Chromium(II) acetate 2988743 224268984 2008-07-08T02:16:24Z DMacks 712163 Reverted edits by [[Special:Contributions/138.16.68.11|138.16.68.11]] ([[User talk:138.16.68.11|talk]]) to last version by Rifleman 82 {{Chembox new | ImageFile = Chromium(II)-acetate-dimer-3D-balls.png | Name = Chromium(II) acetate | IUPACName = Chromium(II) acetate hydrate | OtherNames = chromous acetate,<br />chromium diacetate | Section1 = {{Chembox Identifiers | SMILES = | CASNo = 14976-80-8 | RTECS = AG3000000 }} | Section2 = {{Chembox Properties | Formula = C<sub>8</sub>H<sub>16</sub>Cr<sub>2</sub>O<sub>10</sub> | MolarMass = 376.2 g/mol | Appearance = brick-red solid | Density = 1.79 g/cm<sup>3</sup> | Solubility = soluble in hot water, MeOH | MeltingPt = dehydrates >100C }} | Section3 = {{Chembox Structure | MolShape = quadruple Cr--Cr bond | Coordination = octahedral<br />counting the Cr-Cr bond | CrystalStruct = [[monoclinic]] | Dipole = 0 [[Debye|D]] }} | Section7 = {{Chembox Hazards | ExternalMSDS = | MainHazards = could react exothermically in air | RPhrases = | SPhrases = }} | Section8 = {{Chembox Related | OtherCpds = [[Rhodium(II) acetate|Rh<sub>2</sub>(OAc)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>]]</br> [[Copper(II) acetate|Cu<sub>2</sub>(OAc)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>]] }} }} '''Chromium(II) acetate''', better known as chromous acetate, is the compound Cr<sub>2</sub>(CH<sub>3</sub>CO<sub>2</sub>)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>. This formula is commonly abbreviated Cr<sub>2</sub>(OAc)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>. This compound and some of its simple derivatives illustrate one of the most remarkable properties of some [[metal]]s - the ability to engage in [[quadruple bonds]]. The preparation of chromous acetate once was a standard test the synthetic skills of students due to its considerable sensitivity to [[air]]. It exists as the [[dihydrate]] and the [[anhydrous]] forms. Cr<sub>2</sub>(OAc)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub> is a reddish [[diamagnetic]] powder, although diamond-shaped tabular [[crystal]]s can be grown. Consistent with the fact that it is non-[[ion]]ic, Cr<sub>2</sub>(OAc)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub> exhibits poor solubility in [[water]] and [[methanol]]. ==Structure== The Cr<sub>2</sub>(OAc)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub> molecule contains two atoms of [[chromium]], two [[ligand|ligated]] molecules of water, and four mono[[anion]]ic [[acetate]] [[ligand]]s. The coordination environment around each chromium atom consists of four [[oxygen]] atoms (one from each acetate ligand) in a square, one water molecule (in an axial position), and the other chromium atom (opposite the water molecule), giving each chromium centre an [[Octahedral molecular geometry|octahedral geometry]]. The chromium atoms are joined together by a quadruple bond, and the molecule has D<sub>4h</sub> symmetry (ignoring the position of the hydrogen atoms). The same basic structure is adopted by [[Rhodium(II) acetate|Rh<sub>2</sub>(OAc)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>]] and [[Copper(II) acetate|Cu<sub>2</sub>(OAc)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>]], although these species do not have such short M---M contacts.<ref>Cotton, F. A.; Walton, R. A. “Multiple Bonds Between Metal Atoms” Oxford (Oxford): 1993. ISBN 0-19-855649-7.</ref> The quadruple bond between the two chromium atoms arises from the overlap of four [[Atomic orbital|''d''-orbitals]] on each metal with the same orbitals on the other metal: the z<sup>2</sup> orbitals overlap to give a [[sigma bond]]ing component, the xz and yz orbitals overlap to give two [[pi bond]]ing components, and the xy orbitals give a [[delta bond]]. This quadruple bond is also confirmed by the low [[magnetic moment]] and short intermolecular distance between the two atoms of 236.2±0.1 [[picometer]]s.The Cr-Cr distances are even shorter, 184 pm being the record, when the axial ligand is absent or the carboxylate is replaced with isoelectronic nitrogenous ligands.<ref>{{cite journal | author = Cotton, F. A.; Hillard, E.A.; Murillo, C. A.; Zhou, H.