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 PdPd 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.