Intermolecular aurophilic interactions

In many cases the molecules associate though intermolecular aurophilic interactions leading to the formation of chains, some examples are [Au2 S2CNPr2 2],... 

Replacement of the N-methyl groups with the bulkier N-benzyl or N-isopropyl groups did not reproduce any columnar stack in the crystal structure that was found in 9, and no solvoluminescent behavior was observed [110, 111]. The closest intermolecular Au-Au contact of 3.662 and 6.417 A in the crystal packing in 10a and 10b (Fig. 14), respectively, indicated the absence of any intermolecular aurophilic interaction. 

Each trinuclear molecule of the polymer is planar and displays a very similar structure to that of the individual molecule of Au3( jl-. C3H 4)3]2 with Au- -Au distances of 3.309(2) and 3.346(3) A within the molecule. As in the case of the hexanuclear unit, the intermolecular Au- -Au contacts are closer than the intramolecular ones, with a pairwise Au- -Au distance of 3.146(3) A and a single Au- -Au interaction at the other end of the molecular triangle of 3.077(2) A. It is worth noting that the presence of two different types of intermolecular aurophilic interactions in one crystal is unusual. However, in the solid state [S Au(PMe3) 3]+ does display a chain motif that includes alternating single and double sets of Au- - Au contacts.117... 

Stacking in all of these complexes is the result of additional intermolecular aurophilic interactions between four of the six Au1 atoms in adjacent units giving rise to stacked linear-chain structures with a -BBABBA- pattern. The intermolecular Au1- -Au1 distances, between 3.0658(7) and 3.3298(5) A, are usually similar or slightly shorter (in the case of the mercury derivative) than the intramolecular ones, with average distances between 3.08 and 3.493 A (see Table XXI). Only in the case of the TCNQ derivative the intermolecular aurophilic contacts (3.152 A) are clearly shorter than the intramolecular ones (3.457, 3.471 and 3.534 A), which could be ascribed to charge-transfer from the electron-rich gold center to the electron acceptor TCNQ. 

FIGURE 5.8 Structure of [Au3(MeN=COMe)3] and a diagram showing the extensive intermolecular aurophilic interactions between the gold atoms in the indefinite columnar stacks. 

The electron-rich trinudear Au3 (bzim) 3 and Au3 (carb) 3 react with F6 to yield the sandwich clusters [n Au3(bzim)3 2](PF6) 29 and [n Au3(carb)3 2](PF6) 30 [54]. The cation of both compounds contains atom which interacts in a distorted trigonal prismatic coordination with six Au(I) atoms from two cyclic Au3C3N3 moieties at Au- distances ranging from 2.971(1) to 3.107(1) A, indicative of appretiable metal-metal interaction. Two Au(I) atoms on each planar trinudear unit are involved in intermolecular aurophilic bonding interactions [Au-Au 3.109(1)/3.066(1) A in 29 3.059(1)/3.052(1) A in 30], thus resulting in an infinite columnar chain with a BBABBA- pattern (Figure 4.11). 

The aurophilic interaction appears to be an important paradigm in inorganic supramolecular chemistry because it calibrates intermolecular interactions between domains M. However, because gold is different (for relativistic reasons) [43a, 43b], extension to other metals is ambiguous. 

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