Synthesis and reactivity of peroxymolybdenum (VI) complexes of the types [MoO(O₂)] (QO=8-quinolinolate anion) [MoO(O₂)₂(L-L](L-L-neutral N-N donors), and crystal and molecular structure of (PPN)₂ [Mo₂O₇]^†

Abstract

The binuclear oxo-bridged (peroxo) dimolybdate(VI) anion, [Mo₂O₂<i>(µ</i>₂- O)(O₂)₄(H₂O)₂]^2- obtained by dissolving MoO₃ in H₂O₂ reacts with QOH(8-quinolinol) producing [MoO(O₂)(QO)₂](l); 1,10-phenanthroline(phen), 2,2'-bipydine(bipy), 2,2'-pyridylbenzimidazole (PBIH) and 8-aminoqui oline (AQ), however, form [MoO(O₂) ₂(L- L)] {L- L= phen (2), bipy (3), PBIH (4) and AQ (5)}. The compounds have been characterized on the basis of <i>v</i>(Mo = 0), <i>v</i>O - O), and <i>v (</i>MoO₂<i>) </i> vibrations in their infrared and laser Raman spectra. Vibrational data also indicate that while 2-5 have a Symmetrical structure, 1 has an asymmetrical structure in the pentagonal bipyramidal framework. The electronic spectrum of 1 also corroborates this. All the complexes exhibit a high tendency of stoichiometric oxygen transfer towards 3A (R = Ph; A= P, As, Sb) and cyclohexene, forming the corresponding R₃AO and cyclohexene oxide, respectively. The complex 1 is most effective in this regard. Such an oxygen transfer from [Mo₂O₂(µ₂-O)(O₂)₄(H₂O)₂]^2- yields Mo₂O<img src='http://www.niscair.res.in/jinfo/seven.gif' border=0><i>, </i> the details of the crystal structure of the PPN salt (6) of which are described herein. Cyclic voltammograms of 2 and 3 show 2-electron (coulometry) oxidation wave (~1.8 V vs SCE), via dioxygen elimination corresponding to the formation of [MoO(O₂)(L- L)]²⁺. Both of them also exhibit an irreversible one electron reduction (-1.2 V vs SCE) at the metal centre, presumably producing [Mo^vO(O₂)₂(L-L)]^-.