Dimeric cyclopalladated azobenzenes: structural differences between 2-hydroxypyridine and 2-mercaptopyridine bridged complexes

Binuclear chloro-bridged cyclopalladated azobenzenes [Pd(A)Cl]2 (A=ortho-metallated azobenzene or its derivatives) have been reacted with aqueous (aq.) AgNO3 followed by the addition of 2-hydroxypyridine (2-PyOH; donor centres of deprotonated form abbreviated N,O)/2-mercaptopyridine (2-PySH; donor centres of deprotonated form abbreviated N,S) in presence of Et3N to synthesise bridged dinuclear compound [Pd(A)(μ-N,O)]2–[Pd(A)(μ-N,S)]2. The compositions of the complexes have been established by elemental analyses, IR, UV–vis, 1H and 13C-NMR spectral data. The structural confirmation has been carried out by X-ray crystallography. The structures show anti-symmetric metallacycle in the dimer and N,O/N,S bridging arrangement. The dimer [Pd(A1)(μ-N,X)]2 shows strong Pd⋯Pd interaction (A1=2-(phenylazo)benzene). The coordination mode in [Pd(A1)(μ-N,O)]2 shows trans pyridine-N to PdN(azo) bond while in [Pd(A1)(μ-N,S)]2 pyridine-N is trans to the PdC bond. The square planes are convergent towards heterocyclic bridging side.