Weak aurophilic interactions in a series of Au(iii) double salts

Abstract

In this work, several new examples of rare Au(III)Au(III) aurophilic contacts are reported. A series of gold(iii) double salts and complexes, viz. [AuX2(L)][AuX4] (L = 2,2'-bipyridyl, X = Cl , Br ; L = 2,2'-bipyrimidine, X = Cl , Br ; L = 2,2'-dipyridylamine, X = Cl , Br ), [AuX3(biq)] (biq = 2,2'-biquinoline, X = Cl , Br ), [LH][AuX4] (L = 2,2'-bipyridyl, X = Cl ; L = 2,2'-bipyrimidine, X = Cl ; L = 2,2'-dipyridylamine, X = Cl , Br ; L = 2,2'-biquinoline, X = Cl , Br ), [AuBr2(bpy)]2[AuBr4][AuBr2] , [AuCl2(bpm)][AuCl2] , (bpmH)2[AuBr4][AuBr2] , and (dpaH)[AuBr2] (, , and were reported earlier) was synthesized by coordination of a particular ligand to the Au(III) center and subsequent reduction of the formed product with acetone. Inspection of the X-ray structural data for , , and indicates that the Au(III) metal centers approach each other closer than the sum of their van der Waals radii, thus forming the aurophilic contacts, which were confirmed by topological charge density analysis according to the Quantum Theory of Atoms in Molecules (QTAIM). In , , and , such contacts are located only between the metal centers of the ion pair, whereas in , the aurophilic interactions form the cation-anion-anion array, and in , the aurophilicity exists between the gold atoms of the cations. It was also demonstrated that the interatomic distance alone is not a reliable measure of the aurophilic interactions, at least at the weakest limit of the interaction strength, and it needs to be complemented with structural analysis of the whole molecule and computational results.

Probing Conformational Variation in Luminescent Dinuclear Gold(I) N‐Heterocyclic Carbene Complexes

“…The calculated density at the BCPs is slightly greater than reported in a study of Au III –Au III interactions (0.036–0.078 e Å –3 ). [22a] The marginally greater electron density with the pyridine linker is consistent with the shorter Au ··· Au bond length.…”

“…It has been argued that Bondi's vdW radii are too small, which limits their use in the identification of aurophilic interactions . In contrast, twice the largest proposed vdW radius yields 4.86 Å,[22b] which is much larger than typical aurophilic interaction distances. There are clear difficulties in identifying aurophilic interactions based purely on structural properties, nevertheless, it provides an initial indication of the presence of aurophilic interactions.…”

“…In the open conformations the Au ··· Au distances (7.143–7.190 Å with methyl wingtips) clearly exhibit no aurophilic interaction, being significantly greater than the largest proposed vdW radius of 4.86 Å. [22b]…”

“…[4a] The generally accepted value for the vdW radius of gold is 1.66 Å as proposed by Bondi, which is the smallest of the values that have been suggested (values range from 1.64 to 2.43 Å). [4a], The sum of two Bondi gold vdW radii is 3.32 Å, which is at the upper end of typical aurophilic interaction distances of 2.80 to 3.50 Å. [4a] Schmidbaur[2a] has proposed an Au I vdW radius of 1.90 Å (sum is 3.80 Å).…”

Molecular Gold Wire from Mixed‐Valent AuI/III Complexes

“…The differences of the aurophilic interactions between Au II atoms and between Au I and Au III atoms as well as the interconversion of these has been of high interest . However, there are still only few examples for unsupported aurophilicity in mixed‐valent gold(I/III) or between gold(III) complexes –. A crystal structure of an Au III dioximato complex with a dichloridoaurate anion was first published in 1954 and revised in 2006 reporting a linear arrangement of the gold atoms and a gold(I)–gold(III) distance of 325.35(5) pm.…”