Peroxo complexes solid state structures

Solid state structures for bimetallic /r-peroxo complexes have been obtained for aU the coordination modes of 02 moiety indicated in Scheme 3. Several examples can be found in a special issue of Chemical Reviews. ... 

In the previous sections it has been shown that for a large variety of peroxo metal complexes only few types of solid state structures come across. Moreover, the structural motifs (bond lengths, bond angles etc.) are very similar also for very diverse species and only poor relationships with reactivity have been recognized ... 

Exposure of the crystalline palladium(O) complex 10 to air at room temperature caused a color change from deep red to pale yellow. The formation of the palladium(II)peroxocarbonate complex 12 was confirmed by spectroscopic analysis as well as a solid-state structure. Control reactions revealed that the first intermediate is a palladium(II)peroxo complex 11. 

The reactivity of the peroxo metal complexes indicated in Scheme 1 is much higher than that of the peroxidic precursor, either H2O2 or ROOH. This fundamental feature is the direct link between the chemistry of metal catalyzed oxidations and that of peroxo metal complexes These are in fact, in the majority of the systems, well defined species in solutions and in numerous cases they can be isolated and fully characterized also in the solid state. As far as the structure of the active complexes indicated in Scheme 1 is concerned, both in the solid state and/or in solution, several pieces of evidence indicate that most of them share a triangular arrangement of the peroxo moiety around the metal center (see below). In principle, all the /z-peroxo complexes structures, named following... 

As anticipated beforehand, bis( -peroxo)-rhenium complexes have been characterized in the solid state " . The noticeable feature is that the active catalyst (CH3)Re0(02)2H20 (1) does not crystallize as it is, but a modification of the seventh apical ligand is required, as indicated in compounds 11 and 12. The molecular structure of these peroxo rhenium complexes is yet again a pentagonal bipyramid, and the bond lengths are in the expected range. 

The peroxo-complexes provide further examples of the ability of oxygen to coordinate to the metals in their high oxidation states. The production of blue solutions when acidified dichromates are treated with H2O2 is a qualitative test for chromium. The colour arises from the unstable CrO. which can, however, be stabilized by extraction into ether, and blue solid adducts such as tCrOs(py)] can be isolated. This is more correctly formulated as lCr0(02>2py] and has an approximately pentagonal pyramidal structure (Fig. 23.6a). Bidenlate ligands, such as phenanlhroline and bipyridyl produce pentagonal bipyramidal complexes in which the second N-donor atom is loosely bonded irons to the =0 (Fig. 23.6b). This 7-coordinate structure is favoured in numerous peroxo-complexes of Mo and W, and the dark-red peroxo anion [Mo(02)4] is 8-coordinate, with Mo-O 197 pm and 0-0 155 pm. 

H nmr studies in non-polar solvents have shown that whereas the sulphide and selenide of the heterocyclic system (224) involve intramolecular coordinative interactions between tin and sulphur or selenium, the related phosphine oxide prefers to bind intermolecularly. In the solid state, a similar situation applies.Structural studies of adducts of triphenylphosphine oxide with monoorganotrichlorostannanes have also been reported. Various types of phosphine oxides are able to complex alkali and alkaline earth metal cations, and to facilitate their transfer across aqueous/organic interfaces.Organogallium complexes of phosphine oxide ligands have been isolated from the reactions of organogallium peroxo derivatives with phosphines. ... 

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