Aryldiazenido derivatives: A new entry to the functionalization of Keggin polyoxometalates

A series of aryldiazenido polyoxomolybdates of the type (nBu4N)2[Mo5O13(OMe)4(NNAr){Na(MeOH)}] (Ar = C6F5, 1; Ar = O2N-o-C6H4, 2; Ar = O2N-m-C6H4, 3; Ar = O2N-p-C6H4, 4a; Ar = (O2N)2-o,p-C6H3, 5) have been obtained by controlled degradation of the parent compounds (nBu4N)3[Mo6O18(NNAr)] with NaOH in methanol. They have been characterized by elemental analysis and UV–Vis and IR spectroscopy. In addition, 4a has been characterized by 95Mo NMR spectroscopy and the crystal structure of (nBu4N)2[Mo5O13(OMe)4(NNC6H4-p-NO2){Na(H2O))]·H2O (4b) has been determined by X-ray diffraction. The molecular structure of the anion of 4b features a lacunary Lindqvist-type anion [Mo5O13(OMe)4(NNC6H4-p-NO2)]3− interacting with a sodium cation through the four terminal axial oxygen atoms. The 1:1 sodium complexes react with BaCl2 and BiCl3 to yield 2:1 complexes which have been isolated as (nBu4N)4[Ba{Mo5O13(OMe)4(NNAr)}2] (Ar = C6F5, 6; Ar = O2N-p-C6H4, 7) and (nBu4N)3[Bi{Mo5O13(OMe)4(NNAr)}2] (Ar = C6F5, 8; Ar = O2N-p-C6H4, 9). X-ray crystallography analysis of 9·Me2CO has shown that the tetradentate [Mo5O13(OMe)4(N2C6H4-p-NO2)]3− anions provide a square-antiprismatic environment for Bi. In contrast, IR spectroscopy provides evidence for a square-prismatic environment of Ba in 6 and 7. In acetonitrile–methanol mixed solvent, [Mo5O13(OMe)4(NNAr)]3− and [PW11O39]7−, generated in situ by alkaline degradation of their respective parents, [Mo6O18(NNAr)]3− and [PW12O40]3−, react together to give the Keggin-type diazenido compounds (nBu4N)4[PW11O39(MoNNAr)] (Ar = O2N-o-C6H4, 10; Ar = O2N-m-C6H4, 11; Ar = O2N-p-C6H4, 12), which have been characterized by 31P and 183W NMR spectroscopy.