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

Three Mn-viologen complexes containing 1-carboxyethyl-4,4′-bipyridinium (CEbpy) were synthesized, [Mn(H 2 O) 6 ]·2(CEbpy)·(TPDC)·3H 2 O ( 1 ), [Mn(H 2 O) 6 ]·2(CEbpy)·( m -BDC)·2H 2 O ( 2 ) and [Mn(H 2 O) 6 ]·2(CEbpy)·( p -BDC)·2H 2 O ( 3 ) (H 2 TPDC = thiophene-2,5-dicarboxylic acid, m -H 2 BDC = 1,3-benzenedicarboxylic acid, p -H 2 BDC = 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. Three Mn-viologen complexes containing CEbpy were prepared and displayed excellent photochromic properties by intramolecular or intermolecular electron transfer.