Download Transition metal complexes

Transition metal complexes.
Purpose: The objective is to investigate reactions between transition metal ions and electrically charged ion
and neutral molecules.
Introduction.
Chemical bond (From Wikipedia, the free encyclopedia): In chemistry, a chemical bond is the force, which
holds together atoms in molecules or crystals.
All chemical bonding arises from the energetically favourable (that is, low-energy) interaction between
electrons on different atoms. The types of bonding are distinguished by the extent to which electron density
is:
 Localized - ionic bonding: electrons are mainly associated with individual atoms

Delocalized - covalent bonding the electron density distributions within bonds are not assigned to
individual atoms, but are instead delocalized across the molecule.
Unlike pure ionic bonds, covalent bonds may have directed anisotropic properties.
Complex compound: In chemistry, a complex is a structure composed of a central metal atom or ion,
generally a cation, surrounded by a number of negatively charged ions or neutral molecules possessing lone
pairs. A complex may also be called a coordination compound or metal complex.
The ions or molecules surrounding the metal are called ligands. A ligand that is bound to a metal ion is said
to be coordinated with the ion.
Simple ligands like water or chlorine form only one link with the central atom and are said to be monodentate.
The process of binding to the metal ion with more than one coordination site per ligand is called chelation.
Compounds that bind avidly to form complexes are thus called chelating agents.
Some ligands are capable of forming multiple links to the same metal atom, and are described as bidentate,
tridentate etc.
Typically, the chemistry of complexes is dominated by interactions between s and p orbitals of the ligands
and the d (or f) orbitals of the metal ions. Because of this, the simple octet bonding theory fails in the case of
complexes.
Ligander
ClChloroBrBromoIIodoCNCyanoOHHydroxoS2O32- ThiosulfatoH2O
AquoNH3
Ammin-
Cu
Ag
Au
Hg
Fe
Pb
Chemicals.
0.2 M CuSO4.5H2O
0.2 M Ni(NO3)2.2H2O
0.2 M CoCl2
0.2 M FeCl3
0.2 M KSCN
Conc. NH3
Conc. HCl
1 w/o Dimethylglyoxim (DMG)
Metaller
Cuprum
Argentum
Aurum
Mercurum
Ferrum
Plumbum
Equipment.
Beakers, 100 mL
Test tubes
Magnetic stirrer
Preparations.
All preparations are made in either 100 mL beakers, or in test tubes.
First, add a suitable amount of the first solution to the beaker/test tube.
Slowly add the second solution, drop by drop and observed the changes.
Compare the reactions and the chemical reactions below.
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Copper (Cu)
CuSO4.5H2O(s)
H2O
Cu(OH)2(aq)
NH3
Cu(H2O)42+(aq)
HCl
Cu(H2O)2Cl2(aq)
HCl
NH3
CuCl42-(aq)
Cu(NH3)42+(aq)
Electron configuration:
NH3(aq) + H2O(l) <=> NH4+(aq) + OH-(aq)
Cu:
Cu2+(aq) + 2OH-(aq) => Cu(OH)2(s)
Cu2+:
Cu+:
Name and coordination number (CN):
CuSO4.5H2O
Cu(OH)2
Cu(H2O)42+
Cu(NH3)42+
CuCl42Cu(H2O)2Cl2
CN =
CN =
CN =
Diaquo-dichlorokobber(II)
Diaquokobber(II)chlorid
Kobber(II)chloriddihydrat
CN =
Comments:
Cu(OH)2 has been used as a blue pigment (solid color) in paint. It is unstable and convert to black CuO
through: Cu(OH)2 => CuO + H2O.
Addition of NH3(aq) to transition metal solutions has been used as an analytical tool for determination of
Cu2+ (dark blue color). The method cannot be used in solutions containing Co2+ (why ?). The method has
been used for determination of Cu2+ after reaction between Cu and Br2 (1g kemi).
