Auxiliary ligand-controlled photochromism and decolourization of two bipyridinium-based metal–organic hybrid materials with various water clusters

Abstract

Two bipyridinium-based metal–organic hybrid materials, {[Cd(Bpyen)_0.5(p-BDC)(H₂O)Br]·5H₂O} (1) and {[Cd(Bpyen)(o-BDC)Br₂]·8H₂O} (2), have been synthesized. 1 is a 2D coordination polymer while 2 shows 1D chain-like structure. Both compounds exhibit rapid color change under light irradiation. However, the decolourization of the photochromic products is very different. The influence of the auxiliary ligands on the photochromism and decolourization process of the bipyridinium-based hybrid materials has been explored. Interestingly, water molecules are encapsulated in these two compounds and form novel water aggregates consisting of novel water building units, such as the (H₂O)₁₀ water cluster in 1 and the (H₂O)₁₂ water cages in 2 through hydrogen-bond interactions. The effect of these water aggregates on the stability of the two compounds has been studied.