Rhodium(III) Complexes with 2‐(1<i>H</i>‐Pyrazol‐1‐yl)pyrimidine Ligands: Synthesis, Structures, Luminescence, and Cytotoxicity

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‐1 H ‐pyrazol‐1‐yl)‐4,6‐diphenylpyrimidine (HL Me ) and 2‐(3,5‐diphenyl‐1 H ‐pyrazol‐1‐yl)‐4,6‐diphenylpyrimidine (HL Ph ) with RhCl 3 gives two complexes, [RhL Me (H 2 O)Cl 2 ][RhL Me (EtOH)Cl 2 ]∙EtOH ( 1 ) and [RhL Ph (H 2 O)Cl 2 ] 0.49 [RhL Ph (EtOH)Cl 2 ] 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 (H 2 O)Cl 2 ] 0.49 [RhL Ph (EtOH)Cl 2 ] 0.51 ∙0.5EtOH complex emits in the solid state at room temperature and at 77 K, while [RhL Me (H 2 O)Cl 2 ][RhL Me (EtOH)Cl 2 ]∙EtOH emits only at 77 K. The complexes reveal significant differences in cytotoxic activity: while [RhL Ph (H 2 O)Cl 2 ] 0.49 [RhL Ph (EtOH)Cl 2 ] 0.51 ∙0.5EtOH is low‐toxic against tumor Hep2 cells and non‐tumor MRC5 cells, [RhL Me (H 2 O)Cl 2 ][RhL Me (EtOH)Cl 2 ]∙EtOH exhibits more pronounced toxicity against both cell lines.