Factors affecting the magnitude of 10 Dq

The presentation discusses briefly the factors affecting the magnitude of 10 Dq and also the term Dq for undergraduates.
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1. Factors affecting the magnitude of 10 Dq . Dr. Mithil S. Fal Desai Assistant Professor in Chemistry SHREE MALLIKARJUN & Shri Chetan Manju Desai College Canacona Goa

2. Background and references 2 Concise Inorganic Chemistry, J. D. Lee, Chapman & Hall India, 4rth Edition, Year 1991 Inorganic Chemistry: Principle of structure and reactivity, J . E . Huheey , E. A . Keiter . R. L. Keiter , O. K. Medhi , Pearson Education India, 4rth Edition, Year 2006 Crystal Field splitting Crystal field stabilization energy Degenerate orbitals Spectrochemical series 3d and 4d transition series Octahedral and tetrahedral field

3. 10 Dq Five degenerate d orbitals in free metal ion Five d orbitals in octahedral field d orbitals are split into two groups d z 2 d x 2 -y 2 d xy d yz d xz e g t 2g energy The difference in energy between the two d levels ( e g and t 2g ) in a octahedral field is given either of the symbols Δ o or 10 Dq . 10 Dq or Δ o M +z -z -x -y +x +y L L L L L L The term Dq is derived from quantum mechanics and is product of two terms D (L=2) and q and is called Differential of quanta (implying the energy).

4. Δ o and Δ t Five degenerate d orbitals in free metal ion Five d orbitals in octahedral field d z 2 d x 2 -y 2 d xy d yz d xz e g t 2g d z 2 d x 2 -y 2 d xy d yz d xz e g t 2g Five d orbitals in tetrahedral field energy -0.4 Δ o +0.6 Δ o +0.4 Δ t - 0.6 Δ t Δ t Δ o Bari centre (average energy level)

5. 1) The nature of the ligands Spectrochemical series I - < Br - < S 2- < Cl - < NO 3 - < F - < OH - < EtOH < oxalate < H 2 O < EDTA < (NH 3 and pyridine) < ethylenediamine < dipyridyl < o-phenanthrolir:ie < NO 2 - < CN - < CO Weak field ligand Strong field ligand e g t 2g Δ o e g t 2g Δ o Complex Absorption peak in cm -1 Energy in kJ mol -1 [CrCl 6 ] 3- 13640 163 [Cr(CN) 6 ] 3- 26280 314 Five degenerate d orbitals Five degenerate d orbitals The crystal field splitting produced by the strong field like CN - ions is about double that for weak field ligands like the halide ions.

6. 2)The charge on the metal ion. e g t 2g Δ o e g t 2g Δ o Complex Absorption peak in cm -1 Energy in kJ mol -1 Electronic configuration [Co(H 2 O) 6 ] 2+ 9300 111 d 7 [Co(H 2 O) 6 ] 3+ 18600 222 d 6 Five degenerate d orbitals Five degenerate d orbitals In 3d transition metal ions, the values of 10 Dq for M 3+ complexes are approximately 50% larger than the values for M 2+ complexes

7. 3 ) Position of metal ion in 3d or 4d or 5d transition series. e g t 2g Δ o e g t 2g Δ o Complex Absorption peak in cm -1 Energy in kJ mol -1 [Co(NH 3 ) 6 ] 3+ 24800 296 [Rh(NH 3 ) 6 ] 3+ 34000 490 Five degenerate d orbitals Five degenerate d orbitals The value of 10 Dq also increases by about 30% between adjacent members down a group for the transition elements

8. 4) Number of Ligands The magnitude of crystal field splitting(10 Dq ) increases with the increase of the number of ligands .   ∆ O   > ∆ t