Osmium borides are compounds of
osmium
Osmium (from Greek grc, ὀσμή, osme, smell, label=none) is a chemical element with the symbol Os and atomic number 76. It is a hard, brittle, bluish-white transition metal in the platinum group that is found as a trace element in alloys, mos ...
and
boron. Their most remarkable property is potentially high hardness. It is thought that a combination of high electron density of osmium with the strength of boron-osmium
covalent bonds will make osmium borides
superhard materials
A superhard material is a material with a hardness value exceeding 40 gigapascals (GPa) when measured by the Vickers hardness test. They are virtually incompressible solids with high electron density and high bond covalency. As a result of their u ...
, however this has not been demonstrated yet. For example, OsB
2 is hard (hardness comparable to that of
sapphire
Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sap ...
), but not superhard.
Synthesis
Osmium borides are produced in vacuum or inert atmosphere to prevent formation
of
osmium tetroxide
Osmium tetroxide (also osmium(VIII) oxide) is the chemical compound with the formula OsO4. The compound is noteworthy for its many uses, despite its toxicity and the rarity of osmium. It also has a number of unusual properties, one being that the ...
, which is a hazardous compound. Synthesis occurs at high temperatures (~1000 °C) from a mixture of
MgB2 and OsCl
3.
[
]
Structure
Three osmium borides are known: OsB, Os2B3 and OsB2. The first two have hexagonal structure, similar to that of rhenium diboride. Osmium diboride was first also sought as hexagonal, but one of its phases was later reassigned to orthorhombic.[ In recent methods of synthesis, it has also been found that a hexagonal phase of OsB2 exists with a similar structure to ReB2.]
References
{{DEFAULTSORT:Osmium Borides
Osmium compounds
Borides
Superhard materials