Chemical Structure: Chemical Bonding. Properties of Coordination Compounds
description
Transcript of Chemical Structure: Chemical Bonding. Properties of Coordination Compounds
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Properties of Coordination Compounds
University of Lincoln presentation
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Coordination Compounds
What is their main characteristic property?
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
A clue…A clue…
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Nearly all coordination compounds are COLOURED
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Breathalyzers
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Presumptive tests for drugs
e.g. the Duquenois test for marijuana
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Remember! Coordination compounds are the
compounds of the transition metals
(d block elements)Why are TM compounds coloured?
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
We need to look at the electronic configuration of the transition metals, to
answer this question
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Sc Ti V Cr Mn Fe Co Ni Cu Zn
d1 d2 d3 d4 d5 d6 d7 d8 d9 d10
[Ar] 4s23dn
H
BeLi
Na
K
Rb
Cs
Fr
Mg
Ca
Sr
Ba
Ra
Sc
Y
La
Ac
Ti V Cr Mn Fe Co Ni Cu Zn
Zr
Hf Ta W Re Os Ir Pt Au Hg Tl
Nb Mo Tc Ru Rh Pd Ag Cd In Sn
Pb Bi Po At Rn
Xe
Kr
Ar
Ne
Sb Te I
Ga
Al
Ge
Si P S Cl
As Se Br
Ce Pr Nd Pm Sm
Eu Gd Tb Dy Ho Er Tm Yb Lu
Th Pa U Np Pu Am Cm Bk Cf Es Fm Md No Lr
He
B C N O F
LanthanoidsActinoids
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
There are 5 d-orbitalsz
y
x
z
y
x
z
y
x
z
y
x
z
x
y
dyz dxy dxz
dz2 dx
2 y2
Note change of axis
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Energ
y
1s
2s
3s
2p
3p3d
N = 1
N = 2
N = 3
Each orbital will hold 2 electrons
d-orbitals can hold from 1 – 10
electrons
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
We get a clue as to how their colour arises, by considering
zinc
Zn = d10
(completely FULL d-orbitals)
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Zinc (d10) compounds are WHITE (not coloured!)
When d-orbitals are FULL there is no colour
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
COLOUR must have something to do with
partially filled d-orbitals
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Crystal Field Theory
This theory explains why TM compounds are coloured
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Crystal Field theory says…
““In the ELEMENT, In the ELEMENT,
the d-orbitals are the d-orbitals are DEGENERATE (of DEGENERATE (of the same energy)the same energy)
Each orbital will hold 2 electrons
Energ
y
3d
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
……But, in a COORDINATION But, in a COORDINATION COMPOUND,COMPOUND,
NOT all of the orbitals have the NOT all of the orbitals have the same energy”same energy”
For example, in an octahedral For example, in an octahedral coordination compound, the d-coordination compound, the d-
orbitals are split as follows:orbitals are split as follows:Energ
y
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
How does this help us to explain COLOUR?
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Consider the Fe2+ ion (d6)
If this ion makes an octahedral complex, its 6 d-electrons will sit in the split d-orbitals, as shown:
Energ
y
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
If we shine light on the Fe2+ complex…
An electron could absorb enough energy (=) to move from the bottom orbitals to the top orbitals:
Energ
y Energ
y
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Note: we haven’t changed the number of PAIRED
electrons
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
ONE ONE pair of pair of
electronelectronss
ONE ONE pair of pair of
electronelectronss
Energ
y Energ
y
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
When an electron is promoted from a low energy
level to a higher energy level, the process is called an
ELECTRONIC TRANSITION
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
How do electronic transitions make compounds
COLOURED?
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
If the electron is going to jump from the lower level to the higher level, it has to ABSORB energy from visible light
It needs to absorb an amount of energy =
Energ
y
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Electronic Spectrum – Visible light
LOW HIGH
Energy
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Whatever energy is absorbed, the remainder is
TRANSMITTEDIt is the TRANSMITTED light that
gives the compound its colour
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
For Example
TRANSMITTED LIGHTTRANSMITTED LIGHT
COLOUR of compound would be a mixture of
these
ABSORBED ABSORBED LIGHTLIGHT
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
is largeis large
High energy is High energy is needed to needed to
promote electron:promote electron:
Blue end is Blue end is absorbedabsorbed
RedRed end is end is transmittedtransmitted
is smallis small
Low energy is Low energy is needed to needed to
promote electron:promote electron:
Red end is Red end is absorbedabsorbed
BlueBlue end is end is transmittedtransmitted
Energ
y
Energ
y
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
So, why are Zinc compounds white?
Because the orbitals are
completely filled, there is no room
for electronic transitions to take
place
NO COLOUR NO COLOUR (WHITE)(WHITE)
Energ
y
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
What happens if is so big, that electrons prefer to pair
up in the lower level, and not jump up to the higher level?
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
There comes a point, when is so big, that it is easier for electrons to pair up in the lower level, rather than staying unpaired, by jumping up to the higher level
Energ
y
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Consider the Fe2+ octahedral complex, again
SMALL
VERY LARGE
Energ
y
Energ
y
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
How does this affect the COLOUR?
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Extended Electronic Spectrum
ULTRA VIOLETINFRARED
When is very large, the amount of energy required to promote an electron from the lower to the higher level is outside the visible range – hence the compound will appear WHITE
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
What other characteristic properties do the TM compounds display?
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Look again at the Fe2+ octahedral complex
The MAGNETIC properties of these two Fe2+ compounds are very
different
Energ
y
Energ
y
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
PARAMAGNETIPARAMAGNETICC
DIAMAGNETICDIAMAGNETIC
Energ
y
Energ
y
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
This dual magnetic behaviour is another characteristic property of coordination
compounds
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
SUMMARY
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
What you need to know…
• Two characteristic properties of coordination compounds are:– Colour– Dual magnetic behaviour
•E.g. Some iron(II) compounds are paramagnetic, whilst others are diamagnetic
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Crystal Field Theory
In a coordination compound the d-orbitals are not all the same energy
Colour arises from electronic transitions within the d-orbitals
Dual magnetic behaviour arises due to different values of
There are two reasons for coordination compounds to be white:
• Electronic transitions cannot occur (e.g. if the d-orbitals are full)
is so large that the absorbed energy in an electronic transition is in the UV region and not the visible region of the electronic spectrum
This work is licensed under a Creative Commons Attribution-Noncommercial-Share Alike 2.0 UK: England & Wales License
Acknowledgements
• JISC• HEA• Centre for Educational Research and
Development• School of natural and applied sciences• School of Journalism• SirenFM• http://tango.freedesktop.org