1. Coordination Compounds
H.V.KUMBHAR

2. Introduction
Most amazing field of inorganic chemistry.
The branch of chemistry which deals with the study of coordination compounds or complex compounds is known as Coordination chemistry.

3. Introduction
Coordination compound contains a central metal ion surrounded by number of oppositely charged ions or neutral molecules.
e.g [Cu(NH3)4]2+
In this complex copper is the central metal ion while ammonia is a neutral molecule.

4. Werner’s Theory Basic Postulates:
Most of the metallic elements exhibits two types of valence. Primary valence and
Secondary valence.
Every metal tends to satisfy both valences.
Every metal has fixed number of secondary valence.
The secondary valence is always directed towards fixed position in space.

5. Salient features 1.1.Principal valence = primary valence (__)
= oxidation state of the
metal ion.
2.Secondary valence =
= Non-ionisable valence (----)
= Coordination number (CN)

6. Two spheres - groups in inner sphere strongly bound by metal ion
inner /first sphere
- groups in inner sphere
strongly bound by metal ion
– can not be separated easily
- coordination sphere
(field of secondary valence) M
Outer /second sphere
- groups in ionization
sphere loosely bound
-form ions in suitable solvent
(field of primary valence)
Two spheres Cl
NH3
_____________
-----
NH3
NH3
-----
--- Co
_______________
-----
----- Cl
-----
NH3
NH3
_______________
NH3 Cl

7. 2.The primary valences are those which a metal ion exercises towards the negative groups so that its normal charge is satisfied by the formation of simple salt (PtCl4,CoCl2,CuCl2).
for e.g. primary valences of Pt, Co ,Cu, Ag are 4,3,2,1
resptly
Secondary valences – satisfied by negative ions, neutral molecules or both so that a coordination sphere is formed.
e.g.[Co(NH3)6] 3+ , [Co(NH3)5Cl] 2+ , [Co(NH3)4Cl2] + , [Co(NH3)3Cl3] 0 Negative group –both primary & secondary valence

8. 3. Every element is characterized by its fixed secondary valence. e. g
3.Every element is characterized by its fixed secondary valence. e.g. Fe(II) , Co(III) and Pt(IV) have coordination number 6, 4 and 2 respectively. 4. Primary valence – non-rigid, non directional . Secondary valence – have directional properties. Geometry of complex is determined by the number and position of secondary valence.

9. 2 3 4 5 6 sp sp2 sp3 dsp2 dsp3 d2sp3 Linear Trigonal planar
Secondary valence
(coordination
Number, No.of ligands) M+
Type Of
hybridisation
Geometry
Of complex
Geometrical shape 2 3 4 5 6 sp
sp2
sp3
dsp2
dsp3
d2sp3
Linear
Trigonal planar
Tetrahedral
Square planar
Trigonal bipyramidal
Octahedral
coordination polyhedron: spatial arrangement of ligands around metal ion.
Above plane :
below plane :
no.of corners- 6
triangular faces-8

10. Werner’s theory in the light of modern electronic theory of valence ( See slide no. 7)
According to --- Primary valence – as the ionisable valence of electrovalency. Secondary valence– as coordination no. of M+ ion Two attraction spheres can be represented / written/ formulated as : [ Metal ion & Ligands] Ions of ionization sphere, Counter sphere Coordination sphere outside square bracket Non-ionisable sphere Ionisable sphere e.g. CoCl3.6NH3 Ξ [ Co(NH3)6 ] Cl3 Metal ion Ligand Ionisable sphere

11. Cobalt amines : , , , Werner’s Theory : Observations : 1. Prim
Cobalt amines : , , , Werner’s Theory : Observations : 1. Prim. Valence = Oxidation state = 3 for Co Sec. valence = coordination number = 6 2. Cobalt amines + HCl No NH3 evolved .. NH3 molecules strongly bound to metal ion Cobalt .. NH3 molecules are present in coordination sphere. 3. Differ in electrical properties. 4. Differ in their reactivity towards AgNO3
CoCl3.6NH3
CoCl3.5NH3
CoCl3.4NH3
CoCl3.3NH3
[Co(NH3)6]Cl3, [Co(NH3)5Cl]Cl2 , [Co(NH3)4Cl2] Cl [Co(NH3)3Cl3] 0
373K

