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)(H 2 O)]·2DMF} n (1), [Cd(3-PBI)(DMF)] n (2), {[Zn 4 (μ 4 -O)(4-PBI) 3 ]·3DMF} n (3), {[Cd 4 (4-PBI) 4 (H 2 O) 6 ]·13H 2 O} n (4), have been constructed from two isomeric flexible multi-carboxylate ligands, 3-H 2 PBI = 5-(3-(pyridin-3-yl)benzamido)isophthalic acid and 4-H 2 PBI = 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 2- 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 2+ metal ions are connected by carboxylate groups to form [Cd 2 (COO) 4 ] 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 2 ·6 10 ·8 3 )(4·6 2 ) 2 . As for 3, Zn(ii) ions are bridged by one μ 4 -O and six carboxylate groups to form a tetranuclear [Zn 4 (μ 4 -O)(COO) 6 ] 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 2 ) topology and B denotes kgd 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 -1 and a reversible capacity of 200 mA h g -1 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.