CRYSTAL FIELD STABILISATION ENERGY (CFSE):

The difference in energy of eg and t₂g Orbitals are called crystal field stabilisation energy (CFSE):

Where m and n = are number of electrons in t₂g and eg orbitals respectively and del.oct is crystal field splitting energy in octahedral Complexes.

l = represents the number of extra electron pair formed because of the ligands in comparison to normal degenerate configuration.
P= (Pairing energy) the energy required for electron pairing in a single orbital. The actual configuration of complex adopted is decided by the relative values of delta and P
Case (1): If del.oct is less than P :
We have so called weak field or high spin situation, the fourth electron entered one of the eg orbitals giving configuration (t₂g³ and eg¹)
If now 5th electron is added to a weak field the configuration become  (t₂g³ and eg²).
Case (2): If del.oct  is more than P: we have the strong field , low spin situation and pairing will occur in the t₂g level with eg level remaining unoccupied in entities of d¹ and d⁶ ions .

Calculation shows that coordination entities with four to seven d electron are more stable for strong field as compared to weak field cases.

(A)For configuration (d⁰, d¹, d², d³, d⁸, d⁹, d¹⁰):

SN	METAL ION	EXAMPLE	CONF IN L.F	CFSE(del.oct)
1	d0	Sc3+	t2g 0,0,0  eg 0	=0.0
2	d1	Ti3+	t2g 1,0,0 eg 0	=-0.4
3	d2	V3+	t2g 1,1,0 eg 0	=-0.8
4	d3	Cr3+ , V2+	t2g1,1,1  eg 0	=-1.2
5	d8	Ni2+	t2g 2,2,2  eg1,1	= -2.4 +1.2+ 3P =-1.2+3P
6	d9	Cu2+	t2g2,2,2  eg 2,1	=-2.4 +1.8+4P =-0.6+ 4P
7	d10	Zn2+	t2g2,2,2  eg 2,2	=-2.4 +2.4+ 5P =  5P

Therefore, for the above configurations, there is no effect of the nature of ligand. They may be strong or weak; the formula for CFSE will remain the same.

(A)For configuration (d⁴, d⁵, d⁶, d⁷):

SN	METAL ION	EXAMPLE	CONF IN L.F	CFSE(del.oct)
1	d4	Cr2+ (S.L.) Cr2+ (W.L.)	t2g 2,1,1  eg 0,0 t2g 1,1,1  eg 1,0	=-1.6  +1P =-1.6
2	d5	Mn2+,Fe3+(S.L.)                  (W.L)	t2g 2,2,1  eg 0,0 t2g 1,1,1  eg 1,1	=-2.0+2P =0.0
3	d6	Co3+,Fe2+(S.L.)                 (W.L.)	t2g 2,2,2 eg 0,0 t2g 2,1,1 eg 1,1	=-2.4 +3P =-0.4+ 1P
4	d7	Co2+ (S.L.)          (W.L.)	t2g2,2,2  eg 1,0 t2g2,2,1  eg 1,1	=-1.8+3 P -0.8+2P

Crystal field stabilisation energy (CFSE) in Tetrahedral:

The difference in energy of eg and t₂g Orbitals are called crystal field stabilisation energy (CFSE) in tetrahedral complexes:

Where m and n = are number of electrons in t₂g and eg orbitals respectively and del.oct is crystal field splitting energy in octahedral Complexes.
l = represents the number of extra electron pair formed because of the ligands in comparison to normal degenerate configuration.
P= (Pairing energy) the energy required for electron pairing in a single orbital. The actual configuration of complex adopted is decided by the relative values of delta and P

HYBRIDISATION AND GEOMETRY:

SN	CN	Hybridisation	Geometry	Bond angle	Examples
1	2	Sp	Linear	180	[Cu(CN)2]-, [Ag(CN)2]-, [Au(CN)2]-, [Ag(Cl)2]-, [Ag(NH3)2]+,
2	3	Sp2	Trigonal planer	120	[Hg(I3)2]2-,
3	4	Sp3	Tetrahedral	109. 28	[Ni(Cl)4]2-,[Zn(NH3)4]2+, [Cd(CN)4]2-,[Hg(I)4]2-, [Ag(S2O3)2]2,[Co(SCN)4]2
4	4	d3S                    /dxy,dyz,dzx,S	tetrahedral	109.28	CrO42-, MnO41-, MnO42- VO43-, Cr2O72-
5	4	dsp2             /dx2-y2Sp3	Square planer	90	[Ni(en)2]2+,[Cu(NH3)4]2+, [Ag(F)4]1-,[Pt(Cl)4]2-, [Au(F)4]1-,[Pd(H2O)4]2+, [Ni(dmg)2]
6	5	dz2Sp3                       / Sp3dz2	TBP	120, 90	[Fe(CO)5] , [Mn(CO)5] , [Cu(Cl)5]3
7	5	dx2-y2Sp3	Square pyramidal	90, 90	[Ni(CN)5] 3-
8	6	d2Sp3               /dx2-y2,dz2Sp3	Octahedral	90, 90	[Cr(NH3)6] 3+ , [NiF6] 2- , [Co(H2O)6] 3+ , [IrF6] 3-, [Rh(H2O)6] 3+ , [Ptcl6] 2- , [Pd(H2O)6] 4+,[Co(NH3)6] 3+
9	6	Sp3d2                          / Sp3 dx2y2,dz2	Octahedral	90, 90	[Fe(NH3)6] 2 ,[Fe(H2O)6] 3+   [Cr(H2O)6]2,[Ni(en)3]2+ [Mn(NH3)6] 2+