1 Chapter 7-1 Chemistry 481, Spring 2017, LA Tech Instructor: Dr. Upali Siriwardane e-mail: [email protected]Office: CTH 311 Phone 257-4941 Office Hours: M,W 8:00-9:00 & 11:00-12:00 am; Tu,Th, F 9:30 - 11:30 a.m. April 4 , 2017: Test 1 (Chapters 1, 2, 3, 4) April 27, 2017: Test 2 (Chapters (6 & 7) May 16, 2016: Test 3 (Chapters. 19 & 20) May 17, Make Up: Comprehensive covering all Chapters Chemistry 481(01) Spring 2017 Chapter 7-2 Chemistry 481, Spring 2017, LA Tech Chapter 7. An introduction to coordination compounds The language of coordination chemistry 7.1 Representative ligands 7.2 Nomenclature Constitution and geometry 7.3 Low coordination numbers 7.4 Intermediate coordination numbers 7.53Higher coordination numbers 7.6 Polymetallic complexes Isomerism and chirality 7.7 Square-planar complexes 7.8 Tetrahedral complexes 7.9 Trigonal-bipyrmidal and square-pyramidal complexes 7.10 Octahedral complexes 7.11 Ligand chirality Chapter 7-3 Chemistry 481, Spring 2017, LA Tech Chapter 7. An introduction to coordination compounds Thermodynamics of complex formation 7.12 Formation constants 7.13 Trends in successive formation constants 7.14 Chelate and macrocyclic effects 7.15 Steric effects and electron delocalization Chapter 7-4 Chemistry 481, Spring 2017, LA Tech Coordination compound A compound formed from a Lewis acid and Lewis base . A metal or metal ion acting Lewis acid (being an electron pair acceptor) and a atom or group of atoms with lone electron pairs Lewis base electron pair donor forms an adduct with dative or coordinative covalent bonds. Ni(ClO 4 ) 2 ( aq )+ 6NH 3 → [Ni(NH 3 ) 6 ](ClO 4 ) 2 ( aq ) The Lewis bases attached to the metal ion in such compounds are called ligands. Chapter 7-5 Chemistry 481, Spring 2017, LA Tech The coordination number (CN) CN of a metal ion in a complex is defined as the number of ligand donor atoms to which the metal is directly bonded . [Co(NH 3 ) 5 Cl] 2+ CN is 6, 1 chloride and 5 ammonia ligands each donating an electron pair. For organometallic compounds. An alternative definition of CN would be the number of electron pairs arising from the ligand donor atoms to which the metal is directly bonded . Chapter 7-6 Chemistry 481, Spring 2017, LA Tech 1) What is a coordination compound?
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May 17, Make Up: Comprehensive covering all Chapters
Chemistry 481(01) Spring 2017
Chapter 7-2Chemistry 481, Spring 2017, LA Tech
Chapter 7. An introduction to coordination compounds
The language of coordination chemistry 7.1 Representative ligands
7.2 Nomenclature
Constitution and geometry7.3 Low coordination numbers
7.4 Intermediate coordination numbers
7.53Higher coordination numbers
7.6 Polymetallic complexes
Isomerism and chirality7.7 Square-planar complexes
7.8 Tetrahedral complexes
7.9 Trigonal-bipyrmidal and square-pyramidal complexes
7.10 Octahedral complexes
7.11 Ligand chirality
Chapter 7-3Chemistry 481, Spring 2017, LA Tech
Chapter 7. An introduction to coordination compounds
Thermodynamics of complex formation
7.12 Formation constants
7.13 Trends in successive formation constants
7.14 Chelate and macrocyclic effects
7.15 Steric effects and electron delocalization
Chapter 7-4Chemistry 481, Spring 2017, LA Tech
Coordination compound
A compound formed from a Lewis acid and Lewis base.
A metal or metal ion acting Lewis acid (being an electron pair acceptor) and a atom or group of atoms with lone electron pairs Lewis base electron pair donor forms an adduct with dative or coordinative covalent bonds.
Ni(ClO4)2 (aq)+ 6NH3 → [Ni(NH3)6](ClO4)2 (aq)
The Lewis bases attached to the metal ion in such
compounds are called ligands.
