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CHM2911 > Transition Metal Complexes > Flashcards

Transition Metal Complexes Flashcards

1
Q

Definition

the collective name for the dxy, dxz and dyz orbitals

A

T2g orbital

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2
Q

Show that the following complexes obey the 18-electron rule:

(a) [Ni(CO)4]
(b) [Mn(CO)5]-

A
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3
Q

Definition

The energy of the electron configuration in the ligand field minus the energy of the electronic configuration in the isotropic field

A

Crystal field stabilisation energy

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4
Q

In the elements, which orbital is filled first: 3d or 4s?

A

4s

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5
Q

Definition

Crystal field designation for an outer orbital complex; all t2g and eg orbitals are singly occupied before any pairing occurs

A

High spin

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6
Q

Definition

similar to the chelate effect however the effect is further enhanced by the cyclic conformation of the ligand. These ligands are not only multidentate, but because of their pre-organised structure there is little entropy penalty for wrapping it around the metal ion

A

Macrocycle effect

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7
Q

Predict which of the following complexes would be most stable:

(a) [Fe(OH2)6]2+
(b) [Fe(OH2)6]3+

A
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8
Q

Definition

a technique used to determine analyte concentration by measuring light absorption across the ultraviolet and visible light wavelengths

A

UV-vis spectroscopy

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9
Q

What causes low-spin arrangments?

A

When Δo is large and too much energy is required to promote electrons into the eg orbital

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10
Q

How are values of Δo measured experiementally?

A

UV-vis spectroscopy

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11
Q

Define

Coordination number

A

the number of atoms or ions immediately surrounding a central atom in a complex or crystal

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12
Q

Calculate CFSE for the low-spin and high-spin configurations of d7 . Which one looks as if it should be the most stable

A
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13
Q

Definition

A rule based on the fact that the valence shells of transition metals consist of nine valence orbitals (one s orbital, three p orbitals and five d orbitals), which collectively can accommodate 18 electrons as either bonding or nonbonding electron pairs

A

Eighteen electron rule

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14
Q

Using the formula Δ0 = hcNo/λ, convert the value of Δ0 = 12600 cm-1 for [Cu(OH2)6]2+ into kJ/mol

A
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15
Q

Definition

the difference in energy between eg and t2g

A

ΔO

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16
Q

Define

Lewis acid

A

a compound or ionic species which can accept an electron pair from a donor compound

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17
Q

Define

Metal-ligand charge transfer

A

when the electronic charge shifts from the MO with metal-like character to the ligand-like one resulting in the oxidation of the metal centre

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18
Q

Definition

a spectroscopic selection rule that states the a change in spin multiplicity is forbidden

A

Spin selection rule

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19
Q

Define

High spin

A

Crystal field designation for an outer orbital complex; all t2g and eg orbitals are singly occupied before any pairing occurs

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20
Q

Assuming that the following complexes obey the 18-electron rule, determine n in each complex:

(a) [Fe(CO)<em>n</em>]
(b) [Fe(CO)<em>n</em>(PPh3)2]

A
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21
Q

Define

Crystal field stabilisation energy

A

The energy of the electron configuration in the ligand field minus the energy of the electronic configuration in the isotropic field

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22
Q

Is [Fe(CN)6]4- more stable in high spin or low spin?

A

Low spin; CN is a carbon donor and therefore the crystal field splitting is large making it more stable to have low spin

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23
Q

Definition

the number of atoms or ions immediately surrounding a central atom in a complex or crystal

A

Coordination number

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24
Q

Define

Low spin

A

Crystal field designation for an inner orbital complex; contains electrons paired t2g orbitals before eg orbitals are occupied in octahedral complexes

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25
Q

Define

Lewis base

A

a compound or ionic species which can donate an electron pair to an acceptor compound

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26
Q

Definition

the collective name for the dz2 and the dx2-y2 orbitals

A

Eg orbital

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27
Q

What is the electron configuration of chromium metal?

A

Cr: [Ar] 4s13d5

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28
Q

How does oxidation state effect crystal field splitting?

