Nickel Chemistry
An excellent site for finding the properties of the elements,
including nickel is at 
For the chapter on Nickel chemistry from the Elsevier text
"Chemistry of the Elements" by Greenwood and Earnshaw see
On-Line Metals Based Surveys
Further information on Nickel can be found at the
Nickel Institute
and
the page on Nickel at Wikipedia.
History
Nickel had been in use centuries before its actual discovery and
isolation. As far back as 3500 BC Syrian bronzes contained a
small amount of the element. In 235 BC, coins in China were
minted from nickel. However there was no real documentation of
the element until thousands of years later.
In the 17thcentury, German miners discovered a red
coloured ore they believed to contain copper. They discovered
upon analysis that there was no copper but that a useless, smelly
material was actually present. Thinking the ore was evil they
dubbed it "Kupfernickel" or Old Nick's Copper, which meant false
or bad copper. Swedish scientist Baron Axel Frederich Cronstedt
in 1751 finally isolated nickel from an ore closely resembling
kupfernickel. Hence, he named this new element after the
traditional mineral.
At the time of its discovery nickel was thought to be useless but
over time as its valuable properties came to light the demand for the metal
dramatically increased. The usefulness of nickel as a material in
alloys was eventually appreciated since it added to the strength, corrosion
resistance and hardness of the other metals. In the 1800s, the technique of
silver plating was developed with a nickel-copper-zinc alloy being utilised
in the process. Today, stainless steel, another nickel containing alloy,
is recognised as one of the most valuable materials of the 20th and
21st centuries.
Occurrence
Nickel is the earth's 22nd most abundant element and
the 7th most abundant transition metal. It is a silver
white crystalline metal that occurs in meteors or combined with
other elements in ores. Two important groups of ores are:
- Laterites: oxide or silicate ores such as garnierite, (Ni,Mg)6
Si4O10(OH)8
which are predominantly found in tropical areas such as New
Caledonia, Cuba and Queensland.
- Sulphides: these are ores such as pentlandite, (Ni,Fe)9S8 which contain
about 1.5%, nickel associated with copper, cobalt and other
metals. They are predominant in more temperate regions such as
Canada, Russia and South Africa.
Canada is the world's leading nickel producer and the Sudbury
Basin of Ontario contains one of the largest nickel deposits in
the world.
Extraction of
Nickel
In 1899 Ludwig Mond developed a process for extracting and
purifying nickel. The so-called "Mond Process" involves the
conversion of nickel oxides to pure nickel metal. The oxide is
obtained from nickel ores by a series of treatments including
concentration, roasting and smelting of the minerals.
In the first step of the process, nickel oxide is reacted with
water gas, a mixture of H2 and CO, at atmospheric
pressure and a temperature of 50 °C.
The oxide is thus reduced to impure nickel. Reaction of this
impure material with residual carbon monoxide gives the toxic and
volatile compound, nickel tetracarbonyl, Ni(CO)4. This
compound decomposes on heating to about 230 °C to give pure nickel metal
and CO, which can then be recycled.
The actual temperatures and pressures used in this process may
very slightly from one processing plant to the next. However the
basic process as outlined is common to all.
The process can be summarised as follows:
50°C
230°C
Ni + 4CO → Ni(CO)4 → Ni + 4CO.
(impure)
(pure)
Properties
Nickel is a hard silver white metal, which occurs as cubic
crystals. It is malleable, ductile and has superior strength and
corrosion resistance. The metal is a fair conductor of heat and
electricity and exhibits magnetic properties below
345°C. Five isotopes of nickel are
known.
In its metallic form nickel is chemically unreactive. It is
insoluble in cold and hot water and ammonia and is unaffected by
concentrated nitric acid and alkalis. It is however soluble in
dilute nitric acid and sparingly soluble in dilute hydrochloric
and sulphuric acids.
Nickel Compounds
Nickel is known primarily for its divalent compounds since the
most important oxidation state of the element is +2. There do
exist however certain compounds in which the oxidation state of
the metal is between -1 to +4. Blue and green are the
characteristic colours of nickel compounds and they are often
hydrated.
Nickel hydroxide usually occurs as green crystals that can be
precipitated when aqueous alkali is added to a solution of a
nickel (II) salt. It is insoluble in water but dissolves readily
in acids and ammonium hydroxide.
