Ligand-Field Strength

Title:

The Influence of Ligand-Field Strength Upon The Spectra of Cu(II) Complex

Objective:

To obtain the visible spectra of a series of solutions containing the aqueous copper(II) salt with and without ammonia solution at various concentrations

Introduction:

Crystal Field Theory is a theory that proposed by Bethe and van Vieck. This theory illustrates the effects on a metal d orbital energy of moving a set of negative charges close to a metal ion. Energie s of the d orbitals rise as the negative or neutral molecule approach the metal ion, owing the repulsions between the d orbital electrons and the surrounding charge. Bonding between the central metal and ligands in the complex is considered to be purely electrostatic which is ionic. Central

Using these solutions, aqueous solutions of the ions [Cu(H2O)n(NH3)6-n]2+ ( n= 1 to 6) were prepared as follows:

1.) To 5 cm3 copper solution (a), solid ammonium nitrate was added until saturated. Then 5 cm3 of 1 mole dm-3 ammonium hydroxide was added slowly. Further solid ammonium nitrate was added to resaturate. 1 cm3 of this solution was diluted to 25 cm3 with 2 mole dm-3 ammonium nitrate. The resulting solution contains [Cu(H2O)5(NH3)]2+.

2.) Repeat (1) twice but use 2 mole dm-3 and 3 mole dm-3 ammonium hydroxide instead of the 1 mole dm-3 solution and thereby prepare solutions of [Cu(H2O)4(NH3)2)2+ and [Cu(H2O)3(NH3)3]2+ respectively.

3.) 1 cm3 concentrated ammonia (d = 0.880) was added to 1 cm copper solution (a). This solution was diluted to 50 cm3 with water, giving [Cu(H2O)2(NH3)4]2+.

4.) 0.5 cm3 copper solution (a) was diluted to 25 cm3 with conc. ammonia to give [Cu(H2O){NH3}5]2+ in solution.

5.) 0.5 cm3 copper solution (a) was diluted to 25 cm3 with

Firstly, safety glasses or goggles and lab coats must be worn at all times in the laboratory. Gloves must be worn while performing experiments or working with chemicals to avoid injuries. Moreover, cuvette has to be cleaned and dried at outside or lower portion of cuvette before taking any readings because fingerprints, liquid droplets and smudges on the cuvette surface can give false light absorbance readings. Conclusion:

The increase of the ligand field strength, the wavelength, λmax will decrease and the Energy difference in d-d orbital splitting, Δo will increase. The relative ligand field strength of ammonia ligand is stronger than the aqua ligand.

References:

Department of Chemical Science. (2015). UDEC 2114 Transition Elements and Coordination Chemistry handbook and lab manual. University Tunku Abdul Rahman. Energy Level Splitting. [Online]. Available at: http://www.chm.davidson.edu/vce/coordchem/splitting.html. [Accessed 17 March 2015]. Shriver, D. F., & Atkins, P. W. (2006). Inorganic Chemistry. (4th ed.). Oxford: OUP. Jones, C. J. (2003). Basic concepts on chemistry: d- and f- block chemistry. WileyBlackWell: