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Structure of orthorhombic OsB₂. Green atoms are Os, pink – boron

Osmium borides are compounds of osmium 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, however this has not been demonstrated yet. For example, OsB₂ is hard (hardness comparable to that of sapphire), but not superhard.^[1]

Synthesis

Osmium borides are produced in vacuum or inert atmosphere to prevent formation of osmium tetroxide, which is a hazardous compound. Synthesis occurs at high temperatures (~1000 °C) from a mixture of MgB₂ and OsCl₃.^[1]

Structure

Three osmium borides are known: OsB, Os₂B₃ and OsB₂. The first two have hexagonal structure,^[2] similar to that of rhenium diboride. Osmium diboride was first also sought as hexagonal,^[3] but one of its phases was later reassigned to orthorhombic.^[1]^[4] In recent methods of synthesis, it has also been found that a hexagonal phase of OsB₂ exists with a similar structure to ReB₂.^[5]

References

^ ^a ^b ^c Cumberland, Robert W.; et al. (April 27, 2005). "Osmium Diboride, An Ultra-Incompressible, Hard Material". Journal of the American Chemical Society. 127 (20): 7264–5. doi:10.1021/ja043806y. PMID 15898746.
^ M. Hebbache; et al. (2006). "A new superhard material: Osmium diboride OsB2". Solid State Communications. 139 (5): 227–231. Bibcode:2006SSCom.139..227H. doi:10.1016/j.ssc.2006.05.041.
^ Kempter, C. P.; Fries, R. J. (1961). "Crystallography of the Ru-B and Os-B Systems". The Journal of Chemical Physics. 34 (6): 1994. Bibcode:1961JChPh..34.1994K. doi:10.1063/1.1731807.
^ Roof, R. B.; Kempter, C. P. (1962). "New Orthorhombic Phase in the Ru-B and Os-B Systems". The Journal of Chemical Physics. 37 (7): 1473. Bibcode:1962JChPh..37.1473R. doi:10.1063/1.1733309. OSTI 4787761.
^ Xie, Zhilin; Blair, Richard G.; Orlovskaya, Nina; Cullen, David A.; Andrew Payzant, E. (2014-11-01). "Thermal stability of hexagonal OsB2". Journal of Solid State Chemistry. 219: 210–219. Bibcode:2014JSSCh.219..210X. doi:10.1016/j.jssc.2014.07.035.