Chapter 7-5Chemistry 481, Spring 2017, LA Tech
The coordination number (CN)
CN of a metal ion in a complex is defined as the
number of ligand donor atoms to which the metal
is directly bonded.
[Co(NH3)5Cl]2+
CN is 6, 1 chloride and 5 ammonia ligands each
donating an electron pair.
For organometallic compounds. An alternative
definition of CN would be the number of electron
pairs arising from the ligand donor atoms to which
the metal is directly bonded.
Chapter 7-6Chemistry 481, Spring 2017, LA Tech
1) What is a coordination compound?
2
Chapter 7-7Chemistry 481, Spring 2017, LA Tech Chapter 7-8Chemistry 481, Spring 2017, LA Tech
Coordination sphere
• Coordination sphere - the sphere around the
central ion made up of the ligands directly
attached to it. Primary and secondary coordination
sphere.
Chapter 7-9Chemistry 481, Spring 2017, LA Tech
Preparation of Complexes
• The figure at left shows cyanide ions (in the form of KCN), being added to an aq. solution of FeSO4.
• Since water is a Lewis base, the Fe2+ ions were originally in the complex [Fe(H2O)6]
2+
• The CN- ions are driving out the H2O molecules in this substitution reaction that
form the hexacyanoferrate(II) ion, [Fe(CN)6]4- .
[Fe(H2O)6]2+ + 6 CN- [Fe(CN)6]
4- + 6 H2O
Chapter 7-10Chemistry 481, Spring 2017, LA Tech
Various Colors of d-Metal Complexes
The color of the complex depends
on the identity of the ligands as
well as of the metal..
Impressive changes of color often
accompany substitution reactions.
Chapter 7-11Chemistry 481, Spring 2017, LA Tech Chapter 7-12Chemistry 481, Spring 2017, LA Tech
3
Chapter 7-13Chemistry 481, Spring 2017, LA Tech
Structures and symmetries
• Six-coordinate complexes are almost all
octahedral (a).
• Four-coordinate complexes can be tetrahedral (b)
or square planar (c).
• (Square planar usually occurs with d8 electron
configurations, such as in Pt2+ and Au3+.)
Chapter 7-14Chemistry 481, Spring 2017, LA Tech
Representing Octahedral Shapes
• Instead of a perspective drawing (a), we can
represent octahedral complexes by a simplified
drawing that emphasizes the geometry of the
bonds (b).
Chapter 7-15Chemistry 481, Spring 2017, LA Tech
Ligands
The Brønsted bases or Lewis base attached to the
metal ion in such compounds are called ligands.
These may be
Simple ions such as Cl–, CN–
Small molecules such as H2O or NH3,
Larger molecules such as H2NCH2CH2NH2
N(CH2CH2NH2)3
Macromolecules, EDTA and biological molecules
such as proteins.
Chapter 7-16Chemistry 481, Spring 2017, LA Tech
Representative Ligands and Nomenclature
Bidentate Ligands
Polydentate Ligands
• Some ligands can simultaneously occupy more than one binding site.
• Ethylenediamine (above) has a nitrogen lone pair at each end, making it bidentate. It is widely used and abbreviated “en”, as in [Co(en)3]
3+.
Chapter 7-17Chemistry 481, Spring 2017, LA Tech Chapter 7-18Chemistry 481, Spring 2017, LA Tech
Ethylenediaminetetraacetate Ion (EDTA)
• EDTA4- is another example of a chelating agent. It is hexadentate.
• This ligand forms complexes with many metal ions, including Pb2+, and is used to treat lead poisoning.
• Unfortunately, it also removes Ca2+ and Fe2+ along with the lead.
• Chelating agents are common in nature.
4
Chapter 7-19Chemistry 481, Spring 2017, LA Tech
Porphyrins and phthalocyanins
Chapter 7-20Chemistry 481, Spring 2017, LA Tech
Chelates• The metal ion in [Co(en)3]
3+ lies
at the center of the three
ligands as though pinched by
three molecular claws. It is an
example of a chelate,
• A complex containing one or
more ligands that form a ring
of atoms that includes the
central metal atom.
Chapter 7-21Chemistry 481, Spring 2017, LA Tech
Naming Transition Metal Complexes
• Cation name first then anion name.
