Unusual coordination for gold: an imidazolium salt was synthesized and used as a precursor for an N-heterocyclic carbene, which can be considered as the carbene analogue of 1,10-phenanthroline. Like the diimine congener, this ligand gives luminescent metal complexes. Remarkably, the Au(III) complex features a gold atom in an unusual environment: it is surrounded by six donor atoms, two of which interact electrostatically with the Au atom.

Six examples from a series of complex salts containing bis(1,3-dialkylimidazol-2-ylidene)silver(I) cations (with dialkyl = dimethyl, diethyl, methyl, ethyl, diisopropyl) with [PF 6 ] − , [SbF 6 ] − , [ClO 4 ] − , or [AgBr 2 ] − anions, respectively, were prepared in high yields and characterized by elemental analysis, 1 H and 13 C NMR spectroscopy, and mass spectrometry. Single-crystal X-ray diffraction experiments reveal unprecedentedly large contractions of the metallophilic Ag(I)−Ag(I) distances in the solid-state structures upon cooling. In the salt containing diisopropylsubstituted ligands and [PF 6 ] − anions, a contraction from 3.498(8) to 3.180(2) Å was observed on cooling from 293(1) to 100(1) K. Photochemical measurements show strong hypsochromic shifts of the emission maxima upon cooling, underlining the metallophilic-based nature of the emission bands. Ab initio calculations show that the strong temperature dependence of the observed Ag−Ag distances can be attributed to some extent to both the shallowness and the anharmonicity of the intermetallic interaction potential. The Ag−Ag interaction potentials are found to be attractive only when relativity is accounted for in the calculations.

We report on the synthesis and characterization of an NHC ligand based on the imidazo[1,5‐a]quinolinol scaffold. The benzyl‐protected NHC precursor was used for the preparation of the corresponding AgI, AuI and AuIII complexes. The molecular structures of the AuI and AuIII halide complexes determined by single‐crystal X‐ray diffraction reveal considerable distortion of the rigid NHC moiety due to steric repulsion between the gold and oxygen atoms. At ambient temperature, the complexes are weakly fluorescent from an intraligand excited state, whereas at 77 K the emission spectra are dominated by intraligand phosphorescence.

CsBr3 was investigated as a new and convenient oxidant for NHC-Au(I) complexes (NHC = imidazo[1,5-a]pyridin-3-ylidene) for the preparation of the respective Au(III) complexes. The Au(I) complexes were synthesized by the silver salt method using [(NHC)2Ag]PF6 and (tht)AuBr. Unexpectedly, the reactions yielded both neutral (NHC)AuBr and ionic [(NHC)2Au]PF6, depending on the N-substituent of the NHC ligand. Oxidation with CsBr3 gave the complexes (NHC)AuBr3 and [(NHC)2AuBr2]PF6 in high yields and purity, which proves the suitability of this reagent. The complexes were further characterised by X-ray diffraction and electronic absorption and emission spectroscopy. The Au(I) complexes exhibit a dual emission attributable to intraligand fluorescence and phosphorescence at both room temperature and 77 K. Upon irradiation with polychromatic light (λ > 305 nm), the Au(III) complexes are cleanly photo-reduced to the Au(I) congener.

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