Aurophilicity

In chemistry, aurophilicity refers to the tendency of gold complexes to aggregate via formation of weak metallophilic interactions.

[1][2] The main evidence for aurophilicity is from the crystallographic analysis of Au(I) complexes.

[1][3] Observations and theory show that, on average, 28% of the binding energy in the aurophilic interaction can be attributed to relativistic expansion of the gold d orbitals.

[5] The similarity in strength between hydrogen bonding and aurophilic interaction has proven to be a convenient tool in the field of polymer chemistry.

[6] An important and exploitable property of aurophilic interactions relevant to their supramolecular chemistry is that while both inter- and intramolecular interactions are possible, intermolecular aurophilic linkages are comparatively weak and easily broken by solvation; most complexes that exhibit intramolecular aurophilic interactions retain such moieties in solution.

When the ligand on the left is treated with 3 equivalents of a gold(I) halide (with each phosphine group coordinating a separate gold center), the aurophilic interaction between gold atoms hinders free rotation around single bonds. The temperature required to restore free rotation on the NMR timescale is a measure of the strength of the aurophilic interaction. [ 1 ]
Gold(I) complexes can polymerize by intermolecular aurophilic interaction. Nanoparticles that form from this polymerization often give rise to intense luminescence in the visible region of the spectrum . Strength of particular intermolecular aurophilic interactions can be gauged by solvating the nanoparticles and observing the extent to which luminescence diminishes. [ 1 ]