12. 4 ions / particles 3 ions / particles 4 charges Complex CoCl3.6NH3
Reaction with
AgNO3
Conclusion
CoCl3.6NH3 + Ag+ (ex) AgCl
3 Cl- present in ionisable sphere which satisfy primary valence of
Cobalt ion
CoCl3.5NH3 + Ag+ (ex) AgCl
2 Cl- present in ionisable sphere which satisfy primary valence of
Cobalt ion. one Cl- remains unprecipitated & satisfy both valence
HCl
NH3 is not evolved
.. Bond between NH3 & Cobalt is strong .NH3 satisfy secondary valence of cobalt ion
Cryoscopic study
4 ions / particles
3 ions / particles
Molar Conductivity
6 charges
4 charges
Formulation
[Co(NH3)6] Cl3
[Co(NH3)5Cl ] Cl2

13. Ligands Types of Ligands
The molecules or ions which are coordinated to the central metal atom or ion in a coordination complex are called ligands or donor groups.
M(acceptor) L(donor)
e.g. K4 [ Fe (CN)6 ] [ Co Cl2 (NH3)4 ] Cl
Types of Ligands
Negative ions
Positive ions
Neutral molecules
CN Cyanide
NO+ Nitrosylium
CO Carbon monooxide
OH Hydroxide
NH Ammonia
O Oxide
H2O Water
NO Nitrite
NH2OH Hydroxylamine

14. Classification of Ligands
Mono / uni dentate
Poly / multi dentate
Ambidentate
-Has two or more donor atoms
-Available sites two or more
- Has only one donor atom
- Has two or more point of attachment
- Has only one point of attachment
-But coordinate with M+ at only one site
- Coordinate with M+ at two or more sites
- Coordinate with M+ at one site
NO2-
. .
. .
. .
NH3
NH2
-CH2-CH2-
NH2
M NO2
Ethylene diammine
As Bidentate
M ONO

15. Classification of Ligands
Polydentate ligands form ring structure in complex
( metal being a part of ring) . Ring structure called Metal Chelate & ligands as chelate ligands.
Chelation : The process of forming metal chelate
(Chele = Crab’s claw)
NH NH2
+ Cu Cu
NH NH2
Five membered ring
. . 2 1 5 3 4
. .

16. Classification of Ligands
Ethylene diamine tetra acetate ion [EDTA]4-
o O
O C C O-
N N
O C C O-
O O
Hexa dentate ligand -- Six donor atoms ‘ O’
2 ‘ N’
Both form five membered five heterocyclic rings.

17. Coordination Number (CN) : Legancy
The no. of ligands which are directly attached central metal atom or ion in a complex is known as CN.
Light transition metals CN and 6
Heavier transition metals --- CN
In metal chelates (Polydentate ) , CN = No.of ligands
In such cases, CN = No.of electron pairs donated by L
e.g. [Cu (en)2]2+ , CN (4) = No.of ligands (2)
CN = No.of electron pairs donated by L
= 4 electron pairs by en

18. Coordination Number (CN) : Legancy
The CN of M+ is influenced by----
i) Charge on the metal ion ii) Charge on the ligand
iii)The relative size of metal & ligand
iv) The forces of repulsion between the ligands.
These parameters decide the CN of M+
Some unusual trends in CN are observed
C N acts as deciding factor to govern the geometry or shape of the complex.
Same metal ions with different CN i.e. 4 & 6
Different metal ions with Same CN i.e. 6
Fe Co Ni2+
Co Fe Fe3+
Sn Pt Sn4+

19. Classification of Ligands
Type of ligands
Name
Abbreviation
Monodentate
1) Water
Ammonia
aqua
ammine
Bidentate
1) Ethylene diamine
2) Oxalate
3)Dimethyl glyoximato en ox
dmg
Tridentate
Diethylenetriamine
dien
Tetradentate
Triethylenetetraamine
trien
Hexadentate
Ethylene diamine tetra acetate
[EDTA]

20. Complex Ion
A complex ion is more or less stable charged aggregate formed when an ion, mostly of a metal is directly linked to a group of neutral molecules or ions.
In [Cu(NH3)4] [Fe(CN)6]3- [ CoCl(NH3)5]2+ [Ni(CO)4]
Neutral NH3 linked to
Cu(II) ion
Cyanide ions
Linked to
Fe(III) ion
Both Cl- & NH3
linked to
Co(III) ion CO
Linked to
Ni (o)
Coordination entity , coordination sphere , oxidation number of the central metal atom, Homoleptic & Heteroleptic complexes, Cationic complexes ,anionic complexes, Neutral complexes

