Triosmium dodecacarbonyl is a
chemical compound
A chemical compound is a chemical substance composed of many identical molecules (or molecular entities) containing atoms from more than one chemical element held together by chemical bonds. A molecule consisting of atoms of only one element ...
with the formula Os
3(CO)
12. This yellow-colored
metal carbonyl cluster is an important precursor to
organo-osmium compounds. Many of the advances in cluster chemistry have arisen from studies on derivatives of Os
3(CO)
12 and its lighter analogue
Ru3(CO)12.
Structure and synthesis
The cluster has D
3h symmetry
Symmetry () in everyday life refers to a sense of harmonious and beautiful proportion and balance. In mathematics, the term has a more precise definition and is usually used to refer to an object that is Invariant (mathematics), invariant und ...
, consisting of an
equilateral triangle
An equilateral triangle is a triangle in which all three sides have the same length, and all three angles are equal. Because of these properties, the equilateral triangle is a regular polygon, occasionally known as the regular triangle. It is the ...
of Os atoms, each of which bears two axial and two equatorial
CO ligand
In coordination chemistry, a ligand is an ion or molecule with a functional group that binds to a central metal atom to form a coordination complex. The bonding with the metal generally involves formal donation of one or more of the ligand's el ...
s. Each of the three osmium centers has an octahederal structure with four CO ligands and the other two osmium atoms.
The Os–Os bond distance is 2.88 Å (288 pm). Ru
3(CO)
12 has the same structure, whereas Fe
3(CO)
12 is different, with two bridging CO ligands resulting in C
2v symmetry. In solution, is fluxional as indicated by
13C NMR measurements. The barrier is estimated at 70 kJ/mol
Os
3(CO)
12 is prepared by the direct reaction of
OsO4 with carbon monoxide at 175 °C under high pressures:
: 3 OsO
4 + 24 CO → Os
3(CO)
12 + 12 CO
2
The yield is nearly quantitative.
Reactions
Many chemical reactions of Os
3(CO)
12 have been examined. Direct reactions of ligands with the cluster often lead to complex product distributions. Os
3(CO)
12 converts to more labile derivatives such as Os
3(CO)
11(
MeCN) and Os
3(CO)
10(MeCN)
2 using
Me3NO as a decarbonylating agent:
:
:
Os
3(CO)
11(MeCN) reacts with a variety of even weakly basic ligands to form adducts.
Purging a solution of triosmium dodecacarbonyl in boiling
octane
Octane is a hydrocarbon and also an alkane with the chemical formula C8H18, and the condensed structural formula CH3(CH2)6CH3. Octane has many structural isomers that differ by the location of branching in the carbon chain. One of these isomers ...
(or similar inert solvent of similar boiling point) with
H2 gives the dihydride
Os3H2(CO)10:
:
Osmium pentacarbonyl is obtained by treating solid triosmium dodecacarbonyl with 200 atmospheres of
carbon monoxide
Carbon monoxide (chemical formula CO) is a poisonous, flammable gas that is colorless, odorless, tasteless, and slightly less dense than air. Carbon monoxide consists of one carbon atom and one oxygen atom connected by a triple bond. It is the si ...
at 280-290 °C.
:
References
{{Osmium compounds
Organoosmium compounds
Carbonyl complexes
Osmium compounds
Chemical compounds containing metal–metal bonds