Synthesis and crystal structure of two new lead(II) coordination polymers with substituted 2,2′-bipyridine ligands with dicyanamide and nitrate as co-ligands

The two lead(II) coordination polymers [Pb(4,4′-dm-2,2′-bpy)(Dca)(NO3)]n (1) and [Pb(4,4′-dmo-2,2′-bpy)(Dca)(NO3)]n (2) were prepared by treatment of lead(II) nitrate, sodium dicyanamide with 4,4′-dimethyl-2,2′-bipyridine and 4,4′-dimethoxy-2,2′-bipyridine, respectively. Both polymers were characterized by elemental analysis, IR and 1H NMR spectroscopy, thermogravimetric analysis and X-ray crystallography. The coordination polymers can be described as one-dimensional double-chains with Pb(II) centers bridged by Dca and nitrate co-ligands, containing trinuclear rings, [Pb3(L)3(NO3)2(Dca)], and bridging nitrate and Dca co-ligands in cis and trans positions, respectively. The coordination number of the Pb(II) ions in 1 and 2 is seven, with the PbN4O3 coordination polyhedron containing a stereochemically active lone pair of electrons with hemi-directed coordination spheres. The polymer chains form networks via supramolecular interactions that include O⋯O, CH⋯O, CH⋯N interactions, in addition to hydrogen bonding and π-π stacking.