Two Zn-viologen coordination polymers constructed from 1-carboxyethyl-4,4′-bipyridinium ligands: Crystal structures, photochromism and theoretical calculations

Abstract

Two Zn-viologen coordination polymers constructed from 1-carboxyethyl-4,4′-bipyridinium (CEbpy) ligands were prepared {[Zn(CEbpy)2(H2O)2]·[Zn(p-BDC)(H2O)4]·2Br}n (1) and {[Zn(CEbpy)2(H2O)2]·[Zn(BTEC)(H2O)3]·6H2O}n (2) (p-H2BDC = 1,4-benzenedicarboxylic acid, H4BTEC = 1,2,4,5-benzenetetracarboxylic acid). The crystal structures and photochromism were examined for compounds 1 and 2. Each Zn (II) ion of compound 1 connects four CEbpy ligands and two p-BDC2− anions to form one dimensional (1D) coordination polymer chains on the upper and lower layers, respectively. Each Zn (II) ion of compound 2 connects four CEbpy ligands and two BTEC4− anions to form two dimensional (2D) coordination polymer chains. Compounds 1 and 2 both display superior photochromic performance. Density functional theory (DFT)-B3LYP/6–311 (d,p) method was used to study the noncovalent interactions and frontier molecular orbitals. The results indicate that π − π interactions are conducive to the improvement of photo-response rates.