Four new Zn(ii) and Cd(ii) coordination polymers using two amide-like aromatic multi-carboxylate ligands: synthesis, structures and lithium-selenium batteries application.

Four new coordination polymers, {[Zn(3-PBI)(HO)]·2DMF} (1), [Cd(3-PBI)(DMF)] (2), {[Zn(μ-O)(4-PBI)]·3DMF} (3), {[Cd(4-PBI)(HO)]·13HO} (4), have been constructed from two isomeric flexible multi-carboxylate ligands, 3-HPBI = 5-(3-(pyridin-3-yl)benzamido)isophthalic acid and 4-HPBI = 5-(3-(pyridin-4-yl)benzamido)isophthalic acid. Structural analysis reveals that compound 1 is a one-dimensional (1D) ladder-like chain assembled by Zn(ii) ions and 3-PBI ligands, which further extend into a 3D supramolecular structure through π⋯π stacking and interlayer (O-H⋯O) hydrogen bonding interactions. In compound 2, Cd metal ions are connected by carboxylate groups to form [Cd(COO)] secondary building units (SBUs). The whole framework possesses a quadrilateral channel and constitutes a unique 3D (3,6)-connected rutile net with the Schläfli symbol of (4·6·8)(4·6). As for 3, Zn(ii) ions are bridged by one μ-O and six carboxylate groups to form a tetranuclear [Zn(μ-O)(COO)] cluster, resulting in a rare (3,9)-connected 3D network. Compound 4 has an appealing 2D layered architecture involving two distinct topologies in the crystal structure, stacking in an unusual ABBABB mode (where A represents (4·8) topology and B denotes topology). Moreover, compound 2 is prepared as a support for active selenium through a melt-diffusion method. The obtained Cd-CP/Se electrode can be tested for lithium-selenium batteries and shows an initial capacity of 514 mA h g and a reversible capacity of 200 mA h g at 1C after 500 cycles. The good storage performance of Cd-CP/Se demonstrates it to be a prospective cathode material for lithium-selenium batteries.