In chemistry a boride is a chemical compound between boron and a less electronegative element. " Electronegativity " is the opposite of " Electropositivity," which describes an element's ability to donate electrons This is a very large group of compounds that are generally high melting and are not ionic in nature. Some borides exhibit very useful physical properties. The term boride is also loosely applied to compounds such as B₁₂As₂ (N. B. Arsenic has an electronegativity higher than boron) that is often referred to as icosahedral boride. Boron arsenide is a chemical compound of Boron and Arsenic. It is a cubic ( Sphalerite) Semiconductor with a Lattice constant

Contents 1 Ranges of compounds 2 Boron rich borides (B:M 4:1 or more) 3 Metal rich borides (B:M less than 4:1) 4 Boride structures 5 See also 6 General References 7 Footnotes

Ranges of compounds

The borides can be classified loosely as boron rich or metal rich, for example the compound YB₆₆ at one extreme through to Nd₂Fe₁₄B at the other. The generally accepted definition is that if the ratio of boron atoms to metal atoms is 4 : 1 or more the compound is boron rich, if it is less then it is metal rich.

Boron rich borides (B:M 4:1 or more)

The main group metals, lanthanides and actinides tend to form boron rich borides. Terminology The Trivial name " Rare earths " is sometimes used to describe all the lanthanoids together with Scandium and Yttrium History of the actinoid series From the earlier known chemical properties of actinium (89 up to uranium (92 indicating a relation to the Transition metals it was generally The boron rich group is much larger than the metal rich. The properties of this group vary from one compound to the next, and includes examples of compounds that are semi conductors, superconductors, diamagnetic, paramagnetic, ferromagnetic or anti-ferromagnetic. Diamagnetism is the property of an object which causes it to create a magnetic field in opposition of an externally applied Magnetic field, thus causing a repulsive effect Paramagnetism is a form of magnetism which occurs only in the presence of an externally applied magnetic field Ferromagnetism is the basic mechanism by which certain materials (such as Iron) form Permanent magnets and/or exhibit strong interactions with Magnets it In materials that exhibit antiferromagnetism, the magnetic moments of atoms or molecules usuallyrelated to the spins of Electrons align in a regular pattern with neighboring ^[1]. An example is LaB₆ an inert refractory compound. Lanthanum hexaboride ( La[[Boron B]]6, also called lanthanum boride and LaB) is an inorganic chemical a Boride of Lanthanum A refractory is a material that retains its strength at high Temperatures ASTM C71 defines refractories as "non-metallic materials having those chemical and physical

Metal rich borides (B:M less than 4:1)

The transition metals tend to form metal rich borides. Metal-rich borides as a group are high melting and inert. Some are easily formed and this explains their use in making turbine blades, rocket nozzles etc. Some examples include AlB₂ and TiB₂. Titanium Diboride (chemical formula TiB2 is an extremely hard Ceramic compound (33 GPa composed of Titanium and Boron that has very good Recent investigations into this class of borides have revealed a wealth of interesting properties such as super conductivity at 39 K in MgB₂ and the ultra-incompressibility of OsB₂ and ReB₂

Boride structures

The boron rich borides contain 3-dimensional frameworks of boron atoms that can include boron polyhedra. Magnesium diboride (MgB2 is an inexpensive and simple Superconductor. Rhenium diboride ( Re[[Boron B]]2 is a synthetic Superhard material. The metal rich borides contain single boron atoms, B₂ units, boron chains or boron sheets/layers.

Examples of the different types of borides are :-

• isolated boron atoms, example Mn₄B
• B₂ units, example V₃B
• chains of boron atoms, example FeB
• sheets or layers of boron atoms CrB₂
• 3-dimensional boron frameworks that include boron polyhedra, example NaB₁₅ with boron icosahedra

See also

• lanthanum hexaboride (LaB₆)
• magnesium diboride (MgB₂)
• titanium boride (TiB₂)

See category for a fill list. Lanthanum hexaboride ( La[[Boron B]]6, also called lanthanum boride and LaB) is an inorganic chemical a Boride of Lanthanum Magnesium diboride (MgB2 is an inexpensive and simple Superconductor. Titanium Diboride (chemical formula TiB2 is an extremely hard Ceramic compound (33 GPa composed of Titanium and Boron that has very good

General References

• WebElements

Greenwood, N. N. ; Earnshaw, A. (1997). Chemistry of the Elements, 2nd Edition, Oxford:Butterworth-Heinemann. ISBN 0-7506-3365-4.  
Cotton, F. Albert; Wilkinson, Geoffrey; Murillo, Carlos A. Frank Albert Cotton ( April 9 1930 – February 20 2007) was the W Sir Geoffrey Wilkinson ( 14 July 1921 &ndash 26 September, 1996) was an English Chemist. ; Bochmann, Manfred (1999). Advanced Inorganic Chemistry (6th Edn. ) New York:Wiley-Interscience. ISBN 0-471-19957-5.

Footnotes

1. ^ Lundstrom T Pure & Applied Chem. (1985) 57, 10,1383

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