Transcript Complexes of metal ions and nomenclature for inorganic compounds

Complexes of metal ions and
nomenclature for inorganic
compounds
Cobalt(III) ion
ammonia ligands
blue = nitrogen
donor atom
[Co(NH3)6
]3+
white =
hydrogen atom
Complexes of metal ions.
Prior to the work of Werner on
coordination complexes,
formulated at the time as
CoCl3.6NH3, for example, there
was no understanding of why
the six ammonia molecules
were so strongly bound in this
compound. Werner showed
that the ammonia molecules
were in fact chemically bound
to the cobalt, and that the three
Cl- ions were present only to
act as counter-ions to the 3+
charge on the [Co(NH3)6]3+
cation.
Alfred Werner (1866-1919)
Nobel prize 1913 for his work
on Coordination compounds
(a)
(b)
[Co(NH3)6]3+
[Co(NH3)5Cl]2+
(c)
[Co(NH3)3Cl3]
Werner proposed that Co(III) (trivalent cobalt) had a coordination
number of six, which could be satisfied by six ammonias in ‘a’, five
ammonias and a Cl- in ‘b’, and three ammonias and three Cl- in ‘c’.
His theory explained why conductivity showed that in solution ‘a’
was a 3+ cation, ‘b’ was a 2+ cation, and ‘c’ was neutral. The
molecules or ions coordinated to the Co(III) are called ligands, from
the Latin ‘ligare’ meaning ‘to join’. The coordination geometry of the
Co(III) is octahedral, which means that the six ligands are placed
around the Co(III) at the corners of an octahedron.
Some complexes of metal ions:
nickel
Cobalt
water molecule
cyanide
ion
ammonia
2+
nickel
2+
2-
C
O
[Co(H2O)6]2+
N
N
[Ni(NH3)6]2+
[Ni(CN)4]2-
Hexaaquacobalt(II)
hexamminenickel(II)
tetracyanonickelate(II)
A complex is written such that everything inside the square brackets is
a ligand chemically bonded to the metal ion. Everything outside the brackets
is a counter-ion or something simply present in the crystal lattice. Thus, we
might have [Co(H2O)6](NO3)2 where the NO3- ions are counter-ions.
Formal Oxidation State:
The formal oxidation state of metal ions
in their complexes is determined by
ascribing formal charges to all ligands
which correspond to those they
possess as the free molecules or ions:
Neutral: NH3, H2O, CO, PH3, (CH3)2S
Anionic: OH-, F-, Cl-, Br-, I-, CN-, SCNCationic: NO+
Examples of oxidation states:
[Co(NH3)6]3+
=
Co(III)
hexamminecobalt(III)
K3[Fe(CN)6]
=
Fe(III)
potassium hexacyanoferrate(III)
[Co(NH3)4Cl2]Cl =
Co(III)
tetrammiinedichlorocobalt(III) chloride
[FeNO(NH3)5]Cl3 =
Fe(II)
pentamminenitrosyliron(II) chloride
[Cr(CO)6]
=
Cr(0)
=
V(-I)
hexacarbonylchromium(O)
K[V(CO)6]
potassium hexacarbonylvanadate(-I)
[Mn(NO)3CO]
=
trinitrosylcarbonylmanganese(-III)
Mn(-III)
Identifying which are ligands:
In the formula for a complex, everything inside the
square brackets (blue in formula below) is
coordinated to the metal ion, everything outside
(red) is a counterion or a lattice molecule.
When the name of a complex is written, all the
ligands that are coordinated to the metal ion come
before it, while counter-ions come after the name of
the metal:
[Co(NH3)4Cl2]Cl is:
ligands bonded to metal ion
counterion
tetramminedichlorocobalt(III)chloride
Naming of ligands in complexes:
Neutral ligands:
When naming a complex, the ligands are indicated by
names as follows:
Neutral ligands:
NH3
H2O
CO
=
=
=
ammine
aqua
carbonyl
The number of each type of ligand present is indicated
by the Latin prefixes di-, tri-, tetra-, penta-, hexa-, hepta-,
octa-, nona-, and deca-:
[Co(NH3)6]Cl3
[La(H2O)9](NO3)3
=
=
K2[Ti(CO)6]
=
hexamminecobalt(III) chloride
nona-aqua lanthanum(III)
nitrate
potassium hexacarbonyl
titanate(-II)
Naming of ligands in complexes: anionic
ligands:
Anionic ligands: To indicate that they are anions, ligands
in complexes are given an ‘o’ ending: fluoro, chloro, bromo,
iodo, hydroxo, cyano, sulfato, nitro, etc. If the overall
charge on the complex is negative, the metal ion is given
an ‘ate’ ending to indicate this:
K3[Fe(CN)6]
=
K4[Fe(CN)6]
Na3[AlF6]
[Co(NH3)3F3]
=
=
=
potassium hexacyanoferrate(III)
or potassium hexacyanoiron(III)
potassium hexacyanoferrate(II)
sodium hexafluoroaluminate(III)
triamminetrifluorocobalt(III)
Nomenclature of complexes:
Cations, including complex cations, come first, anions,
including complex anions come second:
[Co(NH3)6]Cl3
Na3[CrCl6]
[Ni(H2O)6]Cl2
K3[Rh(CN)6]
= hexammine cobalt(III) chloride,
= sodium hexachlorochromate(III),
= hexaaquanickel(II) chloride
= potassium hexacyanorhodate(III)
[Co(NH3)6][Co(CN)6] = hexamminecobalt(III)
hexacyanocobaltate(III)
Naming more complex ligands:
Many ligands are more complex and have more than one donor
atom, such as en (ethylenediamine), bipy (2,2’-bipyridyl) and acac
(acetyacetonate) below:
H3C
H2N
NH2
N
en
bipy
N
CH3
O
Oacac
Where more complex ligands are present, one indicates the
number of these present with prefixes bis-, tris-, tetrakis, pentakis,
or hexakis, followed by the name of the ligand in parentheses.
