Coordination Numbers in Inorganic Compounds: Geometries and Structures
Coordination
numbers of
inorganic compounds
(15-11-2018)
In
the
field
of
inorganic coordination complexes
it is the
geometrical
pattern
formed
by
the
atoms
in the
ligands
that
are
bonded
to
the
central
atom
in
a
molecule
or
a
coordination
complex
.
The
geometrical
arrangement will
vary
according
to
the
number
and
type
of
ligands
bonded
to the
metal
centre,
and
to
the
coordination
preference
of
the
central
atom,
typically a metal
in
a
coordination complex
.
The
number
of
atoms bonded,
(i.e. the
number
of
σ-bonds
between central
atom and
ligands) is
termed
the
coordination number
. The
geometrical
pattern
can
be
described
as
a
polyhedron
where the
vertices
of
the
polyhedron
are the
centres
of
the
coordinating
atoms
in
the
ligands.
The
coordination
preference
of
a
metal often
varies
with
its oxidation
state.
The
number
of
coordination bonds (
coordination
number
)
can
vary
from
two
as
high
as 20
in
Th(η
5
-C
5
H
5
)
4
.One of
the
most
common
coordination
geometries
is
octahedral
,
where
six
ligands
are
coordinated
to the
metal
in
a
symmetrical
distribution, leading
to
the
formation
of
an
octahedron
if
lines
were
drawn between
the
ligands.
Other common
coordination
geometries
are
tetrahedral
and
square
planar
like
complexes
of
AuCl
4
-
,
PtCl
2
Py
2
and
[Ni(en)
2
]
2+
ion.
Here,
we
will
focus
on
the
common coordination numbers
in
most metal
complexes
and
ions
of transition
elements
which involve
C.N=4,5
and 6,
whereas
the
high
coordination numbers
like 7,8,9,10
and
12
are well-
known
in large
atomic
radium
metals
like tungsten (W),
Re,
OS,
Nb,
Mo,Ta,Zr
and
lanthanides such
as
U,Nb,Sm
etc.
Coordination
Number
4
Two
different
geometries are
possible.
The tetrahedron is
the
more
common
while
the square
planar is found in
particular
with
metal
ions
having a d
8
electronic
configuration.
4
Geometry of
NiCl
2-
ion
(SP
3
hybridization
Geometry of
dsp
2
square
planner
complexes
of Pt(II)
complexes
C.N=5.
The five-coordinate symmetry
have
been shown
in
two
expected
geometries: Square pyramid,
and
trigonal
bi pyramid
as
below:
Square
pyramid,
(C
4v
) with (d
4
s)
hybridization
Oxovanadium
salts
(Vanadyl,
VO
2+
)
often
show
square
pyramidal
geometry,
for
example, VO(acac)
2
. Note
that the
Vanadium(IV) can
be
considered coordinatively unsaturated
and addition
of
pyridine leads
to
the
formation
of an
octahedral
complex.
Trigonal
Bipyramid,
(D
3h
)
The
structure
of
[Cr(en)
3
][Ni(CN)
5
] 1.5 H
2
O
was
reported
in
1968
to
be
a
remarkable example
of
a complex exhibiting
both
types of geometry
in
the
same
crystal.
Geometry
of
CN=5
of dsp
3
for [Mn(CO)
5
]
-
ion
Geometry of
[Ni(CN)
5
]
3-
ion
(dSP
3
hybridization)
Octahedral,
(O
h
)
The
most
common geometry
found for
first
row
transition
metal
ions,
including
all aqua
ions.
In
some
cases
distortions
are
observed and
these
can
sometimes
be
explained
in
terms of
the
Jahn-Teller
Theorem.
Geometry of
[Cu(NH
3
)
6
]SO
4
complex
of
sp
3
d
2
hybridization
Coordination
Number
7
Three
geometries are
possible:
Not very
common
for
1st row
complexes
and
the
energy difference
between
the
structures
seems
small
and
distortions
occur
so that
prediction
of
the closest
"idealised"
shape
is
generally
difficult.
Capped
octahedron,
(C
3v
)
Capped trigonal
prism,
(C
2v
)
Pentagonal Bipyramid,
(D
5h
)
3
-
Pentagonal bipyramid
d
3
sp
3
hybridization
of ZrF
7
ion
2-
3
3
Trigonal prismatic
TaF
7
ion
(d sp
)
Coordination
Number
8
Dodecahedron,
(D
2d
)
Cube,
(O
h
)
Square antiprism,
(D
4d
)
Hexagonal
bipyramid,
(D
6h
)
3
-
Geometry of
TaF
8
Geometry of
[Nd(H
2
O)
9
]
2+
ion
Handout about
coordination compounds(lectures
1,2,3)
1.Indicate the
coordination
number
for the
central
metal atom
in
each
of
the
following coordination
compounds:
(a)
[Pt(H
2
O)
2
Br
2
]
(b)
[Pt(NH
3
)(py)(Cl)(Br)] (py
= pyridine,
C
5
H
5
N)
(c)
[Zn(NH
3
)
2
Cl
2
]
(d)
[Zn(NH
3
)(py)(Cl)(Br)]
(e)
[Ni(H
2
O)
4
Cl
2
]
(f)
[Fe(en)
2
(CN)
2
]
+
(en
= ethylenediamine,
C
2
H
8
N
2
)
2.
