pH and Ligand Dependent Assembly of Well–Dawson Arsenomolybdate Capped Architectures

Five Well–Dawson-type arsenomolybdates, formulated as [Cu­(2,2′-bpy)2]­[{Cu­(2,2′-bpy)}3­{As2VMo2VMo16VIO62}]·4H2O (1), [H2(4,4′-bpy)]2.5­[AsIII(As2VMo2VMo16VIO62)]·5H2O (2), (pyr)­(imi)­(Himi)3­[As2III(As2VMo3VMo15VIO62)]·3H2O (3), [As3III(As2VMo3V­Mo15VIO62)]·4H2O (4), and (H2btp)3[As2V­Mo18VIO62]·6H2O (5) (bpy = bipyridine, pyr = pyrazine, imi = imidazole, btp = 1,5-bis­(triazol)­pentane), have been hydrothermally synthesized and structurally characterized by the elemental analysis, TG, IR, UV–vis–NIR, XPS, XRD, and single-crystal X-ray diffraction. The structural analysis indicates that compounds 1–4 contain rare reduced Dawson {As2Mo18O62} (abbreviated as {As2Mo18}) anions as parent cluster unit, which are capped by a certain number of Cu­(II) or As­(III) species on different coordination positions via altering pH values and organic ligand of the reaction system. Compounds 1 and 2 are asymmetric tricopper and monoarsenate­(III) capped assemble by three {Cu­(bpy)}2+ and a {AsO3} fragments, respectively. Compounds 3 and 4 are symmetric biarsenate­(III) and triarsenate­(III) capped cluster by four and six half occupancy {AsO3} units, respectively. Compound 5 is uncapped {As2Mo18} structures. Compounds 1–4 represent infrequent Dawson arsenomolybdate capped architectures, especially 2–4, as arsenate­(III) capped Dawson-type assemblies are observed for the first time. Compounds 1–5 display good electrocatalytic activity on reduction of nitrite. Compounds 1, 2, 3, and 5 exhibit fluorescent properties in the solid state at room temperature. In addition, magnetic properties of 1–4 have been investigated in detail.