M−X···X‘−C Halogen-Bonded Network Formation in MX₂(4-halopyridine)₂ Complexes (M = Pd, Pt; X = Cl, I; X‘ = Cl, Br, I)

The syntheses and crystal structures of five compounds, trans-[MCl2(4-Xpy)2] (M = Pd, Pt; 4-Xpy = 4-halopyridine; X = Cl, Br) and trans-[PdI2(4-Ipy)2], are reported. All except trans-[PdCl2(4-Clpy)2] adopt crystal structures comprising 1D or 2D networks propagated via intermolecular M−X···X‘−C halogen bonds. Halogen bond geometries exhibit near linear angles (157−173°) at the organic halogen (C−X‘) and much smaller angles (85−112°) at the inorganic halogen (M−X), consistent with the behavior of these halogen environments as electrophile and nucleophile, respectively. Powder diffraction studies suggest that these compounds are polymorphic.