Undergraduate level Chemistry

1. 23-1
Mr.G.M.Dongare
(M.Sc,B.Ed,SET)
Associate Professor
Dept.of Chemistry
Shri Shivaji Colege of Arts,Commerce and
Science College, Akola.
TRANSITION ELEMENTS AND THEIR
COORDINATION COMPOUNDS
Part II
Academic year 2018-19

2. 23-2
Colors of representative compounds of the Period 4
transition metals.
titanium(IV) oxide sodium chromate
potassium
ferricyanide
nickel(II) nitrate
hexahydrate
zinc sulfate
heptahydrate
scandium oxide vanadyl sulfate
dihydrate
manganese(II)
chloride
tetrahydrate
cobalt(II)
chloride
hexahydrate
copper(II) sulfate
pentahydrate

3. 23-3
Some Properties of Group 6B(6) Elements
Element
Atomic Radius
(pm) IE1(kJ/mol)
E° (V) for
M3+(aq)/M(s)
Cr 128 653 -0.74
Mo 139 685 -0.20
W 139 770 -0.11
IE1 increases down the group, so reactivity decreases. This
trend is opposite to that seen in main-group elements.

4. 23-4
Lanthanides and Actinides
The lanthanides are also called the rare earth elements.
The atomic properties of the lanthanides vary little
across the period, and their chemical properties are
also very similar.
Most lanthanides have the ground-state electron
configuation [Xe]6s24fx5d0.
All actinides are radioactive, and have very similar physical
and chemical properties.
The +3 oxidation state is common for both lanthanides
and actinides.

5. 23-5
Sm is the eighth element after Xe. Two electrons go into the 6s
sublevel. In general, the 4f sublevel fills before the 5d, so the
remaining six electrons go into the 4f sublevel.
SOLUTION:
Finding the Number of Unpaired Electrons
PROBLEM: The alloy SmCo5 forms a permanent magnet because
both samarium and cobalt have unpaired electrons. How
many unpaired electrons are in Sm (Z = 62)?
PLAN: We write the condensed electron configuration of Sm and
then, using Hund’s rule and the aufbau principle, place
electrons into a partial orbital diagram and count the
unpaired electrons.
The condensed configuration of Sm is [Xe]6s24f6.

6. 23-6
5d 6p
↑
4f
↑ ↑ ↑ ↑ ↑
6s
↑↓
Sm has six unpaired electrons.
The partial orbital diagram is:

7. 23-7
Coordination Compounds
A coordination compound contains at least one complex
ion, which consists of a central metal cation bonded to
molecules and/or anions called ligands.
The complex ion is associated with counter ions of
opposite charge.
The complex ion [Cr(NH3)6]3+ has a central Cr3+ ion bonded to six
NH3 ligands. The complex ion behaves like a polyatomic ion in
solution.

8. 23-8
Coordination Number
The coordination number is the number of ligand atoms
bonded directly to the central metal ion.
Coordination number is specific for a given metal ion in a
particular oxidation state and compound.
The most common coordination number in complex ions is
6, but 2 and 4 are often seen.
- [Cr(NH3)6]3+ has a coordination number of 6.

9. 23-9
Components of a coordination compound.
[Co(NH3)6]Cl3 dissolves in water. The six
ligands remain bound to the complex ion.
[Pt(NH3)4]Br2 has four
NH3 ligands and two Br-
counter ions.

10. 23-10
Coordination Numbers and Shapes of Some Complex Ions
Coordination
Number Shape Examples
2 Linear [CuCl2]-, [Ag(NH3)2]+, [AuCl2]-
4 Square planar [Ni(CN)4]2-, [PdCl4]2-,
[Pt(NH3)4]2+, [Cu(NH3)4]2+
4 Tetrahedral [Cu(CN)4]3-, [Zn(NH3)4]2+,
[CdCl4]2-. [MnCl4]2-
6 Octahedral [Ti(H2O)6]3+, [V(CN)6]4-,
[Cr(NH3)4Cl2]+, [Mn((H2O6]2+,
[FeCl6]3-, [Co(en)3]3+
The geometry of a given complex ion depends both on the
coordination number and the metal ion.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

11. 23-11
Ligands
The ligands of a complex ion are molecules or anions
with one or more donor atoms.
Each donor atom donates a lone pair of electrons to
the metal ion to form a covalent bond.
Ligands are classified in terms of their number of donor
atoms, or “teeth”:
- Monodentate ligands bond through a single donor atom.
- Bidentate ligands have two donor atoms, each of which bonds to
the metal ion.
- Polydentate ligands have more than two donor atoms.

12. 23-12
Some Common Ligands in Coordination Compounds

13. 23-13
Chelates
Bidentate and polydentate ligands give rise to rings in
the complex ion.
A complex ion containing this type of structure is called a
chelate because the ligand seems to grab the metal ion
like claws.
EDTA has six donor atoms and forms very stable complexes
with metal ions.

