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)(H₂O)]·2DMF}_n (1), [Cd(3-PBI)(DMF)]_n (2), {[Zn₄(μ₄-O)(4-PBI)₃]·3DMF}_n (3), {[Cd₄(4-PBI)₄(H₂O)₆]·13H₂O}_n (4), have been constructed from two isomeric flexible multi-carboxylate ligands, 3-H₂PBI = 5-(3-(pyridin-3-yl)benzamido)isophthalic acid and 4-H₂PBI = 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, Cd²⁺ metal ions are connected by carboxylate groups to form [Cd₂(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 (4²·6¹⁰·8³)(4·6²)₂. As for 3, Zn(ii) ions are bridged by one μ₄-O and six carboxylate groups to form a tetranuclear [Zn₄(μ₄-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 (4·8²) 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.