Transcript complex ion

LECTURE 4
THEME: Complex compound in
biological systems.
associate prof. Dmukhalska Ye. B.
Outline
1. Concept of complex compounds and complexing
2.
3.
4.
process. Nomenclature of complex compounds.
Types of complexes.
Structure of complex compounds. Isomerism of
complex compounds. Chemical bonds in complex
compounds molecule.
Stability of complexes and influence of different
factors on it.
Biological role of complex compounds. Usage of
complexing in chemistry.
A coordination complex
• Coordination compounds are the
compounds in which the central atom
(usually metallic), is linked to а number
of ions or neutral molecules by
coordinate bonds i.е. by donation of
lone pairs of electrons by these ions or
neutral molecules to the central metal
atom.
• nickel tetracarbonyl, [Ni(CO)4]
Complex compounds
А) Structure
CuSO4 + 4 NH3 = [Cu (NH3)4] SO4
[Cu (NH3)4] SO4
Complex compound
• Cu2+ - central atom
•NH3 – ligand
• [Cu (NH3)4]2+ - complex ion
• SO42- -anion
Aqueous solutions that contain [Ni(H2O)6]2+, [Ni(NH3)6]2+ and [Ni(en)3]2+
(from left to right). The two solutions on the right were prepared by
adding ammonia and ethylenediamine, respectively, to aqueous
nickel(II) nitrate.
Werner’s Theory
• Alfred Werner suggested in
1893 that metal ions exhibit
what he called primary and
secondary valences.
– Primary valences were the
oxidation number for the metal
(+3 on the cobalt at the right).
– Secondary valences were the
coordination number, the
number of atoms directly
bonded to the metal (6 in the
complex at the right).
Co-ordination Werner’s theory
Charge
+1
+2
+3
+4
coordination number
example
of the metal ion
2
Ag+, Cu+
4, 6
Cu2+, Zn2+, Pd2+, Pt2+
6, 4
Pt4+, Cr3+, Co3+, Fe3+
8
Sn4+
• The species formed by linking of а number
of ions or molecules by co-ordinate bonds
to the central metal atom (or ion) carries
positive or negative charge, it is called a
complex ion (coordination sphera).
[Fe(СN)6]4-, [Cu(NH3)4]2+, [Ag(CN)2]-
Coordination sphere.
• The central atom and the ligands which
are directly attached to it are enclosed in
square brackets and are collectively
termed as the coordination sphere.
Metal-Ligand Bond
• This bond is formed between a Lewis acid
and a Lewis base.
– The ligands (Lewis bases) have nonbonding
electrons.
– The metal (Lewis acid) has empty orbitals.
• Transition metals act as Lewis acids
• Form complexes/complex ions
Fe3+(aq) + 6CN-(aq)  [Fe(CN)6]3-(aq)
Lewis acid
Lewis base
Complex
ion
Ni2+(aq) + 6NH3(aq)  [Ni(NH3)6]2+(aq)
Lewis acid
Lewis base
Complex
ion
Complex with a net charge = complex ion
Complexes have distinct properties
• Coordination compound
– Compound that contains 1 or more
complexes
– Example
•[Co(NH3)6]Cl3
•[Cu(NH3)4][PtCl4]
•[Pt(NH3)2Cl2]
• The donor atoms, molecules or anions,
which donate а pair of electrons to the
metal atom and form co-ordinate bond
with it are called ligands.
