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

2-Benzoylpyridine N-methyl-N-phenylhydrazone, HL, is a versatile ligand which reacts with [Pd(PhCN)(2)Cl-2] forming the coordination compound [H LPdCl2], 1. characterized by the presence of the N(py)<^>N(im) chelate ring. When HL reacts with [Pd-3(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-boolean AND(im) ring fused to the N(im)(boolean AND)(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-boolean AND(im)C-boolean AND terdentate ligand. As solid samples only compounds 3-5 exhibited luminescence at room temperature (lambda(max) approximate to 610 nm). This property, quite unusual in Pd(II) complexes, is discussed in terms of pi-pi interactions, which are mainly responsible for the existence in the crystalline solid state of dimeric units.