Anion-Controlled Architecture and Photochromism of Naphthalene Diimide-Based Coordination Polymers

Three new cadmium coordination polymers, namely [Cd(NO3)2(DPNDI)(CH3OH)]·CH3OH (1), [Cd(SCN)2(DPNDI)] (2), and [Cd(DPNDI)2(DMF)2]·2ClO4 (3) (DPNDI = N,N-di(4-pyridyl)-1,4,5,8-naphthalene diimide, DMF = N,N-dimethylformamide) have been synthesized by reactions of DPNDI with Cd(NO3)2, Cd(SCN)2, and Cd(ClO4)2, respectively. Compound 1 is a one-dimensional coordination polymer with strong lone pair-π interactions between the coordinated NO3− anions and the imide ring of DPNDI; while 2 is a two-dimensional network with a (4, 4) net topology. In the case of 3, due to the presence of uncoordinated perchlorate counter ions, it exhibits a non-interpenetrated square-grid coordination polymer containing one-dimensional rhomboid channels. The structural diversity in these compounds is attributed to different coordination abilities and geometries of counter anions. Due to the presence of electron-deficient NDI moiety, the photochromic behavior of these compounds was studied. Interestingly, only compounds 1 and 3 exhibit color changes under light irradiation. The influence of the anions on the photochromism process of the NDI-based materials has been discussed.