A

The higher the oxidation state of the metal, the greater the crystal field splitting

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29
Q

Definition

a compound or ionic species which can accept an electron pair from a donor compound

A

Lewis acid

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30
Q

Define

UV-vis spectroscopy

A

a technique used to determine analyte concentration by measuring light absorption across the ultraviolet and visible light wavelengths

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31
Q

Definition

a spectroscopic selection rule that only applies to centrosymmetric molecules (those with an inversion centre) and atoms. It states that transitions can only occur if they result in a change in the value of the subsidiary quantum number, l. Thus, allowed transition are s -> p, p -> d and d ->f.

A

Laporte’s selection rule

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32
Q

Define

Macrocycle effect

A

similar to the chelate effect however the effect is further enhanced by the cyclic conformation of the ligand. These ligands are not only multidentate, but because of their pre-organised structure there is little entropy penalty for wrapping it around the metal ion

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33
Q

Show both high-spin and low-spin filling for d4

A
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34
Q

Ligands up to an including _______ in the spectrochemical series usually give rise to high spin complexes

A

H2O

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35
Q

How does the crystal field splitting change from the second transition series compared to the first?

A

Increases by 50%

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36
Q

What causes high-spin arrangements?

A

When Δo is small

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37
Q

Define

Barycentre

A

the zero-energy reference in octahedral complexes

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38
Q

Definition

a compound or ionic species which can donate an electron pair to an acceptor compound

A

Lewis base

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39
Q

Define

Laporte’s selection rule

A

a spectroscopic selection rule that only applies to centrosymmetric molecules (those with an inversion centre) and atoms. It states that transitions can only occur if they result in a change in the value of the subsidiary quantum number, l. Thus, allowed transition are s -> p, p -> d and d ->f.

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40
Q

Define

Eg orbital

A

the collective name for the dz2 and the dx2-y2 orbitals

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41
Q

Definition

a model that describes the breaking of degeneracies of electron orbital states, usually d or f orbitals, due to a static electric field produced by a surrounding charge distribution

A

Crystal field theory

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42
Q

What is the general rule used to determine the value of the crystal field theory?

A

X- donor < O donor < N donor < C donor

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43
Q

What happens when 5 degenerate d orbitals are split into two sets?

A

3 t2g orbitals of lower energy and 2 eg orbitals of higher energy are produced

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44
Q

Define

Spin selection rule

A

a spectroscopic selection rule that states the a change in spin multiplicity is forbidden

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45
Q

Definition

Crystal field designation for an inner orbital complex; contains electrons paired t2g orbitals before eg orbitals are occupied in octahedral complexes

A

Low spin

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46
Q

Define

Chelate effect

A

the enhanced affinity of chelating ligands for a metal ion compared to the affinity of a collection of similar nonchelating (monodentate) ligands for the same metal

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47
Q

What is the electron configuration of Fe3+ ?

A

[Ar] 3d5

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48
Q

What factors effect crystal field splitting?

A
  1. The identity of the metal
  2. The oxidation state of the metal
  3. The number of the ligands
  4. The nature of the ligands
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49
Q

What does the splitting of d orbitals lead to?

A

Overall lowering of energy and consequently the complex is more stable than before the splitting

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50
Q

Define

ΔO

A

the difference in energy between eg and t2g

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51
Q

In compounds, what is an easy way to determine the number of d electrons?

A

The group number of the metal

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52
Q

Define

Crystal field theory

A

a model that describes the breaking of degeneracies of electron orbital states, usually d or f orbitals, due to a static electric field produced by a surrounding charge distribution

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53
Q

What is the energy separation between the t2g and the eg orbitals called?

A

Δoct

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54
Q

Definition

a geometric distortion of a non-linear molecular system that reduces its symmetry and energy. This distortion is typically observed among octahedral complexes where the two axial bonds can be shorter or longer than those of the equatorial bonds

A

Jahn-Teller distortion

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55
Q

Define

Eighteen electron rule

A

A rule based on the fact that the valence shells of transition metals consist of nine valence orbitals (one s orbital, three p orbitals and five d orbitals), which collectively can accommodate 18 electrons as either bonding or nonbonding electron pairs

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56
Q

What does the 18-electron rule state?

A

a complex is stable if there are 18 electrons around the metal

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57
Q

What is the electron configuration of V3+ ?

