Nickel Carbonyl, Preparation, Structure and Properties | Organometallic Chemistry | Inorganic Chem

Описание: #NickelCarbonyl, #Preparation, #Structure and #Properties | #Organometallic #Chemistry | #Inorganic Chem

Preparation, Structure and Properties of Nickel tatra carbonyl.
Nickel forms only one carbonyl Nickel carbonyl or tetracarbonyl nickel. This organo nickel compound is having formula Ni(CO)4. It is colour less liquid at room temperature. Nickel carbonyl is one of the most dangerous substances yet encountered in nickel chemistry due to its very high toxicity, compounded with high volatility and rapid skin absorption.

Preparations

1. By direct combination:
Nickel tetracarbonyl is prepared by passing carbon monoxide, at one atmospheric pressure, over freshly reduced nickel, at room temperature.

2. By reductive carbonylation:
It is prepared by treating nickel iodide, or sulphide, with carbon monoxide, under pressure of 200 atmosphere, and at 473 degree Kelvin, in presence of reducing agent, like copper.

3. By disproportionation of Nickel one cyanide:
Potassium tetra cyano nickel, is first reduced by potassium amalgam, to Nickel one complex. This is treated with carbon monoxide, at 264 degree kelvin, to form potassium hexa cyano dai carbonyl Nickel, which disproportionates, with water, or acid, and forms Nickel tetra carbonyl.

Properties

1. Nickel tetracarbonyl is a toxic, colourless liquid, with melting point 248 degree Kelvin, and boiling point 316 degree Kelvin.

2. Its vapours form explosive mixture with air.

3. When heated at 353 degree Kelvin, it decomposes, and liberates carbon monoxide. This reaction is used in Mond's process for the extraction of nickel, from its ore.

4. It undergoes exchange reaction when treated with electron pair donors like, P,X,3, where X is any halogen.

5. It reacts with halogens, in organic solvent, and form dai halides.

6. Slightly moist nitric oxide, attacks nickel tetra carbonyl, in the gaseous state, to form intense blue complex.

7. ortho Phenanthroline, reacts with alcoholic solution of nickel tetra carbonyl, and forms ruby red coloured complex.

8. It reacts with sulphuric acid, and liberates carbon monoxide.

Structure
.
Electronic Configuration of Nickel is, Argon. 3d8. 4s2.

So at ground state, there are 8 electrons in 3d orbital. and 2 electrons in 4s orbital.

In excited state, 2 electrons from 4s orbital, shift to 3d orbital. and make available 4 empty orbitals, for electrons coming from ligands.

In this case, 4s orbital, and 4p orbital mix, to form sp3 hybridised orbital, of same energy. where 8 electrons from, 4 carbonyl ligands are accommodated.

As all the electrons are paired, the molecule is, diamagnetic in nature.

And as, sp3 hybridisation takes place, it should be tetrahedral in geometry.

Geometry of molecule is confirmed with Electron diffraction data.

Since, Nickel undergoes sp3 hybridisation, Nickel tetra carbonyl, has tetrahedral structure, with Nickel at the centre, and four carbon monoxide groups, at the four corners of a regular tetrahedron.

The bond between Nickel, and Carbon monoxide groups is actually not a pure sigma bond, but it also involves pi bonding.

From the structure of Nickel tetra carbonyl, it is clear that, two out of four carbon monoxide groups are linked to Nickel through sigma bonds, and the remaining two are linked through multiple bonds, that is, one sigma, and one pi bond.

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