2. BINUCLEAR CARBONYL
Mn2(CO)10, Dimanganese decacarbonyl:
Preparation:
• It can be prepared by carbonylation of manganese iodide with carbon
monoxide using magnesium as a reducing agent
2MnI2+10CO + 2Mg diethyl ether Mn2 (CO)10 + 2MgI2 (25 C, 210 atm)
It can also be obtained by carbonylation of anhydrous manganese
chloride with carbon monoxide in presence of sodium benzophenone ketyl.
2 MnCl2+ 10CO + 4(C6 H5)2CONa 165 C, 140 atm. Mn2(CO)10 + 4(C6 H 5)2 CO + 4 NaCl
3. PROPERTIES
• It forms stable golden yellow crystals having melting point of 155 C.
• It is oxidized by trace amount of oxygen in solution. Hence, the
solution must be stored in inert atmosphere.
• Halogenation of dimanganese decacarbonyl proceeds with breaking of
Mn-Mn bond and formation of carbonyl halides.
Mn2 (CO)10 + X (X = Br, I) 2 Mn(CO)5 X
• It reacts with sodium metal in liquid ammonia to give carbonylate anion
Mn 2(CO)10 + 2 Na 2 Na [Mn(CO)5 ]
5. • Manganese pentacarbonyl does not exist as Mn (Z=25) has an odd atomic
number.
• The structure of dimanganese decacarbonyl consists of two manganese
pentacarbonyl groups .
• Two Mn joined through a Mn-Mn (2.79 Å) bond. The formation of this
inter metallic bond effectively adds one electron to each of the manganese
atoms.
• Thus, manganese, an element with odd atomic number forms a binuclear
carbonyl. Since the molecule does not have any unpaired electrons, it is
diamagnetic.
7. PROPERTIES
• Di iron nonacarbonyl forms golden yellow triclinic crystals melting at
100C
• It is insoluble in water but soluble in toluene and pyridine.
• A solution of diiron nonacarbonyl in toluene disproportionates when heated
to 70C
8. • Diiron nonacarbonyl reacts with sodium metal in
liquid ammonia to give carbonylate anion.
10. STRUCTURE
• Each of the iron atoms in diiron nonacarbonyl has three terminal carbonyl
groups.
• The remaining three carbon monoxide ligands act as µ2–CO groups.
• There is a weak Fe-Fe bond (2.46 Å) formed by sharing of two unpaired
electrons present in the 3d orbitals of iron atoms.
• Thus, both the iron atoms in the molecule are identical with coordination
number seven.
• Since the molecule does not have any unpaired electron, it is diamagnetic.
• d2sp3hybridization in Fe atoms
11. Co2(CO)8, Dicobalt octacarbonyl
PREPARATION
• It can be prepared by direct combination of carbon monoxide with cobalt
metal.
• It can also be prepared by carbonylation of cobalt iodide/cobalt
sulphide/cobalt carbonate using reducing agents like copper metal or
hydrogen gas.
12. PROPERTIES
• It is an orange crystalline substance having melting point 51 C
• Turns deep violet upon exposure to air.
• It is soluble in alcohols, ether and carbon tetrachloride.
• Upon heating at 50 C it forms tetracobalt dodecacarbonyl
• It reacts with nitric oxide to form cobalt carbonyl nitrosyl.
14. BRIDGED STRUCTURE
• Dicobalt octacarbonyl is known to exist in two isomeric forms.
• A bridged structure of this molecule is observed in the solid state as well as
solution state at a very low temperature.
• A non -bridged structure predominates in a solution at temperatures above
ambience.
• In the bridged structure, the cobalt atoms are in d2sp3 hybrid state.
• Three such hybrid orbitals on each cobalt atom accept lone pair of electrons
from three carbon monoxide molecules to form total six Co.CO coordinate
bonds.
• A Co-Co bond is formed by the overlapping of two half filled- d2sp3 hybrid
orbitals on the cobalt atoms.
• Remaining two half–filled hybrid orbitals on each Co atom overlap with
appropriate orbital on carbon atom of the carbonyl to form two bridging CO
groups.
• Thus, all electrons in this molecule are paired and it is diamagnetic.
15. NON BRIDGED STRUCTURE
• In the structure without bridge, the cobalt atoms are in
dsp3hybrid state.
• Out of the five hybrid orbitals on each cobalt atom, four orbitals on each
cobalt atom accept a lone pair of electrons from the carbon monoxide
molecules to form eight Co.CO coordinate bonds.
• One half–filled orbitals on each cobalt overlap to form a Co-Co bond.
• Co atoms have dsp3 hybridization
