Series of Cd(II) and Pb(II) Coordination Polymers Based on a Multilinker (<i>R,S</i>-)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-<i>trans</i>-bis­(4-pyridyl)­ethene (bpe)), namely, [Cd­(bpdado)­(H₂O)₂]_<i>n</i> (<b>1</b>), {[Cd₂(bpdado)₂­(bpa)­(H₂O)₂]­·DMF·3H₂O}_<i>n</i> (<b>2</b>), {[Cd₂(bpdado)₂­(bpe)­(H₂O)₂]­·8.5H₂O}_<i>n</i> (<b>3</b>), {[Pb₂(bpdado)₂­(bpa)]­·10H₂O}_<i>n</i> (<b>4</b>), {[Pb₂(bpdado)₂­(bpe)]·10H₂O}_<i>n</i> (<b>5</b>), [Pb₂(bpdado)­Cl₂(H₂O)₂]_<i>n</i> (<b>6</b>), 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 <b>1</b>–<b>6</b> 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)), <b>6</b> exhibits a 2D covalent grid layer, whereas complex <b>1</b> displays a 1D chain. Meanwhile, Cd­(II) atom in <b>1</b> shows an unprecedented triangular prism coordination geometry. Although bpe/bpa ligands act as pillars between 2D [M­(bpdado)]_<i>n</i> layer subunits in complexes <b>2</b>–<b>5</b>, the Cd­(II)-based complexes <b>2</b> and <b>3</b> are extended into a 3D layered-pillared network, while the Pd­(II)-based complexes <b>4</b> and <b>5</b> just exhibit the 2D double layers. Moreover, the 2D [Cd­(bpdado)]_<i>n</i> layer subunits of <b>2</b> and <b>3</b> can be derived from replacing hydrogen bonds in 1D <b>1</b> with coordination bonds dependent on different coordination modes of bpdado. In addition, the solid-state luminescence (for <b>1</b>–<b>6</b>) and gas adsorption properties (for <b>2</b> and <b>3</b>) have been studied and discussed in detail