Give
the
coordination
numbers
and
write
the formulas
for
each
of
the
following, including
all
isomers
where
appropriate:
(a)
tetrahydroxozincate(II)
ion
(tetrahedral)
(b)
hexacyanopalladate(IV)
ion
(c)
dichloroaurate(I)
ion
(note that
aurum
is
Latin
for
“gold”)
(d)
diaminedichloridooplatinum(II)
(e)
potassium
diaminetetrachlorochromate(III)
(f)
hexaaminecobalt(III)
hexacyanidochromate(III)
(g)
dibromo
bis(ethylenediamine)
cobalt(III)
nitrate
3.Give
the
coordination number
for
each
metal
ion
in
the
following
compounds:
(a)
[Co(CO
3
)
3
]
3−
(note that
CO
3
2−
is
bi
dentate
in
this
complex)
(b)
[Cu(NH
3
)
4
]
2+
(c)
[Co(NH
3
)
4
Br
2
]
2
(SO
4
)
3
(d)
[Pt(NH
3
)
4
][PtCl
4
]
(e)
[Cr(en)
3
](NO
3
)
3
(f)
[Pd(NH
3
)
2
Br
2
]
(square
planar)
(g)
K
3
[Cu(Cl)
5
]
(h)
[Zn(NH
3
)
2
Cl
2
]
1.
Sketch
the
structures of
the
following complexes. Indicate
any
cis
,
trans
, and
optical
isomers.
(a)
[Pt(H
2
O)
2
Br
2
] (square
planar)
2.
Draw
diagrams
for any
cis
,
trans
,
and
optical isomers
th t
could exist
for
the
following
(en is
ethylenediamine):
(a)
[Co(en)
2
(NO
2
)Cl]
+
(b)
[Co(en)
2
Cl
2
]
+
(c)
[Pt(NH
3
)
2
Cl
4
]
(d)
[Cr(en)
3
]
3+
(e)
[Pt(NH
3
)
2
Cl
2
]
3.
Name
each
of
the
compounds
or
ions
given
in
Exercise
3
,
including
the
oxidation
state
of
the
metal.
4.
Name
each
of
the
compounds
or
ions
given
in
Exercise
5
.
5.
Specify whether
the
following
complexes
have
isomers.
(a)
tetrahedral [Ni(CO)
2
(Cl)
2
]
(b)
trigonalbipyramidal
[Mn(CO)
4
NO]
(c)
[Pt(en)
2
Cl
2
]Cl
2
3
6. Predict
whether
the
carbonate
ligand
carbonate
(CO
2-
)
will
coordinate to a
metal
center
as
a uni dentate,
bi dentate,
or
tridentate
ligand.
7. Draw the geometric, linkage,
and ionization
isomers
for
K
3
[Co(SCN)
4
(gly)
2
]
In inorganic coordination complexes, the coordination number refers to the number of atoms bonded to the central atom. Common geometries include octahedral, tetrahedral, and square planar, depending on the type and number of ligands. Transition metal complexes exhibit different coordination numbers and geometries. Examples include square pyramidal and trigonal bipyramidal arrangements for coordination number 5. The structure diversity can be seen in complexes such as [Cr(en)3][Ni(CN)5]·1.5H2O, showcasing multiple geometries in one crystal.
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Presentation Transcript
Coordination numbers of inorganic compounds (15-11-2018) In the field of inorganic coordination complexes it is the geometrical pattern formed by the atoms in the ligands that are bonded to the central atom in a molecule or a coordination complex. The geometrical arrangement will vary according to the number and type of ligands bonded to the metal centre, and to the coordination preference of the central atom, typically a metal in a coordination complex. The number of atoms bonded, (i.e. the number of -bonds between central atom and ligands) is termed the coordination number. The geometrical pattern can be described as a polyhedron where the vertices of the polyhedron are the centres of the coordinating atoms in the ligands. The coordination preference of a metal often varies with its oxidation state. The number of coordination bonds (coordination number) can vary from two as high as 20 in Th( 5-C5H5)4.One of the most common coordination geometries is octahedral, where six ligands are coordinated to the metal in a symmetrical distribution, leading to the formation of an octahedron if lines were drawn between the ligands. Other common coordination geometries are tetrahedral and square planar like complexes of AuCl4-, PtCl2Py2 and [Ni(en)2]2+ion. Here, we will focus on the common coordination numbers in most metal complexes and ions of transition elements which involve C.N=4,5 and 6, whereas the high coordination numbers like 7,8,9,10 and 12 are well- known in large atomic radium metals like tungsten (W), Re, OS, Nb, Mo,Ta,Zr and lanthanides such as U,Nb,Sm etc. Coordination Number 4 Two different geometries are possible. The tetrahedron is the more common while the square planar is found in particular with metal ions having a d8 electronicconfiguration.