14. 23-14
Formulas of Coordination Compounds
 A coordination compound may consist of
 a complex cation with simple anionic counterions,
 a complex anion with simple cationic counterions, or
 a complex cation with complex anion as counterion.
 When writing the formula for a coordination compound
 the cation is written before the anion,
 the charge of the cation(s) is/are balanced by the charge of the
anion(s), and
 neutral ligands are written before anionic ligands, and the
formula of the whole complex ion is placed in square brackets.

15. 23-15
Determining the Charge of the Metal Ion
The charge of the cation(s) is/are balanced by the charge
of the anion(s).
K2[Co(NH3)2Cl4] contains a complex anion.
The charge of the anion is balanced by the two K+ counter ions, so
the anion must be [Co(NH3)2Cl4]2-.
There are two neutral NH3 ligands and four Cl- ligands. To have an
overall charge of 2-, the metal ion must have a charge of 2+.
Charge of complex ion = charge of metal ion + total charge of ligands
2- = charge of metal ion + [(2 x 0) + (4 x -1)]
Charge of metal ion = (-2) – (-4) = +2 or 2+
The metal ion in this complex anion is Co2+.

16. 23-16
[Co(NH3)4Cl2]Cl contains a complex cation.
The charge of the cation is balanced by the Cl- counter ion, so the
cation must be [Co(NH3)4Cl2]+.
There are four neutral NH3 ligands and two Cl- ligands. To have an
overall charge of 1+, the metal ion must have a charge of 3+.
Charge of complex ion = charge of metal ion + total charge of ligands
1+ = charge of metal ion + [(4 x 0) + (2 x 1-)]
Charge of metal ion = (+1) – (2-) = +3 or 3+
The metal ion in this complex cation is Co3+.

17. 23-17
Naming Coordination Compounds
 The cation is named before the anion.
 Within the complex ion, the ligands are named in alphabetical order
before the metal ion.
 Anionic ligands drop the –ide and add –o after the root name.
 A numerical prefix is used to indicate the number of ligands of a
particular type.
 Prefixes do not affect the alphabetical order of ligand names.
 Ligands that include a numerical prefix in the name use the
prefixes bis (2), tris (3), or tetrakis (4) to indicate their number.
 A Roman numeral is used to indicate the oxidation state for a metal
that can have more than one state.
 If the complex ion is an anion, we drop the ending of the metal name
and add –ate.

18. 23-18
Names of Some Neutral and Anionic Ligands
Neutral Anionic
Name Formula Name Formula
Aqua H2O Fluoro F-
Ammine NH3 Chloro Cl-
Carbonyl CO Bromo Br-
Nitrosyl NO Iodo I-
Hydroxo OH-
Cyano CN-

19. 23-19
Names of Some Metal Ions in Complex Anions
Metal Name in Anion
Iron Ferrate
Copper Cuprate
Lead Plumbate
Silver Argentate
Gold Aurate
Tin Stannate

20. 23-20
Mr.G.M.Dongare
(M.Sc,B.Ed,SET)
Associate Professor
Dept.of Chemistry
Shri Shivaji Colege of Arts,Commerce and
Science College, Akola.
TRANSITION ELEMENTS AND THEIR
COORDINATION COMPOUNDS
Part III

21. 23-21
PLAN: We use the rules for writing formulas and names of
coordination compounds.
Writing Names and Formulas of
Coordination Compounds
PROBLEM:
(a) What is the systematic name of Na3[AlF6]?
(b) What is the sytematic name of [Co(en)2Cl2]NO3?
(c) What is the formula of tetraamminebromochloroplatinum(IV) chloride?
(d) What is the formula of hexaamminecobalt(III) tetrachloroferrate(III)?
SOLUTION:
(a) The complex ion is [AlF6]3-. There are six (hexa-) F- ions (fluoro)
as ligands. The complex ion is an anion, so the ending of the
metal name must be changed to –ate. Since Al has only one
oxidation state, no Roman numerals are used.
sodium hexafluoroaluminate

22. 23-22
(b) There are two ligands, Cl- (chloro) and en (ethylenediamine).
The ethylenediamine ligand already has a numerical prefix in
its name, so we indicate the two en ligands by the prefix bis
instead of di.
The complex ion is a cation, so the metal name is unchanged,
but we need to specify the oxidation state of Co. The counter
ion is NO3
-, so the complex ion is [Co(en)2Cl2]+.
Charge of complex ion = charge of metal ion + total charge of ligands
1+ = charge of metal ion + [(2 x 0) + (2 x 1-)]
Charge of metal ion = (+1) – (-2) = +3 or 3+
The ligands must be named in alphabetical order:
dichlorobis(ethylenediamine)cobalt(III) nitrate