• Ligands
– classified according to the number of
donor atoms
– Examples
•monodentate = 1
chelating
•bidentate = 2
agents
•tetradentate = 4
•hexadentate = 6
Ligands
• Monodentate
– Examples:
•H2O, CN-, NH3, NO2-, SCN-, OH-, X(halides), CO, O2–Example Complexes
•[Co(NH3)6]3+
•[Fe(SCN)6]3-
Ligands
• Bidentate
– Examples
•oxalate ion = C2O42•ethylenediamine (en) =
NH2CH2CH2NH2
•ortho-phenanthroline (o-phen)
– Example Complexes
•[Co(en)3]3+
•[Cr(C2O4)3]3•[Fe(NH3)4(o-phen)]3+
Ligands
oxalate ion
O
O
C
O
*
ethylenediamine
2-
CH2 CH2
C
H2N
*
O
*
Donor Atoms:
*
NH2
*
ortho-phenanthroline
*
*
N
CH
N
CH
C
CH
HC
C
C
HC
C
CH
CH
CH
Ligands
oxalate ion
ethylenediamine
H
C
C
M
O
M
N
Ligands
• Chelation is a process in which a
polydentate ligand bonds to a metal
ion, forming a ring. The complex
produced by this process is called a
chelate, and the polydentate ligand is
referred to as a chelating agent.
– ethylenediaminetetraacetate (EDTA)
= (O2CCH2)2N(CH2)2N(CH2CO2)24– Example Complexes
•[Fe(EDTA)]-1
•[Co(EDTA)]-1
* Donor Atoms
Ligands
EDTA
O
*O
C
CH2
*O
C
CH2
O
*
N
*
CH2 CH2 N
O
CH2 C
O*
CH2 C
O*
O
Ligands
EDTA
O
H
C
M
N
Ligands
EDTA
• Some
•
•
•
important
characteristics
of
chelates.
(i) Chelating ligands form more stable complexes
than the monodentate analogs. This is called
chelating effect.
(ii) Chelating ligands, which do not contain
double bonds e.g. ethylenediamine form five
membered stable rings. The chelating ligands
such as acetylacetone form six membered stable
ring complexes.
(iii) Ligands with large groups form unstable
rings than the ligands with smaller groups due
to steric hindrance.
• The complexes formed by Cu (II) and Pt
(II) ions with ethylenediamine are metal
chelates represented as follows:
Coordination number
• The number of ligand donor atoms that surround
a central metal ion in a complex is called the
coordination number of the metal
• Originally, a complex implied a reversible
association of molecules, atoms, or ions through
weak chemical bonds.
• [Ag(СN)2]-, [Cu(NН3)4]2+ and [Cr(Н2О)6]3+
Common Geometries of Complexes
Coordination Number
Geometry
2
Linear
Example: [Ag(NH3)2]+
Common Geometries of Complexes
Coordination Number
4
tetrahedral
Examples: [Zn(NH3)4]2+,
[FeCl4]-
Example:
[Ni(CN)4]2-
square planar
Geometry
Common Geometries of Complexes
Coordination Number
Geometry
6
Examples: [Co(CN)6]3-,
[Fe(en)3]3+
octahedral
Charge on the complex ion.
• The charge carried by а complex ion is the
algebraic sum of the charges carried by
central metal ion and the ligands
coordinated to the central metal ion.
• [Ag (CN)2]• [Cu (NH3)4]2+
Complex charge = sum of charges
on the metal and the ligands
[Fe(CN)6]3-
Complex charge = sum of charges on
the metal and the ligands
[Fe(CN)6]3-
+3
6(-1)
Neutral charge of coordination
compound = sum of charges on metal,
ligands, and counterbalancing ions
[Co(NH3)6]Cl2
+
2
6(0)
neutral compound
2(-1)
Oxidation number or oxidation state.
• It is а number that represents an electric charge
•
•
•
•
•
•
which an atom or ion actually has or appears to
have when combined with other atoms,
oxidation number of copper in [Cu(NH3)4]2+ is
+2 but coordination number is 4.
oxidation number of Fe in [Fe(СN)6]3- is + 3 but
the coordination number is 6.
(i) [Cu (NНЗ)4]SO4.
(ii) Fe in [Fe (СN)6]3(iii)К3[Fe(С2О4)3].
(iv) [Ni(CO)4].
