Crystal field theory describes the splitting of d orbital energies when transition metal ions are surrounded by ligands. In an octahedral field, the d orbitals split into a lower-energy t2g set and higher-energy eg set. In a tetrahedral field, the splitting is intrinsically smaller and the orbital labels are e and t2. Stronger ligands or higher oxidation states result in larger crystal field splitting (Δ). Metal complexes can exist as high-spin or low-spin depending on Δ and ligand strength.
Theories of coordination compounds, CFSE, Bonding in octahedral and tetrahedral complex, color of transition metal complex, magnetic properties, selection rules, Nephelxeuatic effect, angular overlap model
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Using the crystal field theory, different properties of transition metal compounds can be explained, such as Ionic radii, hydration and lattice energies and spinel types
Theories of coordination compounds, CFSE, Bonding in octahedral and tetrahedral complex, color of transition metal complex, magnetic properties, selection rules, Nephelxeuatic effect, angular overlap model
Properties of coordination compounds part 1 (2018)Chris Sonntag
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The Roman Empire A Historical Colossus.pdfkaushalkr1407
The Roman Empire, a vast and enduring power, stands as one of history's most remarkable civilizations, leaving an indelible imprint on the world. It emerged from the Roman Republic, transitioning into an imperial powerhouse under the leadership of Augustus Caesar in 27 BCE. This transformation marked the beginning of an era defined by unprecedented territorial expansion, architectural marvels, and profound cultural influence.
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How to Create Map Views in the Odoo 17 ERPCeline George
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The people of Punjab felt alienated from main stream due to denial of their just demands during a long democratic struggle since independence. As it happen all over the word, it led to militant struggle with great loss of lives of military, police and civilian personnel. Killing of Indira Gandhi and massacre of innocent Sikhs in Delhi and other India cities was also associated with this movement.
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TESDA TM1 REVIEWER FOR NATIONAL ASSESSMENT WRITTEN AND ORAL QUESTIONS WITH A...
Lec3.pdf
1. Crystal Field Splitting in an Octahedral Field
eg
Energy
3/5 o
o
t2g
2/5 o
eg - The higher energy set of orbitals (dz2 and dx2-y2)
t2g - The lower energy set of orbitals (dxy, dyz and dxz)
Δo or 10 Dq - The energy separation between the two levels
The e orbitals are repelled by an amount of 0 6 Δ
The eg orbitals are repelled by an amount of 0.6 Δo
The t2g orbitals to be stabilized to the extent of 0.4 Δo.
2. Tetrahedral Field
t2
2/5
Energy
2/5 t
t
e
3/5 t
The higher energy set of orbitals (dxz, dyz, dxy) is labeled
as t2 and the lower energy set (dz2 and dx2-y2) is labeled
2 gy ( z x y )
as e.
The crystal field splitting in the tetrahedral field is intrinsically smaller than in the octahedral
field For most purposes the relationship may be represented as Δ = 4/9 Δ
field. For most purposes the relationship may be represented as Δt = 4/9 Δo
4. [Ti(H2O)6]3+ – a d1 system
The single electron in the t2g orbitals absorb energy in the form of light and gets excited to the eg
orbitals. In case of [Ti(H2O)6]3+, this corresponds to 520 nm (20,300 cm-1).
520 nm
(243 kJ/mol)
5. Factors Affecting the Magnitude of Δ
1. Higher oxidation states of the metal atom correspond to larger Δ.
Δ =10,200 cm-1 for [CoII(NH3)6]2+ and 22,870 cm-1 for [CoIII(NH3)6]3+
Δ =32,200 cm-1 for [FeII(CN)6]4- and 35,000 cm-1 for [FeIII(CN)6]3-
2. In groups, heavier analogues have larger Δ.
For hexaammine complexes [MIII(NH3)6]3+:
Δ 22 870 1 (C )
Δ = 22,870 cm-1 (Co)
34,100 cm-1 (Rh)
41,200 cm-1 (Ir)
3. Geometry of the metal coordination unit affects Δ greatly.
Tetrahedral complexes ML4 have smaller Δ than octahedral ones ML6:
Δ = 10,200 cm-1 for [CoII(NH3)6]2+
5,900 cm-1 for [CoII(NH3)4]2+
4. Nature of the ligands.
For [CoIIIL ] Δ in cm-1: 13 100 (F-); 20 760 (H O); 22 870 (NH )
For [Co L6], Δ in cm : 13,100 (F ); 20,760 (H2O); 22,870 (NH3)
For [CrIIIL6], Δ in cm-1: 15,060 (F-); 17,400 (H2O); 26,600 (CN-)
6. Spectrochemical Series
An arrangement of ligands according to their ability to increase Δ for a given metal center
Weak – I-, Br-, SCN-, Cl-, N3
-, F-, H2NC(O)NH2, OH-, ox2-, O2-, H2O, NCS-, py, NH3, en , bpy,
phen, NO2
-, CH3
-, C6H5
-, CN-, CO – Strong
Strong
Field (Ligand)
Weak
Field
Field (Ligand)
7. Distribution of Electrons in an Octahedral Complex
d1 d2 d3
Strong field Weak field Strong field Weak field Strong field Weak field
d1 d2 d3
Net energy decrease is called crystal field stabilization energy (CFSE)
For d1, CFSE = 1 × 0.4 = 0.4 Δo
For d , CFSE 1 0.4 0.4 Δo
For d2, CFSE = 2 × 0.4 = 0.8 Δo
For d3, CFSE = 3 × 0.4 = 1.2 Δo
o
8. Distribution of Electrons in an Octahedral Complex
d4 There are two possibilities for metal ions having d4-d7
electronic configuration. Depending on the nature of the
ligands and the metal they could be high-spin or low-
i l
2 spin complexes.
2 u.e.
4 u.e.
For the d4 system, CFSE =
For high-spin, (3 × 0.4) – (1 × 0.6) = 0.6 Δo and
g p ( ) ( ) o
for low-spin, 4 × 0.4 = 1.6 Δo
2.0 Δo 2.4 Δo 1.8 Δo
0.0 Δo 0.4 Δo 0.8 Δo
d5 d6 d7
1 u.e. 5 u.e. 0 u.e. 4 u.e. 1 u.e. 3 u.e.
9. Distribution of Electrons in an Octahedral Complex
d8 d9 d10
2 u.e. 2 u.e. 1 u.e. 1 u.e. 0 u.e. 0 u.e.
For d8, CFSE = (6 × 0.4) – (2 × 0.6) = 1.2 Δo
For d , CFSE (6 0.4) (2 0.6) 1.2 Δo
For d9, CFSE = (6 × 0.4) – (3 × 0.6) = 0.6 Δo
For d10, CFSE = (6 × 0.4) – (4 × 0.6) = 0.0 Δo
Metal ions with 4 7 electrons in the d orbital can exist as high spin or low spin
In all electronic configurations involving two electrons in the same orbital, the actual CFSE is
reduced by the energy spent on pairing the electrons.
Metal ions with 4 – 7 electrons in the d orbital can exist as high-spin or low-spin
complexes. Weaker ligands tend to give high-spin complexes, whereas stronger ligands
tend to give low-spin complexes.
11. Distribution of Electrons in a Tetrahedral Complex
T t h d l litti i ld l h t lt i i i f th l t
Tetrahedral splitting is seldom large enough to result in pairing of the electrons.
As a result, low-spin tetrahedral complexes are not common.
A rare example is Cr[N(SiMe3)2]3[NO]
d1 e1 t2
0 0.6 Δt
d2 e2 t2
0 1.2 Δt
d3 e2 t2
1 0.8 Δt
d4 e2 t2
2 0.4 Δt
d5 e2 t2
3 0 0 Δt
d e t2 0.0 Δt
d6 e3 t2
3 0.6 Δt
d7 e4 t2
3 1.2 Δt
d8 e4 t2
4 0.8 Δt
d9 e4 t2
5 0.4 Δt
d10 e4 t2
6 0.0 Δt
2 t
12. When to Expect Tetrahedral Geometry
If ligands are large; so as to avoid ligand-ligand repulsion
If ligands are large; so as to avoid ligand ligand repulsion
In case of metal ions with zero CFSE (d0, d5 and d10) or
MnO4
- (d0), FeCl4
- (d5, h.s.), ZnCl4
2- (d10)
4 ( ) 4 ( ) 4 ( )
In case of metal ions with small CFSE (d2 and d7)
CoCl4
2- (d7, h.s.) – 0.8 Δo vs 1.2 Δt
13. Square Planar Field
Ligands along the Z
axis are removed from
axis are removed from
an octahedral complex
to get a square planar
complex
Energy
14. When to Expect Square Planar Geometry
In the case of d8 metals and strong ligands:
Ni2+, in the presence of strong field ligands such as CN- forms a square planar complex.
2nd and 3rd row d8 metals form square planar geometry irrespective of the nature of the
ligand:
With Pd2+ (which already generates a strong field) even a weak field ligand such as Cl-
l d t th f ti f l l f l [PdCl ]2
leads to the formation of a square planar complex, for example, [PdCl4]2-.