21. Charge number of Complex ion
Net charge carried by complex ion is called its charge number.
It is equal to algebraic sum of charges carried out by central metal ion and ligands attached to it.
e.g:- The charge number of [Fe(CN)6]4- is -4.
= ( -1)
= = -4
Calculation of O.S. / O.N. of metal ion Fe in [Fe(CN)6]-4
O.N. of Fe , X + 6 (-1)= -4
X-6 = -4
X =+2

22. Difference between double salts and coordination compounds.
They are molecular solids or addition compounds
They are molecular solids or addition compounds
They do not dissociate into ions in water
They dissociate into ions in water
They retain their identity
They lose their identity
FeSO4+(NH4)2SO4 + 6H2O
FeSO4.(NH4)2SO4 .6H2O
K4[Fe( CN)6] K+ + [Fe(CN)6] 4-

23. Effective atomic number (EAN)
It is a total number of electrons around central metal ion present in a complex and calculated as sum of electrons on metal ion and number of electronY donated by ligands
EAN = Z-X+Y
Metal
Complex Z X Y
EAN Ni
Ni(CO)4 28 08 36 Fe
[Fe(CN)6]4- 26 2 12 Co
[Co(NH3)6]3+ 27 3 Zn
[Zn(NH3)4]2+ 30 Pt
[Pt(NH3)6]4+ 78 4 86

24. Effective atomic number (EAN)
Metal
Complex Z X Y
EAN Fe
[Fe(CN)6]3- 26 03 12 35 Cu
[Cu(NH3)4]2+ 29 02 08 Pt
[Pt(NH3)4]2+ 78 84

25. IUPAC nomenclature of mono nuclear coordination compound
A. To name a coordination complex ( cation or anion) always name the cation before the anion.
B. In naming the complex ion:
1. Name the ligands first ( in alphabetical order)
then the metal atom or ion.
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:
-ide -o; -ate -ato; -ite -ito

26. For Neutral ligands
Name of For neutral ligands, the common the molecule is used
e.g. H2NCH2CH2NH2 ( ethylenediamine ).
[Ni(CO)4] --- Tetracarbonylnickel(0)
Important exceptions:
water = ‘aqua’,
ammonia = ‘ammine’,
carbon monoxide = ‘carbonyl’,
N2 = ‘dinitrogen’
O2 = ‘dioxygen’.

27. Names of Some Common Ligands
Name of ligand in
Coordination Compound
Bromide Br-
Bromo
Nitrite NO2-
Nitro
Cyanide CN-
Cyano
Oxalate C2O4--
Oxalato
Oxide O--
Oxo
Ammonia NH3
Ammime
Acetate CH3COO-
Acetato
Carbon monoxide CO
Carbonyl
Carbonate CO3--
Carbonato
Water H2O
Aqua
Ethylene diammine tetraacetate
Ethylene diammine tetraacetato
Ethylammine
Ethyl ammine
Chloride Cl-
chloro NO
Nitrosyl

28. Greek prefixes
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. ethylenediammine
OR If it is polydentate ligands prefixes bis-, tris-,
tetrakis-, pentakis-, are used instead.
[Pt(H2NCH2CH2NH2)2Cl2]Cl2
dichlorobis ( ethylenediammine) platinum(IV) chloride
[Co(H2NCH2CH2NH2)3](SO4)3
tris (ethylenediammine ) cobalt (III) sulfate

29. Numerical prefixes 1 mono 5 Penta (pentakis) 9 Nona (ennea) 2 Di (bis)
Number
Prefix 1
mono 5
Penta
(pentakis) 9
Nona
(ennea) 2 Di
(bis) 6
Hexa
(hexakis) 10
deca 3
Tri
(tris) 7
heptakis 11
undeca 4
Tetra
(tetrakis) 8
octakis 12
dodeca

30. For cationic complex
After naming the ligands, name the central metal. If the complex ion is a cation, the metal is named same as the element.
e.g. Co in a complex cation is called cobalt
Pt is called platinum.
[Cr(NH3)3(H2O)3]Cl3
Triamminetriaquachromium (III) chloride
Pentaamminechloroplatinum (IV) bromide
[Pt(NH3)5Cl]Br3

31. For anionic complex
If the complex ion is an anion, the name of the metal ends with the suffix –ate.
e.g. Co in a complex anion is called cobaltate
Pt is called platinate.
For some metals, the Latin names are used in the complex anions e.g. Fe is called ferrate (not ironate).
K4[Fe(CN)6] potassium hexacyanoferrate (II)
Na2[NiCl4] sodium tetrachloronickelate (II)

