Synthesis and solid state characterisation of mononuclear 2-benzoylpyridine N-methyl-N-phenylhydrazone palladium(ii) complexes

Abstract

2-Benzoylpyridine N-methyl-N-phenylhydrazone, HL, is a versatile ligand which reacts with [Pd(PhCN)₂Cl₂] forming the coordination compound [HLPdCl₂], 1, characterized by the presence of the N(py)^N(im) chelate ring. When HL reacts with [Pd₃(OAc)₆] this gives rise to the orthometallated complex [LPd(OAc)], 2. In this case the Pd(II) environment consists of a N(py)^N(im) ring fused to the N(im)^C palladacycle and a monodentate acetate anion. Complex 2 undergoes methatetical reactions with alkaline halides and complexes of general formula [LPdX] (3: X = Cl; 4: X = Br; 5: X = I) are obtained. The molecular structures of 3–5 determined by single-crystal X-ray analysis proved the formation in all cases of mononuclear Pd(II) complexes containing a N(py)^N(im)^C terdentate ligand. As solid samples only compounds 3–5 exhibited luminescence at room temperature (λ_max ≈ 610 nm). This property, quite unusual in Pd(II) complexes, is discussed in terms of π–π interactions, which are mainly responsible for the existence in the crystalline solid state of dimeric units.