Transition Metal Chemistry Flashcards
(89 cards)
1
Q
Vanadium favoured oxidation state (and why)
A
+3
because of relatively low Zeff and accessible low I3
2
Q
Reaction of V (II) with water
A
V (II) is a powerful reducing agent and reduces water forming H2 gas
3
Q
What is formed on reuction of V (V) in acid
A
V (III)
4
Q
What is the most stable form of V (IV) in water
A
[V=O(H2O)5]2+
which is the vanadyl ion
the hexaquo ion for V (IV) is not known
5
Q
What is the most common form of V (V)
A
V2O5
6
Q
What is the most stable and common oxidation state of Cr
A
+3
7
Q
How can Cr (II) be formed
A
reduction of Cr (III) with Zn/HCl
8
Q
What special kind of complexes can Cr metal ions form
How might these be produced?
A
dimeric complexes with Cr-Cr multiple bonds
These are formed by reacting Cr (II) with acetate
9
Q
What is a common property of Cr complexes
A
Jahn-Teller distorted
10
Q
What is formed by Cr (II) and fluorides/chlorides
A
octahedral coordinated complexes which adopt the distorted rutile structure
(because of Jahn-Teller distortion)
11
Q
What is a powerful oxidising agent which contains Cr
A
Cr (VI) in acid for example [Cr2O7]2-
12
Q
What is a useful property of Mn
A
Mn exhibits the widest range of oxidation states of any of the 3d metals.
13
Q
What is the most stable oxidation state of Mn
A
+2
(half filled shell stabilisation)
14
Q
What is a strong oxidising agent containing Mn
A
[MnO4]-
15
Q
What structure does MnO2 adopt
A
distorted rutile structure
16
Q
Many forms of MnO2 are __________
A
polymeric
17
Q
What are two properties of MnO2
A
- used in alkaline batteries
- is an oxidising agent
18
Q
Are most Mn (III) complexes high or low spin
A
high spin
note: expect with strong field ligand e.g. CN-
19
Q
Mn (II) complexes are generally stable to both ____ _____
A
oxidation and reduction
20
Q
What is the order of orbitals in square planar crystal field splitting
include the position of the barycentre
A
d x^2-y^2
dxy
barycentre
dz^2
dxz dyz
21
Q
what is Δsp =
A
Δsp = Δo
22
Q
relate Δo and Δt
A
Δt = 4/9 Δo
23
Q
what is the symmetry notation for dxy dxz and dyz in octahedral crystal field splitting
A
t2g
24
Q
what is the symmetry notation for dxy dxz and dyz in tetrahedral crystal field splitting
A
t2
25
what is the symmetry notation for dx2-y2 and dz2 in octahedral crystal field splitting
eg
26
what is the symmetry notation for dx2-y2 and dz2 in tetrahedral crystal field splitting
e
27
What are the dominant oxidation states of Fe
Fe (II) and Fe (III)
28
What happens to Fe (II) in water over time
oxidation to Fe (III)
29
Why does oxidation of Fe (II) happen spontaneously if it is the most stable form
This occurs despite the +2 oxidation state being the most stable because of the lower than expected I3 of Fe (d6 not exchange energy stabilised)
## Footnote
this is why both +2 and +3 oxidation states are accessible
30
[Fe(en)3]2+ is high or low spin
high spin even though en is just above NH3 in the spectrochemical series
31
Why are weak field ligands weak
π donors leading to Δ decreasing by overlap with t2g
32
why are mid field ligands mid
are neither π donors or π acceptors - only σ donors
33
Why are strong field ligands strong
they are π acceptors and this leads to an increase in Δ
34
[Fe(en)3]3+ is high or low spin
low spin!