Nickel oxide is a powdery green solid that becomes yellow on
heating.
It is difficult to prepare this compound by simply heating nickel
in oxygen and it is more conveniently obtained by heating nickel
hydroxide, carbonate or nitrate. Nickel oxide is readily soluble
in acids but insoluble in hot and cold water.
Nickel oxides
| Formula |
Colour |
Oxidation State |
MP |
Structure / comments |
| NiO |
green powder |
Ni2+ |
1955 |
NaCl |
Thermal decomposition of Ni(OH)2, NiCO3, or
NiNO3 gives NiO.
Nickel sulfides consist of NiS2, which has a pyrite
structure, and Ni3S4, which has a spinel
structure.
All the nickel dihalides are known to exist. These compounds are
usually yellow to dark brown in colour. Preparation directly from
the elements is possible for all except NiF2, which is
best prepared from reaction of F2 on NiCl2
at 350°C. Most are soluble in water
and crystallisation of the hexahydrate containing the
[Ni(H2O)6]2+ ion can be
achieved. NiF2 however is only slightly soluble in
water from which the trihydrate crystallizes. The only nickel
trihalide known to exist is an impure specimen of
NiF3.
Nickel(II) halides
| Formula |
Colour |
MP |
μ (BM) |
Structure |
| NiF2 |
yellow |
1450 |
2.85 |
tetragonal rutile |
| NiCl2 |
yellow |
1001 |
3.32 |
CdCl2 |
| NiBr2 |
yellow |
965 |
3.0 |
CdCl2 |
| NiI2 |
Black |
780 |
3.25 |
CdCl2 |
Preparations:
Ni + F2 55°C /slow → NiF2
Ni + Cl2 EtOH/ 20°C → NiCl2
Ni + Br2 red heat → NiBr2
NiCl2 + 2NaI → NiI2 + 2NaCl
Nickel carbonate usually occurs as a light green crystalline
solid or a brown powder. It dissolves in ammonia and dilute acids
but is insoluble in hot water. It exhibits vigorous reaction with
iodine, hydrogen sulphide or a mixture of barium oxide and air.
It decomposes on heating before melting occurs.
Nickel carbonyl is a colourless, volatile, liquid. It is soluble
in alcohol, benzene, and nitric acid but only slightly soluble in
water, and insoluble in dilute acids and alkalis. Upon heating or
in contact with acid or acid fumes, nickel carbonyl emits toxic
carbon monoxide gas, a property exploited in preparation of
nickel metal. When exposed to heat or flame the compound explodes
and it can react violently with air, oxygen and bromine.
Identification of nickel compounds can be achieved by employing
the use of an organic reagent dimethylglyoxine. This compound
forms a red flocculent precipitate on addition to a solution of a
nickel compound.
Nickel complexes
The Nickel (II) ion forms many stable complexes as predicted by the
Irving Williams series.
Whilst there are no other
important oxidation states to consider, the Ni(II) ion can exist
in a wide variety of CN's which complicates its coordination
chemistry.
For example, for CN=4 both tetrahedral and square planar complexes can be found.
For CN=5 both square pyramid and trigonal bipyramid complexes are formed.
The phrase "anomalous nickel" has been used to describe
this behaviour and the fact that equilibria often exist between
these forms.
Some examples include:
(a) addition of
ligands to square planar complexes to give 5 or 6 coordinate
species
(b)
monomer/polymer equilibria
(c)
square-planar/ tetrahedron equilibria
(d)
trigonal-bipyramid/ square pyramid equilibria.
(a) substituted acacs react with Ni2+ to give green
dihydrates (6 coordinate). On heating, the two coordinated water
groups are generally removed to give tetrahedral species. The
unsubstituted acac complex, Ni(acac)2 normally exists
as a trimer, see below.
Lifschitz salts
containing substituted 1,2-diaminoethanes can be isolated as
either 4 or 6 coordinate species depending on the presence of
coordinated solvent.