A

[Ar] 3d2

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58
Q

Definition

a substance whose molecules can form several bonds to a single metal ion. i.e. multidentate

A

Chelating agent

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59
Q

Definition

the zero-energy reference in octahedral complexes

A

Barycentre

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60
Q

Define

Chelating agent

A

a substance whose molecules can form several bonds to a single metal ion. i.e. multidentate

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61
Q

Definition

the enhanced affinity of chelating ligands for a metal ion compared to the affinity of a collection of similar nonchelating (monodentate) ligands for the same metal

A

Chelate effect

62
Q

Define

T2g orbital

A

the collective name for the dxy, dxz and dyz orbitals

63
Q

Definition

when the electronic charge shifts from the MO with metal-like character to the ligand-like one resulting in the oxidation of the metal centre

A

Metal-ligand charge transfer

64
Q

Define

Jahn-Teller distortion

A

a geometric distortion of a non-linear molecular system that reduces its symmetry and energy. This distortion is typically observed among octahedral complexes where the two axial bonds can be shorter or longer than those of the equatorial bonds

65
Q

How does the number of ligands effect crystal field splitting?

A

The crystal field splitting is greater for a larger number of ligands

66
Q

Convert the value of ΔO= 12600cm-1 for[Cu(OH2)6]2+ into kJ mol-1

ΔO = E = hvNO = hcNO/λ

Where h = 6.63 x 10-34 (J s; Plank’s constant)

c = 3 x 108 (m s-1; Speec of light)

NO = 6.022 x 1023 (mol-1; Avogadro’s constant)

A
67
Q

Which two selection rules determine whether a particular transition is allowed or forbidden?

A

Laporte’s selection rule

Spin selection rule

68
Q

What type of molecules does Laporte’s selection rule apply to?

A

Molecules that have a centre of inversion

69
Q

According to Laporte’s selection rule, why are tetrahedral complexes more strongly coloured than octahedral ones?

A

Tetrahedral complexes do not have a centre of inversion so Laporte’s rule does not apply to them like it does octahedral complexes which means that more transitions are allowed

70
Q

What orbital transitions occur in ligand-metal charge transfer?

A

p -> d

71
Q

When can metal-ligand charge transfer occur?

A

When the ligand has an empty p orbital that can accept electrons from the metal

72
Q

Why do d5 complexes only give a series of very weak absorption bands?

A

According to the spin selection rule, changes in spin multiplicity is forbidden. Since d5 complexes have 1 electron in each orbital no transitions are possible that wouldn’t break this rule

73
Q

(a) TiO2 is the most common white pigment, why is it white?

A
74
Q

(b) Explain why [Mn(OH2)6]2+ is a very pale pink colour

A
75
Q

(c) Explain why metal chromates (CrO42-) have been used as yellow pigments

A
76
Q

Why are tetrahedral complexes almost always high spin?

A

ΔT = 4/9 ΔO

77
Q

How does the splitting diagram for a tetrahedral complex compare to an octahedral complex? Why?

A

It is inverted; t2 (xy, xz, yz) orbitals are higher in energy, e (x2-y2, z2) orbitals are lower

Since tetrahedral complexes have only four ligands instead of six, the ligands don’t quite point directly at the three d orbitals, causing the crystal field splitting to be much less than in the octahedral case making them less stable

78
Q
A
79
Q

What geometric formation do complexes with 8d electrons tend to form?

A

Square planar

80
Q

True or False:

ΔSP > ΔO

A

True

81
Q

Show arrangement of electron in an a) octahedral, b) tetrahedral and c) square planar d8 metal ion

A
82
Q

Which octahedral complexes are effected by Jahn-Teller distortion? Why?

A

Octahedral complexes of d9, low-spin d7 and high spin d4 due to unsymmetrically filled eg orbitals

83
Q

True or False:

Jahn-Teller distortion decreases stability of complexes

A

False; the distortion increases crystal field splitting and enhances stability

84
Q
A
85
Q

What is the chelate effect caused by?

