Synthesis and characterization of a homologous series of mononuclear palladium complexes containing different cyclometalated ligands

New mononuclear palladium(II) complexes formed by with 2-hydroxy-4-(n-hexyloxybenzylidene)-4′-n-hexyaniline (HL) and 2-phenylpyridine (I), benzo[h]quinoline (II), azobenzene (III), 2-benzoylpyridine (IV) or phenyl-2-pyridylketone-2,4-dinitrophenylhydrazone (V) have been synthesized and characterized by analytical and spectroscopic methods and the single-crystal structures of [(IVa)Pd(L)] and [(Va)Pd(L)] have been established. The spectroscopic and diffractrometric data account for molecular structures wherein the palladium(II) center is part of two chelate rings involving HL and one of the I–V ligands which form a five-member N,C{[(Ia)PdL], [(IIa)Pd(L)] and [(IIIa)Pd(L)]}, a six-member N,C{[(IVa)Pd(L)]}, or a six-member N,N′{[(Va)Pd(L)]} metallacycle. The electronic spectra of [(IIIa)Pd(L)] and [(Va)Pd(L)] show an absorption maxima, at 495 (ε∼3×103 M−1 cm−1) and 531 nm (ε∼2×104 M−1 cm−1), respectively, which results are significantly affected by the polarity of the solvent. These chromophores should therefore be of interest for the preparation of nonlinear optical materials.