A two-dimensional CdII coordination polymer based on naphthalenediimide: synthesis, crystal structure and photochromic properties.

Naphthalenediimides, a class of organic dyes with an expanded π-electron-deficient plane, have attracted considerable interest because of their photoinduced electron transfer from neutral organic moieties to stable anionic radicals. This makes them excellent candidates for organic linkers in the construction of photochromic coordination polymers. Such a photochromic two-dimensional coordination polymer has been prepared using N,N'-bis(pyridin-4-ylmethyl)naphthalene-1,8:4,5-bis(dicarboximide) (DPMNI). In crystallization tubes, upon slow diffusion of an MeOH solution of cadmium perchlorate into a CHCl3 solution of DPMNI, the complex poly[[bis[µ2-2,7-bis(pyridin-4-ylmethyl)benzo[imn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetrone-κ2N:N']bis(perchlorato-κO)cadmium(II)] chloroform tetrasolvate], {[Cd(C26H16N4O4)2(ClO4)2]·4CHCl3}n, (I), was obtained. The asymmetric unit contains one Cd2+ cation, two DPMNI ligands, two coordinated ClO4- anions and four CHCl3 solvent molecules. Each Cd2+ cation is interconnected by four DPMNI linkers to generate a neutral two-dimensional naphthalenediimide coordination network with all the ClO4- anions above or below this plane. Strong interlaminar anion-π interactions between the coordinated ClO4- anions and the imide rings of an adjacent layer lead to a three-dimensional supramolecular structure. Compound (I) exhibits reversible photochromic behaviour and photocontrolled tunable luminescence properties, which may originate from the photoinduced electron-transfer generation of radicals in the DPMNI ligand.