Neutral charge of coordination
compound = sum of charges on metal,
ligands, and counterbalancing ions
[Co(NH3)6]Cl2
+
2
6(0)
neutral compound
2(-1)
Nomenclature of Coordination
Compounds: IUPAC Rules
• The cation is named before the anion
• When naming a complex:
– Ligands are named first
•alphabetical order
– Metal atom/ion is named last
•oxidation state given in Roman
numerals follows in parentheses
– Use no spaces in complex name
Naming Coordination Compounds
Names of Some Common Metallate
Anions
Names of Some Common Ligands
Examples of Complexes with
Various Coordination Numbers
• [Co(NН3)6]Cl3,
hexaamminecobalt
(III)
chloride.
• K2[PtCl6], potassium hexachloroplatinate (IV).
• [Co(NO2)(NH3)3], triamminetrinitrocobalt (III)
• [PtCl4(NH3)2], diamminetetrachloroplatinum
(IV).
Types of complexes.
• (i) А complex in which the complex ion carries а
•
•
•
net positive charge is called cationic complex:
[Co(NН3)]3+, [Ni(NH3)6]2+
(ii) А complex in which the complex ion carries а
net negative charge is called anionic complex:
[Ag(CN)2]-, [Fe (CN)6]4(iii) А complex carrying no net charge is called а
neutral complex or simply а complex:
[Ni(CO)4], [CoCl3 (NН3)3]
Main types of complex compounds
1. With one central atom
• Ammonia complex [Cu(NH3)4]SO4
• Aqua complex[Al(H2O)6]Cl3
• acidic complex K2[PtCl4]
• complex with difference ligands K[Pt(NH3)Cl3]
• cyclic (chelates)
Me
NH2 CH2
NH2 CH2
Me
O
O
C
C
O
O
HOOC H2C
CH2
N
N
Me
H2C
Polycentral compoynds
Chain
[Cr(NH3)5 – OH – (NH3)Cr]Cl3
chelaes
(CO)5Mn – Mn(Co)5
CH2
O
O
CH2
CH2
C
C
O
O
COOH
Isomerism
• Isomers
– compounds that have the same
composition but a different
arrangement of atoms
• Major Types
– structural isomers
– stereoisomers
Structural Isomers
• Structural Isomers
– isomers that have different bonds
• Coordination-sphere isomers
– differ in a ligand bonded to the metal in
the complex, as opposed to being outside
the coordination-sphere
• Example
[Co(NH3)5Cl]Br vs. [Co(NH3)5Br]Cl
Coordination-Sphere Isomers
• Example
[Co(NH3)5Cl]Br vs. [Co(NH3)5Br]Cl
• Consider ionization in water
[Co(NH3)5Cl]Br  [Co(NH3)5Cl]+ + Br-
[Co(NH3)5Br]Cl  [Co(NH3)5Br]+ + Cl-
Coordination-Sphere Isomers
• Example
[Co(NH3)5Cl]Br vs. [Co(NH3)5Br]Cl
• Consider precipitation
[Co(NH3)5Cl]Br(aq) + AgNO3(aq) 
[Co(NH3)5Cl]NO3(aq) + AgBr(s)
[Co(NH3)5Br]Cl(aq) + AgNO3(aq) 
[Co(NH3)5Br]NO3(aq) + AgCl(aq)
Structural Isomers
• Linkage isomers
–differ in the atom of a ligand
bonded to the metal in the
complex
• Example
–[Co(NH3)5(ONO)]2+ vs.
[Co(NH3)5(NO2)]2+
Linkage Isomers
Stereoisomers
–Isomers that have the same bonds,
but different spatial arrangements
• Geometric isomers
–Differ in the spatial arrangements of
the ligands
– Have different chemical/physical
properties
•different colors, melting points,
polarities, solubilities, reactivities, etc.
Geometric Isomers
cis isomer
trans isomer
Pt(NH3)2Cl2
Geometric Isomers
cis isomer
trans
[Co(H2O)4Cl2isomer
]+
Stereoisomers
• Optical isomers
–isomers that are
nonsuperimposable mirror images
•said to be “chiral” (handed)
•referred to as enantiomers
–A substance is “chiral” if it does not
have a “plane of symmetry”
Example 1
mirror plane
cis-[Co(en)2Cl2]+
Thank you for attention