Luminescence of neutral and ionic gold(I) complexes containing pyrazole or pyrazolate-type ligands

A series of pyrazole (Hpz) and pyrazolate (pz−) Au(I) complexes of types [Au(Hpz2R(n))(PPh3)]+ (I), [Au(Hpz2R(n))2]+ (II), [Au(μ-pzR(n))]3 (III), [Au(pzR(n)/2R(n))(PPh3)] (IV), [AuCl(HpzR(n)/2R(n))] (V) and [(PPh3)Au(μ-pzR(n))Au(PPh3)]+ (VI), R(n) and 2R(n) represent C6H4OCnH2n+1 substituents at the 3- or 3- and 5-positions of the heterocyclic ring, respectively, have been shown to be luminescent in the solid state at 77 K, independently of the presence or not of inter-metallic Au–Au interactions. The emission spectra of all complexes consist of structured bands in the region 395–500 nm, attributed to ligand-to-metal charge transfer (LMCT) transitions involving the Hpz or pz− ligands, the pattern of bands of compounds being related with the molecular structure and/or the nature of the ligands. The thermal behaviour of several complexes of the types III, IV and V containing long-chain substituents (n ⩾ 12) was examined by polarising light optical microscopy (POM). The derivative [AuCl(HpzR(12))] was proved to have liquid crystal properties exhibiting a mesophase SmA but the remaining complexes were not liquid crystal materials. This complex is one of the scarce examples of Au(I) derivatives exhibiting both liquid crystal and luminescent properties.

Graphical abstractGold(I) complexes based on pyrazole (Hpz) and pyrazolate (pz−) type ligands have been shown to be luminescent in solid state independently of the presence or not of inter-metallic Au–Au interactions. They exhibit different patterns of emission bands attributed to ligand-to-metal charge transfer (LMCT) transitions involving Hpz or pz− ligands.Figure optionsDownload full-size imageDownload as PowerPoint slide