Geometry of NiCl 2-ion (SP3hybridization 4 Geometry of dsp2 square planner complexes of Pt(II) complexes C.N=5. The five-coordinate symmetry have been shown in two expected geometries: Square pyramid, and trigonal bi pyramid as below: Square pyramid, (C4v) with (d4s) hybridization Oxovanadium salts (Vanadyl, VO2+) often show square pyramidal geometry, for example, VO(acac)2. Note that the Vanadium(IV) can be considered coordinatively unsaturated and addition of pyridine leads to the formation of an octahedral complex. Trigonal Bipyramid, (D3h)
The structure of [Cr(en)3][Ni(CN)5] 1.5 H2O was reported in 1968 to be a remarkable example of a complex exhibiting both types of geometry in the same crystal. Geometry of CN=5 of dsp3 for [Mn(CO)5]-ion Geometry of [Ni(CN)5]3-ion (dSP3 hybridization)
Octahedral, (Oh) The most common geometry found for first row transition metal ions, including all aqua ions. In some cases distortions are observed and these can sometimes be explained in terms of the Jahn-Teller Theorem. Geometry of [Cu(NH3)6]SO4 complex of sp3d2hybridization Coordination Number 7 Three geometries are possible: Not very common for 1st row complexes and the energy difference between the structures seems small and distortions occur so that prediction of the closest "idealised" shape is generally difficult. Capped octahedron, (C3v) Capped trigonal prism, (C2v)
Pentagonal Bipyramid, (D5h) 3- Pentagonal bipyramid d3sp3 hybridization of ZrF7ion 2- 3 3 Trigonal prismatic TaF7 ion (d sp) Coordination Number8 Dodecahedron, (D2d) Cube, (Oh) Square antiprism, (D4d)
Hexagonal bipyramid, (D6h) 3- Geometry of TaF8 Geometry of [Nd(H2O)9]2+ion Handout about coordination compounds(lectures1,2,3)
1.Indicate the coordination number for the central metal atom in each of the following coordination compounds: (a) [Pt(H2O)2Br2] (b) [Pt(NH3)(py)(Cl)(Br)] (py = pyridine, C5H5N) (c) [Zn(NH3)2Cl2] (d) [Zn(NH3)(py)(Cl)(Br)] (e) [Ni(H2O)4Cl2] (f) [Fe(en)2(CN)2]+ (en = ethylenediamine, C2H8N2) 2.Give the coordination numbers and write the formulas for each of the following, including all isomers where appropriate: (a) tetrahydroxozincate(II) ion (tetrahedral) (b) hexacyanopalladate(IV) ion (c) dichloroaurate(I) ion (note that aurum is Latin for gold ) (d) diaminedichloridooplatinum(II) (e) potassium diaminetetrachlorochromate(III) (f) hexaaminecobalt(III) hexacyanidochromate(III) (g) dibromo bis(ethylenediamine) cobalt(III) nitrate 3.Give the coordination number for each metal ion in the following compounds: (a) [Co(CO3)3]3 (note that CO32 is bi dentate in this complex) (b) [Cu(NH3)4]2+ (c) [Co(NH3)4Br2]2(SO4)3 (d) [Pt(NH3)4][PtCl4]
(e) [Cr(en)3](NO3)3 (f) [Pd(NH3)2Br2] (square planar) (g) K3[Cu(Cl)5] (h) [Zn(NH3)2Cl2] 1. Sketch the structures of the following complexes. Indicate any cis, trans, and optical isomers. (a) [Pt(H2O)2Br2] (square planar) 2. Draw diagrams for any cis, trans, and optical isomers th t could exist for the following (en is ethylenediamine): (a) [Co(en)2(NO2)Cl]+ (b) [Co(en)2Cl2]+ (c) [Pt(NH3)2Cl4] (d) [Cr(en)3]3+ (e) [Pt(NH3)2Cl2] 3. Name each of the compounds or ions given in Exercise 3, including the oxidation state of the metal. 4. Name each of the compounds or ions given in Exercise 5. 5. Specify whether the following complexes have isomers. (a) tetrahedral [Ni(CO)2(Cl)2] (b) trigonalbipyramidal [Mn(CO)4NO] (c) [Pt(en)2Cl2]Cl2 6. Predict whether the carbonate ligand carbonate (CO 2-) will coordinate to a metal center as a uni dentate, bi dentate, or tridentate ligand. 7. Draw the geometric, linkage, and ionization isomers for K3[Co(SCN)4(gly)2] 3