32. Examples [Ag(NH3)2][Ag(CN)2] diamminesilver(I) dicyanoargentate (I)
(NH4)2[Ni(C2O4)2(H2O)2]
ammoniumdiaquabis(oxalato)nickelate(II)
The oxalate ion is a bidentate ligand.
[CoBr(NH3)5]SO4 pentaamminebromocobalt(III) sulfate
[Fe(NH3)6][Cr(CN)6]
hexaammineiron(III) hexacyanochromate (III)
[Co(SO4)(NH3)5] pentaamminesulfatocobalt(III) ion
[Fe(OH)(H2O)5] pentaaquahydroxoiron(III) ion

33. Names of anion containing metal atoms
Names of metal in anionic complex
Aluminum
Alluminate
Manganese
Mangenate
Chromium
Chromate
Molybdenum
Molybdate
Cobalt
Cobaltate
Nickel
Nicklate
Copper
Cuprate
Silver
Argentate
Gold
Aurate
Tin
Stannate
Iron
Ferrate
Zinc
Zincate
Lead
Plumbate

34. Isomerism in coordination compounds
Isomerism is very common phenomenon in coordination compounds.
Isos meaning equal and meros meaning part.
There are two principlal types of isomerism in coordination compounds:
Stereo isomerism
Structural isomerism

35. Stereoisomerism
Optical isomerism: It will give rise to dextro (d) and leavo (l) form. It will shift plane of plane polarized light. Co Cl en Co Cl en
d- form
l-form

36. Cis/trans-Isomers of [CoCl2(en)2]+
geometrical & optical, Cis – unsymmetrical , trans -symmetrical
Cis shows optical isomerism

37. Optical Isomerism
Simplest case: metal cation surrounded by three identical bidentate ligands,e.g. [Co(en)3]3+:
–> the two isomers are non-superimposable images of each other and therefore chiral molecules (d- & l- isomer)

38. Structural isomerism Structural isomerism is further subdivided into:
I o n i z a t i o n isomerism.
L i n k a g e isomerism.
C o o r d i n a t i o n isomerism.
S o l v a t e isomerism.

39. Ionization isomerism Compounds Color Ions present
An exchange of ions inside and outside the
coordination sphere.
Compounds
Color
Ions present
[Co(NH3)5SO4]Br
Red violet
[Co(NH3)5SO4]++ Br -
[Co(NH3)5Br]SO4
Red
[Co(NH3)5Br]2++ SO4- -

40. Linkage isomerism Compounds Color
The same ligand is bonded to central metal atom or ion
through different atoms
Compounds
Color
[Co(NH3)5NO2]Cl2
Yellow
[Co(NH3)5ONO]Cl2
Red

41. Coordination isomerism
This type of isomerism arise from different complex ions having same molecular formula.
[ Cu ( NH3 )4 ] [ Pt Cl4 ]
and
[ Cu Cl4 ] [ Pt (NH3)4 ]

42. Solvate isomerism It is also called as Hydrate isomerism.
In hydrate isomerism there is an exchange of H2O molecule inside or outside coordination sphere.
Compound
Colour
Number of H2O molecule inside coordination sphere
Number of H2O molecule outside coordination sphere
[ Cr (H2O)6 ] Cl3
Violet 6
[ Cr (H2O)5Cl ]Cl2. H2O
Blue green 5 1
[ Cr (H2O)4 Cl2] Cl. 2H2O
Green 4 2

43. Bonding in Coordination compounds
Warner was the first to discuss the bonding features in coordination compounds.
There are many theories which can explain the nature of bonding as well as various properties of coordination compounds. They are:
Valence Bond Theory
Crystal field theory
Ligand field theory
Molecular Orbital Theory

44. Valence Bond Theory
The valence bond theory was developed by Linus Pauling
This theory accounts for coordinate bond formation due to overlap of vacant hybrid orbital of central metal atom with filled orbitals of ligands each containing lone pair of electron.
Bond between metal ion & ligand is purely covalent coordinate .

45. Valence Bond Theory
Central metal ion present in a complex provides a definite number of vacant orbitals s , p and d for the formation of coordinate bonds with ligands.
Each ligand has at least one orbital containing a lone pair of electron.

