Coordination Complexes

1
Coordination Complexes
Fred J. Grieman
Vitamin B12
California defeated fourth-ranked UCLA 76-69
yesterday in the quarterfinals of the Pacific-10
Conference basketball tournament.
In 1957 Dorothy Crowfoot Hodgkin (19101994)
determined the molecular structure of vitamin
B12 using X-ray crystallography. Nobel Prize
in Chemistry 1964
Co
2
Heme Involved in transport of oxygen in blood
Fe (II)
Mg
chlorophyll a
3
Transition Metal Compounds Coordination
Complexes Complex - Molecule made of simpler
species E.g., Pt(NH3)2(Cl)2, Cr(CO3) 33-,
Ni(CO)4 Transition metal (usually ion) bond to
ligands
Lewis acid / base interaction
Ligand ? L
M ? positive center (central metal atom)
Lewis acid (electron pair acceptor)
Lewis base (electron pair donor)
Coordinate covalent bond (e- pair from ligand
only) Less strong complex breaks up into
individual species e.g., Pt(NH3)2(Cl)2
? Pt2 2NH3 2Cl-
4
Transition metals have different oxidation states
in these compounds
Remember!!! E(3d) lt E(4s) for transition metal
ions So Transition Metal ions do not have 4s
electrons (e.g., Fe2 3d6)
Remember H (r 2.6ao 1.38Å 138 pm) These are
covalent radii (from molecules) Much smaller For
H rcovalent 37 pm
IE1(H) 13.6 eV
5
Ligands
Ligands
tooth
Monodentate (unidentate)
6 SCN-(aq) Fe3(aq) ? Fe(SCN)63-(aq)
N?C?S Fe 6 times
Name hexathiocyanatoferrate(III)
N C S NCS
SCN ? Fe? NCS ?SCN
S C N
Structure
Octahedral
?
6
Polydentate or Multidentate Ligands
Like NH3
1 Ligand, but 2 bonds
oxalate anion in gravimetric Ca lab
EDTA in volumetric determination of zinc in
Cold-Eeze
Called Chelates (claw)
7
Writing Chemical Formula Complex enclosed in
, other ions outside of
Ni(CO)4 all neutral K3Fe(SCN)6
Cr(NH3)5ClCl2
Not Ligands!!!
N C S NCS
SCN ? Fe? NCS ?SCN
S C N
3K
?
complex ion
Ionic bonds in solid
In solution K3Fe(SCN)6 ? 3K(aq)
Fe(SCN)63-(aq)
Covalent bonds
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Nomenclature (Names) From text Your
responsibility given name ? formula Laboratory

• Additions
• Isomer labels cis, trans d, l
• Other ligands (Additions to table 19-1)
• O2- 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 thiocyanato M?NCS isothiocyanto
• Pages 814-815
• Negative Complex ions Latin name ate
• e.g. Fe ferr ate ferrate -- Fe(CN)63-
  hexacyanoferrate(III)

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Coordination Number of bonding sites on
central metal atom Most common number is 6
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Properties to be explained
A. Colors Complexes tend to absorb in visible
transmitting complementary
color electronic transition of d
electrons Why different colors?
B. Reaction Rates (Kinetics to be studied
next) Labile (Fast reaction) Cu(NH3)42 4H ?
Cu(H2O)42 4NH4 Slow reaction
Co(NH3)63 6H ? Co(H2O)63 6NH4 Even
though Keq 3 x 1021 !!!!! Why?
C. Magnetic Properties via d electrons CoF63-
paramagnetic but Co(NH3)63 is diamagnetic !!!!
Why?
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D. Structures Can we understand why we get
certain structures? Can we explain structure
changes that occur with change in oxidation
number?
Coordination 4 4 6
tetrahedral
E. d orbital occupation stability d0, d5 are
stable, but so are d3, d6, d8 where as d4 is
unstable Why?
Square planar
octahedral
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1. Isomers

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nitro
n-butyl t-butyl alcohol in gc
experiment Cr(H2O)6Cl3 vs.
Cr(H20)5ClCl2H20
nitrito
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Try MX3Y3
cis (adjacent)
trans (across)
trans
cis
square planar
octahedral
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Molecules can have mirror images !!!!
Square planar - no Tetrahedral - yes
mirror
mirror image
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 superimpose - impossible
Keep the same
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Octahedral also has optical isomers!!!
MX2Y2Z2 MXYZABC
180?
mirror
X Z X ? Fe? Z ?Y
Y
X X Z ? Fe? Y ?Z
Y
?
?
Flip around X-Fe-Y axis to align Z ligands
Superimpose?
X Z Y ? Fe? Z ?X
Y
Again impossible
?
Ligand Exchange is Labile nullifies effect
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Not so for chelates because you must break 2 or
more bonds
Next begin bonding models to explain properties
Cannot superimpose!!!!!
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Have a great Spring Break!!!
19
Not used