• List first the ligands, then the central atom
• The ligand names are made to end in -O if negative
• Anion part of the complex ends in -ate
Eg. Cu(CN)64- is called the hexacyanocuprate(II) ion
• The ligands are named in alphabetic order
• Number of each kind of ligand by Greek prefix
• The oxidation state of the central metal atom
shown in parenthesis after metal name
• Briding is shown with ( -oxo)
Chapter 7-22Chemistry 481, Spring 2017, LA Tech
Some Common Ligand Names
Chapter 7-23Chemistry 481, Spring 2017, LA Tech
Names of Ligands (continued)
Chapter 7-24Chemistry 481, Spring 2017, LA Tech
Coordination Sphere Nomenclature
• Cationic coordination sphere
• -ium ending
Anionic coordination sphere
• -ate ending
5
Chapter 7-25Chemistry 481, Spring 2017, LA Tech
Examples
• [Co(NH3)4Cl2]Cl:
• dichlorotetramminecobalt(III) chloride
• [Pt(NH3)3Cl]2[PtCl4]:
di(monochlorotriammineplatinum(II))
tetrachloroplatinate(II).
• K3[Fe(ox)(ONO)4] :
• potassium tetranitritooxalatoferrate(III)
Chapter 7-26Chemistry 481, Spring 2017, LA Tech
Use bis and tris for di and tri
for chelating ligands• [Co(en)3](NO3)2 :
• tris(ethylenediamine)cobalt(II) nitrate
• [Ir(H2O)2(en)2]Cl3
• bis(ethylenediamine)diaquairidium(III)
chloride
• [Ni(en)3]3[MnO4] :
• Tris(ethylenediamine)nickel(II)
tetraoxomanganate(II)
Chapter 7-27Chemistry 481, Spring 2017, LA Tech
Naming
• [Cu(NH3)4]SO4
tetraaminecopper(II) sulfate
• [Ti(H2O)6][CoCl6]
hexaaquatitanium(III)
hexachlorocobaltate(III)
K3[Fe(CN)6]
• potassium hexacyanoferrate(III)
Chapter 7-28Chemistry 481, Spring 2017, LA Tech
2) Give the formula of following coordination
compounds
a)Dichlorobis(ethylenediammine)nickle
b) Potasium trichloro(ethylene)platinate(1-)
Chapter 7-29Chemistry 481, Spring 2017, LA Tech
c) Tetrakis(pyridine)platinum(2+)
tetrachloroplatinate(2-)
d) Tetraamminebis(ethylenediamine)
--hydroxo- -amidodicobalt(4+) chloride
Chapter 7-30Chemistry 481, Spring 2017, LA Tech
3) Give the names of following coordination
compounds
a) [Co(NH3)6]Cl3;
b) trans-[Cr(NH3)4(NO2)2]+ ;
c) K[Cu(CN)2] ;
d) cis-[PtCl2(NH3)2] ;
e) fac-[Co(NO2)3(NH3)3]Cl3
6
Chapter 7-31Chemistry 481, Spring 2017, LA Tech
The Eta(h) System of Nomenclature
• For for p bonded ligands number of
atoms attached to the metal atom is
shown by hn
(h5 -cyclopentadienyl) tricarbonyl manganese
tetracarbonyl (h3-allyl) manganese, Mn(C3H5)(CO)4
Chapter 7-32Chemistry 481, Spring 2017, LA Tech
Isomers
• Both structural and stereoisomers are found.
• The two ions shown below differ only in the
positions of the Cl- ligand, but they are distinct
species, with different physical and chemical
properties.
Chapter 7-33Chemistry 481, Spring 2017, LA Tech
4) What is the geometry and coordination
number of compounds in the problem above?
a) [Co(NH3)6]Cl3;
b) trans-[Cr(NH3)4(NO2)2]+ ;
c) K[Cu(CN)2] ;
d) cis-[PtCl2(NH3)2] ;
e) fac-[Co(NO2)3(NH3)3]Cl3
Chapter 7-34Chemistry 481, Spring 2017, LA Tech
5) Draw the formula and find the BITE of following
ligands.
a) 2,2'-bipyridine (bipy) ;
b) terpy;
c) cyclam;
d) edta;
Chapter 7-35Chemistry 481, Spring 2017, LA Tech Chapter 7-36Chemistry 481, Spring 2017, LA Tech
Ionization Isomers• These differ by the exchange of a ligand with an
anion (or neutral molecule) outside the
coordination sphere. [CoSO4(NH3)5]Br has the Br-
as an accompanying anion (not a ligand) and
[CoBr(NH3)5]SO4 has Br - as a ligand and SO42-as
accompanying anion.
