Chapter 9.
Coordination Chemistry I:
Structures and Isomers
Synthetic Chemisty
Organic Chemistry
Inorganic Chemistry
C, O, H, N Chemistry
Main group
s, p blocks
Alloys
Thin films
Transition metals
d block
Rare earth
f block
Biological molecules Catalysts
1
Definitions
Transition metal complex (Coordination compound)
L4
L3
L1
A metal atom, ion, surrounded by a set
of ligands
More specifically (or mostly), a
transition metal cation surrounded by
neutral molecules or anions with a
definite geometry.
L2
Definitions
:
:L1
L2
electron donor, Lewis Base, nucleophile (org. term)
electron acceptor, Lewis acid, electrophile (org. term)
:
L3 :
Any molecule or ion than has at least
one electron pair that can be donated
to the cetral metal atom ot ion. (can
exist independently)
:Cl:
:
:
Ligand
L4
:NH3
2
Definitions
Organometallic compound
L4
L3
C
A transition metal surrounded in part or
entirely by organic groups in which a
carbon atom is directly bonded to the
metal ion.
C
Types of ligands
monodentate ligands
ambidentate
3
Types of ligands
multidentate amine ligands
bidentate
tridentate
tetradentate
hexadentate
chelate
Types of ligands
multidentate ligands
bidentate
tridentate
tetradentate
hexadentate
chelate
4
Nomenclatures of complexes
1. cation-anion (same as in salts)
[Ag(NH3)2]Cl : diamminesilver(I) chloride
K3[Fe(CN)6]: potassium hexacyanoferrate(III)
2. complexes (or inner coordination sphere)
formula: metal-ligand
nomenclature: ligand-metal
[Cu(NH3)4]SO4 : tetraamminecopper(II) sulfate
[Co(NH3)6]Cl3: hexaamminecobalt(III) chloride
3. # of ligands
2
3
4
5
6
di
bis
tri
tris
tetra terakis
penta pentakis
hexa hexakis
7 hepta heptakis
8 octa
octakis
9 nona nonakis
10 deca decakis
[Co(en)2Cl2]+ : dichlorobis(ethylenediamine)cobalt(II)
[Fe(bipy)3]2+ : tris(bipyridine)iron(II)
Nomenclatures of complexes
4. ligand: alphabetical order of ligands (not prefix)
many exceptions
[Co(NH3)4Cl2]+: tetraamminedichlorocobalt(III)
Pt(NH3)BrCl(CH3NH2): amminebromochloromethylamineplatinum(II)
5. anionic ligand : -o suffix neutral ligand: usual name
water: aqua
NH3: ammine
6. metal oxidation number:
Stock system: Roman numeric in parenthese
Ewing-Bassett system: charge on the coordination sphere in parenthese
[Pt(NH3)4]2+: tetraammineplatinum(II)
tetraammineplatinum(2+)
[PtCl4]2-: tetrachloroplatinate(II) tetrachloroplatinate(2-)
hexachloroplatinate(2-)
[PtCl6]2-: hexachloroplatinate(IV)
7. anionic complexes: -ate suffix on metal
special names: iron(Fe) ferrate
silver(Ag) argentate
gold(Au) aurate
lead(Pb) plumate
tin(Sn) stannate
5
Nomenclatures of complexes
7. geometrical isomers: cis-, trans-
mer-, fac-
[Pt(NH3)2Cl2]: cis-, trans-diamminedichloroplatinum(II)
8. optical isomers: Λ-, ∆9. bridging ligand: µ-
tris(tetraammine-µ-dihydroxocobalt)cobalt(6+) bromide
Two most important concepts
in transition-metal complex chemistry
Oxidation states of metals
Sc
V
Cr
Mn
Fe
Co
Ni
Cu
≤0
o
o
o
o
o
o
o
+1
o
o
o
o
o
o
O
o
O
o
O
O
O
O
O
o
o
O
o
O
O
o
o
O
o
o
O
o
o
o
O
o
o
△
o
O
o
o
+2
+3
+4
+5
+6
+7
O
Ti
Coordination numbers and geometries
Zn
O
O
O : most common
6
Two most important concepts
in transition-metal complex chemistry
Oxidation states of metals
Coordination numbers and geometries (structures)
CN
Geometries
Factors
1
rare
1.
2.
3.
4.
5.
