6 coordinative comp

1
The Coordination Compounds
(Complexes).

2
Complex compounds are the most widespread
and diverse class of inorganic substances. They
also include many organometallic compounds
that combine the previously isolated inorganic
chemistry and organic chemistry into a single
entity. Many complex compounds – vitamin
B12
, hemoglobin, chlorophyll and others – play
a great role in physiological and biochemical
processes.

3
The properties and structure of complex
compounds are explained most successfully by
the coordination theory proposed by Alfred
Werner, a Swiss chemist, Nobel Prize winner.
He was one of the founders of the concept of
complex compounds.

4
According to the coordination theory, one of the
ions in a molecule of any complex compound
generally a positively charged one, occupies a
central position and is called a complexing agent or
central ion.
Around it are arranged, or, as we say,
coordinated, a certain number of oppositely charged
ions or electrically neutral molecules called ligands
(or addends) and forming the inner coordination
sphere of the compound. The remaining ions not
accommodated in the inner sphere are farther from
the central ion and form the outer coordination
sphere.

5
For example, the coordination formula of the
complex salt having the composition
PtCl4·2KCl is K2[PtCl6]. Here the inner sphere
consist of a central platinum atom in the
oxidation number +4 and chloride ions, while
the potassium ions are in the outer sphere.
The main characteristic of central ion is the
coordination number. It shows how many
bonds the central ion may forms with ligands.

6
The coordination number is not a constant
quantity for given complexing agent, but also
depends on the nature of the ligand and its
electron properties. Even for the same
complexing agents and ligands, the
coordination number depends on the state of
aggregation, the concentration of the
components, and the temperature of the
solution.

7
Central atom
charge
Coordinative
number
Type of hybrid. Example
+1 2 Sp [Ag(NH3)2]Cl
+2 4,6 sp3
, dsp2
K4[Fe(CN)6]
[Cu(NH3)4]Cl2
+3 6,4 dsp2
K3[Fe(CN)6]
+4 8 d2
sp3
[Pt(NH3)4Cl4]
The Coordination Number

8
Chemical Bonding
29
Cu 1s2
2s2
2p6
3s2
3p6
4s1
3d10
4p0
, the outer layer 4s1
4p0
Cu+2
3d9
4s0
4p0
it has 4 free orbitals (4 bonds).

9
The bonds between central ion and ligands are donor-
acceptor (dative).
27
Co 1s2
2s2
2p6
3s2
3p6
4s2
3d7
4p0
Co+3
[Ar]3d6
4s0
4p0
6 free orbitals remain (6 bonds).
d2
sp3
hybridization

10
Ligands occupying one site in the
inner coordination sphere are called
monodentates (examples of
monodentate ligands are OH , Cl , I ,‾ ‾ ‾
Br , CN , H‾ ‾ 2
O, NH3
). Ligands that
occupy two or several sites in the
inner sphere are called bi- and
polydentates.

11
Classification
I. According to the inner sphere
charge there are:
1.The Anionic complexes - Na2
[NiCl4
]-2
2. The Cationic complexes –
[Zn(NH3
)4
]+2
Cl2
3. The Neutralic complexes –
Pt(NH3
)2
Cl2
]0

12
II. According to the nature of the ligands.
1.Ammines – complexes in which ammonia
molecules are the ligands, for instance [Cu(NH3
)4
]SO4
– tetraamminecupper (II) sulfate; [Co(NH3
)6
]Cl3
–
hexaamminecobalt (III) chloride.
2.Aquacomplexes contain water as the ligand:
[Co(H2
O)6
]Cl2
, [Al(H2
O)6
]Cl3
. Hydrated cations in an
aqueous solution contain an aquacomplex as the
central unit.

13
3.Acidocomplexes. In these complexes, anions
are the ligands. They include complexes of the
double salt type, for example, K2
[PtCl4
], K4
[Fe(CN)6
]
(they can be represented as the product of the
coupling of two salts - PtCl4
·2KCl, Fe(CN)2
·4KCN, etc.),
complex acids – H2
[SiF6
], H2
[CoCl4
],
hydroxocomplexes – Na2
[Zn(OH)4
].
4. Transition series exist between these classes,
which include complexes with different ligands.
K[Pt(NH3
)Cl3
].

