Gold-donor atom interactions

Crystal structures of [Au2(E E)2]2+ (E = chalcogen donor atom) have been described with dithiocarbamate [265-271], xantate [272], MNT [273-275], dithiopho-sphonate [276], dithiophosphinate [277], dithiophosphate [278, 279] or trithiocarbo-nate [280] ligands. The gold-gold interaction in complexes shown in Figure 2.48 has been analyzed by ab initio Hartree-Fock calculations [281]. 

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. 

The use of asymmetric bridging ligands, which permits a selective coordination of the different donor atoms to the metal centers and leads to supported gold-thallium interactions forced by the ligand. 

Complexes of Silver(i) and Gold(i).—Only three reports have appeared on the structures of gold(i) complexes. There has been rather more interest in the stereochemistry of silver(i) two-co-ordinate linear complexes in which the metal co-ordination is sometimes augmented by weak interactions with other potential donor atoms and organometallic w-complexes have both attracted attention. 

In complexes of gold(I), linear coordination is usual, although Au""Au interactions in the solid state are a common feature (Fig. 22.31a). Trigonal planar and tetrahedral complexes are also found. For Ag(I), Unear and tetrahedral complexes are common, but the metal ion can tolerate a range of environments and coordination numbers from 2 to 6 (the latter is rare) are well established. Both Ag(I) and Au(I) favour soft donor atoms, and there are many complexes with M—P and M—S bonds, including some thiolate complexes with intriguing structures (Fig. 16.12d and Fig. 22.31b). 

In this section I will comment on some examples of gold complexes that display supramolecular entities in the solid state, although in these cases the metal atom is not directly involved in the van der Waals interactions. As in the previous section, the electron density donor can be a non-metal different from hydrogen, which can be a halogen or a chalcogen a hydrogen atom of a covalent NM — H bond or a doud of n electron density. 

Another interesting characteristic of the trinuclear [Au3(CH3N = COR)3] (R = Me, Et) complexes is that they can act as electron donors with organic acceptor molecules such as nitro-9-fluorenones [46]. Thus, they form adducts with 2,4,7-trinitro-9-fluorenone (deep yellow and red R=Me, Et, respectively), 2,4,5,7-tetranitro-9-fluorenone (red R = Me), 2,7-dinitro-9-fluorenone (red R = Et). The solid state structures of the complexes formed with [Au3(CH3N = COMe)3] and 2,4,7-trinitro-9-fluorenone or 2,4,5,7-tetranitro-9-fluorenone consist of planar gold(I) trimers interleaved with the nitro-9-fluorenones to form columns in the crystal. The distances between the faces of both portions indicate that interactions occur between the gold atoms, rich in electronic density, and the nitroaromatic portion of the electron acceptor. The difference between them stems from the greater complexity of the... 

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