This document discusses spectroscopic methods in inorganic chemistry, focusing on infrared (IR) spectroscopy. It provides information on: 1. The interactions of light with molecules and what spectroscopic methods involve excitation by light. 2. How polarity and dipole moments are calculated and why CO2 and CCl4 do not have a dipole moment. 3. The factors that influence the wavenumber of a bond vibration, including bond energy, multiple bonds, atom weights and hybridization, and types of vibrational motions.

1. Spectroscopic Methods in
Inorganic Chemistry
Dr.Chris UP August 2018
IR Spectroscopy
PART 1 General
1

2. Interactions light - molecules
We need to understand the different interactions dependent on the wavelenght
or energy of light:
① ② ③ ④ ⑤
Whatarethespectroscopicmethods1-4?
2

3. Animation
https://www.youtube.com/watch?v=0S_bt3JI150
3

4. Polarity and Dipole moments
Dipole moment can be calculated as the product of the charge (abbreviated Q)
times the distance (abbreviated r) between the charges.
4

5. Why do CO2 and CCl4 do not have a dipole moment ?
5

6. Absorption of energy
uv/vis
IR
6

7. Raman vs. IR
7

8. WHAT INFLUENCES THE WAVENUMBER
OF A BOND VIBRATION ?
8

9. (1) Bond energy
https://www.youtube.com/watch?v=9HfJNnoRMPA
9

10. 10
That is perhaps the most important point for IR:
We can estimate bond-strengths !
Example: compare keto, amide and nitro group
Which is at higher energy ?

11. (2) Multiple bonds
11

12. (3) Atom weights and hybridization
12

13. (4) Types of motions
Stretch:
symmetric asymmetric
wagging twisting scissoring rocking
Bending:
http://chemwiki.ucdavis.edu/Physical_Chemistry/Spectroscopy/Vibrational_Spectroscopy/Infrared_
Spectroscopy/Infrared%3A_Theory
13

14. Which modes are stretching and bending ?
14http://www1.lsbu.ac.uk/water/water_vibrational_spectrum.html#ir2

15. Examples
Identify stretching and
bending modes !
15

16. 16
https://webbook.nist.gov/chemistry/name-ser/

17. 17
Zinc Oxide
Zinc Hydroxide
Additional O-H stretches

18. 18
Exercises: FTIR of ZnO NP
https://www.sciencedirect.com/science/article/pii/S0001868617301197

19. Preparation (1)
precipitation method
19
The aqueous solution was prepared by mixing zinc nitrate hexahydrate
and sodium hydroxide aqueous solutions. In a typical procedure, 2.28 g
of zinc nitrate hexahydrate was dissolved in 75 ml of deionized water
and then, 0.6 g of NaOH in 150 ml of deionized water was added
dropwise under magnetic stirring.
After the addition was completed, the stirring was continued for 30 min
and then cooled with cold water.
The precipitates were filtered and washed by pure water several times.
Then the obtained precipitates were dried at 60◦C for 24 h and
calcinated at 200◦C for 2 h.
https://www.ias.ac.in/article/fulltext/boms/038/04/1033-1038

20. Lab method
20
Prepare 2 solutions:
• 5 mmol Zn(Oac)2 = 1.10 g in 50 ml water
• 10 mmol NaOH = 0.4 g in 100 ml water
Add the NaOH sol. slowly to the Zinc acetate solution
under stirring. Continue stirring for 10 minutes.
Filtrate the mix over Buchner filter, wash with water and
ethanol, then dry in oven.
.

21. Characterization
21
Figure 2 shows the FTIR spectra of the
synthesized ZnO nanoparticles in the
range of 4000–400 cm−1.
The broadband at 3504 cm−1 is the
stretching vibration of O–H group.
The peak at 1386 cm−1 is due to the O–
H bending of water.
The peak at 447 cm−1 is attributed to
the Zn–O stretching of vibration

22. Preparation (2)
sol-gel method
22
Zinc Oxide nanostructure was synthesized by using sol-gel method. In order to
prepare a sol, 2 g of Zinc Acetate Dihydrate and 8 g of Sodium Hydroxide were
weighted using a weighting balance. Then, 10 ml and 15 ml of distilled
water were measured by a measuring cylinder. After that, 2 g of zinc acetate
dihydrate was dissolved with a 15 ml of distilled water and 8 g of sodium
hydroxide was dissolved in a 10 ml of distilled water. The solutions were stirred
with a constant stirring for about five minutes each. After well mixed, sodium
hydroxide solution was poured to the solution containing zinc acetate with a
constant stirring by magnetic stirrer for about five minutes. Then, a burette
was filled with 100 ml of ethanol and tilt rate dropwise to the solution
containing both sodium hydroxide solution and zinc acetate.
After the reaction, white precipitate was formed..
https://core.ac.uk/download/pdf/82238669.pdf

23. Lab Method
23
Prepare 2 solutions:
• 1.0 g of Zn(OAc)2 in 7 ml H2O
• 4.0 g NaOH in 5 ml H2O
Add NaOH sol. to the Zn acetate solution slowly under stirring
Add 100 ml EtOH denat. slowly under stirring.
Let the mix stand for about 30 minutes.
ZnO should sediment out.
Decantate and disperse the precipitation in water by US.
Let product sediment and decantate -> collect and dry in oven

24. Preparation (3)
solid-state method
24
https://link.springer.com/article/10.1007/s00339-008-4533-z

25. Lab method
25
Weight 5 mmol Zn(Oac)2 = 1.10 g into mortar.
Grind it to a fine powder..
Add 10 mmol NaOH = 0.8 g into the mortar.
Grind the mix for about 15 minutes.
Wash the mix with water into a beaker, filtrate by suction,
wash with water, then wash with Ethanol. Put the filter
residue on a petri dish and let dry in the oven.

26. IR / Raman Simulation
http://chemtube3d.com/Organic%20Structures%20and%20Bonding.html
26

27. IR Spectrum of “Rennie”
Example: identify products in Antacids
http://www.ptfarm.pl/pub/File/Acta_Poloniae/2000/2/083.pdf
(1) Carbonate Compound
27

28. Ref. spectra
Mg CO3
Ca CO3
O-HCa-O
Mg-O
28

29. (2) Hydroxy Compounds
IR of “Maalox (an)”
IR of “Alusal”
29

30. Ref. spectra
Al(OH)3
Mg(OH)2
Al(OH)3
Mg(OH)2
30