46. Valence Bond Theory
The number of vacant orbitals provided by the central ion is the same as it’s CN.
In [Cu(NH3)4]SO4 ,Cu2+ provide 4 vacant orbitals.
These vacant orbitals undergo hybridisation to form the same number of hybrid orbitals.

47. Valence Bond Theory
The geometrical shape of the complex ion depends upon hybridization of metal orbitals.
Coordinate bond is stronger if the overlapping between orbitals is greater .

48. Valence Bond Theory
If (n-1 )d orbitals are used for hybridisation complexes are called inner complexes.
when strong field ligands like NH3 and CN- are involved in formation of complexes, they cause pairing of electrons present in metal ions. This process is called spin pairing

49. Structure of [Ni(CO)4] based on VBT
Neutral complex
Outer elec. confn of Ni (Z=28) : 3d84s2
In presence of strong field ligand CO,
One 4s & three 4p four sp3 hybrid orbitals
3d8
4s2 4p
HO-
hybridisation

50. Structure of [Ni(CO)4] :
Four sp3 hybrid orbitals of Ni overlap with filled orbitals of four CO ligands to form 4 coordinate bond between Ni and CO. CO ligands donate
4 ˣ 2 = 8 electrons to vacant 4sp3 hybrid orbitals. Ni
Geometry—Tetrahedral
Diamagnetic (no unpaired e-)

51. Structure of complexes based on VBT
Outer ele.confn
M/M+
Elec.conf.in presence of Ligand
Type of hybridisation
Electrons donated by Ligands
Geometry
Magne
tic property
[NiCl4]2-
Ni,Z=28
Ni,3d84s2
Ni++
3d8 4s0 4p0
3d8 4s0 4p0
sp3
4 ˣ 2 = 8
Tetrahedral
paramagnetic
[Ni(CN)4]2-
dsp2
Square planar
Diamagn
[Cu(NH3)4]2+
z=29
3d9 4s2 4p0
3d94s04p0
3d8 4s0 4p1
Paramag
[Co(NH3)6]3+
Z= 27
Co 3d74s24p0
3d64s04p0
d2sp3
6 ˣ 2 = 12
Octahedral
[CoF6]3-
4d0
3d64s04p04d0
sp3d2

52. Salient features of CFT
Crystal Field Theory
In1929 – Bethe –nature of bonding in ionic crystals.
In Schalpp ,Penny & Van Vleck –magnetic properties of transition metal ions &their complexes.
In complex,metal ion is surrounded by various atoms called ligands L . M
Ligands may be negative ions or neutral molecules.
Salient features of CFT L L L L L L

53. Salient features of CFT
Interaction between metal ion and ligand is purely electrostatic.
Ligands
approach
Repulsion between electrons of Ligands and metal ion
5 d-orbitals of metal ion
t2g eg
dxy
dyz
dzx
dx2-y2
dz2
Orientation between ligand -
metal bond axis.
Planar orbitals.
Lesser repulsion betn them.
Maximum electron density in
planes and in between the axis.
Acquire lower energy.
Orientation along ligand –metal ion axis.
Maximum repulsion betn them.
Maximum electron density along axis
Acquire higher energy
CFSE= Diff.in energy betn eg & t2g Dq

54. CFT-Assumptions z •The interactions between the
metal ion and the ligands are
purely electrostatic (ionic).
The ligands are regarded as point
charges
If the ligand is negatively charged:
ion-ion interaction. If the ligand is
neutral : ion-dipole interaction
The electrons on the metal are
under repulsive from those
on the ligands
The electrons on metal occupy
those d-orbitals farthest away from
the direction of approach of ligands y x z y z x y z x y x

55. Salient features of CFT
No overlapping between metal ion & ligands.
The magnitude of CFSE depends upon the nature and number of ligands and also upon the geometry of complex.(CFSE < O) _

56. Application of CFT to Octahedral Complex
In octahedral complex ,
Metal atom at the center
6 ligands at 6 vertices of regular octahedron.
Enegry
dx2-y2
dz2 eg
0.6 Δ 0/6Dq
Δ 0
0.4 Δ 0/4Dq
Degenerated-orbitals of metal ion in crystal field
t2g
dxy
dyz
dzx
Degenerated-orbitals of metal ion
Splitting of d-orbitals in octahedral crystal field.

57. Octahedral Field
Not all d orbitals will interact to the same extent with the six point charges located on the +x, -x, +y, -y, +z and -z axes respectively.
The orbitals which lie along these axes ( dx2-y2, dz2) will
be destabilized more than
the orbitals which
lie in-between the
axes (i.e. dxy, dxz, dyz).

