The first example of linkage isomerism for pyrazole ligands in platinum complexes

The cationic complex [Pt(Me-Pz)4](Cl)2 (12+ · (Cl)2) has been prepared by the reaction of [PtCl2(Me-Pz)2] with an excess of 3(5)-methylpyrazole (3(5)-Me-Pz) and it was characterized by elemental analyses (C, H, N), ESI+-MS, IR, 1H and 13C NMR spectroscopies. Linkage isomerism of the coordinated pyrazole was observed in a solution for 12+ · (Cl)2 with an overall 3:4 ratio for 3-Me-Pz and 5-Me-Pz metal-bound species, respectively. X-ray diffraction studies of two complexes, 12+ · [PtCl4] and 12+ · (pic)2, allows the observation of different coordination modes of the 3(5)-Me-Pz ligand in the solid state, i.e. three coordinated 5-Me-Pz and one 3-Me-Pz in 12+ · [PtCl4] and three coordinated 3-Me-Pz and one 5-Me-Pz in 12+ · (pic)2.