Coordination Complexes

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Coordination Complexes
Fred J. Grieman
Vitamin B12
In 1957 Dorothy Crowfoot Hodgkin
(19101994) determined the molecular
structure of vitamin B12 using
X-ray crystallography. The Nobel Prize in Chemis
try 1964
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Transition Metal Compounds Coordination
Complexes Complex - E.g., Pt(NH3)2(Cl)
2, Cr(CO3) 33-, Ni(CO)4 Transition metal (us
ually ion) bond to ligands
Lewis acid / base interaction
? L
M ?
bond (e- pair from
ligand only) Less strong e.g., Pt(NH3)2
(Cl)2 ? Pt2 2NH3 2Cl-
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Transition metals have different oxidation states
in these compounds
Remember!!! ) for transition
metal ions So Transition Metal ions do not have
4s electrons (e.g., Fe2 3d6)
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Ligands
Ligands
(unidentate)
6 SCN-(aq) Fe3(aq) ?
N ?C?S Fe 6 times
Name hexathiocyanatoferrate(III)
Structure
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Polydentate or Multidentate Ligands
in volumetric determination
of zinc in Cold-Eeze
Called (claw)
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Writing Chemical Formula Complex enclosed in
, other ions outside of
all neutral K3Fe(SCN)6
Cr(NH3)5ClCl2
N C S N
CS SCN ? Fe? NCS ?SCN
S
C N
3K
?
In solution K3Fe(SCN)6 ?)
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Nomenclature (Names) From text
Your responsibility
Laboratory
Additions Isomer labels cis, trans d,
? Other ligands (Additions to table 19-1) O
2- oxo O22- peroxo H- hydro or hydrido
C5H5- cyclopentadienyl SH- mercapto
S2- thio 3) Linkage Isomers NO2- M?NO2
nitro M?ONO nitrito SCN- M?SCN thiocyana
to M?NCS isothiocyanto Pages 814-815 Negati
ve Complex ions e.g. Fe ferr ate ferrate
-- Fe(CN)63-
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Coordination Number
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Properties to be explained
A. ________ Complexes tend to absorb in visible
transmitting complementary c
olor electronic transition of __________
Why different colors?
B. _______________ (Kinetics to be studied next)
__________ (Fast reaction) Cu(NH3)42 4H ? Cu
(H2O)42 4NH4 _____ reaction Co(N
H3)63 6H ? Co(H2O)63 6NH4
Even though Keq 3 x 1021 !!!!! Why?
C. ________________________________
CoF63- paramagnetic but Co(NH3)63 is diamagneti
c !!!! Why?
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D. _____________ Can we understand why we get c
ertain structures? Can we explain structure ch
anges that
occur with change in oxidation number?
Coordination
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___________
E. ___________________________
d0, d5 are stable, but so are d3, d6, d8 where
as d4 is unstable
Why?
____________
____________
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Isomers
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________
n-butyl t-butyl alcohol in gc experiment
Cr(H2O)6Cl3 vs.
Cr(H20)5ClCl2H20
_______
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Try MX3Y3
_____________
___________
____
____
______________
________
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Molecules can have mirror images !!!!
Square planar - Tetrahedral -
A B \ / C ? ? C
D
B A \ / C ? D
C

?
Flip to align A and B
A B \ / C ? ? C
D
A B \ / C ? ? D
C
Try to ______________________
Keep the same
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____________ also has __________ isomers!!!
MX2Y2Z2 MXYZABC
180?
X Z X ? Fe? Z ?Y
Y
X X Z ? Fe? Y ?Z
Y
?
?
Flip around X-Fe-Y axis to align Z ligands
X Z Y ? Fe? Z ?X
Y
?
____________________________________
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Not so for ___________ because you must
_______________________
Cannot _____________