14
5.Cyclic, or chelate (from the Greek
word “chele” – claw) complex
compounds contain a bi- or polydentate
ligand that grips the central atom like
the claws of a crab:
:NH2 – CH2
M
:NH2 – CH2
In such complexes, the symbol M stands for a metal
atom, and the arrow depicts a donor–acceptor
mechanism of covalent bonding.

15
Examples of such complexes are the
oxalate complex of iron (III) [Fe(C2O4)3]3-
and the ethylenediamine complex of
platinum (IV) [PtEn3]4+
. The group of
chelates also includes intracomplex
compounds in which the central atom is
part of a ring, forming covalent bonds
with ligands in various ways – donor–
acceptor mechamism of covalent bond
and bonds at the expense of unpaired
atomic electrons.

16
Complexes of this kind are very characteristic of the
aminocarboxylic acids. For example: EDTA

17
Hemoglobin
Chelate compounds are extremely stable because
their central atom is “blocked”, as it were, by the
cyclic ligand. Chelates with five- and six- membered
rings have the highest stability.

18
Naming complexes.
The coordination compounds are named in the
following way.
A. To name a coordination compound, no
matter whether the complex ion is the cation
or the anion, always name the cation before
the anion. (This is just like naming an ionic
compound.)

19
B. In naming the complex ion:
1. Name the ligands first, in alphabetical order, then
the metal atom or ion. Note: The metal atom or ion
is written before the ligands in the chemical formula.
2. The names of some common ligands are listed in
Table 1..
� For anionic ligands end in "-o"; for anions that
end in "-ide"(e.g. chloride), "-ate" (e.g. sulfate,
nitrate), and "-ite" (e.g. nirite), change the endings as
follows: -ate -ideato; -ito.-o; -ite

20
For neutral ligands, the common name of
the molecule is used e.g. H2
NCH2
CH2
NH2
(ethylenediamine). Important exceptions:
water is called ‘aqua’, ammonia is called
‘ammine’, carbon monoxide is called
‘carbonyl’, and the N2
and O2
are called
‘dinitrogen’ and ‘dioxygen’.

21
Anionic
Ligands
Names Neutral
Ligands
Names
Br-
Bromo NH3 Ammine
F-
Fluoro H2O Aqua
O2-
Oxo NO Nitrosyl
OH-
Hydroxo CO Carbonyl
CN-
Cyano O2 Dioxygen
C2O4
2-
Oxalato N2 Dinitrogen
CO3
2-
Carbonato C5H5N Pyridine
CH COO-
Acetato H2NCH2CH2NH2 Ethylenediamine
Table 1. Names of Some Common Ligands

22
3. Greek prefixes are used to designate the
number of each type of ligand in the complex
ion, e.g. di-, tri- and tetra-. If the ligand already
contains a Greek prefix (e.g. ethylenediamine)
or if it is polydentate ligands (ie. can attach at
more than one binding site) the prefixes bis-,
tris-, tetrakis-, pentakis-, are used instead. The
numerical prefixes are listed in Table 2.

23
Numb
er
Prefix Numb
er
Prefix Numb
er
Prefix
1 mono 5 penta
(pentakis)
9 nona
(ennea)
2 di (bis) 6 hexa
(hexakis)
10 deca
3 tri (tris) 7 hepta 11 undeca
4 tetra
(tetrakis)
8 octa 12 dodeca

24
4. After naming the ligands, name the central metal.
If the complex ion is a cation, the metal is named
same as the element. For example, Co in a complex
cation is call cobalt and Pt is called platinum. (See
examples 1-4). If the complex ion is an anion, the
name of the metal ends with the suffix –ate. (See
examples 5 and 6.). For example, Co in a complex
anion is called cobaltate and Pt is called platinate.
For some metals, the Latin names are used in the
complex anions e.g. Fe is called ferrate (not ironate).

