Proton-Conductive Magnetic Metal-Organic Frameworks, {NR_3(CH_2COOH)}[M_a~ⅡM_b~Ⅲ(ox)_3]: Effect of Carboxyl Residue upon Proton Conduction

摘要

Proton-conductive magnetic metal-organic frameworks (MOFs), {NR_3(CH_2COOH)}[M_a~ⅡM_b~Ⅲ(ox)_3] (abbreviated as R-M_aM_b: R = ethyl (Et), n-butyl (Bu); M_aM_b = MnCr, FeCr, FeFe) have been studied. The following six MOFs were prepared: Et-MnCr-2H_2O, Et-FeCr-2H_2O, Et-FeFe-2H_2O, Bu-MnCr, Bu-FeCr, and Bu-FeFe. The structure of Bu-MnCr was determined by X-ray crystallography. Crystal data: trigonal, R3c (#161), a = 9.3928(13) A, c = 51.0080(13) A, Z = 6. The crystal consists of oxalate-bridged bimetallic layers interleaved by {NBu_3(CH_2COOH)}~+ ions. Et-MnCr·2H_2O and Bu-MnCr (R-MnCr MOFs) show a ferromagnetic ordering with T_c of 5.5-5.9 K, and Et-FeCr·2H_2O and Bu-FeCr (R-FeCr MOFs) also show a ferromagnetic ordering with T_c of 11.0-11.5 K. Et-FeFe·2H_2O and Bu-FeFe (R-FeFe MOFs) belong to the class II of mixed-valence compounds and show the magnetism characteristic of Neel N-type ferrimagnets. The Et-MOFs (Et-MnCr·2H_2O, Et-FeCr·2H_2O and Et-FeFe·2H_2O) show high proton conduction, whereas the Bu-MOFs (Bu-MnCr, Bu-FeCr, and Bu-FeFe) show moderate proton conduction. Together with water adsorption isotherm studies, the significance of the carboxyl residues as proton carriers is revealed. The R-MnCr MOFs and the R-FeCr MOFs are rare examples of coexistent ferromagnetism and proton conduction, and the R-FeFe MOFs are the first examples of coexistent Neel N-type ferrimagnetism and proton conduction.