The interaction of HL^Ph and HL^Me with RhCl₃ under slow evaporation conditions promotes the activation of the C─H bond and leads to the formation of two complexes, [RhL^Me(H₂O)Cl₂][RhL^Me(EtOH)Cl₂]∙EtOH and [RhL^Ph(H₂O)Cl₂] _0.5 [RhL^Ph(EtOH)Cl₂] _0.5 ∙0.5EtOH. The substituents in the pyrazole ring of the ligand molecules affect emission properties and cytotoxicity of the complexes.

Abstract

The effect of substituents in pyrazolylpyrimidine ligands and their rhodium(III) complexes with regard to their structures and properties was investigated. Complexation of 2-(3,5-dimethyl-1H-pyrazol-1-yl)-4,6-diphenylpyrimidine (HL^Me) and 2-(3,5-diphenyl-1H-pyrazol-1-yl)-4,6-diphenylpyrimidine (HL^Ph) with RhCl₃ gives two complexes, [RhL^Me(H₂O)Cl₂][RhL^Me(EtOH)Cl₂]∙EtOH (1) and [RhL^Ph(H₂O)Cl₂] _0.49 [RhL^Ph(EtOH)Cl₂] _0.51 ∙0.5EtOH. The substituents in the pyrazole ring of the ligand molecules affect the emission properties and cytotoxicity of the complexes. The [RhL^Ph(H₂O)Cl₂] _0.49 [RhL^Ph(EtOH)Cl₂] _0.51 ∙0.5EtOH complex emits in the solid state at room temperature and at 77 K, while [RhL^Me(H₂O)Cl₂][RhL^Me(EtOH)Cl₂]∙EtOH emits only at 77 K. The complexes reveal significant differences in cytotoxic activity: while [RhL^Ph(H₂O)Cl₂] _0.49 [RhL^Ph(EtOH)Cl₂] _0.51 ∙0.5EtOH is low-toxic against tumor Hep2 cells and non-tumor MRC5 cells, [RhL^Me(H₂O)Cl₂][RhL^Me(EtOH)Cl₂]∙EtOH exhibits more pronounced toxicity against both cell lines.