Ligand-to-metal charge-transfer spectra of tetrahaloaurate(III) and trans-dicyanodihaloaurate(III) ions

Stable AuIII complexes with four N-heterocyclic carbene groups can be prepared in high yield directly from KAuCl4

“…Au(L 1 ) 2 Cl 2 ]Cl 2 and [Au(L 2 ) 2 Cl 2 ]Cl 3 (but not for [AuL 3 Cl 2 ]Cl 4) a weaker absorbance is observed in the region 300-350 nm. These weaker absorption bands have energies and molar extinction coefficients (ε on the order of 10 3 -10 4 M −1 cm −1 ) similar to those of ligand-to-metalcharge-transfer (LMCT) bands of the [AuCl 4 ] − ion, which has been studied in detail by Mason et al41 Similar absorptions were also displayed by other NHC adducts of Au III halides 17,35. Therefore, we tentatively attribute these low energy absorption bands seen for [Au(L 1 ) 2 Cl 2 ]Cl 2 and [Au(L 2 ) 2 Cl 2 ]Cl 3 to LMCTs from the chlorido ligands to the Lewis acidic Au III centres.…”

Formation of Dinuclear AuII and AuI/AuIII Mixed‐Valence Complexes is Directed by Structural Constraints Imposed by Cyclophane‐NHC Ligands

“…[10] Lower-energy absorption bands in the range 300-400 nm are seen in the spectra of all Au II -NHC and Au I / Au III -NHC complexes. These low-energy absorption bands have extinction coefficients (ε) in the order of 10 3 -10 4 M -1 cm -1 , in the region reported for ligand-to-metal charge-transfer (LMCT) bands of complexes of the type [AuX 4 ] -(X = Cl, Br) [11] and various NHC-Au III halide complexes. [10a,12] Many dinuclear Au complexes that contain short Au···Au distances are inherently luminescent due to aurophilic interactions, [3b,6f,13] and so the luminescence properties of the new complexes were of interest.…”

Photooxidation of Dicyanoaurate(I) Induced by Metal-to-Ligand Charge Transfer Excitation

“…After prolonged irradiation (Fig. 1) the absorption spectrum approaches that of [AuCl4]_ (Amax = 323 nm, e = 5800; 227 nm, 44800) [15].…”

“…The irradiation leads to a photo substitution which finally yields [AuCU]-. The na ture of the reactive excited state of [Au(CN)2Cl2]~ is not clear since low-energy LF as well as LMCT states exist in close proximity [15]. In analogy to other d8 metals such as Pt(II) [20], LF states are certainly reasonable candidates for inducing substi tutions.…”