A

Differences in reaction entropy between chelated and nonchelated complexes in dilute solution. The chelation reaction results in an increase in the number of independent molecule in solution. By contrast, the nonchelating reaction produces no net change. The former therefore has the more positive reaction entropy and hence is the more favoured process

86
Q

Define

Antibonding orbital

A

a type of molecular orbital (MO) that weakens the chemical bond between two atoms and helps to raise the energy of the molecule relative to the separated atoms

87
Q

Define

Destructive interference

A

the interference of two waves of equal frequency and opposite phase, resulting in their cancellation where the negative displacement of one always coincides with the positive displacement of the other

88
Q

Define

Dissociation constant

A

a quantity expressing the extent to which a particular substance in solution is dissociated into ions, equal to the product of the concentrations of the respective ions divided by the concentration of the undissociated molecule

89
Q

Define

Electrode potential

A

the electromotive force of a cell built of two electrodes

90
Q

Define

Equilibrium constant

A

a number that expresses the relationship between the amounts of products and reactants present at equilibrium in a reversible chemical reaction at a given temperature

91
Q

Define

Formation constant

A

the equilibrium constant for the formation of a complex ion from its components in solution

92
Q

Define

Hess’s law

A

A law that states that regardless of the multiple stages or steps of a reaction, the total enthalpy change for the reaction is the sum of all changes

93
Q

Define

Hund’s rule

A

every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin

94
Q

Define

Irving-Williams series

A

the relative stabilities of complexes formed by transition metals as represented in a diagram

95
Q

Define

Latimer diagram

A

a summary of the standard electrode potential data of that element

96
Q

Define

Ligand field theory

A

one of several theories that describe the electronic structure of coordination or complex compounds, notably transition metal complexes. It factors in the effects of π bonds as well as σ bonds

97
Q

Define

Oxidation

A

the loss of electrons during a reaction by a molecule, atom or ion

98
Q

Define

Pauli exclusion principle

A

in an atom or molecule, no two electrons can have the same four electronic quantum numbers

99
Q

Define

π-acids

A

a ligand that accepts electron density into it’s p orbital from the metal center

100
Q

Define

π-bases

A

a ligand with filled π-type orbitals that donates electron density to the metal center

101
Q

Define

π bond

A

a covalent bond formed between two neighboring atom’s unbonded p-orbitals

102
Q

Define

σ bond

A

the strongest type of covalent chemical bond that are formed by head-on overlapping between atomic orbitals

103
Q

Define

σ-donor ligands

A

A ligand that when coordinated to metal, it forms one single sigma bond

104
Q

Define

Reduction

A

reaction that involves the gaining of electrons by one of the atoms involved in the reaction

105
Q

Define

Thermodynamic cycle

A

a series of thermodynamic processes which returns a system to its initial state

106
Q

Definition

a type of molecular orbital (MO) that weakens the chemical bond between two atoms and helps to raise the energy of the molecule relative to the separated atoms

A

Antibonding orbital

107
Q

Definition

the interference of two waves of equal frequency and opposite phase, resulting in their cancellation where the negative displacement of one always coincides with the positive displacement of the other

A

Destructive interference

108
Q

Definition

a quantity expressing the extent to which a particular substance in solution is dissociated into ions, equal to the product of the concentrations of the respective ions divided by the concentration of the undissociated molecule

A

Dissociation constant

109
Q

Definition

the electromotive force of a cell built of two electrodes

A

Electrode potential

110
Q

Definition

a number that expresses the relationship between the amounts of products and reactants present at equilibrium in a reversible chemical reaction at a given temperature

A

Equilibrium constant

111
Q

Definition

the equilibrium constant for the formation of a complex ion from its components in solution

A

Formation constant

112
Q

Definition

A law that states that regardless of the multiple stages or steps of a reaction, the total enthalpy change for the reaction is the sum of all changes

A

Hess’s law

113
Q

Definition

every orbital in a subshell is singly occupied with one electron before any one orbital is doubly occupied, and all electrons in singly occupied orbitals have the same spin

A

Hund’s rule

114
Q

Definition

the relative stabilities of complexes formed by transition metals as represented in a diagram

A

Irving-Williams series

115
Q

Definition

a summary of the standard electrode potential data of that element

A

Latimer diagram

116
Q

Definition

one of several theories that describe the electronic structure of coordination or complex compounds, notably transition metal complexes. It factors in the effects of π bonds as well as σ bonds

