1. Coordination Compounds
Peculiar compounds of transition metals

2. Coordination Compounds
Transition metals have s, d and p orbitals all available for bonding
Don’t obey the octet rule
They are most stable with filled d, s and p orbitals
s2d10p6 (18 e-)
Transition metals act like a Lewis acid (electron pair acceptor) so as to fill valence orbitals
Transition metals will bond with Lewis bases (e- pair donors) – species with lone pairs, these are called ligands

3. Transition Metal Complexes
Most often these complexes are octahedral or tetrahedral in shape with the metal at the center
Here we see
Cl- F-
H2O
NH3
are behaving as ligands

4. Ligands
Lewis bases that bind with transition metals are also called ligands
Some ligands bind once to the metal (monodentate)
NH3, H2O, CO, Cl-, Br-, I-, CN-, SCN-
Some bind twice (bidentate)
oxalate, ethylenediamine, salicylate
Some three times (tridentate)
diethylenetriamine
Some are even hexadentate
Ethylenediaminetetraacetic acid

5. Coordination Number of TM ions
Transition Metals will have a coordination number (CN) that helps get them as close to 18 valence electrons as possible (can go higher up to 20 or lower)
Cu2+ [Ar] 3d9 *CN = 4 (total 17 e-)
Cr3+ [Ar] 3d3 CN = 6 (total 15 e-)
Fe3+ [Ar] 3d5 CN = 6 (total 17 e-)
Fe2+ [Ar] 3d6 CN = 6 (total 18 e-)
Ni2+ [Ar] 4s23d8 CN = 4 (total 18 e-)
Co2+ [Ar] 3d CN = 6 (total 15 e-)
Mn2+ [Ar] 3d5 CN = 6 (total 17 e-)
Zn2+ [Ar] 3d10 CN = 4 (total 18 e-)
Jahn Teller CN=6 also

6. MO Diagram Octahedral Complex (CN = 6)
d-orbitals split, and the gap is responsible for the color of many TM complexes

7. Jahn-Teller Distortion in Cu2+
In some cases like [Cu(NH3).2H2O]2+ an distorted octahedron is more stable than CN=4
more stable

8. Color of TM Complexes Cu2+
In transition metal complexes the d-orbitals (essentially non-bonding) split in energy
Electrons in the lower d-orbitals can absorb visible light and go into an unoccupied d-orbital
free ion
octahedron
distorted
Cu2+
Lowest energy transition is determined by Δoct

9. Color of TM Complexes
In transition metal complexes the d-orbitals (essentially non-bonding) split in energy
Electrons in the lower d-orbitals can absorb visible light and go into an unoccupied d-orbital

10. Weak and Strong Ligands
The size of the splitting Δoct depends on the type of ligand
The stronger the ligand metal bond the larger Δoct is
Small Δoct
large Δoct

11. The Experiment Part A: To make [Cu(NH3)4]SO4.H2O(s)
Part B: To determine y in CuLy where L = ethylenediamine, diethylenetriamine, salicylate, and Ethylenediaminetetraacetic acid
To determine the spectrochemical series for these ligands L

12. Part A: Synthesis of [Cu(NH3)4]SO4.H2O(s)
3g Copper (II) sulfate pentahydrate
Add 15 mL H2O (dissolve solid)
Add 2.5x calculated volume of conc. NH3 (fume hood)
Add 25 mL ethanol to reduce solubility
Place in ice water for 10 mins
Filter out solid using a Buchner funnel
Wash in ammonia/ethanol
Allow to dry till next lab

13. Part B: Determining y in CuLy
One of the objectives of this experiment is to determine y for different ligands L that complex with Cu2+
We will do this using Job’s method
First find a strong absorption wavelength λmax for the CuLy
The mole fraction x=[L]/[Cu2+] is varied from small to large while the intensity of the color of the solution is measured at that wavelength λmax
when y = x the color will have the largest absorbance
Complex
Ligand
[Cu(dien)y]2+
dien=ethylenediamine
[Cu(trien)y]2+
trien = diethylenetriamine
[Cu(EDTA)y]2-4y
EDTA = Ethylenediaminetetraacetic acid
[Cu(sali)y]2-y
sali = salicylate