A metaborate is a

borate A borate is any of a range of boron oxyanions, anions containing boron and oxygen, such as orthoborate , metaborate , or tetraborate ; or any salt of such anions, such as sodium metaborate, and borax . The name also refers to esters of su ...

anion An ion () is an atom or molecule with a net electrical charge. The charge of an electron is considered to be negative by convention and this charge is equal and opposite to the charge of a proton, which is considered to be positive by conven ...

consisting of

boron Boron is a chemical element; it has symbol B and atomic number 5. In its crystalline form it is a brittle, dark, lustrous metalloid; in its amorphous form it is a brown powder. As the lightest element of the boron group it has three ...

and

oxygen Oxygen is a chemical element; it has chemical symbol, symbol O and atomic number 8. It is a member of the chalcogen group (periodic table), group in the periodic table, a highly reactivity (chemistry), reactive nonmetal (chemistry), non ...

, with

empirical formula In chemistry, the empirical formula of a chemical compound is the simplest whole number ratio of atoms present in a compound. A simple example of this concept is that the empirical formula of sulfur monoxide, or SO, is simply SO, as is the empir ...

. Metaborate also refers to any

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

ester In chemistry, an ester is a compound derived from an acid (either organic or inorganic) in which the hydrogen atom (H) of at least one acidic hydroxyl group () of that acid is replaced by an organyl group (R). These compounds contain a distin ...

of such anion (e.g. salts such as

sodium metaborate Sodium metaborate is a chemical compound of sodium, boron, and oxygen with formula . However, the metaborate ion is trimeric in the anhydrous solid, therefore a more correct formula is or . The formula can be written also as to highlight the re ...

or calcium metaborate , and esters such as methyl metaborate ). Metaborate is one of the boron's

oxyanion An oxyanion, or oxoanion, is an ion with the generic formula (where A represents a chemical element and O represents an oxygen atom). Oxyanions are formed by a large majority of the chemical elements. The formulae of simple oxyanions are determine ...

s. Metaborates can be

monomeric A monomer ( ; ''mono-'', "one" + '' -mer'', "part") is a molecule that can react together with other monomer molecules to form a larger polymer chain or two- or three-dimensional network in a process called polymerization. Classification Chemis ...

oligomeric In chemistry and biochemistry, an oligomer () is a molecule that consists of a few repeating units which could be derived, actually or conceptually, from smaller molecules, monomer, monomers.Quote: ''Oligomer molecule: A molecule of intermediate ...

polymeric A polymer () is a substance or material that consists of very large molecules, or macromolecules, that are constituted by many repeating subunits derived from one or more species of monomers. Due to their broad spectrum of properties, bot ...

. In aqueous solutions metaborate anion

hydrolyzes Hydrolysis (; ) is any chemical reaction in which a molecule of water breaks one or more chemical bonds. The term is used broadly for substitution reaction, substitution, elimination reaction, elimination, and solvation reactions in which water ...

to tetrahydroxyborate . For this reason, solutions or hydrated salts of the latter are often improperly named "metaborates".

Structure

Solid state

In the solid state of their

salts In chemistry, a salt or ionic compound is a chemical compound consisting of an assembly of positively charged ions ( cations) and negatively charged ions (anions), which results in a compound with no net electric charge (electrically neutral). ...

, metaborate ions are often

, conceptually resulting from the fusion of two or more through shared oxygen atoms. In these anions, the boron atom forms covalent bonds with either three or four oxygen atoms. Some of the structures are: * A trimer with formula or , consisting of a six-membered ring of alternating boron and oxygen atoms with one extra oxygen atom attached to each boron atom. This form is found, for example, in some anhydrous

alkali metal The alkali metals consist of the chemical elements lithium (Li), sodium (Na), potassium (K),The symbols Na and K for sodium and potassium are derived from their Latin names, ''natrium'' and ''kalium''; these are still the origins of the names ...

salts like

or potassium metaborate, in α- and β- barium metaborate , and in the mixed salt potassium cadmium metaborate . The three B–O distances are nearly equal in the

potassium Potassium is a chemical element; it has Symbol (chemistry), symbol K (from Neo-Latin ) and atomic number19. It is a silvery white metal that is soft enough to easily cut with a knife. Potassium metal reacts rapidly with atmospheric oxygen to ...

salt (133.1, 139.8, and 139.8 pm) but significantly different in the

sodium Sodium is a chemical element; it has Symbol (chemistry), symbol Na (from Neo-Latin ) and atomic number 11. It is a soft, silvery-white, highly reactive metal. Sodium is an alkali metal, being in group 1 element, group 1 of the peri ...

one (128.0, 143.3, and 143.3 pm). * A polymer of units connected by single shared-oxygen bridges; that is, . Occurs in calcium metaborate or . * A tridimensional network of tetrahedral groups, as in "zinc metaborate", which is actually a mixed salt zinc metaborate oxide, with the formula . * A tridimensional regular array of tetrahedra sharing oxygen vertices, as in the high-pressure and high-temperature γ form of lithium metaborate .

Aqueous solution

The cyclic trimer anions dissociate almost completely in

aqueous solution An aqueous solution is a solution in which the solvent is water. It is mostly shown in chemical equations by appending (aq) to the relevant chemical formula. For example, a solution of table salt, also known as sodium chloride (NaCl), in water ...

giving mainly tetrahydroxyborate anions: : 3 Other molecules and anions, such as , , , and are less than 5% at 26 °C. In 1937, Nielsen and Ward claimed that the metaborate anion in solution has a linear symmetric structure with negative charges on the oxygens and a positive charge on the boron, or with negative charge on the boron. However, this claim has been disproved.