(b) Ni(acac)2 is only found to be monomeric at
temperatures around 200°C in non-coordinating solvents such as
n-decane. 6-coordinate monomeric species are formed at room
temperature in solvents such as pyridine, but in the solid state
Ni(acac)2 is a trimer, where each Ni atom is
6-coordinate. Note that Co(acac)2 actually exists as a
tetramer.
|
[Ni(acac)2]3
|
[Co(acac)2]4
|
(c) Complexes of the type NiL2X2, where L
are phosphines, can give rise to either tetrahedral or square
planar complexes. It has been found that:
L=P(aryl)3 are tetrahedral
L=P(alkyl)3 are square planar
for L= mixed aryl and alkyl phosphines, both
stereochemistries can occur in the same crystalline substance.
The energy of activation for conversion of one form to the other
has been found to be around 50kJ mol-1.
Similar changes have been observed with variation of the X group:
| Ni(PΦ3)2Cl2 |
green |
tetrahedral |
μ =2.83 BM |
| Ni(PΦ3)2(SCN)2 |
red |
sq. planar |
μ =0 BM |
where Φ is shorthand for
C6H5
Ni2+
reacts with CN- to give Ni(CN)2.nH2O
(blue-green) which on heating at 180-200°C is dehydrated to yield
Ni(CN)2. Reaction with excess KCN gives
K2Ni(CN)4.H2O (orange crystals)
which can be dehydrated at 100°C. Addition of strong
concentrations of KCN produces red solutions of
Ni(CN)53-.
The crystal
structure of the double salt prepared by addition of
Cr(en)33+ to
Ni(CN)53- showed that two types of Ni
stereochemistry were present in the crystals in approximately
equal proportions.
50% as square pyramid and 50% as trigonal bipyramid.
|
Uses of Nickel and its Compounds
The primary use of nickel is in the preparation of alloys such as
stainless steel, which accounts for approximately 67% of all
nickel used in manufacture. The greatest application of stainless
steel is in the manufacturing of kitchen sinks but it has
numerous other uses as well.
Other nickel alloys also have important applications. An alloy of
nickel and copper for example is a component of the tubing used
in the desalination of sea water. Nickel steel is used in the
manufacture of armour plates and burglar proof vaults. Nickel
alloys are especially valued for their strength, resistance to
corrosion and in the case of stainless steel for example,
aesthetic value.
Electroplating is another major use of the metal. Nickel plating
is used in protective coating of other metals. In wire form,
nickel is used in pins, staples, jewellry and surgical wire.
Finely divided nickel catalyses the hydrogenation of vegetable
oils. Nickel is also used in the colouring of glass to which it
gives a green hue.
Other applications of nickel include:
-Coinage
-Transportation and construction
-Petroleum industry
-Machinery and household appliances
-Chemical industry.
Nickel compounds also have useful applications. Ceramics, paints
and dyes, electroplating and preparation of other nickel
compounds are all applications of these compounds. Nickel oxide
for example is used in porcelain painting and in electrodes for
fuel cells. Nickel acetate is used as a mordant in the textiles
industry. Nickel carbonate finds use in ceramic colours and
glazes.
Nickel and Human Health
For an account of the limited information known about the role of
nickel in human health see:
http://www.nutrition.org/nutinfo/
http://www.vitaminsplus.com/vplus/nickel.htm
Nickel utilisation in microorganisms - 1987 review
The first crystallisation of an enzyme was reported in the 1920's. The enzyme
was urease which converts urea to ammonia and bicarbonate. One source of
the enzyme is the bacterium Helicobacter Pylori. The release of
ammonia is beneficial to the bacterium since it partially
neutralizes the very acidic environment of the stomach (whose function in part
helps kill bacteria). In the initial study it was claimed that there were no
metals in the enzyme. Fifty years later this was corrected when it was discovered
that nickel ions were present and an integral part of the system.
The Nobel Prize in Physiology or Medicine for 2005 was awarded to
Barry J. Marshall and J. Robin Warren
"for their discovery of the bacterium Helicobacter pylori and its role in
gastritis and peptic ulcer disease".
The display below shows the crystal structure found
for a Helicobacter Pylori urease [published 2001].
The nickel ions can be identified by clicking the
approriate button.
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Copyright © 2000-2010 by Robert John
Lancashire, all rights reserved.
Created and maintained by Prof. Robert J.
Lancashire
(with grateful assistance from Jodi-Ann Swaby),
The Department of Chemistry, University of the West Indies,
Mona Campus, Kingston 7, Jamaica.
Created July 2000. Links checked and/or last
modified 23rd November 2010.
URL
http://wwwchem.uwimona.edu.jm/courses/nickel.html