Thus, [Co(en)3]Cl3 is tris(ethylenediamine)cobalt(III) chloride.
Some cobalt(III) complexes of more
complex ligands:
CH3
H2N
NH2 H
2
N
N
Co
H2N
NH2
Co
O
N
N
CH3
O
O
N
Co
N
H2
O
H3C
N
H3C
N
O
O
CH3
CH3
.Cl3
tris(ethylenediamine)
cobalt(III)chloride
.(N O3)3
tris(2,2’-bipyridyl)
cobalt(III) nitrate
tris(acetylacetonato)
cobalt(III)
NOMENCLATURE
1.1 Formulas of Simple Ionic substances.
For ionic compounds, the cation (more
electropositive element) should always
be first. (KCl, Na2S). If several cations
are present, they should be listed in
alphabetical order, followed by anions
in alphabetical order (LiMgClF2). An
exception is the proton, which is
always listed last in the sequence of
cations, (RbHF2).
Nomenclature (contd.)
1.2. Sequence of atoms in formulas of
polyatomic ions and molecules:
For polyatomic species with a central atom,
these are generally listed first followed by
the attached atoms in alphabetical order
(SO42-, CCl2H2, PCl3O, SO3, -CF3, -SCN). An
exception is the linear thiocyanate group
(-SCN), where the atoms are placed in the
order in which they occur in the thiocyanate
ion:
-S=C=N
Formulas and Names of Common substances.
Acid
Name
HNO3
H3PO4
H2SO4
HClO4
HClO3
HClO2
HClO
HCl
Nitric acid
Phosphoric acid
Sulfuric acid
Perchloric acid
Chloric acid
Chlorous acid
Hypochlorous acid
Hydrochloric acid
Name of anion
nitrate
phosphate
sulfate
perchlorate
chlorate
chlorite
hypochlorite
chloride
Chemical Names
Names of the Elements: These originated
with Berzelius (1813) who developed the
system that the symbol for an element was
the first letter of its name, e.g., F, O, N, C, B. If
there was more than one element whose
name started with the same letter, then a
second, lower-case letter, was added, which
was usually the second letter of the name of
the element. e.g. C for carbon, but Ca, Cd,
Ce, Cf, Cl, Cm, Co, Cr, Cs, Cu. B for Boron,
but Ba, Be, Bi, Bk, Br, and so on.
Names of metallic elements you should
know (pretty much all of them):
H
hydrogen
Li
Be
lithium
beryllium
Na
Mg
sodium
magnesium
K
Ca
Sc
Ti
V
potassium
calcium
scandium
titanium
vanadium
Rb
Sr
Y
Zr
Nb
rubidium
strontium
yttrium
zirconium
niobiuim
Cs
Ba
La
Hf
Ta
cesium
barium
lanthanum
hafnium
tantalum
Names of metallic elements you should
know (continued):
Cr
chromium
Mo
Mn
Fe
manganese
Tc
iron
tungsten
Rh
rhodium
Ni
Cu
Zn
nickel
copper
zinc
Pd
Ag
Cd
palladium
silver
cadmium
Re
Os
Ir
Pt
Au
Hg
rhenium
osmium
iridium
platinum gold
mercury
Lanthanides:
La
Ce
lanthanum
….
cerium
Actinides:
Ac
Th
actinium
cobalt
Ru
molybdenum technetium ruthenium
W
Co
thorium
Gd
……. Lu
gadolinium
….
lutetium
U
Np
Pu
Am
uranium
neptunium
plutonium
americium
Geometrical Isomerism
ammonia
chloride
Pt
cis-diamminedichloro
platinum(II)
Pt
trans-diamminedichloroplatinum(II)
Geometrical isomers can exist with two identical ligands placed
next to each (cis) or at 180º to each other (trans). Again, Werner’s
theory could explain how two different complexes corresponding
to [(NH3)2Cl2Pt] could exist.
Cis and trans isomerism of octahedral complexes:
green
= Cl
trans-[Co(NH3)4Cl2]+
(green)
cis-[Co(NH3)4Cl2]+
(violet)
An important aspect of Werner’s theory was that it could explain how
two compounds of identical formula, i.e. [Co(NH3)4Cl2]Cl, could exist
as two entirely different forms, which we now know to be the cis and
trans forms above.
fac (facial) and mer (meridional) geometrical
isomers of the [Co(NH3)3Cl3] complex
mer
mer-[Co(NH3)Cl3]
fac
fac-[Co(NH3)Cl3]
Optical isomerism:
mirror plane
Λ (lambda) form
Δ (delta) form
The tris(ethylenediamine)cobalt(III) complex exists as optical isomers.
the Δ and Λ forms, which are non-superimposable mirror images of
each other. This will be discussed further under group theory.