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.