Proton-Conductive Magnetic Metal-Organic Frameworks, {NR3(CH2COOH)}[MaIIMbIII(ox)3]: Effect of Carboxyl Residue upon Proton Conduction

Proton-conductive magnetic metal-organic frameworks (MOFs), {NR3(CH2COOH)}[(MaMbIII)-M-II(ox)(3)] (abbreviated as R-MaMb: R = ethyl (Et), n-butyl (Bu); MaMb = MnCr, FeCr, FeFe) have been studied. The following six MOFs were prepared: Et-MnCr center dot 2H(2)O, Et-FeCr center dot 2H(2)O, Et-FeFe center dot 2H(2)O, 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) angstrom, c = 51.0080(13) angstrom, Z = 6. The crystal consists of oxalate-bridged bimetallic layers interleaved by {NBu3(CH2COOH)}(+) ions. Et-MnCr center dot 2H(2)O and Bu-MnCr (R-MnCr MOFs) show a ferromagnetic ordering with T-C of 5.5-5.9 K, and Et-FeCr center dot 2H(2)O and Bu-FeCr (R-FeCr MOFs) also show a ferromagnetic ordering with T-C of 11.0-11.5 K. Et-FeFe center dot 2H(2)O 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 center dot 2H(2)O, Et-FeCr center dot 2H(2)O and Et-FeFe center dot 2H(2)O) 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.