35
what is a common property of Fe (VI) complexes
strong oxidising agents
36
what is the highest oxidation state exhibited by cobalt
+4
37
what is cobalt's most stable oxidation state
+2
38
why are higher (>4) oxidation states not available for cobalt
higher Zeff in the late transition metal series
39
is [CoF6]2- high or low spin
low spin (high oxidation state outweighs low field ligand)
40
Is [CoF6]3- high or low spin
high spin (+3 not high enough to overcome effect of low field ligand)
41
Is Co (III) with mid-field H2O ligands high or low spin
low spin
42
[Co(H2O)6]3+ is a ___
powerful oxidising agent
43
[Co(H2O)6]3+ is ____ in aqueous solution and ___
1. unstable
2. decomposes to give Co (II)
44
is [Co(NH3)6]2+ high or low spin
low spin
## Footnote
as are most Co (III) complexes
45
[Co(H2O)6]2+ is ____ to oxidation because...
1. stable
2. because of the high I3
46
[Co(H2O)6]2+ + HCl --> ?
[CoCl4]-
47
how can you stabilise Ni (0) complexes (give an example of this)
π acceptors such as CO:
Ni(CO)4
48
what is the most stable (and only significant) oxidation state of Nickel
+2
49
metallic Cu + acid -->
no reaction (doesn't product H2)
50
why doesn't metallic Cu react with acid to produce hydrogen gas
not reducing
51
Cu+ is unstable in water (acid) with respect to ____
disproportionation to Cu and Cu (II)
52
when is Cu+ stable
when stabilised by ligands such as thiourea which are soft
this is because there is a good match between the soft Lewis acid and soft ligands
53
Cu+ + air --> ?
Cu2+
54
Cu2+ can be reduced by which organic functional group and what is produced
Red Cu2O precipitates when Cu2+ is reduced by **aldehydes**
This is Fehling's solution to test for aldehydes
55
Tetrahedral and octahedral Cu (II) complexes are both...
distorted due to the Jahn-Teller distortion
56
what structure does CuF2 adopt...
CuF2 adopts the distorted rutile structure
57
The chemical properties of transition metals generally depend on...
1. exchange energy
2. ionisation energies
3. electron-electron repulsion
4. (for aqueous cations) hydration enthalpies
58
Trends in hydration and lattice enthalpies are accounted for by...
1. trends in cation radius with an increase in Zeff across the period
2. LFSE trends
3. Jahn-Teller distortion
59
What is the limitation of Crystal Field Theory
it cannot explain the spectrochemical series and this instead requires the use of ligand-field theory
60
What is chelation and what effect does this have
chelation involves binding multidentate ligands to transition metals, and this improves the stability of the complex (chelate effect) mainly through entropic effects
61
what is the order of orbitals in trigonal bipyramidal crystal field splitting
include the position of the barycentre
dz^2
barycentre
dxy, dx^2-y^2
dxz, dyz
62
what is the order of orbitals in octahedral crystal field splitting
include the position of the barycentre
dz^2 + dx^2-y^2 (eg)
barycentre
dxz + dxy + dyz (t2g)
63
what is the distance of the t2 orbitals from the barycentre for tetrahedral
+2/5 Δt
64
what is the distance of the e orbitals from the barycentre for tetrahedral
-3/5 Δt
65
what is the distance of the t2g orbitals from the barycentre for octahedral
-2/5 Δo
66
what is the distance of the eg orbitals from the barycentre for octahedral
+3/5 Δo
67
what are the different types of isomerism exhibited by transition metal compounds
1. linkage isomerism
2. geometric
3. ionisation
4. chirality and optical isomerism
5. hydrate isomerism
68
what are the different geometric isomers of transition metal complexes
1. square planar:
cis or trans
2. octahedral:
(if two same) cis or trans
(if 3 same) fac or mer
3. trigonal bipyramidal:
axial or equatorial
69
what transition metal complexes can be chiral?