23. 23-23
(c) The central metal ion is written first, followed by the neutral
ligands and then (in alphabetical order) by the negative ligands.
Charge of complex ion = charge of metal ion + total charge of ligands
= (4+) + [(4 x 0) + (1 x 1-) + (1 X 1-)]
= +4 + (-2) = +2 or 2+
We will therefore need two Cl- counter ions to balance the charge on the
complex ion.
[Pt(NH3)4BrCl]Cl2

24. 23-24
(d) This compound consists of two different complex ions. In the
cation, there are six NH3 ligands and the metal ion is Co3+, so
the cation is [Co(NH3)6]3+.
The anion has four Cl- ligands and the central metal ion is Fe3+,
so the ion is [FeCl4]-.
The charge on the cation must be balanced by the charge on
the anion, so we need three anions for every one cation:
[Co(NH3)6][FeCl4]3

25. 23-25
Constitutional Isomers of Coordination
Compounds
Compounds with the same formula, but with the atoms
connected differently, are constitutional isomers.
Coordination isomers occur when the composition of
the complex ion, but not the compound, is different.
- This can occur by the exchange of a ligand and a counter ion, or be
by the exchange of ligands.
Linkage isomers occur when the composition of the
complex ion is the same but the ligand donor atom is
different.
- Some ligands can bind to the metal through either of two donor
atoms.

26. 23-26
A pair of linkage (constitutional) isomers
The nitrite ion can bind either through the N atom or either one of
the O atoms.

27. 23-27
Ligands that have more than one donor atom

28. 23-28
Stereoisomers of Coordination
Compounds
Stereoisomers are compounds that have the same atomic
connections but different spatial arrangements of their
atoms.
Geometric or cis-trans isomers occur when atoms or
groups can either be arranged on the same side or on
opposite sides of the compound relative to the central
metal ion.
Optical isomers (enantiomers) are non-superimposable
mirror images of each other.

29. 23-29
Geometric (cis-trans) isomerism.
In the cis isomer, identical ligands are adjacent to each other, while in
the trans isomer they are across from each other.
The cis and trans isomers of [Pt(NH3)2Cl2].
The cis isomer (cisplatin) is an antitumor agent while the trans
isomer has no antitumor effect.

30. 23-30
Geometric (cis-trans) isomerism.
The cis and trans isomers of [Co(NH3)4Cl2]+.
Note the placement of the Cl- ligands (green spheres).

31. 23-31
Optical isomerism in an octahedral complex ion.
Structure I and its mirror image, structure II, are optical isomers
of cis-[Co(en)2Cl2]+.

32. 23-32
Optical isomerism in an octahedral complex ion.
The trans isomer of [Co(en)2Cl2]+ does not have optical isomers.
Structure I can be superimposed on its mirror image, structure II.

33. 23-33
Important types of isomerism in coordination
compounds.

34. 23-34
Determining the Type of Stereoisomerism
PROBLEM: Draw stereoisomers for each of the following and state the
type of isomerism:
(a) [Pt(NH3)2Br2] (square planar) (b) [Cr(en)3]3+ (en = H2NCH2CH2NH2)
PLAN: We determine the geometry around each metal ion and the
nature of the ligands. If there are different ligands that can be
placed in different positions relative to each other, geometric
(cis-trans) isomerism occurs. Then we see whether the mirror
image of an isomer is superimposable on the original. If it is
not, optical isomerism also occurs.

35. 23-35
SOLUTION:
(a) The square planar Pt(II) complex has two different types of
monodentate ligands. Each pair of ligands can be next to
each other or across from each other. Thus geometric
isomerism occurs.
These are geometric isomers; they do not have optical isomers
since each compound is superimposable on its mirror image.

36. 23-36
(b) Ethylenediamine (en) is a bidentate ligand. The Cr3+ ion has
a coordination number of 6 and an octahedral geometry, like
Co3+. The three bidentate ligands are identical, so there is
no geometric isomerism. However, the complex ion has a
nonsuperimposable mirror image. Thus optical isomerism
occurs.

37. 23-37
Bonding in Complex Ions
In terms of valence bond theory, the filled orbital of the
ligand overlaps with an empty orbital of the metal ion.
When a complex ion is formed, each ligand donates an
electron pair to the metal ion.
The ligand acts as a Lewis base, while the metal ion acts as a Lewis
acid.
This type of bond is called a coordinate covalent bond
since both shared e- originate from one atom in the pair.
The VB model proposes that the geometry of the complex
ion depends on the hybridization of the metal ion.

38. 23-38
Hybrid orbitals and bonding in the octahedral
[Cr(NH3)6]3+ ion.

39. 23-39
Hybrid orbitals and bonding in the square planar
[Ni(CN)4]2- ion.

40. 23-40
Hybrid orbitals and bonding in the tetrahedral
[Zn(OH)4]2- ion.