OUTLINE
General properties of metal complexes and ligands
Basic definitions
Inner sphere vs outer sphere of coordination
Electronegativity
Formal oxidation state and dn configuration
Hard vs soft acids and bases, small vs large atoms and ions
Structure of ligands : Lewis structures, VSEPR
Hapticity
Denticity
Spectator vs actor ligands, innocent vs non-innocent ligands
Coordination chemistry: Structure
Coordination number and geometry
Nuclearity
Isomerism
Nomenclature
Werner’s complexes - Isolation
Alfred
Werner
1866
-‐
1919
CoCl3
.
6NH3
orange-‐yellow
Luteo
CoCl3
.
5NH3
purple
Purpureo
CoCl3
.
4NH3
green
Praseo
CoCl3
.
4NH3
violet
Violeo
CoCl3
.
3NH3
green
Praseo
… COMPLEXES!
http://www.nobelprize.org/nobel_prizes/chemistry/laureates/1913/#
Werner’s complexes
Reactivity and coordination number
Experimental
observaEons:
CoCl3
.
6NH3
+
xs
AgNO3
give 3
AgCl(s)
CoCl3
.
5NH3
+
xs
AgNO3
give
2
AgCl(s)
CoCl3
.
4NH3
+
xs
AgNO3
give
1
AgCl(s)
CoCl3
.
3NH3
+
xs
AgNO3
give
no
reacEon
Werner’s
conclusion:
There
are
two
types
of
chloride
ions
(coordinated
and
uncoordinated)
and
a
constant
coordina9on
number
of
6
[Co(NH3)6]Cl3
+
3AgNO3
→
[Co(NH3)6][NO3]3
+
3AgCl
[Co(NH3)5Cl]Cl2
+
2AgNO3
→
[Co(NH3)5Cl][NO3]2
+
2AgCl
[Co(NH3)4Cl2]Cl
+
AgNO3
→
[Co(NH3)4Cl2]NO3
+
AgCl
[Co(NH3)3Cl3]
+
AgNO3
→
no
reacEon
Werner’s complexes - Isolation
Alfred
Werner
1866
-‐
1919
CoCl3
.
6NH3
orange-‐yellow
Luteo
CoCl3
.
5NH3
purple
Purpureo
CoCl3
.
4NH3
green
Praseo
CoCl3
.
4NH3
violet
Violeo
CoCl3
.
3NH3
green
Praseo
[Co(NH3)6]Cl3
[Co(NH3)5Cl]Cl2
[Co(NH3)4Cl2]Cl
[Co(NH3)4Cl2]Cl
… COMPLEXES!
[Co(NH3)3Cl3]
Werner’s complexes
Isomer counting and geometry assignment
Werner’s complexes
Isomer counting and geometry assignment
MA4B2
planar
trigonal
prismatic
octahedral
Only
the
octahedral
spa9al
arrangement
accounts
for
the
presence
of
two
isomers
for
CoCl3
.
4NH3
Werner’s complexes
Isomer counting and geometry assignment
Only
the
octahedral
spa9al
arrangement
accounts
for
the
presence
of
two
isomers
for
CoCl3
.
4NH3
Note: There is a NEGATIVE EVIDENCE argument in Werner’s conclusion!
Werner’s complexes
CoCl3
.
6NH3
orange-‐yellow
Luteo
CoCl3
.
5NH3
purple
Purpureo
CoCl3
.
4NH3
green
Praseo
CoCl3
.
