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Heating a solution of Cr(CO) 6 in an aromatic solvent results in replacement of three CO ligands. The reactions are especially favorable for electron-rich arenes: Cr(CO) 6 + C 6 H 5 R → Cr(CO) 3 (C 6 H 5 R) + 3 CO. The products are "piano stool complexes". These species are typically yellow solids. One example is (benzene)chromium tricarbonyl.
The organochromium compound (phenylmethoxycarbene)pentacarbonylchromium, Ph(OCH 3)C=Cr(CO) 5 was the first carbene complex to be crystallographically characterized by Fischer in 1967 (now called a Fischer carbene). [14] The first ever carbyne, this one also containing chromium, made its debut in 1973. [15]
Chromium compounds are compounds containing the element chromium (Cr). Chromium is a member of group 6 of the transition metals. The +3 and +6 states occur most commonly within chromium compounds, followed by +2; charges of +1, +4 and +5 for chromium are rare, but do nevertheless occasionally exist. [3] [4]
6 carbon: C −4: −3: ... The oxidation states are also ... bt bu bv bw bx by bz ca cb cc cd ce cf cg ch ci cj ck cl cm cn co cp cq cr cs ct cu cv cw cx cy cz da db ...
It can be prepared by treating chromium metal with fluorine at 400 °C and 200 bar pressure. The peroxochromate(V) is another example of the +5 oxidation state. Potassium peroxochromate (K 3 [Cr(O 2) 4]) is made by reacting potassium chromate with hydrogen peroxide at low temperatures. This red brown compound is stable at room temperature but ...
Because of the very high melting point of chromium, chromium thermite casting is impractical. Heating with chlorine and carbon yields chromium(III) chloride and carbon monoxide: Cr 2 O 3 + 3 Cl 2 + 3 C → 2 CrCl 3 + 3 CO. Chromates can be formed by the oxidation of chromium(III) oxide and another oxide in a basic environment: 2 Cr 2 O 3 + 4 MO ...
8, has been described as having a carbon oxidation state of − 8 / 3 . [19] Again, this is an average value since the structure of the molecule is H 3 C−CH 2 −CH 3, with the first and third carbon atoms each having an oxidation state of −3 and the central one −2.
Chromium is a very common naturally occurring element. It is the 21st most abundant element in the Earth's crust with an average concentration of 100 ppm. The most common oxidation states for chromium are zero, trivalent, and hexavalent states. Most naturally occurring chromium is in the hexavalent state. [20]