Four compounds containing 1-(2-carboxyethyl)-4,4′-bipyridine: Synthesis, crystal structure and chromic behavior

Abstract

Herein, four compounds containing the neutral viologen derivative, 1-(2-carboxyethyl)-4,4′-bipyridine (CBbpy) have been synthesized, (CBbpy)·(H2TPDC)·H2O (1), [Co0.5(CBbpy)(H2O)2](HTPDC)·2 H2O (2), [Ni0.5(CBbpy)(H2O)2](HTPDC)·2 H2O (3) and {[Cd(CBbpy)2(H2O)2][Cd(TPDC)2]·4 H2O}n (4) (H2TPDC = thiophene-2,5-dicarboxylic acid). Compound 1 is a co-crystal that forms the donor-acceptor (D-A) system through non-covalent interactions. Compounds 2 and 3 own the same isolated structure, in which metal ions coordinate with CBbpy to form cations, while H2TPDC loses a proton to form anions. Compound 4 contains one-dimensional (1D) {[Cd(CBbpy)2(H2O)2]2+}n double chain and two-dimensional (2D) {[Cd(TPDC)2]2-}n layer, which leads to a 1D + 2D→three-dimensional (3D) interdigitated supramolecular architecture. Although four compounds comprise the same bipyridinium moiety, their chromic behaviors are different. Compounds 1 and 4 own reversible photochromic action, while 2 and 3 reveal hydrochromic action upon heating. Based on the photochromic properties of 1 and 4, the photo-modulated fluorescence and the potential applications of inkless and erasable printing are investigated.