Gas phase

The vapor of cesium metaborate has neutral monomers and dimers as well as ionized versions thereof. The same situation holds for thallium metaborate .

Solid solutions

In 1964 Hisatsune and Surez investigated the infrared spectrum of metaborate anions in dilute solid solutions of potassium salt in alkali

halide In chemistry, a halide (rarely halogenide) is a binary chemical compound, of which one part is a halogen atom and the other part is an element or radical that is less electronegative (or more electropositive) than the halogen, to make a fl ...

s such as

potassium chloride Potassium chloride (KCl, or potassium salt) is a metal halide salt composed of potassium and chlorine. It is odorless and has a white or colorless vitreous crystal appearance. The solid dissolves readily in water, and its solutions have a sa ...

KCl.

References

P. Ney, M. D. Fontana, A. Maillard, and K. Polgár (1998): "Assignment of the Raman lines in single crystal barium metaborate (β-BaB2O4)". ''Journal of Physics: Condensed Matter'', volume 10, issue 3, pages 673-. David H. Feather and Alfred Buechler (1973): "Gaseous thallium(I) metaborate and thallium(I) aluminum fluoride". ''Journal of Physical Chemistry'', volume 77, issue 12, pages 1599–1600. Yongquan Zhou, Souta Higa, Chunhui Fang, Yan Fang, Wenqian Zhang, and Toshio Yamaguchi (2017): "B(OH)4− hydration and association in sodium metaborate solutions by X-ray diffraction and empirical potential structure refinement". ''Physical Chemistry Chemical Physics'', volume 19, pages 27878-27887 W. H. Zachariasen (1931): "The Crystal Lattice of Calcium Metaborate, CaB2O4". ''Proceedings of the National Academy of Sciences (PNAS)'', volume 17, issue 11, pages 617-619. Y. Roussigné, R. Farhi, C. Dugautier, and J. Godard (1992): "A Raman study of both phases of barium metaborate (BBO)". ''Solid State Communications''. volume 82, issue 4, pages 287-293. Yongquan Zhou, Chunhui Fang, Yan Fang, Fayan Zhu, Song Tao, Sha Xu (2012): "Structure of aqueous sodium metaborate solutions: X-ray diffraction study". ''Russian Journal of Physical Chemistry, volume 86, issue 8, pages 1236–1244. Fayan Zhu, Yongquan Zhou, Chunhui Fang, Yan Fang, Haiwen Ge, and Hongyan Liu (2017): "Ion association in lithium metaborate solution: a Raman and ab initio insight". ''Physics and Chemistry of Liquids'', volume 55, issue 2, pages 186-195. Mitsuru Asano, Yoshihiko Yasue, and Kenji Kubo (1984): "Mass Spectrometric Study of Ions Formed from Cesium Metaborate Vapor under Electron Impact". ''Journal of Nuclear Science and Technology'', volume 21, issue 8,pages 614-624. C. S. Willand and A. C. Albrecht (1986): "The second-order nonlinear optical properties of β-barium metaborate: A semiempirical theoretical investigation". ''Optics Communications'', volume 57, issue 2, 15 February , Pages 146-152. Shifeng Jin, G. Chai, J. Liu, W. Wang and X. Chen (2009): "The centrosymmetric metal meta-borate KCdB₃O₆". ''Acta Crystallographica Section C'', volume C65, issue 7, pages i42-i44. Robert K. Momii and Norman H. Nachtrieb (1967): "Nuclear Magnetic Resonance Study of Borate-Polyborate Equilibria in Aqueous Solution". ''Inorganic Chemistry'', volume 6, issue 6, pages 1189-1192. I. C. Hisatsune and Noelia Haddock Suarez (1964): "Infrared Spectra of Metaborate Monomer and Trimer Ions". ''Inorganic Chemistry'', volume 3, issue 2, pages 168-174. J. Rud Nielsen and N. E. Ward (1937): "Raman Spectrum and Structure of the Metaborate Ion". ''The Journal of Chemical Physics'', volume 5, Issue 3, page 201 M. Marezio, H. A. Plettinger and W. H. Zachariasen (1963): "The bond lengths in the sodium metaborate structure", ''Acta Crystallographica'', volume 16, pages 594-595. M. Marezio, H. A. Plettinger and W. H. Zachariasen (1963): "Refinement of the calcium metaborate structure". ''Acta Crystallographica'', volume 16, pages 390-392. M. Marezio and J. P. Remeika (1966): "Polymorphism of LiMO2 Compounds and High‐Pressure Single‐Crystal Synthesis of LiBO2". ''Journal of Chemical Physics'', volume 44, issue 9, pages 3348-. W. Schneider and G. B. Carpenter (1970) "Bond lengths and thermal parameters of potassium metaborate, K3B3O6". ''Acta Crystallographica - Section B'' volume B26, pages 1189-1191 (1964): "The crystal structure of anhydrous zinc metaborate Zn4O(BO2)6". ''Zeitschrift für Kristallographie'', volume 119, issue 5-6 (1961): "A new structural type of metaborate anion". ''Zeitschrift für Kristallographie'', volume 115, issue 5-6. W. H. Zachariasen (1937): "The Crystal Structure of Potassium Metaborate, K3(B3O6)". ''Journal of Chemical Physics'', volume 5, issue 11, page 919. {{Borates Borate minerals Industrial minerals Inorganic compounds Boron oxyanions