Three Mn–viologen complexes containing 1-carboxyethyl-4,4′-bipyridinium: crystal structures, photochromism and theoretical calculations

Abstract

Three Mn–viologen complexes containing 1-carboxyethyl-4,4′-bipyridinium (CEbpy) were synthesized, [Mn(H₂O)₆]·2(CEbpy)·(TPDC)·3H₂O (1), [Mn(H₂O)₆]·2(CEbpy)·(m-BDC)·2H₂O (2) and [Mn(H₂O)₆]·2(CEbpy)·(p-BDC)·2H₂O (3) (H₂TPDC = thiophene-2,5-dicarboxylic acid, m-H₂BDC = 1,3-benzenedicarboxylic acid, p-H₂BDC = 1,4-benzenedicarboxylic acid), which were investigated based on crystal structures, photochromism, molecular orbitals, Hirshfeld surfaces and 2D fingerprint plots. All three complexes present sensitive photoresponse behaviors in the sequence of 1 ≫ 3 > 2, due to the existence of electron-deficient viologen fractions. Compound 1 exhibits two electron transfer modes: intramolecular and intermolecular electron transfer. Compounds 2 and 3 exhibit intramolecular electron transfer. The density functional theory (DFT)-B3LYP/6-311(d,p) method was used to gain insight into the donor–acceptor structures, matching rules between CEbpy and the acid moiety as well as inter/intramolecular atom–atom close contacts based on the fraction of intercontact.