7
Chapter 7-37Chemistry 481, Spring 2017, LA Tech
Ionization IsomersThe red-violet solution of
[Co(NH3)5Br]SO4 (left) has
no rxn w/ Ag+ ions, but
forms a ppt. when Ba2+ ions
are added.
The dark red solution of
[CoSO4(NH3)5]Br (right)
forms a ppt. w/ Ag+ ions,
but does not react w/ Ba2+
ions.
Chapter 7-38Chemistry 481, Spring 2017, LA Tech
Hydrate Isomers• These differ by an ex-change
between an H2O molecule and
another ligand in the
coordination sphere.
• The solid, CrCl3. 6H2O, may be
any of three compounds.
• [Cr(H2O)6]Cl3 (violet)
• CrCl(H2O)5]Cl2.H2O (blue-green)
• CrCl2 (H2O)4Cl.2H2O (green)
• Primary and secondary
coordination spheres
Chapter 7-39Chemistry 481, Spring 2017, LA Tech
Linkage Isomers
The triatomic ligand is the isothiocyanato, NCS-
. In (b) it is the thiocyanato, SCN-.
Other ligands capable or forming linkage isomers are
NO2- vs. ONO -
CN - vs. NC - .
(a) NSC-
ligand (the N is closest to the center); (b) SCN- ligand (S is closest the
center)
Chapter 7-40Chemistry 481, Spring 2017, LA Tech
Coordination Isomers
• These occur when one or more ligands are exchanged between a cationic complex and an anionic complex.
• An example is the pair [Cr(NH3)6][Fe(CN)6] and[Fe(NH3)6][Cr(CN)6].
Chapter 7-41Chemistry 481, Spring 2017, LA Tech
Stereoisomers• Ionization, hydrate, linkage, and coordination
isomers are all structural isomers.
• In stereoisomers, the formulas are the same. The atoms have the same partners in the coordination sphere, but the arrangement of the ligands in space differs.
• The cis- and trans- geometric isomers shown in next slide differ only in the way the ligands are arranged in space.
• There can be geometric isomers for octahedral and square planar complexes, but not for tetrahedral complexes.
Chapter 7-42Chemistry 481, Spring 2017, LA Tech
Square Planar Complexes
Geometric Isomers
• Properties of geometric isomers can vary greatly.
• The cis- isomer below is pale orange-yellow, has a
solubility of 0.252 g/100 g water, and is used for
chemotherapy treatment.
• The trans- isomer is dark yellow, has a solu-bility
of 0.037 g/100 g water, and shows no
hemotherapeutic effect.
8
Chapter 7-43Chemistry 481, Spring 2017, LA Tech
6) Describe the geometrical isomerism in following
compounds:
a) [Co(NH3)4Cl2]+ ;
b) [IrCl3(PPh3)3] ;
c) [Cr(en)2Cl2] ;
Chapter 7-44Chemistry 481, Spring 2017, LA Tech
cis and trans-PtCl2(NH3)2
Chapter 7-45Chemistry 481, Spring 2017, LA Tech
Trans Effect & Influence
Chapter 7-46Chemistry 481, Spring 2017, LA Tech
Preparation Geometrical Isomers
Chapter 7-47Chemistry 481, Spring 2017, LA Tech
Optical IsomerismThe two complexes at left are mirror
images. (The gray rectangle represents
a mirror, through which we see
somewhat darkly.)
No matter how the complexes are
rotated, neither can be superimposed
on the other.
Note only four of the six ligands are
different.
Chapter 7-48Chemistry 481, Spring 2017, LA Tech
Combined Stereoisomerisms• Both geometrical and optical isomerism can
occur in the same complex, as below. The trans-
isomer is green.
