Synthesis, spectroscopic properties and structural characterisation of Pd(II) and Pt(II) complexes with 1,3,5-pyrazole derived ligands. Rotation around the metal-N bond

The 1-ethyl-5-methyl-3-phenyl-1H-pyrazole (L1) and 5-methyl-1-octyl-3-phenyl-1H-pyrazole (L2) ligands, react with [PdCl2(CH3CN)2] and K2PtCl4 to lead to trans-[MCl2(L)2] (M = Pd(II), Pt(II); L = L1, L2). These complexes have been prepared and characterised. The NMR study of the complex [PdCl2(L1)2], in CDCl3 solution, is consistent with a very slow rotation of ligands around the Pd-N bond, so that two conformational isomers can be observe (syn and anti). Different hehaviour is observed for complexes [PdCl2(CH3CN)2] and [PtCl2(L)2] (L = L1, L2) which present an isomer in solution at room temperature (anti). The crystal structure of trans-[PdCl2(L1)2] is reported.