Inorganic Chemistry Assignment: Detailed Question Solutions, Answers

This document provides comprehensive solutions to an inorganic chemistry assignment, addressing various key concepts. The solutions cover reaction mechanisms, specifically inner-sphere and outer-sphere mechanisms, and the prediction of the most probable mechanism along with experimental evidence. It further explores electronic spectra observed for transition metal complexes, providing examples for each type, and delves into Crystal Field Theory, including its basis, assumptions, and orbital splitting diagrams for octahedral and tetrahedral complexes. Crystal Field Stabilization Energy calculations are also included. The assignment also uses Valence Bond Theory to analyze the variation in magnetic moments of manganese complexes, and examines the structures of different isomers. The document also details the preparation methods of cobalt (III) complexes, structures with seven coordination, the mechanisms for substitution reactions of octahedral metal complexes, the trans-effect, back bonding, and the Jahn-Teller effect. Finally, it explains why cobalt(II) forms tetrahedral complexes, while cobalt(III) forms octahedral complexes, and the square planar complex formation of Ni(II), Pd(II) and Pt(II).

Inorganic Chemistry Questions
Question 1 (a)
Inner sphere mechanism-in this type of reaction, a bond is formed as a bridge between the
reduction-oxidation partners (Eisenstein & Crabtree, 2013).
The reaction occurs in 3 different steps.
i) A substitution occurs to form a bond (bridge) between the reactants
ii) Electron transfer then takes place
iii) The products are then separated usually with transfer of the bridge ligand.
(ii) is oxidized to vanadium (iii).
Outer sphere reaction- in this type of reaction reductant and the oxidant have no direct bridge
¿+2 + [Va]+2 → ¿+2 + [Va]+3
Cobalt (iii) ion donates an electron to vanadium (ii) ion and it is reduced to cobalt (ii) while
vanadium
Since these are two different metal ions, the reaction takes place via the inner sphere reaction
mechanism.
b)
Types of electronic spectra observed for transition metal
complexes
i) Emission spectra
Emission spectra is classified into three groups:
Continuous spectra:
Continuous spectra arises as a result of the molecules or atoms of a material being thermally
excited. It is produced by solids such as carbon and sodium when exposed to intense heat to the
point of glowing (Cox, 2010).
Band spectra:
It is made up of several strips of specific colours which are in turn separated by dark area. This
type of spectrum is emitted by molecules when thermal energy is not enough to split the
molecule into its constituent atoms.
Line spectra:

This type of spectrum displays brightly colored lines in varying bands of the visible frequency
range. More than one element cannot have similar line spectra (Cox, 2010). The lines displayed
have different intensities and their configuration is dependent on the substance being heated.
ii) Absorption spectra:
This is produced as a result of placing a compound between a spectrometer and a light source.
Specific parts of the spectrum are absorbed by the spectrum.
Question 2 (a)
The basis and assumptions of the Crystal Field Theory
Crystal Field Theory was put forward as a model that describes crucial characteristics of
complexes such as oxidation states, magnetic properties, coordination and absorption spectra.
The basis of crystal field theory is the interaction between ligands and the d-orbitals of a central
atom (Morrison, 2012).
Assumptions
 Crystal field theory treats ligands as point charges. Ligand and metal orbitals are not
allowed to overlap.
 It is assumed that the interaction between the ligand and the metal ion is ionic.
Orbital splitting for octahedral complexes.
The following factors determine how the splitting of the orbitals occurs
i) The nature of the metal atom
ii) Configuration (geometry) of the molecules
ii) Ligand nature
The splitting is shown below.
Orbital splitting for tetrahedral complexes.
For a tetrahedral complex, the ligand approaches the complex along a plane inclined to the axis.
The splitting is shown in the diagram below.
Crystal field splitting diagram for
i) Na2 [CoBr4]

ii) K3[MnF6]
b)
i) [Mn(CN)6]4-
Mn+2 = d5
Magnetic moment = √ n(n+1)
Number of unpaired electrons = 5=n
Therefore magnetic moment = √5(5+1) = 5.48
ii) [Mn(CN)6]3-
Mn3+ = d4
Magnetic moment = √n(n+ 1) with n=4
= √4 (4 +1) = 4.47
iii) [MnF6]4-
Mn2+ = d5
Magnetic moment = √5(5+1) = 5.48

Question 3 (a)

(b)
ii) The large difference in the formation constant K is due to the fact that complexes of metals
with polydentate ligands are normally more stable as compared to metal complexes of
monodentate ligands. The stability increase is attributed to the Chelate effect.
Question 4
a)

b (i)

Cobalt (iii) complexes can be prepared via 2 main methods:
a) Oxidizing cobalt (ii) with a ligand present
b) Displacement of ammonia from hexamminocobalt (iii) ion
ii) Structures from complexes whose coordination number = 7
Structures with seven coordinated molecules or atoms usually result in 3 types of geometries
which include: capped trigonal prism, capped octahedron and pentagonal bipyramid.
 Examples of ions with the capped octahedral shape include: WF7− and MoF7− ions.
 Examples of ions with the capped trigonal structure include: NbF72− and TaF72−
Question
5 (a)

5 (b)
Types of mechanisms for the substitution reactions of octahedral
metal complexes.
 Dissociative mechanism
This mechanism takes place in two steps with the formation of an intermediate product. The
intermediate product has a lower coordination number compared to the original complex. This
reaction is similar to the Sn1 reaction which occurs in organic compounds.
 Associative mechanism
This is also a two-step mechanism with the formation of an intermediary. The starting complex
has a lower coordination number than that of the intermediate product.
 Interchange mechanism
This reaction has no intermediate product. The formation of bonds between the incoming group
and the metal occurs simultaneously with the cleavage bond between the outgoing group and the
metal. This reaction is analogous to the Sn2 reaction in inorganic compounds.
Question 6(a)
i) The trans-effect describes a process through which a ligand which is trans- to some other
ligands is labilized (made more active). The trans-effect can be explained using π notation and σ
notation (Deimel et al., 2016). It is mostly observed in complexes with square planar
configuration. Sometimes it is also observable in complexes with octahedral configuration.
ii)
Back bonding is a situation in which a ligand, for example CO gives up its free electrons to a
metal while it accepts electrons from the metal via the interaction of the metal orbital and a
ligand orbital. The name back-bonding is used due to the fact that the ligand donates sigma
electrons to the metal and the metal donates pi electrons to the ligand (Krogman & Thomas,
2014. Thus the ligand acts as sigma donor and a pi acceptor
iii)
The Jahn–Teller effect is a process in which symmetry in molecular compounds breaks down in
a random fashion. It defines symmetry breaking of ions and molecules that often results from
specific electronic arrangements. This effect is usually experienced in transition metals with
octahedral complexes. It is prominent in copper (ii) complexes (Bersuker, 2013).
Question 6(b)

i)
Cobalt (ii) forms tetrahedral complexes while cobalt (iii) forms octahedral complexes
This is because octahedral complexes have larger crystal field stabilization energy compared
with tetrahedral structures. Furthermore, the formation of six bonds is more favored than the
formation of four bonds.
ii) Ni(II), Pd(II) and Pt(II) tends to form square planar complexes compared to tetrahedral.
This is due to the fact that square planar complexes are more common in transition metal
complexes with d8 configuration.