A

Ligand field theory

117
Q

Definition

the loss of electrons during a reaction by a molecule, atom or ion

A

Oxidation

118
Q

Definition

in an atom or molecule, no two electrons can have the same four electronic quantum numbers

A

Pauli exclusion principle

119
Q

Definition

a ligand that accepts electron density into it’s p orbital from the metal center

A

π-acids

120
Q

Definition

a ligand with filled π-type orbitals that donates electron density to the metal center

A

π-bases

121
Q

Definition

a covalent bond formed between two neighboring atom’s unbonded p-orbitals

A

π bond

122
Q

Definition

the strongest type of covalent chemical bond that are formed by head-on overlapping between atomic orbitals

A

σ bond

123
Q

Definition

A ligand that when coordinated to metal, it forms one single sigma bond

A

σ-donor ligands

124
Q

Definition

reaction that involves the gaining of electrons by one of the atoms involved in the reaction

A

Reduction

125
Q

Definition

a series of thermodynamic processes which returns a system to its initial state

A

Thermodynamic cycle

126
Q

What does ligand field theory factor in that crystal field theory doesn’t?

A

Pi bonds

127
Q

What type of bond is this?

Electron density appears along the internuclear axis and cylindrical symmetry around the internuclear axis. That means if we rotate the orbitals around the z-axis there is no change of phase

A

Sigma bond

128
Q

What type of bond is this?

A nodal plane exists along the internuclear axis, lack of cylindrical symmetry. That means if we rotate the orbitals around the z-axis there is a change of phase

A

Pi bond

129
Q

In sigma donor ligands, if no pi bonding is present the energy difference between the t2g and eg orbitals corresponds to what?

A

Δoct

130
Q

Sigma donors _________ electrons from lone pairs to the metal centre from either the s or p orbitals

A

Sigma donors donate electrons from lone pairs to the metal centre from either the s or p orbitals

131
Q

What are the valence shell atomic orbitals for a first row transition metal?

A

3d, 4s and 4p

132
Q

Combinations of the metals and ligand orbitals generate _____ bonding and ____ anti-bonding molecular orbitals

A

Combinations of the metals and ligand orbitals generate 6 bonding and 6 anti-bonding molecular orbitals

133
Q

When there is no pi bonding present, which is the only molecular orbital that does not interact with the ligand group?

A

t2g orbital

134
Q

True or False:

π-acids donate electron density to the metal centre

A

False

π-bases donate electron density to the metal centre

135
Q

How does π-bases affect the molecular orbital splitting diagram from the sigma only version?

A
136
Q

How does π-acids affect the molecular orbital splitting diagram from the sigma only version?

A
137
Q
A
138
Q

What does the formation constant represent?

A

It indicates the strength of binding of the ligand relative to water: if Kf is large, the incoming ligand binds more strongly than the solvent; if Kf is small, the ligand binds more weakly than water

139
Q
A
140
Q
A
141
Q

What is the inverse of Kf? Why is it useful?

A

The inverse of each Kf is the dissociation constant, Kd , which is often preferred when we are interested in the concentration of ligand that is required to give a certain concentration of complex. Kd is the ligand concentration required to obtain 50% complexations

142
Q
A
143
Q

Why is there a consistent decrease in the stepwise formation constant as you replace ligands in a complex?

A

The decrease in the stepwise formation constant reflects the diminishing statistical factor as successive ligands are replaced, coupled with the fact that an increase in the number of bound ligands increases the likelihood of the reverse reaction

144
Q

If Kf<em>n </em>> Kf<em>n+1,</em> what has most likely occurred?

A

A major change in the electronic structure of the complex as more ligands are added (i.e. change in spin)

145
Q
A
146
Q
A
147
Q

Explain the shape of the plot observed in the Irving Williams series. Explain the general increase left to right, the deviation from linear and the maximum at Cu

A
148
Q

True or False:

The smaller the value of EO , the greater the tendency for reaction to occur left to right

A

False

The greater the value of EO , the greater the tendency for reaction to occur left to right

149
Q
A
150
Q
A
151
Q
A

CHM2911 (4 decks)

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