Cobalt (Co):
CoCl2(s)
H2O
Co(NH3)62+(aq)
Electron configuration:
NH3
Co(H2O)62+(aq)
HCl
CoCl42-(aq)
Co:
NH3 has one lone pair:
H2O has two lone pairs:
(One or two may participate)
Co2+:
Cl- is negatively charged:
NH3
H 2O
Cl-
Name and coordination number (CN):
CoCl2
Co(H2O)62+
Co(NH3)62+
CoCl42-
CN =
CN =
CN =
CN =
2
Comments:
The color change is used analytically. Some cobalt compounds are blue in the dry state. When exposed to
moisture (H2O), the aqous Co(H2O)62+ ions are formed and the color changes to red.
Nickel (Ni)
Ni(NO3)2.2H2O(s)
H2O
Ni(NH3)62+(aq)
NH3
HCl
Ni(H2O)62+(aq)
CN-
NiCl42-(aq)
DMG
Ni(DMG)22+(s)
Ni(CN)42-(aq)
Electron configuration:
H3C
Ni:
N
OH
H
O
C
Ni2+:
H3C
H
C
N
OH
H3C
O
N
Ni
Ni3+:
DMG =
DiMethylGlyoxim
H3C
N
CH3
N
CH3
2+
N
O
O
H
H
Chelat: ”Two or more groups from the same molecule
form bonds in such a way as to form a closed ring”.
Bidentat = may bond to the same metalion with 2
bonds (tridentat, tetradentat etc.).
Name and coordination number (CN):
Ni(NO3)2.2H2O
Ni(H2O)62+
Ni(NH3)62+
NiCl42Ni(CN)42Ni(DMG)22+
Bis(dimethylglyoimato)nikkel(II)ion
CN =
CN =
CN =
CN =
CN =
Comments:
The red color associated with the Bis(dimethylglyoimato)nikkel(II)ion is used as an analytical tool for
determination of trace amounts of Ni (se Frk. Hansens Smykkeskrin).
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Iron (Fe)
FeCl3(s)
H2O
Fe(H2O)5(OH)2+(s) + Fe(H2O)4(OH)22+(s) + ..... Fe(OH)3(s)
NH3
Fe(H2O)62+(aq)
HCl
FeCl4-(aq)
SCNFe(SCN)3(aq) + Fe(SCN)4-(aq) + ..... + Fe(SCN)63-(aq)
Electron configuration:
Sure ioner:
Fe:
Fe(H2O)63+ + H2O <=> Fe(H2O)5(OH)2+ + H3O+
Fe2+:
SCN- = thiocyanato-
Fe3+:
Name and coordination number (CN):
FeCl3
Fe(H2O)62+
Fe(OH)3
Fe(H2O)4(OH)22+
Fe(H2O)2(OH)42Fe(SCN)63+
FeCl42-
CN =
CN =
CN =
CN =
CN =
Fe2+ and Fe3+.
K4Fe(CN)6(aq) <=> 4K+ + Fe(CN)64-(aq)
Name: Kaliumhexacyanoferrat(II) (Gult blodludsalt)
K3Fe(CN)6(aq) <=> 3K+ + Fe(CN)63-(aq)
Name: Kaliumhexacyanoferrat(III) (Rødt blodludsalt )
Fe(CN)63-
Fe2+
Fe(II) Fe(III)(CN)6
Fe3+
Fe(CN)64-
Fe(III) Fe(II)(CN)6
Fe(II)[Fe(III)(CN)6] : Jern(II)ferricyanid
Fe(III)[Fe(II)(CN)6] : Jern(III)ferrocyanid
[Turnbull’s blue]
[Prussian blue]
Comments:
Rust is a serious problem i northern Europe. Damages worth approx. £109 pr. year were estimated in the United
Kingdom in the mid-nineties.
Fe[Fe(CN)6] is a powerful blue pigment, discovered in 1704 by Diesbach in Berlin, and produced commercially in
Paris since 1724. It is named Prussian blue, Paris blue, Berliner blue, Iron blue, Milori blue, depending on who
made it and where. It was the first synthetic lightfast and wheather resistant blue pigment since the secret of the
manufacture of aegyptian blue was lost around 500 ad.
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