Molybdenum complexes structural formulae

The existence of at least nine phases in the molybdenum-oxygen system is well established. Their crystal structures are briefly described and it is shown that they can be classified into four main families dependent on whether they possess a basic structure of rutile type, ReOs type, or MoOs type, or have complex structures where polygonal networks can be distinguished. The known tungsten and mixed molybdenum tungsten oxides fit into this scheme. Because of their complicated formulas many of these compounds may be termed "nonstoichiometric," but variance in composition has not been observed for any of them. 

The molybdenum compound with the empirical formula MoClg does not possess the simple Mo + ion its structure is [MogClg]4Cl4, the complex cation being cubic, with chlorine atoms at the eight corners and molybdenum atoms at the six face centres (Fig. 244). Tungsten forms a similar compound but, unlike the Mo complex which is stable in aqua regia, it is easily oxidised. 

Preparation. Mimoun et at.1 prepared this complex of Mo05 and HMPT by dissolving molybdenum trioxide (M0O3, ROC/RIC, 50 g.) at 40° in 30 % H 202 (250 cc.). The yellow solution so obtained is cooled to 10° and HMPT (62.3 g.) is added with efficient stirring. A yellow precipitate is formed immediately and is collected on a filter and washed several times with ether. The dried material is crystallized twice from methanol it is obtained as yellow crystals in 84% yield. The French chemists showed that the complex has the structure shown in formula (1). 

In the previous work [9] we have investigated ethene and propene metathesis reactions proceeding on molybdenaalkylidene centres. In the present work density functional study on ethene metathesis reaction proceeding on molybdenamethylidene centres of M0O3/AI2O3 catalyst is reported. Two variants of theoretical models of the active sites have been applied. In the first case, simple structures of the carbene and molybdacyclobutane complexes, in which hydroxyl groups replace the bonds between molybdenum and the carrier, are proposed. In the second case, molybdenum is attached to a small cluster of formula Al2(OH)6, which represents alumina. 

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