4NH3
violet
Violeo
cis
violeo trans
praseo
COORDINATION COMPOUNDS
coordination number (CN) the number of ligand bonds to the central metal or
the number of central metal coordination sites
occupied
Available range of CN for transition metals: 1 - 12
factors that govern coordination numbers include:
size and charge of the central metal
(large radii, high oxidation states favor higher CN)
steric interactions of the ligands
(bulky, charged ligands favor lower CN)
electronic interactions between central metal and ligands
(geometry and d configuration are linked to type of ligand bonding)
COORDINATION CHEMISTRY OF THE d-BLOCK ELEMENTS
ligands arrange themselves in the lowest energy structure, but there are additional factors
besides electron pair repulsion that govern the shape of coordination compounds
valence shell electron pair repulsion is often NOT the primary determinant of shape for
coordination compounds, with a few exceptions:
d0 Ti4+, Sc3+,Y3+, Zr4+, …
d5 high spin Mn2+ and Fe3+
d10 Ni0, Pd0, Cu+, Ag+, Zn2+, Cd2+, …
COORDINATION NUMBERS AND STRUCTURES
CN 1 gas phase NaCl
CN 2 linear 180°
L–M–L [H3N – Ag – NH3]+ Ag(NH3)2+ HgCl2
rare CN – d10 metals
CN 3 trigonal planar 120°
L SR2 Cu(SR2)3
R 2S Cu Pt(PPh3)3
SR2
M
L L
rare CN – bulky ligands and/or d10 metals
CN
4
square
planar
90,
180°
D4h
L
L
Cl Cl 2- PtCl42-‐
Pt
M
Ni(CN)42-‐
Cl Cl
L L
tetrahedral
109.5°
Td
L Cl -
CrO42-‐
Fe CoCl42-‐
M Cl
L Cl
L Cl
L
intermediate
or
distorted
structures
exist,
and
interconversion
through
a
D4h
Td
equilibrium
process
can
occur
COORDINATION NUMBER 4
tetrahedral complexes are favored by small metal centers and/or large/charged ligands
COORDINATION NUMBER 4
Square planar complexes are favored by d8 configuration and, in the case of 1st row TM,
by small ligands
CN 5 trigonal bipyramidal 90, 120, 180°
(TBP)
Fe(CO)5
L Ni(CN)53-
L
L M
L
L
square pyramidal 90, 180°
(SP)
Ni(CN)53-
L
L L
M
L L
both structures of [Ni(CN)5]3- exist in the [Cr(en)3][Ni(CN)5] unit cell
CN 5 TBP interconversion
pseudorota9on
(Berry
rearrangement)
through
a
SP
intermediate
leads
to
TBP
interconversion,
due
to
the
small
energy
difference
between
the
structural
extremes
A1 A1 E1
E1
E1 A1
E M E M M
3
3 E3
E2 A2
E2
A2
A2 E2
although
structures
can
oVen
be
determined,
soluEon
exchange
is
oVen
too
fast
for
the
NMR
Eme
scale
(≤
ms)
except
at
low
temperatures
Examples
of
fluxional
molecules:
Fe(CO)5
only
one
13C
resonance
PF5
only
one
19F
resonance
CN 5 TBP vs SP
only
a
small
energy
difference
exists
between
the
structural
extremes
CN
6
octahedral
90,
180°
the
most
common
and
thus
most
important
CN
L
TiCl64-‐
L
L
W(CH3)6
M
L L
L
L
L
L
Co(en)33+
M
L
L
chiral
L
CN 6 Oh D3
L L
L L L L
M M
L L L L
L L
nearly all six coordinate complexes approach or possess octahedral
structures rather than the alternative trigonal prismatic (D3h) structure
D3h
COMMON COORDINATION NUMBERS AND GEOMETRIES
CN
2
linear
L
CN
3
L M trigonal
T-‐shaped
L
CN
4
square
tetrahedral
planar
CN
5
trigonal
square
equatorial
bipyramidal
pyramidal
CN
6
octahedral
Structural distorsions
structures rigorously adhering to the highest possible symmetry
for a given MLn complex are rare, even with identical ligands
distortions to lower symmetries are common
ML5 equilibrium between TBP and SP – nonstatic
ML6 Oh to D4h by elongation or compression of trans ligands
L
L
M
L common distortion sources
L L
L L ligand stereochemistry
L
M
L
crystal packing
L
L L Jahn-Teller effect
L
L L
M
fluxional or nonrigid structures
L L
L
Higher coordination numbers: 7 – 12
complexes with CNs exceeding six often contain third series or inner transition metals
Higher coordination numbers: 7 – 12
complexes with CNs exceeding six often contain third series or inner transition metals
CN
7
pentagonal
bipyramidal
L
L
L
L M VF73-‐
L
L
L
monocapped
octahedral
TaF72-‐
monocapped
trigonal
prism
NbF72-‐
CN
8
cubic
L L
L
each
ligand
is
projected
to
the
M
L
corners
of
a
cube
–
rare
in
L L
coordina9on
compounds,
L L
common
in
laQces
square
an9prisma9c
L
L
L
one
half
of
cube
twisted
45°
L M L
TaF83-‐
L L
L
trigonal
dodecahedral
Mo(CN)83-‐
L L
square
an9prisma9c
and
L
M
L
dodecahedral
structures
oRen
L L are
of
similar
energy
L L
CN
9-‐12
common
only
for
the
lanthanides
and
ac9nides
CN in close-packed lattices
metals in close-packed lattices can have CN of 12
close-‐packed
labces
result
in
formaEon
of
both
octahedral
(CN
6)
and
tetrahedral
(CN
4)
holes
CN in close-packed lattices
Binary solids
ions
in
close-‐packed
labces
oVen
have
a
CN
of
6
(e.g.,
NaCl)
or
8
(e.g.,
CsCl),
depending
on
the
relaEve
size
of
the
ions
CN in close-packed lattices
In
solids
of
the
general
formula
ABO3,
CN
of
12
for
A
and
CN
of
6
for
B
Common vs uncommon coordination numbers
CN range from 1 to 12, but the most common ones are 4, 6, 8 and 12, with 6 being most
prevalent
Why are certain CN more common?
