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 center dot center dot center dot X'-C halogen bonds. Halogen bond geometries exhibit near linear angles (157-173 degrees) at the organic halogen (C-X') and much smaller angles (85-112 degrees) 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.