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][Mn^IVMo₉O₃₂]}₂·12H₂O [RE = La³⁺ (1), Pr³⁺ (2), Nd³⁺ (3)] and (NH₄)₃[RE(Hina)₂(H₂O)₆][Mn^IVMo₉O₃₂]·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][Mn^IVMo₉O₃₂]}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.