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NOMENCLATURE IUPAC RULES
Some metals in anions have special names B
Borate Pb Plumbate Au Aurate Sn Stannate Ag
Argentate Cu Cuprate Fe Ferrate
Cr2O(NH3)104
A Roman numeral or a zero in parantheses is used
to Indicate the oxidation state of the central
metal atom
If more than one ligand is present in the
species,then the ligands are named in
alphabetical order. Ligand that bridge two metal
centers are denoted by a prefix ?- added to the
name of the relevant ligand, as
in ?-oxo-bis(pentamminechromium)(III)
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• Practice problem
• Name the following coordination complexes.
• K4Fe(CN)6
• Fe(acac)3
• Cr(en)3Cl3
• Cr(NH3)5(H2O)(NO3)3
• Cr(NH3)4Cl2Cl
• K3Cr(C2O4)3.3H2O
• Re2Cl8 2-

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Answers Potassium hexacyanoferrate(II) Tris(acet
ylacetonato)iron(III) Tris(ethylenediamine)chromi
um(III)trichloride pentammineaquachromium(III)tri
nitrate Tetramminedichlorochromate(III)chloride
Potassium tris(oxalato)chromate(III)trihydrate
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Ambidentate ligands A ligand with different
potentials donors atoms is called ambidentate. An
ambidentate ligand gives rise to the possibility
of linkage isomerism. An example is the
thiocyanate ion (NCS)-which can attach to a
metal Atom either by the N atom, to give
isothiocyanato copm. Or by the S ato, to give
thiocyanato comp.Another example of an
ambidentate Ligand NO2- as M-NO2 the ligand is
nitro and as M-ONO- it is nitrito.
Yellow isomer Co(NO2)(NH3)2
Red isomer Co(NO2)(NH3)2
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The degree of strain in a che- lating ligands is
often express in terms of bite angle which can
cause distortion of standart structure
An example of chelate ligand
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• CONSTITUTION
• Three factors determine the coordination of a
  complex
• The size of the central atom or ion
• The steric interactions between the ligands
• Electronic interaction

The large radii of atoms and ions in Periods 5
and 6 favor higher coordination numbers for the
complexes of these elements. For si miliar steric
reasons, bulky ligands often result in low
coordination numbers.The high C.N. Are common on
the left of a row of the d- blok. Lower C.N. Are
found on the right of the block
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Low coordination number
Two-coordinate complexes are found for Cu and Ag
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Hg(CH3)2
Ag(NH3)2
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Four coordination
Tetrahedral copmlexes of Td symmetry are favored
higher C.N. when the central atom is small and
the ligands are large( such as Cl-,Br- and
I-),They are common for oxoanions of metal atoms
on the left of the d-blok in high oxidation
states,and for haloge- no complexes of M2 ions
on the right of the 3d series.
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CoBr42-
NiCl42-
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Square planar complexes in the first row of the
d-block are typi- cally observed for metal atoms
and ions with d8 configurations and ?-acceptor
ligands four-coordinate d8 complexes of the
e- lements belonging to the second and third rows
of the d-block are almost invariably
square-planar regardless of the ?-donor and
acceptor character of the ligand.
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cis-PtCl(NH3)2
trans-PtCl(NH3)2
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Example Identifying isomers from chemical
evidence Use the reactions in Fig to show how
the cis and trans geometries may be assigned.
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Five coordination Five coordinate complexes,
which are less common than four-or six-coordinate
complexes in the d-block, are either square-pramid
al or trigonal-bipramidal.However, distortion
from ideal geometries are common.A
trigonal-bipyramidal shape minimizes
ligand-ligand repulsions, but steric
constraint on polydentate ligands can favor a
square-pyramidal structure.
Ni(CN)53- trigonal bipyramidal Conformation)
Ni(CN)53- square pyramidal Conformation)
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Square-pyramidal stucture Myoglobin,the oxygen
transport protein where the ligand ring enforces
a square planar structure and fifth ligand
attaches above the plane
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The energies of the various geometries of
five-coordinate complexes differ little from one
another and such complexes are often fluxional
A Berry pseudorotation in which a) a
trigonal-bipyramidal Fe(CO)5 distorts into b)
square-pyramidal isomer and then c) becomes
trigonal-bipyramidal again,but initially
equatorial carbonyl now axial
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Six-coordination Six-coordination is the most
common arrangement for electronic configurations
ranging from d0 to d9 For example,
complexes formed by M3 ions of the 3d series
are usually octahedral.A Examples of
six-coordinated complexes are Sc(OH2)63
(d3), Mo(CN)63- (d6), Fe(CN)63- (d5), and
RhCl63- (d6). Almost all six-coordinate
complexes are octahedral (Oh) symmetry and
found for many complexes of formula ML6
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The simplest distortion from Oh symmetry is
tetragonal (D4h) and occurs when two ligand along
one axis differ from the other four.For Cu (d9)
complexes tetragonal (D4h) distortion may occur
even when all ligand identical.Rhombic (D2h) and
trigonal (D3h) distortions also occur.

• and (b) tetragonal (D4h)
• distortions of regular octa
• hedron (c ) rhombic (D2h) , and
• (d) Trigonal distortions (D3h)
• which can lead to a trigonal prism
• by a further 60o rotation of
• the faces containing the arrows.

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Trigonal-prismatic complexes are rare, but have
been found in solid MoS2 and WS2 the trigonal
prism is also the shape of several complexes of
formula M(S2C2R2)3.Such structure require
either very small sigma donor ligands or
favorable lignad- ligand interactions that can
constrain the complex into a trigonal- prismatic
shape.
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Trigonal-prismatic complex Re(S2C2(CF3)2)3
tris(Maleotriflouromethyldithiolato)rhenium(VI)
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Higher coordination complexes Larger atoms and
ions, particularly those of the f-block, Tend to
form complexes with high coordination
numbers Nine coordination is particularly
important in the f-block.
ReH92- D3h
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Ce(NO3)62- C.N. 12
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Polymetalic complexes A considerable amount of
attention has been given recently to the
synthesis of polymetallic complexes, which are
comp- lexes that contain more than one metal
atom.In some cases, the metal atoms are held
together by bridging ligands which are called as
cage coplexes, inothers there are direct
metal-metal bonds which are called As metal
cluster, and in yet there are both type of link.

• The copper(II) acetate
• dimer(cage comp.). (b)
• Fe-S comp.which model
• biochemically important
• electron-transfer agents.(c)
• Mercury(I) chloride,Hg-Hg
• Bond.(d) the complex
• Mn2(CO)10 (metal clustures)

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Tetrachlorozincate(II) has tetrahedral
geometry.The electronic Configuration of Zn2 is
Ar3d104s04p0
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Tetracyanonickelate(II) has square-planare
geometry. The electronic Configuration of Ni2
is Ar3d84s04p0
Ni(CN)42-