Photochromism and thermochromism: new strategies for (HV)[Co(H2O)6](p-BDC)2(DMF)·H2O

A new strategy for a viologen complex, (HV)[Co(H2O)6](p-BDC)2(DMF)·H2O (1) (p-BDC = 1,4-benzene dicarboxylate, DMF = N,N-dimethylformamide), was designed by keeping highly symmetrical hydrogen bonding and maximum π⋅⋅⋅π stacking interactions. By the reaction of Co(NO3)2·6H2O with 1,1′-bis(n-hexyl)-4,4′-bipyridinium dibromide (HVBr2) and 1,4-benzenedicarboxylic acid (p-H2BDC), the viologen complex 1 was prepared with monoclinic space group P 2/n, which is constituted by HV2+ cation, [Co(H2O)6]2+ cation, DMF and constitution water as well as two p-BDC2− anions to form a supramolecular 3D framework. The viologen complex 1 exhibits photochromic and thermochromic property. The types and regions of intercontacts in viologen complex 1 were illustrated by Hirshfeld surface and two-dimensional (2D) fingerprint plots in crystal stacking. The frontier molecular orbital was evaluated to explain the matching rules between electron acceptor and donor at the density functional theory (DFT)-B3LYP/6-311 (d, p) level. It is of great signifcance to investigate inter/intramolecular interaction and chromic property of viologen complex 1 and provide theoretical guidance for the self assembly design and decoration of viologen complexes.