They represent a balance between stabilization due to bond formation and destabilization due to
ligand-ligand repulsion
if a TM complex of CN 3, 5 or 7 increases its CN by 1, or if a CN 10 complex
increases its CN by 2, the increase in the total bond energy of the complex is
not generally accompanied by a large change in the M – L bond distances
the large gain in total bond energy compensates for the
increase in interligand repulsion
Common vs uncommon coordination numbers
CN range from 1 to 12, but the most common ones are 4, 6, 8 and 12, with 6 being most
prevalent
Why are certain CN more common?
They represent a balance between stabilization due to bond formation and destabilization due to
ligand-ligand repulsion
if a complex of CN 5, 7 or 9 decreases its CN by 1, the loss in total bond energy
is often accompanied by a relatively large change in M – L bond distances, with
ligands approaching the metal center more closely
the decrease in interligand repulsion compensates for the
decrease in total bond energy and ligands come closer to the metal center
Common vs uncommon coordination numbers
CN range from 1 to 12, but the most common ones are 4, 6, 8, and 12 with 6 being most
prevalent
Why are certain CN more common?
They represent a balance between stabilization due to bond formation and destabilization due to
ligand-ligand repulsion
Complexes of CN other than 4, 6, 8 or 12 tend to lose or gain ligands
relatively easily and thus are relatively rare
Uncommon CN tend to be unstable to bond formation (low ligand repulsion)
or bond cleavage (high ligand repulsion)
Generalizations on coordination numbers
high coordination numbers
large metal size and/or high oxidation states; small, hard ligands
low coordination numbers
small metal size and/or low oxidation states; large, soft ligands
metal-metal bonding
multiple ligand-metal bonding
NUCLEARITY and METAL CLUSTERS
[MxLn]z z = complex charge x = nuclearity
mononuclear [MLn]z
binuclear [M2Ln]z
trinuclear [M3Ln]z
etc.
BINUCLEAR SPECIES
BRIDGING LIGANDS
µ-Cl
terminal
µ3-Cl
TRINUCLEAR SPECIES
TETRANUCLEAR SPECIES
HEXANUCLEAR SPECIES
High nuclearity
[Mn84O72(O2CMe)78(OMe)24(MeOH)12(H2O)42(OH)6]·xH2O·yCHCl3
A. J. Tasiopoulos, A.Vinslava, W. Wernsdorfer, K. A. Abboud, G. Christou Angew. Chem. Int. Ed. 2004, 43, 2117
Isomerism
Isomers (from Greek, ‘sharing equally’) are compounds
with
the
same
formula
but
a
different
arrangement
of
atoms
in
the
molecule
(and
different
properEes)
Stereoisomers are molecules with the same empirical formula and atom-to-atom bonding
sequence but differing in atomic spatial arrangements.
Isomers of this type can be
geometric isomers (diastereoisomers)
or
optical isomers (enantiomers)
Structural isomers are molecules with the same empirical formula but different atom-to-
atom bonding sequences (connectivity)
What
type
of
isomers
are
related
tetrahedral
and
square
planar
complexes?
cis/trans isomerism in square planar complexes
DIASTEREOMERS
-‐
CN
4
Pt(n-‐Pr3P)2Cl2
Cl P(n-Pr)3 Cl P(n-Pr)3
Pt Pt
Cl P(n-Pr)3 (n-Pr) 3P Cl
cis trans
NiCl42-‐
Cl
Cl Cl
Ni Ni
Cl Cl
Cl Cl Cl
K+
salt
Ph4As+
salt
Note:
In
soluEon
NiCl42-‐
is
tetrahedral
DIASTEREOMERS
-‐
CN
4
No
isomers
for
MA4
and
MA3B
DIASTEREOMERS
-‐
CN
4
ENANTIOMERS
-‐
CN
4
DIASTEREOMERS
–
CN
6
octahedral
DIASTEREOMERS
–
CN
6
octahedral
CN 6 Geometric isomers
cis/trans
isomerism
in
[CoCl2(NH3)4]+
facial/meridional
isomerism
in
CoCl3(NH3)3
ENANTIOMERS
–
CN
6
octahedral
ENANTIOMERS
–
CN
6
octahedral
nonsuperimosable
mirror
images
Structural
labels:
clockwise
rotaEon
(Δ, delta)
counterclockwise
rotaEon
(Λ, lambda)
Experimental
labels
for
polarized
light
rotaJon:
clockwise
rotaEon
–
d-‐isomer
or
(+)-‐
isomer
counterclockwise
rotaEon
–
l-‐isomer
or
(–)-‐isomer
ENANTIOMERS
–
CN
6
octahedral
[Mn(acac)3]
enanFomers
STEREOISOMERS
–
CN
6
octahedral
