Syntheses, crystal structures and fluorescent properties of two d 10-metal coordination polymers based on 1,5-naphthalenedisulfonic acid

The first examples of two d ¹⁰ metal coordination polymers based on 1,5-naphthalenedisulfonic acid and benzimidazole, namely, [Cd(bim)₄(1,5-nds)] 1 and [Ag(bim)₂]·½1,5-nds 2 (bim = benzimidazole, 1,5-nds = 1,5-naphthalenedisulfonic acid) were synthesized successfully under solvothermal conditions. Their structures were determined by single-crystal X-ray diffraction analyses and further characterized by elemental analyses, IR, TG-DSC, PXRD, UV–Vis, and DFT. 1 exhibits a 3D supramolecular structure which started from 1D helical chain. 2 also shows a 3D architecture which was assembled via π–π interactions and hydrogen bonds. The hydrogen bonds formed by 1,5-nds play an important role in increasing the dimensionality of architectures of 1 (from 1D to 3D) and 2 (from 0D to 1D). Moreover, both 1 and 2 show excellent luminescent properties, 335 nm for 1 (λ _ex = 286 nm) and 341 nm and 389 nm for 2 (λ _ex = 234 nm), and may be the suitable candidates of fluorescent materials. From UV–Vis spectra, the remarkable absorption peaks can be found at 276 nm for 1 and 271 nm for 2. The simulated UV–Vis spectra (290.30 nm for 1 and 271.64 nm for 2) by Gaussian 09 DFT correspond well with the experimental results. From the electron density distribution of frontier molecular orbitals, it is known that the two absorption bands are attributed to the intra-ligand electron transition from HOMO?26 to LUMO and from HOMO?3 to LUMO+1 for 1, from HOMO?1 to LUMO+18 and LUMO+19 for 2.