2
Linear (rare)
3
Trigonal-plane
4
Tetrahedron, Square-plane
5
Trigonal bipyramid, Square pyramid
6
Octahedron, Triogonal prism
7
Pentagnal bipyramid, Capped trigonal prism,
Capped octahedron
8≤
Known up to 16 CN
Number of bonds
VSEPR arguments
Occupancy of d-orbitals (LFT)
Steric inference by large ligands
Crystal packing effects
Coordination Numbers and Structures
CN = 1 : very rare
Tl(I): sterically hindered
VO2+ : as a transient species
7
Coordination Numbers and Structures
CN = 2 : rare, linear (D∞h)
mostly d10 compounds
None d10 complexes also exist.
ex) Mn(II) with bulky ligands
Coordination Numbers and Structures
CN = 3 : rare, trigonal plane (D3h)
HgI3- (d10)
Complexes with bulky ligands
8
Coordination Numbers and Structures
CN = 4 : tetrahedron (Td), square plane (D4h)
Td: very common
D4h: d8 such as Ni(II), Pt(II), Pd(II)
and others
(Td at 75oC)
at 25oC
Coordination Numbers and Structures
CN = 4 : tetrahedron (Td), square plane (D4h)
Td
M
M
D4h
∆E is not big
[NiBr2(P(C6H5)2(CH2C6H5)2]
: both Td and D4h in the same
crystal
(Td at 75oC)
at 25oC
[Ni(PR3)2X2]
9
Coordination Numbers and Structures
CN = 5 : trigonal bipyramid (D3h), square pyramid (C4v)
D3h and C4h coexist
in crystal
4+
O
V
F
F
F
F
V(IV): d1
V(V):d0
Coordination Numbers and Structures
CN = 5 : trigonal bipyramid (D3h), square pyramid (C4v)
CO
Fe(CO)5
180.6 pm
CO
Fe
CO
CO
183.3 pm
CO
crystal
13C NMR in solution
Fluxional behavior (Berry pseudorotation)
∆E between D3h and
C4v is very small.
10
Coordination Numbers and Structures
CN = 6 : octahedron (Oh)
octahedron (Oh): very common
variations of Oh
tetragonal elongation
ex) Cu(II) : d9
tetragonal compression
ex) Ti(III) : d1
D4h
Coordination Numbers and Structures
CN = 6 : octahedron (Oh), trigonal prism (D3h)
variations of Oh
trigonal elongation
: trigonal antiprism (D3d)
and 60o rotation
: trigonal prism (D3h)
usually with three bidentate ligands
11
Coordination Numbers and Structures
CN = 7 : pentagonal bipyramid (D5h)
capped trigonal prism, capped octahedron
Coordination Numbers and Structures
CN > 8 :
12
Multimetallic Complexes
metal clusters: with direct M-M bonds
cage complexes: without direct M-M bonds
don't care much about the terms
in real world
Multimetallic Complexes
Metal-sulfur clusters in Nitrogenase
N2 + 8H+ + 8e+ 16MgATP
2NH3 + H2 + Pi
+ 16MgATP
13
Isomers
Structural Isomers
(different bonds)
Stereo Isomers
(identical bonds)
Hydrate isomers
Ionization isomers
Linkage isomers
Coordination isomers
Geometrical isomers
Optical isomers
Isomers
Hydrate isomers : having water as either a ligand or an added
part of of the crystal structure
3+
+
OH2
H2O
Cr
H2O
Cl
OH2
H2O
3Cl-
OH2
H2O
2+
OH2
violet
OH2
Cr
Cl
H2O
H2O
OH2
Cr
OH2
OH2
OH2
Cl
Cl2H2O
green
2ClH2O
Tetraaquadichlorochromium(III)
chloridedihydrate
blue-green
14
Isomers
Ionization isomers : exchange of ions inside and outside
coordination sphere
2+
+
Br
NH3
NH3
NH3
Co
NH3
SO4
SO42-
NH3
NH3
NH3
NH3
Co
Br-
NH3
NH3
Isomers
Coordination isomers : occurs in compound containing both
anion and cation complexes
[Co(en)3]3+[Cr(CN)6]3[Cr(en)3]3+[Co(CN)6]3-
[Pt(NH3)4]2+[PtCl6]2[Pt(NH3)4Cl2]2+[PtCl4]2-
15
Isomers
Linkage isomers : compounds containing ambidentate ligand
Intramolecular rearrangement
(kinetic and 18O labeling exprt)
Isomers
Geometrical isomers
CN=4
[PtBrCl(PR3)2]
31P NMR
1 peak
31P NMR
2 peaks
16
Isomers
Geometrical isomers
+
CN=6
+
Cl
MX4Y2
Cl
NH3
NH3
Co
NH3
NH3
NH3
NH3
Cl
cis
+
+
O2N
O2N
NH3
NH3
trans
MX3Y3
Cl
Co
NH3
NH3
Co
NH3
O2N
NO2
O2N
Co
NH3
NO2
NH3
NH3
fac (facial)
mer (meridional)
Isomers
Geometrical isomers
CN=6
and many others
17
Isomers
Optical isomers
Chiral complex: complex not superimposable on its own mirror image
Optically active: rotating the plane-polarized light
Enantiomers: mirror-image partners
Molecules with Sn Æ no chirality (i = S2, σ = S1)
Isomers
Isomers of Ma2bcde (Oh)
a
a
b
e
a
b
c
d
e
c
d
b
d
c
e
a
a
a
a
a
a
a
e
a
d
c
c
15 stereoisomers
(6 pairs of enantiomers)
a
a
d
e
e
a
c
c
d
e
d
b
b
b
b
a
a
a
a
a
e
a
b
d
b
e
c
a
d
c
e
c
a
b
b
c
e
d
d
18
Isomers
Optical isomers
Complexes with chelate rings (Λ, ∆)
Handness
Isomers
Optical isomers
Complexes with chelate rings (Λ, ∆)
C3
C3
19
Isomers
Complexes with chelate rings (Λ, ∆)
(CoEDTA-)
O
Co
N
O
O
O
O
N
N
O
O
N
O
O
O
O
O
N
O
Λ
N
O
N
O
N
O
N
O
Co
N
O
N
O
Co
N
O
N
O
Co
O
O
N
O
O
O
O
O
Optical isomers
Λ
∆
Λ∆Λ-(ethylenediaminetetraacetato)cobaltate(III)
= ΛΛ∆"
= ∆ΛΛ"
Isomers
Complexes with chelate rings (Λ, ∆)
(CoEDTA-)
N
O
N
O
O
N
O
O
∆
O
O
O
N
O
O
O
N
N
Λ
O
Optical isomers
∆
Λ∆∆-(ethylenediaminetetraacetato)cobaltate(III)
= ∆Λ∆"
= ∆∆Λ"
20
Isomers
Optical isomers
Ligand ring conformation (λ, δ)
Many chelate rings are not planar, they can have different conformations in different molecules.
