This article contains informative study regarding orgel diagram with attached hand made picture to understand better.

1. TOPIC:- ORGEL DIAGRAM
Name:- Rifat Riyaz
M.Sc. 1st semester
Roll no. :- 2310014175011
Mentor name:- Prof. V.K.Rai sir
Chemistry presentation

2. ORGEL
DIAGRAM

3. Introduction
 Introduced by “ Laslie orgel” .
 It is a diagrammatical representation of electron absorption spectra of transition
metal complexes.
 Particularly useful in interpretation of only spin allowed electronic transition.
 Spin allowed electronic transition occurs between the two energy levels which have
same spin multiplicity.
 It is given only for tetrahedral and high spin octahedral complexes of transition
metal atom.
 Almost all molecules of complex occupy ground state energy levels therefore ,this
diagram shows ground state and only those excited states that have same spin
multiplicity as of ground state.

4. • In an orgel diagram the parent term ( P, D or F) in the presence of no ligand is shown in the
centre and the different energy levels arising from the parent term on either side.
• Different energy level arises in the presence of ligand field and are represented by Mulliken’s
symbols.
• These Mulliken’s symbols have the same spin multiplicity as the unsplitted parent term.
• The parent term used for different configurations in spin allowed electronic transition are
given below:-
Terms used in orgel diagram
Configuration Energy terms
d 1, d9 2D
d2 ,d8 3F , 3P
d3 , d7 4F , 4P
d4 , d6 5D
d5 6S

5. Splitting of parent term in octahedral and tetrahedral ligand field
The parent term under ligand field are splitted into different energy levels which are represented
by Mulliken’s symbols as given below:-
Spectroscopi
c
terms
Splitted
forms
Mulliken’s symbol
Octahedral
field (Oh)
Tetrahedral
Field (Td)
S Remain
unsplitted (1)
A1g A1
P Remain
unsplitted (3)
T1g T1
D 5 orbital→2
sets
(3+2)
T2g + Eg T2 + E
F 7orbital→3
sets
(3+3+1)
T1g+ T2g +
A2g
T1 + T2 + A2

6. ORGEL DIAGRAM
“F” Orgel diagram
“D” Orgel diagram
( for configuration
having D term as a
ground state)
• For d1,d4 , d6 and d9
systems.
( for configuration
having F term as a
ground state)
• For d2,d43, d7 and d8
systems.
Note:- For d⁵ configuration it is a special case which shows spin forbidden transition. The
d⁵ configuration have ⁶S ground state which do not split in ligand field and it has no other
excited state of same spin multiplicity hence in this case only spin forbidden transitions
are possible.

7. “D” Orgel diagram
• It is given for d1 ,d6,d4 and d9 system.
• For the “D” orgel diagram, left side contains d1
and d6 octahedral and d4 and d9 tetrahedral
complexes.
• The right side contains d4 and d9 octahedral, and
d1 and d6 tetrahedral complexes.
• The lowest energy electronic transition or
absorption band on the left side of spectrum is
T2→E ,while on the right side of spectrum it is
E→T2.
• The subscript “g” is used if the same diagram is
used to generalize spectra of octahedral
complexes. Fig:-1)-Orgel diagram for d1,d4,d6 and d9 complexes in octahedral
(Oh) and tetrahedral (Td) crystal fields

8. “F” Orgel diagram
Fig:2):- Orgel diagram for d2, d3, d7 and d8 complexes in
octahedral (Oh) and tetrahedral (Td) crystal fields.
• It is given for d2, d3, d7and d8 systems.
• For the “F” Orgel diagram, left side contains d2 and d7
tetrahedral and d3 and high spin d8 octahedral
complexes.
• The right side contains d3 and d8 tetrahedral and d2
and high spin d7 octahedral complexes.
• The lowest energy absorption band on the left side of
spectrum is of A2(F)→T2(F) transition, while on the right
side of the spectrum it is of T1(F)→T2(F) transition .
• It is clear from given diagram, that there are four
states of same spin multiplicity, two T1 states, one T2
state and one A2 state. The spin multiplicity is omitted
as it is a generalized diagram.
• The subscript “g” is used if the same diagram is used
to generalize spectra of transition metal complexes in
octahedral field.

9. Application of orgel diagram to electronic spectra of transition metal
complexes
The electronic Spectra of transition metal complexes can be obtained by the orgel diagram. With the help of
orgel diagram, it is easy to determine the number and type of electron transition of d-d origin.
Orgel diagram and electronic spectra of d2 and d8 octahedral complexes
Fig:3):-Orgel diagram for d2 metal ion in octahedral field Fig:4):-Orgel diagram for d8 metal ion in octahedral field
The ground state term symbol for d² and d⁸ complexes is ²F, but the splitting pattern is opposite for each other.
The energy order of Mulliken’s state in d⁸ configuration complexes will be just inverse of what is in d²
configuration. The ³F ground state term splits in ³A2g(F), ³T2g, and ³T1g in octahedral field. The excited state with
same spin multiplicity is ³P which transforms to ³T1g(P) in octahedral field.
• For d² metal ion:-
• The order of energy level in
ligand field is ³T1g(F),
³T2g(F), ³T1g(P) and ³A2g(F).
• Thus. There should be
three absorption band due
to ³T1g(F)→³T2g(F),
³T1g(F)→³T1g(P) and

10. ³T1g(F)→³A2g(F) transitions.
• But actually in d² metal ion ,only two absorption bands are observed.
• The third electronic transition ³T1g(F)→³A2g(F) involve simultaneous excitation of both
electrons from t2g to eg orbital and hence is forbidden.
Fig:5):-Electronic spectra of [V(H2O)6]³+ complex (d² metal
complex.
Fig:6):- Electronic spectra of [Ni(H2O)6]²+ complex
For d⁸ metal ion in octahedral field -
For e.g. ,the complex ion [V(H2O)6]³+ is d² metal complex which
shows absorption band at 17,200 cm-1 and 25,600 cm-1 and it’s
aqueous solution is green in colour.
• The order of energy level in ligand field is ³A2g(F), ³T2g(F), ³T1g(F)
and ³T1g(P).
• There are three absorption bands due to ³A2g(F)→³T2g(F),
³A2g(F)→³T1g(F) and ³A2g(F)→³T1g(P) electronic transitions.
• The term ³T1g(F) and ³T1g(P) do not cross each other because they
are of same symmetry
For e.g. ,The complex ion [Ni(H2O)6]²+ is a d⁸ complex ion which
shows absorption band at 8,700cm-1 ,14,500 cm-1 and 25,300
cm-1 and is blue in colour in aqueous medium.

11. ** Hence we construct orgel diagram for any transition metal configuration and their
electronic spectra in the same manner but in accordance with certain rules also which are
given below:-
Rules to be followed:-
1. The ground state and excited state of same spin multiplicity should be taken
2. Same spin multiplicity are written for Mulliken’s symbols obtained by splitting of terms
in crystal field.
3. Lines of the same term diverge due to non crossing rule .
4. For different term the lines of same symmetry do not cross each other but of opposite
symmetry can cross each other .
5. Subscript “g” is used to all term energy levels if the metal ion is subjected to octahedral
field potential and it is omitted in case of tetrahedral field potential.
6. All the possible transition should be shown in the diagram.