Anion-Controlled Dielectric Behavior of Homochiral Tryptophan-Based Metal–Organic Frameworks

Abstract

Three homochiral metal-tryptophanate frameworks, {[Zn2(l-trp)2(bpe)2(H2O)2]·2H2O·2NO3}n (1a, l-Htrp = l-tryptophan, bpe = 1,2-bis(4-pyridyl)ethylene), {[Co(l-trp)(bpe)(H2O)]·H2O·NO3}n (1b), and {[Co(l-trp)(bpa)(H2O)]·H2O·NO3}n (2, bpa = 1,2-bis(4-pyridyl)ethane), were constructed from Zn2+ or Co2+ ions, bipyridyl ligands, and the amino acid l-tryptophan (l-Htrp), respectively. Compounds 1a, 1b, and 2 were characterized by single-crystal X-ray diffraction analysis. All of the compounds crystallize in the monoclinic space group P21 and form homochiral two-dimensional (2D) layers with rectangle-like (4,4) topologies. Anion-controlled dielectric, luminescence, and nonlinear-optic (NLO) properties were measured for these chiral metal–organic frameworks (MOFs) in the solid state. Emission spectra confirmed that compound 1a exhibited a green emission at 546 nm. Dielectric studies of 1a revealed that it had very low dielectric constant (κ = 2.53 at 1 MHz), thus verifying that it is a promising candidate for inter...