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Coordination Compounds
Peculiar compounds of transition
metals
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
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
• 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
Ligands
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
Cr3+ [Ar] 3d3
Fe3+ [Ar] 3d5
Fe2+ [Ar] 3d6
Ni2+ [Ar] 4s23d8
Co2+ [Ar] 3d7
Mn2+ [Ar] 3d5
Zn2+ [Ar] 3d10
CN = 4 (total 17 e-)
CN = 6 (total 15 e-)
CN = 6 (total 17 e-)
CN = 6 (total 18 e-)
CN = 4 (total 18 e-)
CN = 6 (total 15 e-)
CN = 6 (total 17 e-)
CN = 4 (total 18 e-)
MO Diagram Octahedral Complex (CN = 6)
d-orbitals split,
and the gap is
responsible for
the color of many
TM complexes
Jahn-Teller Distortion in Cu2+
• In some cases like [Cu(NH3).2H2O]2+ an distorted octahedron is more
stable than CN=4
more stable
Color of TM Complexes
• In transition metal complexes the d-orbitals (essentially nonbonding) split in energy
• Electrons in the lower d-orbitals can absorb visible light and go
into an unoccupied d-orbital
Cu2+
D oct =
free ion
octahedron
• Lowest energy transition is
determined by Δoct
distorted
octahedron
hc
l
Color of TM Complexes
• In transition metal complexes the d-orbitals (essentially nonbonding) split in energy
• Electrons in the lower d-orbitals can absorb visible light and go
into an unoccupied d-orbital
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
Part A: Synthesis [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
Test Tube
Copper(II)Sulfate
0.1661M
Ligand
0.1661M
1
5 drops
5 mL
diethylenetriamine
Part B:
2 A: To make
5 drops
• Part
[Cu(NH3)4]SO4.H5 2mL
O(s)
ethylenediamine
3
5 drops
5 mL
NH3*
4
5 drops
5 mL
EDTA
5
5 drops
5 mL
sodium salicylate
6
5 drops
1 mL 6M NH3 4 mL DI
H2O
• Measure the spectra, and extract Δ for each ligand
• Determine the spectro-chemical series for these 6 ligands L
Part B
Sample
mass of 0.1661M
Copper Sulfate
mass of 0.1661M
Ligand
1
0.10
0.90
2
0.15
0.85
7
0.45
0.55
The Experiment
• Part
C: Determine
y in CuLy where L0.80
=
3
0.20
ethylenediamine,
diethylenetriamine,
4
0.30
0.70
salicylate,
and Ethylenediaminetetraacetic
5
0.35
0.65
acid
6
0.40
0.60
•
2 ligands to0.50
9examine, ethylene
0.55 diamine, and one
0.45
assigned by me0.60
10
0.40
•
Record the absorbance at the value of λmax
you determine in Part B
8your group will 0.50
be given
Part C: Determining y in CuLy
• One of the objectives of this experiment is to determine y for different ligands L
that complex with Cu2+ Complex
Ligand
[Cu(dien)y]2+
dien=ethylenediamine
[Cu(trien)y]2+
trien = diethylenetriamine
[Cu(EDTA)y]2-
EDTA = Ethylenediaminetetraacetic acid
[Cu(sali)y]2-y
sali = salicylate
4y
• 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