Syntheses, structural characterization and photophysical properties of two series of rare-earth-isonicotinic-acid containing Waugh-type manganomolybdates

Abstract

Two classes of rare-earth-organic-containing Waugh-type manganomolybdates (NH4)8{[RE(Hina)(ina)(H2O)2][MnIVMo9O32]}2·12H2O [RE = La3+ (1), Pr3+ (2), Nd3+ (3)] and (NH4)3[RE(Hina)2(H2O)6][MnIVMo9O32]·7H2O [RE = Sm3+ (4), Eu3+ (5), Gd3+ (6), Tb3+ (7), Dy3+ (8), Ho3+ (9), Er3+ (10), Tm3+ (11), Yb3+ (12), Y3+ (13)] (Hina = isonicotinic acid) were prepared by means of a step-by-step synthetic strategy and further characterized by IR spectroscopy, elemental analyses, UV-visible spectroscopy and single-crystal X-ray diffraction. X-ray diffraction indicates that 1–3 consist of an organic–inorganic hybrid dimeric {[RE(Hina)(ina)(H2O)2][MnIVMo9O32]}28− core constituted by two [MnMo9O32]6− units linked via a dinuclear {[RE(Hina)(ina)(H2O)2]2}4+ cation whereas 4–13 are composed of an organic–inorganic hybrid [RE(Hina)2(H2O)6]3+ fragment and one [MnMo9O32]6− polyoxoanion. It should be pointed out that the nature of RE cations controls these two structure types. As far as we know, 1–13 represent the first examples of Waugh-type manganomolybdates including rare-earth-organic subunits so far. Furthermore, their photocatalytic activities for the degradation of azophloxine were probed in aqueous medium and 3 and 8 as representatives were systematically investigated involving the influence of the optimal pH, catalyst dosage and the doping amount of VK-TA18 nanometer titanium dioxide on the photocatalytic activities. The solid-state photoluminescence properties and lifetime decay behaviors of 3, 4 and 5 in UV-visible or near-infrared regions were also examined at ambient temperature.