• The two cis- isomers, which are optical isomers of
each other, are violet.
9
Chapter 7-49Chemistry 481, Spring 2017, LA Tech Chapter 7-50Chemistry 481, Spring 2017, LA Tech
Identifying Optical IsomerismIf a molecule or ion belong to a point group with a Sn
axis is not optically active
Chapter 7-51Chemistry 481, Spring 2017, LA Tech Chapter 7-52Chemistry 481, Spring 2017, LA Tech
Molecular Polarity and Chirality
Polarity• Polarity:Only molecules belonging to the point
groups Cn, Cnv and Cs are polar. The dipole
moment lies along the symmetry axis
formolecules belonging to the point groups Cn and
Cnv.
• Any of D groups, T, O and I groups will not be
polar
Chapter 7-53Chemistry 481, Spring 2017, LA Tech
ChiralityOnly molecules
lacking a Sn axis
can be chiral.
This includes mirror
planes
and a center of
inversion as
S2=s , S1=I and Dn
groups.
Not Chiral: Dnh,
Dnd,Td and Oh.
Chapter 7-54Chemistry 481, Spring 2017, LA Tech
Optical Activity
10
Chapter 7-55Chemistry 481, Spring 2017, LA Tech
Reactions of Metal Complexes
Formation constants
– the chelate effect
– Irving William Series
– Lability
Chapter 7-56Chemistry 481, Spring 2017, LA Tech
7) Pick the chiral compounds among the
following:
a) [Co(en)3]3+ ;
b) cis-[Cr(en)2Cl2] ;
c) c) trans-[Cr(en)2Cl2] ;
Chapter 7-57Chemistry 481, Spring 2017, LA Tech
Formation of Coordination Complexes
typically coordination compounds are more labile or
fluxional than other molecules X is leaving group
and Y is entering group
MX + Y MY + X
One example is the competition of a ligand, L for a
coordination site with a solvent molecule such as
H2O
[Co(OH2)6]2+ + Cl- [Co(OH2)5Cl]+ + H2O
Chapter 7-58Chemistry 481, Spring 2017, LA Tech
Formation Constants
Consider formation as a series of formation
equilibria:
Summarized as:
Chapter 7-59Chemistry 481, Spring 2017, LA Tech
Typically: Kn>Kn+1
Expected statistically, fewer coordination sites
available to form MLn+1
eg sequential formation of Ni(NH3)n(OH2)6-n 2+
Values of Kn
Chapter 7-60Chemistry 481, Spring 2017, LA Tech
Breaking the Rules
Order is reversed when some electronic or chemical
change drives formation
Fe(bipy)2(OH2)22+ + bipy Fe(bipy)3
2+
jump from a high spin to low spin complex
Fe(bipy)2(OH2)2 t2g4eg2 high spin
Fe(bipy)3 t2g6 low spin
11
Chapter 7-61Chemistry 481, Spring 2017, LA Tech Chapter 7-62Chemistry 481, Spring 2017, LA Tech
Chapter 7-63Chemistry 481, Spring 2017, LA Tech
Irving William Series
Values of log Kf for 2+ ions including transition
metal species Lewis acidity (acceptance of e-)
increases across the per. table, thus forming more
and more stable complexes for the same ligand
system
Kf series for transition metals:
Mn2+< Fe2+ < Co2+ < Ni2+ < Cu2+ >Zn2+
Chapter 7-64Chemistry 481, Spring 2017, LA Tech
Irving William Series
Chapter 7-65Chemistry 481, Spring 2017, LA Tech
Bonding and electronic structure
Bonding Theories of Transition Metal Complexes
• Valance Bond Theory
• Crystal Field Theory
• Ligand Field Theory or Molecular Orbital Theory
Chapter 7-66Chemistry 481, Spring 2017, LA Tech
Valance Bond Theory
”Outer orbital" (sp3d2) and ”Inner orbital" (d2sp3)
[CoF6]3- - Co3+ : d6
[Co(NH3)6]3+ - Co3+ : d6
12
Chapter 7-67Chemistry 481, Spring 2017, LA Tech
Spectrochemical Series for Ligands
• It is possible to arrange representative ligands in