Ex) ethylenediamine (en) :
1st line – conneting atoms bonded to the metal
2nd line – conneting two carbon atoms
1st Æ 2nd : counterclockwise Æ λ
1st Æ 2nd : clockwise Æ δ
[Co(en)3]3+
∆λλλ-[Co(en)3]3+
more stable in calculation
∆δδδ-[Co(en)3]3+
actually, in solution λ ÅÆ δ intercoversion
in soln, δδλ is most abundant in Λ form
Isomers
Optical isomers
Ligand ring conformation (λ, δ)
Chiral structures of trans-[CoX2(trien)]+
δδ
δλ
λλ
only 1 choice of λ
21
Isomers
Optical isomers
Chirality on ligands (R,S)
Cahn-Ingold-Prelog Rules
S (sinister)
R (rectus)
Ligand precedence rules
1. Ligands of the higher atomic number precede those with lower ones, e.g. Br precedes Cl (Br>Cl).
2. For ligands with the same type of atoms linked to the center C, the precedence is determined based on the atomic numbers of
ligands in the next sphere, e.g. ligand with C-O sequence precedes C-C. If no difference is detected, the determination is based
on the distinction in the next spheres, and search is continued until the difference is detected.
3. The coordination number of non-hydrogen atoms is assumed to be 4, i.e. atoms bonded with multiple bonds are considered to
be bonded to multiple atoms, e.g. carbonyl carbon is treated as if it was bonded to two oxygen atoms, and carboxyl carbon as if
it was bonded to three oxygens (these are then called phantom atoms). Ligand duplication is also necessary in the cases of cyclic
systems.
4. Ligands of the same atomic number, but a higher atomic mass precede those with a lower atomic mass, e.g. D precedes H
(D>H). This criterion applies only after the previous ones were exhausted.
5. For compounds where only configurational (not constitutional) differences between ligands are detected, the following rules
apply: a. The olefinic ligand that has the chiral center and another ligand on the same side of the double bond (cis) precedes the
one with the trans-configuration. b. Ligands with R,R or S,S precede R,S or S,R. c. R precedes S.
Isomers
Optical isomers
Chirality on ligands (R,S)
[CoX2(trien)]+
N
N
X
N
geometrical
N
N
N
N
Co
Co
N
X
X
N
N
X
Co
X
N
N
X
Co
N
N
N
N
X
X
α
β
Λ
∆
optical
(chirality on chelate-ring conformation)
Λ
∆
RR
optical
(chirality on ligands)
SS
RR
SS
22
Isomers
Optical isomers (Identification : CD and ORD)
Isomers
Optical isomers (Identification : CD and ORD)
Plane-polarized light
= right circularly polarized light
+ left circularly polarized light
http://www.enzim.hu/~szia/cddemo/edemo0.htm
23
Isomers
Optical isomers (Identification : CD and ORD)
Circular dichroism (CD) is the absorption difference
between left and right circularly polarized light at a given
wavelength. => absorptive
http://www.enzim.hu/~szia/cddemo/edemo0.htm
Optical rotary dispersion (ORD) : The variation of
optical rotation as a function of wavelength. (Cotton effect
for a single band) => dispersive
Isomers
Optical isomers (Identification : CD and ORD)
Circular dichroism (CD) is the absorption difference
between left and right circularly polarized light at a given
wavelength. => absorptive
CD of tris-(S-alaninato) cobalt(III)
Optical rotary dispersion (ORD) : The variation of
optical rotation as a function of wavelength. (Cotton effect
for a single band) => dispersive
24