2 or three bidentate ligands
if two the monodentate ligands must be cis to each other
70
What is the order of energies of 3d, 4s, and 4p orbitals for K
4s < 4p < 3d
71
What is the order of energies of 3d, 4s, and 4p orbitals for Ca
4s < 3d < 4p
3d orbital energy drops faster with increasing nuclear charge than 4s due to a closer average distance to the nucleus
72
What is the order of energies of 3d, 4s, and 4p orbitals for Sc
3d < 4s < rp
This is because the 3d electrons shield the electrons in the 4s orbital since there is also a high probability of the 4s orbitals being further away from the nucleus as seen in the RDF.
73
What is the order of energies of 3d, 4s, and 4p orbitals for Zn
3d << 4s < 4p
74
what is the relative ordering of coloumbic replusion in and between s and d orbitals
R(s-s) < R(s-d) < R(d-d)
Coulombic repulsion is greatest in the 3d orbital because it is more contracted
75
Describe the general trend in ionisation energies of transition metals moving across the period
## Footnote
include note about I1, I2, and I3
There is a general increase in IE across as a result of increasing Zeff.
I1 and I2 are relatively low whilst I3 exhibits pronounced deviations from a linear trend as a result of exchange energy effects.
76
Why is I2 anomalously high fr Cr and Cu
This is due to the shift from the 4s to the 3d orbitals (as a result of only a singularly filled 4s orbital)
77
Why is there a decrease in I3 from Mn to Fe
The extra electron in Fe is not exchange energy stabilised and so is more readily lost - also as a result of Coulombic electron repulsion between the electron pair
78
Describe the change in electronegativity across the 3d block
There is a relatively small increase in χ across. The change is smaller than that for the s or p series. The values also lie between those of their neighbours (the 4s and 4p elements).
79
What is a consequence of increasing electronegativity across the 3d period.
MXn compounds become more covalent across the transition metal series
80
Compounds with transition metals in ____ oxidation states are ____ because...
Compounds with transition metals in higher oxidation states are highly covalent because of the very polarising nature of the cations.
81
81
Discuss the reduction potentials of the M(III)/M(II) redox couples for transition metals
Periodic trends correlate with the ionisation energies in the gas phase. The enthalpy change associated with the reduction depends on the hydration enthalpies of the cations and the ionisation energies, where I3 dominates those trends.
82
What affects the hydration enthalpy of transition metal cations
* d electron configuration
* ligand field stabilisation energy
* cation radius
* cation charge
83
What does the enthalpy of atomisation of a metal refer to
The enthalpy of atomisation refers to the breaking of all metal-metal bonds in a solid to form the isolated metal atoms in the gas phase (also referred to as sublimation).
84
Why does the enthalpy of atomisation of transition metals follow a distinctive M shape with Mn at a local minimum
The overlap of the metal d orbitals leads to bands of different bonding character. The bands are generally filled using the Aufbau principle but exchange energy can lead to non-Aufbau filling of the orbitals.
It would be assumed the maximum would be for Cr where all of the bonding orbitals have been filled and the lowest for Zn. However, non-Aufbau filling of the orbitals means that Mn actually fills all the bonding and non-bonding orbtials to maximise exchange energy, weakening the bonds. This effect is exemplified by the maximised exchange energy in Mn (g).
85
Why are the enthalpies of hydration of M(II) cations greater for Ca, Mn, and Zn
Because they have d electron counts of 0, 5, and 10 respectively. This means that there is no ligand field stabilisation energy (for high spin cases)
86
Why are the enthalpy of hydration of some ions more exothermic than the overall trend
Because they show extra stabilisation in a octahedral coordination environment (e.g. by LFSE)
87
What is the general trend in the enthalpy of hydration of M(II) cations moving across period 4
Decreases (i.e. becomes more exothermic) across the period, mainly due to cation radius effects.
88
What are the factors which affect the lattice enthalpies of transition metal compounds
CFSE is the major cause of deviations (larger CFSE causes a more exothermic lattice enthalpy)
coordination, e.g. octahedral or tetrahedral
cation radius
Jahn Teller distortion for copper octahedral coordinations
