Rhenium compounds

[9] Rhenium trioxide crystallizes with a primitive cubic unit cell, with a lattice parameter of 3.742 Å (374.2 pm).

This molecular species closely resembles manganese heptoxide, consisting of a pair of ReO4 tetrahedra that share a vertex, i.e., O3Re–O–ReO3.

The layers are held together by weak Van der Waals bonds, and can be easily peeled off from the bulk material.

The perrhenate anion is tetrahedral, being similar in size and shape to perchlorate and the valence isoelectronic permanganate.

The perrhenate anion is stable over a broad pH range and can be precipitated from solutions with the use of organic cations.

Unlike fluorine, chlorine cannot oxidize rhenium past +V; the hexachloride is made from the hexafluoride and the heptachloride is entirely unknown.

Historically, the trichloride is one of the earliest cluster compounds with recognizable metal-metal multiple bonds.

Indeed, all the chlorides feature extensive Re-Re bonding, which appears characteristic of rhenium in oxidation states lower than VII.

[34][35] Like tungsten and molybdenum, with which it shares chemical similarities, rhenium forms a variety of oxyhalides.

It is possible to reduce this dimer with sodium amalgam to Na[Re(CO)5] with rhenium in the formal oxidation state −1.

Well known is methylrhenium trioxide ("MTO"), CH3ReO3 a volatile, colourless solid, a rare example of a stable high-oxidation state metal alkyl complex.

It can be prepared by many routes, a typical method is the reaction of Re2O7 and tetramethyltin:[40] Analogous alkyl and aryl derivatives are known.

Although PhReO3 is unstable and decomposes at –30 °C, the corresponding sterically hindered mesityl and 2,6-xylyl derivatives (MesReO3 and 2,6-(CH3)2C6H3ReO3) are stable at room temperature.

[41] MTO and other organylrhenium trioxides catalyze oxidation reactions with hydrogen peroxide as well as olefin metathesis in the presence of a Lewis acid activator.

A variety of half-sandwich compounds have been prepared from (C5H5)Re(CO)3 and (C5Me5)Re(CO)3. Notable derivatives include the electron-precise oxide (C5Me5)ReO3 and (C5H5)2Re2(CO)4.