-C. | title = After 155 Years, A Crystalline Chromium Carboxylate with a Supershort Cr-Cr Bond | journal = [[J. Am. Chem. Soc.]] | year = 2000 | volume = 122 | pages = 416-417 | doi = 10.1021/ja993755i}}</ref> ==History== [[Eugene-Melchior Peligot|Eugene Peligot]] first reported a chromium(II) acetate in [[1844]]. His material was apparently the [[dimer]]ic Cr<sub>2</sub>(OAc)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub>.<ref> Peligot, E. C. R. Acad. Sci. 1844, volume 19, page 609ff. (b) Peligot, E. Ann. Chim. Phys. 1844, volume 12, pages 528ff.</ref> The unusual structure, as well as that of [[copper(II) acetate]], was uncovered in [[1951]].<ref>{{cite journal | author = van Niekerk, J. N. Schoening, F. R. L. | title = X-Ray Evidence for Metal-to-Metal Bonds in Cupric and Chromous Acetate | journal = [[Nature (journal)|Nature]] | year = 1953 | volume = 171 | pages = 36-37 | doi = 10.1038/171036a0}}</ref> ==Preparation== An aqueous solution of a Cr(III) compound is first reduced to the chromous state using [[zinc]] as a [[reductant]].<ref>{{cite book | author=Ocone, L.R.; Block, B.P. | journal = [[Inorganic Syntheses]] | title = Anyhdrous Chromium (II) Acetate, Chromium (II) Acetate 1-Hydrate, and Bis(2,4-Pentanedionato) Chromium (II) | volume=8 | year=1966 |pages=125-129 | doi = 10.1002/9780470132395.ch33}}</ref> The resulting blue chromous solution is treated with [[sodium acetate]]. Immediately chromous acetate [[precipitate]]s as a bright red powder. : Cr<sup>6+</sup> + 2Zn → Cr<sup>2+</sup> + 2 Zn<sup>2+</sup> :2 Cr<sup>2+</sup> + 4 OAc<sup>-</sup> + 2 H<sub>2</sub>O → Cr<sub>2</sub>(OAc)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub> The synthesis of Cr<sub>2</sub>(OAc)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub> has been traditionally used to test the synthetic skills and patience of inorganic laboratory students in [[university|universities]] because the accidental introduction of a small amount of air into the apparatus is readily indicated by the discoloration of the otherwise bright red product.<ref>{{cite book | author=Jolly, W. L. | title=The Synthesis and Characterization of Inorganic Compounds| publisher=Prentice Hall| year=1970| pages=442-445}}</ref> An alternative route to related chromium(II) carboxylates starts with [[chromocene]]: : 4 HO<sub>2</sub>CR + 2 Cr(C<sub>5</sub>H<sub>5</sub>)<sub>2</sub> → Cr<sub>2</sub>(O<sub>2</sub>CR)<sub>4</sub> + 4 [[Cyclopentadiene|C<sub>5</sub>H<sub>6</sub>]] The advantage to this method is that it provides anhydrous derivatives. Because it is so easily prepared, Cr<sub>2</sub>(OAc)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub> is often used as a starting material for other, chromium(II) compounds. Also many analogues have been prepared using other [[carboxylic acid]]s in place of acetate and using different bases in place of the water. ==Applications== Cr<sub>2</sub>(OAc)<sub>4</sub>(H<sub>2</sub>O)<sub>2</sub> is used occasionally to dehalogenate organic compounds such as &alpha;-bromoketones and [[chlorohydrin]]s.<ref>Ray, T. "Chromium(II) Acetate" in Encyclopedia of Reagents for Organic Synthesis (Ed: L. Paquette) 2004, J. Wiley & Sons, New York. {{DOI|10.1002/047084289}}</ref> The reactions appear to proceed via 1e<sup>-</sup> steps, and rearrangement products are sometimes observed. Because the molecule contains Cr in a +2 oxidation state it is a good reducing agent. For this reason it will reduce the O<sub>2</sub> found in air, and so can be used as an oxygen scrubber. Many other applications exist, including those in the [[polymer]] industry.<ref>{{cite journal | author = Lee, M. | coauthors = Nakamura, H.; Minoura, Y. | year = 1976 | title = Graft copolymerization of styrene on rubber containing halogen by chromous acetate | journal = [[Journal of Polymer Science]] | volume = 14 | issue = 4 | pages = 961-971 | doi = 10.1002/pol.1976.170140416}}</ref> ==References== <references/> ==Further reading== * {{cite journal | author = Rice, S. F. | title = Electronic Absorption Spectrum of Chromous Acetate Dihydrate and Related Binuclear Chromous Carboxylates | journal = [[Inorg. Chem.]] | volume = 19 | year = 1980 | pages = 3425-3431 | doi = 10.1021/ic50213a042}} ==External links== *http://www.molecules.org/coordcpds.html#Cr2OAc4H2O *http://alpha.chem.umb.edu/chemistry/ch370/documents/CH371chromiumacetate06.pdf *http://wwwchem.uwimona.edu.jm/courses/chromium.pdf [[Category:Chromium compounds]] [[Category:Acetates]] [[Category:Coordination compounds]] [[ar:خلات كروم ثنائي]] [[fr:Acétate de chrome II]] [[id:Kromium(II) asetat]] [[ja:酢酸クロム(II)]] [[pt:Acetato de cromo (II)]]