25
Name of Metal Name in an Anionic
Complex
Iron Ferrate
Copper Cuprate
Lead Plumbate
Silver Argenate
Gold Aurate
Tin Stannate
Table 3: Name of Metals in Anionic Complexes

26
5. Following the name of the metal, the oxidation
state of the metal in the complex is given as a
Roman numeral in parentheses.
C. To name a neutral complex molecule, follow the
rules of naming a complex cation. Remember: Name
the (possibly complex) cation BEFORE the (possibly
complex) anion.
For historic reasons, some coordination compounds
are called by their common names. For example,
Fe(CN)6
3−
and Fe(CN)6
4−
are named ferricyanide and
ferrocyanide respectively, and Fe(CO)5
is called iron
carbonyl.

27
[Pt(NH3
)5
Cl]Br3
pentaamminechloroplatinum(IV) bromide
[Co(H2
NCH2
CH2
NH2
)3
]2
(SO4
)3
tris(ethylenediamine)cobalt(III) sulfate
.K4
[Fe(CN)6
]
potassium hexacyanoferrate(II)
Na2
[NiCl4
]
sodium tetrachloronickelate(II)
Pt(NH3)2Cl4
diamminetetrachloroplatinum(IV)
Fe(CO)5
pentacarbonyliron(0)

28
Isomerism
Structural isomerism
Structural isomerism occurs when the bonds are
themselves different. Linkage isomerism is only one
of several types of structural isomerism in
coordination complexes (as well as other classes of
chemical compounds).
Stereoisomerism
Stereoisomerism occurs with the same bonds in
different orientations relative to one another.

29
Cis-trans isomerism. When two ligands are mutually
adjacent they are said to be cis, when opposite each
other, trans.

30
Λ-[Fe(ox)3]3−
Δ-[Fe(ox)3]3−
Λ-cis-[CoCl2(en)2]+
Δ-cis-[CoCl2(en)2]+
Optical isomerism.
Optical isomerism occurs when the mirror image of
a compound is not superimposable with the original
compound. It is so called because such isomers are
optically active, that is, they rotate the plane of
polarized light.

31
Stability of Complex Compounds in Solutions.
Constant of Instability.
The aqueous silver forms a complex ion with
ammonia by reacting with NH3
in steps:
Ag+
(aq)
+ NH3 (aq)
[Ag(NH3
)]+
(aq)
Ag(NH3
)+
(aq)
+ NH3 (aq)
[Ag(NH3
)2
]+
(aq)
When we add these equations, we get overall
equation for the formation of the complex ion
Ag(NH3
)2
+
.
Ag+
(aq)
+ 2NH3 (aq)
[Ag(NH3
)2
]+
(aq)

32
The formation constant, or stability constant, Kf
, of a
complex ion is the equilibrium constant for the
formation of the complex ion from aqueous metal
ion and the ligands. Thus, the formation constant of
[Ag(NH3
)2
]+
is:

33
The value of Kf
for [Ag(NH3
)2
]+
is 1.7×107
.
The ionization constant (Ki
) or (Kd
) for a complex ion
is the inverse value of Kf
. The equation for the
dissociation of [Ag(NH3
)2
]+
is:
[Ag(NH3
)2
]+
(aq)
Ag+
(aq)
+ 2NH3 (aq)
and its equlibrium constant is

34
Chemical Properties.
I. Without destruction of inner sphere.
1.(NH4
)2
[Hg(SCN)4
] + ZnSO4
→ (NH4
)SO4
+
+ Zn[Hg(SCN)4
]↓
2. 2K4
[Fe(CN)6
] + H2
O2
→ 2K3
[Fe(CN)6
] + 2KOH
2 [Fe(CN)│ 6
]4-
- ℮ → [Fe(CN)6
]3-
1 H│ 2
O2
+ 2℮ → 2OH-
2[Fe(CN)6
]4-
+H2
O2
→ 2[Fe(CN)6
]3-
+ 2OH-

35
II. With destruction of inner sphere.
1.[Ag(NH3
)2
]Cl + 2HNO3
→ AgCl↓ + 2NH4
NO3
2.H2
[SnCl6
] + Zn → ZnCl2
+ SnCl2
+ 2HCl
1 [SnCl6]│ 2-
+ 2℮ → Sn2+
+ 6Cl-
1 Zn│ 0
- 2℮ → Zn2+
[SnCl6
]2-
+ Zn0
→ Sn2+
+ 6Cl-
+ Zn2+

6 coordinative comp

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6 coordinative comp