Synthesis, spectroscopic and structural characterization of cyclometallated rhodium(III) complexes with 1-phenyl-1H-pyrazole and α-diimines ligands, comparison with their iridium(III) analogues

The paper deals with the synthesis of a series of cationic [Rh(ppz)₂(N^N)]⁺ complexes containing deprotonated 1-phenyl-1H-pyrazole as cyclometallating (C^N) ligands and α-diimines (2,2’-bipyridine, 1,10-phenanthroline and its derivatives) as ancillary (N^N) ligands in the form of salts with PF₆ ⁻ counter ions. These complexes were obtained from [(ppz)₂Rh-μ-Cl]₂ precursor through cleaving the μ-dichloro-bridged dimer with N^N ancillary ligands. The complexes were identified by means of NMR spectroscopy and MS spectrometry and their molecular structures were finally confirmed by X-ray crystallography. These complexes showed strong luminescence in MeOH/EtOH 1:1 glasses at 77 K but were very week or almost non-emitting species in MeCN solutions at room temperature. Their emission properties were compared to analogues Ir(III) complexes.