Photoelectric properties and potential nitro derivatives sensing by a highly luminescent of Zn(ii) and Cd(ii) metal–organic frameworks assembled by the flexible hexapodal ligand, 1,3,5-triazine-2,4,6-triamine hexaacetic acid

Abstract

Two new coordination polymers, [Cd₄(μ₃-O)(TTHA)(H₂O)₂]·3H₂O (1) and [Zn₅Na₂(TTHA)₂(H₂O)₁₀] (2), based on the flexible hexapodal ligand 1,3,5-triazine-2,4,6-triamine hexaacetic acid (H₆TTHA), have been synthesized under hydrothermal condition. The two coordination polymers were characterized by the elemental analysis, IR spectroscopy, PXRD, thermogravimetric analysis and UV-vis spectroscopy. The single crystal X-ray diffraction analysis revealed that coordination polymer 1 exhibited a 2D sheet structure, which was arranged alternately by two different types of building blocks (Cd₄O₆ and Cd₂O₂), and 2 possessed a fascinating 3D network framework with three different types of the building blocks (Zn₄(COO)₆O₈N₂, Zn(COO)₄ and Na(COO)₄O₂). In the structures, all of the coordination modes of the ligand were firstly discovered, which are μ₈–η¹η¹η¹η³η²η¹η²η¹η²η¹η² and μ₉–η¹η¹η¹η¹η¹η¹η¹η¹η²η_N¹η²η¹, respectively. In order to furthermore expand functional characteristics of both the coordination polymers 1 and 2, we also carried out experiments of the surface photovoltage spectroscopy (SPS) and electric-field-induced surface photovoltage spectroscopy (EFISPS), which showed that 1 and 2 could behave as p-type semiconductors. What's more, the fluorescence sensing experiments showed the luminescent quenching of the coordination polymers 1 and 2 were especially obvious with the increasing of the nitro derivatives concentration, even if the nitro derivatives were at a very low concentration, which can also be detected, that indicating both coordination polymers 1 and 2 have very high sensitivity sensing properties.