organization of the molecules in the crystal.105,106... 

In the crystal, most trinuclear carbeniate complexes are known to be stacked with close aurophilic interactions, and organic 7r-acids can be intercalated into these stacks.252 Similar intercalation takes place with the cations of simple silver and thallium(i) salts. The cations become attached to form polymetallic core units through metallophilic bonding. With the trinuclear silver pyrazolates, both metal and ligand exchange have been observed to give new stacks of trinuclear units.254... 

As in the case of the gold-silver analogous systems, perhaps the most productive method for preparing extended systems through metallophilic interactions is the acid-base process, in which basic gold(I) precursors react with metallic Lewis acids forming supramolecular networks via acid-base stacking. The cation-anion interactions assist the formation of extended chains. 

II) 22, Pt(II)-Ag(I)23) have been reported. Theoretical studies of selected examples have been carried out.4 In these complexes, whose number is increasing every day, the metallophilicity promoted by gold seems to be a key factor. In fact, the well-known aurophilicity that justifies the aggregation in gold complexes seems not to be an isolated phenomenon instead, the presence of gold in the complexes seems to increase the metallophilicity of the other metals and, consequently the presence of metal-metal interactions.24... 

The most common strategy in the synthesis of heteronuclear complexes is the use of bidentate donor ligands bearing different donor centers. In that way both donor atoms can be coordinated selectively to two different metal centers in a consecutive way. If the space between the donor atoms of the ligands is short, interactions between both metals usually appear, normally intramolecular. Sometimes, albeit not very often, the bidentate units bind to one another, leading to extended structures through metallophilic interactions. As we have commented, in the case of gold-silver derivatives the number of luminescent studies of these derivatives is very scarce. 

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. 

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