58. Application of CFT to Tetrahedral Complex
Tetrahedral arrangement of four ligands showing their orientation relative to the Cartesian axes and the dxz orbital (the orientation with respect to the other two t2g orbitals dyz and dxy is identical)
The interaction of the four ligands with the t2g orbitals (dxy, dxy and dyz) is considerably greater than with the eg type oritals (dz2 and dx2–y2) –> the eg orbitals are therefore lower in energy

59. Tetrahedral Complex Metal atom at the center of regular tetrahedron
4 ligands at the 4 corners of regular tetrahedron.
T2g (dxy , dyz , dxz )--pointed towards ligands.
T2g experience more repulsion by ligands .
Eg (dx2-y2,dz2)—lie in betn metal –ligand bond axes.
dxy
dyz
dzx
t2g
0.4 Δ t/4Dq
Δ t
0.6 Δ t/6Dq
Degenerated-orbitals of metal ion in crystal field eg
dx2-y2
dz2
Degenerated-orbitals of metal ion
Splitting of d-orbitals in tetrahedral crystal field.

60. Square Planar Complexes
Square planar complexes are expected for all metal cations
with d8 electron configuration
This geometry offers the greatest stabilization according to the ligand field theory,
since the highest energy orbital dx2-y2 remains unoccupied
e.g. Ni (II), Pt (II), Pd (II), Au (III)
Square planar complexes with d8 configuration are always diamagnetic
e.g. [Ni(H2O)6]2+
octahedral –> paramagnetic
[Ni(CN)4]2– : square planar –> diamagnetic
[Ni(Cl)4]2– : tetrahedral –> paramagnetic
dx2-y2
unoccupied
dz2
dzx
dxy
dyz

61. Spectrochemical Series
The strong field ligands have higher splitting power of d- orbitals of the metal ion(paring at lower energy level, low spin)
Order of ligand field strength with decreasing Dq:
CN– > phen ~ NO2 – > en > NH3 ~ py > H3O
> C2O4 – - > OH– > F– > S2– > Cl– > Br– > I–
Order of metals with increasing Dq:
Mn(II) < Ni(II) < Co(II) < Fe(III) < Cr(III) < Co(III)
< Ru(III) < Mo(III) < Rh(III) < Pd(II) < Ir(III) < Pt(IV)

62. Ligand Field Stabilization Energies

63. Low-Spin vs. High-Spin Complexes
Strong-field ligands = low-spin complexes
Strong field ligands have pi-acceptor orbitals or low-lying d-orbitals:
∏* as in CO or CN–
Weak field ligands = high-spin complexes
Weak field ligands have pi-donor orbitals:
Usually multiple p-orbitals as in X–
Intermediate field ligands =
usually high-spin for +2 ions, low-spin for +3 ions
Intermediate field ligands have few, or no pi-donor or acceptor orbitals, or
there is a poor match in energy of available pi-orbitals: NH3, H2O, pyridine

64. Effect of pi-donor/acceptor interactions
Splitting of 5d-orbitals eg eg eg
Δ o
Δ o
Δ o
t2g
t2g
t2g
Sigma + pi- acceptor
High Field Ligands
Sigma + pi-donor
Low Field Ligands
Sigma bonding only Intermediate
Field Ligands

65. What happens for more than 1 electron in d orbitals?
The electron-electron interactions must be taken into
account.
1.For d1-d3 systems: Hund's rule predicts that the electrons
will not pair and occupy the t2g set.
2.For d4-d7 systems :There are two possibilities :--
a) Put the electrons in the t2g set and therefore pair the electrons
(low spin case or strong field situation).
Δ 0 > P
b) Put the electrons in the eg set, which lies higher in energy, but the electrons do not pair (high spin case or weak field situation).
Δ 0 < P
Therefore, there are two important parameters to consider:
The Pairing energy (P), and the eg - t2g Splitting (referred
to as Δ 0, 10Dq or CFSE)

66. Bonding in Metal Carbnyl
Compound containing carbonyl ligands only are known as homoleptic carbonyl.
Such type of compounds are formed by most of the transition metals.
For: Pentacarbonyl iron (O) trigonal bypiramidal Tetracarbonyl nickel (O) is tetrahedral.

67. Fe(Co)5 trigonal bypiramidal

68. Ni(Co)4 tetrahedral Ni Co

69. Thank You