Highly efficient electrochemiluminescence based on pyrazolecarboxylic metal organic framework

A series of transition metal complexes with the ligands 3-pyrazoledicarboxylic acid (H2L(1)) and ethyl 1-(2-ethoxy-2-oxoethyl)-1H-pyrazole-3-carboxylate (epzc) have been synthesized. The epzc generated 1-(carboxymethyl)-1H-pyrazole-3-carboxylic acid (H2L(2)) by an in situ hydrothermal hydrolysis reaction, using a one-pot method. Simple mononuclear [Co(HL(1))2(H2O)2] (1) and [Ni(L(2))(H2O)4] (4), dinuclear [Ni2(L(1))2(H2O)6]·H2O (2) and [Cu2(L(2))2(H2O)4] (5) and 2D frameworks [Cu2(L(1))2]n (3), [Co2(L(2))2(H2O)4]n (6) have been isolated. The structures have been established by single-crystal X-ray diffraction, and the complexes characterized by FT-IR, thermogravimetric analysis (TGA), PRXD, UV-Vis spectroscopy, and fluorescent spectroscopy. 1, 2, 4 and 4 were further assembled to form a supramolecular structure by hydrogen-bonding interactions and/or π···π stacking. 3 and 6 both possess a 2D network structure that is further interlinked via intermolecular hydrogen-bonding interactions. Most importantly, the complexes demonstrated highly intense electrochemiluminescence (ECL) in DMF solution.