Series of Cd(II) and Pb(II) Coordination Polymers Based on a Multilinker (R,S-)2,2′-Bipyridine-3,3′-dicarboxylate-1,1′-dioxide

Six new metal–organic frameworks (MOFs) with structures ranging from a one-dimensional (1D) chain, two-dimensional (2D) layer, even 2D double layer to three-dimensional (3D) network based on 2,2′-bipyridine-3,3′-dicarboxylate-1,1′-dioxide (H2bpdado) and N-donor ligands (1,2-bis­(4-pyridyl)­ethane (bpa) or 1,2-trans-bis­(4-pyridyl)­ethene (bpe)), namely, [Cd­(bpdado)­(H2O)2]n (1), {[Cd2(bpdado)2­(bpa)­(H2O)2]­·DMF·3H2O}n (2), {[Cd2(bpdado)2­(bpe)­(H2O)2]­·8.5H2O}n (3), {[Pb2(bpdado)2­(bpa)]­·10H2O}n (4), {[Pb2(bpdado)2­(bpe)]·10H2O}n (5), [Pb2(bpdado)­Cl2(H2O)2]n (6), were synthesized by hydro­(solvo)­thermal and/or diffusion methods. In these complexes, the bpdado ligand shows four types of coordination modes, three of which appeared for the first time. Polymers 1–6 present diverse motifs with different metal ions and different conformations and/or coordination modes of bpdado, which may show a natural synergy in structural diversity of the resultant MOFs. Under the similar synthetic conditions just with different metals (Cd­(II) and Pb­(II)), 6 exhibits a 2D covalent grid layer, whereas complex 1 displays a 1D chain. Meanwhile, Cd­(II) atom in 1 shows an unprecedented triangular prism coordination geometry. Although bpe/bpa ligands act as pillars between 2D [M­(bpdado)]n layer subunits in complexes 2–5, the Cd­(II)-based complexes 2 and 3 are extended into a 3D layered-pillared network, while the Pd­(II)-based complexes 4 and 5 just exhibit the 2D double layers. Moreover, the 2D [Cd­(bpdado)]n layer subunits of 2 and 3 can be derived from replacing hydrogen bonds in 1D 1 with coordination bonds dependent on different coordination modes of bpdado. In addition, the solid-state luminescence (for 1–6) and gas adsorption properties (for 2 and 3) have been studied and discussed in detail.