A. THE CHEMISTRY OF d-block ELEMENTS COMPARISON BY
ELECTRON
CONFIGURATION
The
d0 Configuration
This configuration
occur for the ions such Sc3+ and Mn(VII). All metals d0
configuration are hard acids and
prefer to interact with hard bases
such as Oxide. Complexation
chemistry is less extensive than in other configurations. Complexes such as
[ScF6]3- and [Sc(OH)6]3- are known
and result when excess F- or OH- is added to insoluble
ScF3 or Sc(OH)3.
The higher oxidation
states [Cr(VII)] and [Mn(VII)] tend to form oxyanions which are good oxidizing agents especially in acidic
solution: The oxides of intermediate species are insoluble (TiO2) or
amphoteric V2O5 [VO4]3-
d0 is the most stable configuration for Titanium. E.g. TiO2, TiCl4
and [TiCl6]2-
The
d1 Configuration
This configuration does not tend to be a stable
configuration. It is completely unknown
for Scandium and strongly reducing in Ti(III). The latter members of the series
tend to disproportionate to more
stable configuration.
3[CrO4]3-
+ 10H+ 2[HCrO4]-
+ Cr3+ + 4H2O
3[MnO4]2-
+ 4H+ 2[MnO4]-
+ MnO2 + 2H2O
The only d1 species of importance is Vanadyl VO2+, which is the
most stable form of vanadium in aqueous solution.
The
d2 Configuration
This
configuration ranges from Ti(II), very
strongly reducing to Fe(VI) Very strongly oxidizing. Both Ti(II) and V(III) are
reducing agents.
The Fe(VI) ion
[FeO4]2- is formed by oxidation of iron or iron
compounds. It is reasonably stable in basic solution and becomes a more
powerful oxidizing agent as the pH is lowered.
The
d3 Configuration
This is not a stable configuration. V(II) is a
strongly reducing while Mn(IV) Is strongly. However Cr3+ is the most
stable chromium in aqueous solution.
The
d4 configuration
The Cr2+
is strongly reducing agent but may be prepared readily
Cr
+ H+ Zn(Hg) Cr2+ + H2
But require
addition of Cr2+ solutions and sodium acetate precipitates chromium
(II) acetate.
2Cr2+
+ 4CH3COO- + H2O Cr2(OOCCH2)4(H2O)2
Complexes
of Mn(III) are relatively unstable except [Mn(CN)6]3-
which forms readily upon exposure of Mn(II) solution and cyanide to air. The d4
configuration contains both high spin
and low spins octahedral complexes.
The cyanide complexes of Mn3+ and Cr2+ are low spin.
The d5
configuration
Important
species in this configuration are Mn3+ and Fe3+.
Almost
all the known complexes of this configuration are high spin. Exceptions to this are the complexes of [Mn(CN)6]4-
and [Fe(CN)6]3-
The d6
configuration
The
complexes that are in this category are the octahedral complexes with strong
field ligands which provide the highest possible ligand field stabilization energy (LFSE). Cobalt (III) and nickel
(IV) are oxidizing agent. Most Fe(II) complexes are high spin exception being
ferrocyanides, [Fe(CN)6]4-.
Cobalt
(III) complexes in contrast tend to be low spin complexes except in the
presence of weak field ligands e.g. [CoF6]3- and [Co(H2O)3F3]
The d7
configuration
The
important species with this configuration are Co(II) and Ni(II). Cobalt (II)
occurs in tetrahedral [CoCl4]2- square planar [Co(Hdmg)2], square pyramidal [Co(ClO4)(OAsMePh2)4],
trigonal bipyramidal [CoBrMe6trenz]+
and octahedral [Co(NH3)]2+ complexes.
Cobalt
(II) is stable in aqueous solution
but in the presence of strong field ligands it is easily oxidized to form Co(III)
complexes.
The d8
configuration
This
configuration is ideal for the formation of low spin square planar complexes with strong field ligands. Ni(II)
complexes are typically red or yellow, although other colors are
found. Tetrahedral high spin complexes are formed with bulky ligands such as
triphenyl phosphine, triphenylphosphine oxide or halides. Five coordinate complexes of Ni(II) may be either high or low spin complexes depending on the nature of the ligands involved.
With soft ligands such as sulfur,
phosphorus or arsenic, the complexes tend to be low spin, while they are high
spin in similar nitrogen-containing ligands.
Both trigonal bipyramidal and square pyramid complexes are known.
Six coordinate
Ni(II) complexes may have equivalent ligands as in [Ni(H2O)]2+,
[Ni(NH3)]2+ and [Ni(en)3]2+
Only
few simple copper (II) salt are known e.g. KCuO2 and Cs3CuF6
but numerous complexes containing organic ligands exist. A few cobalt (I)
complexes are known.
The d9
configuration
This
configuration is found in copper (II) compounds. It has neither the stability
of d10 subshell nor the LFSE possible for d8. Copper (II) may be fairly easily reduced to Cu(I).
Six coordinate
from pure octahedral by the jahn-teller
effect. A number of five
coordinate complexes are known both square pyramidal and trigonal bipyramidal.
Four
coordination are exemplified by the square planar
and the tetrahedral complexes.
The
d10 configuration
For the first
transition series, this configuration is limited to Cu(I) and Zn(II), but it is
also exhibited by the post transition
metals in their highest oxidation states [Ga(III)] and Ge(IV). The copper
(I) complexes are good reducing agents being oxidized to Cu(II).
They can be
stabilized by precipitation with appropriate counter ions to the extent Cu(I)
may form and exclude Cu(II).
Cu2+(aq) + I-(aq)
CuI(s) + 1/2I2(S)
Cu2+(aq)
+ 2CN-(aq) CuCN(s) + ½(CN)2(g)
The
preferred coordination for Cu(I) appears to be linear (SP), two coordination.
Three coordinate as well as several tetrahedral complexes are known. Zn(II) is
typically either tetrahedral [ZnCl4]2- or octahedral e.g.
[Zn(H2O)]2+ but both trigonal bipyramidal and square
pyramidal five coordinate are also known.
B. COVALENT AND IONIC RADII
The
size of atoms and ions are also related to the ionization energies and electron
affinities.
As
the nuclear charge increases the electron are pulled in towards the center of
the atom and the size of any particular orbital decreases. On the other hand as
the nuclear charge increases more electrons are added to the atom and their
mutual repulsion keeps the outer orbital large.
Factors
that influence ionic size include the coordination
number of the ion, the covalent character of the bonding, distortion of regular crystal geometric
and delocalization of electrons. The radius of an anion is
also influenced by the size and charge of the cation.
Lecture 3 translations:
Jahn-teller
effect:
Ø Is
a geometric distortion of a non-linear molecular system that reduces its
symmetry and energy. Most occur in Cu(II) Complexes.
Ø The
distortion is typically observed among octahedral complexes where the two axial
bonds can be shorter or longer than those of the equatorial bonds.
