Download CH160 (Coordination Chemistry – APD) Tutorial

CH160 (Coordination Chemistry – APD) Tutorial
Answer all questions and put your answers in your tutor’s pigeon hole at least 24 hours before
your tutorial – be ready to discuss your answers in the tutorial. Also bring any questions you
might have to clarify anything you are unsure about.
1. For the following list of eight compounds a) to h)
i)
ii)
iii)
Write down the oxidation state of the d-block metal
State the dn electron configuration
Sketch, label (e.g. cis, fac,  etc) and name the type of isomerism (e.g.
“stereoisomerism - optical isomerism”) for all possible isomers
a) [PtCl2(PPh3)2]
b) [CrCl(OH2)5]Cl2
c) [Co(L)(NH3)5]Br2
d) [CoCl2(NH3)4]
e) [PdBrCl(NH3)(PPh3)]
f) [CoCl2(en)2]
g) [Fe(phen)3]Cl3
h) [CrCl3(OH2)3]
en is ethylene diamine (H2NCH2CH2NH2), phen is 1,10-phenanthroline and L is NO2-
a)
Oxid. dn config.
Isomer Sketch
State
+2
[Xe]4f145d8
Isomer
label
Isomerism Type
cis-
Stereoisomerism
- geometric
trans-
b) +3
[Ar]3d3
Strictly as written in the
question you could easily
argue no isomers. However,
this is more of an
opportunity to talk about
solvate isomerism and then
the different stereoisomers
within those
[CrCl(OH2)5]Cl2
[CrCl2(OH2)4]Cl
[CrCl3(OH2)3]
[Cr(OH2)6]Cl3
In aqueous solution:
Constitutional isomerism
- solvate
N.B. in [CrCl2(OH2)4]Cl
possible cis/trans
isomerism and
[CrCl3(OH2)3] – fac/mer
c)
+3
[Ar]3d6
Constitutional isomerism
- linkage
(could also have ionization
isomerism with exchange
of Br outer sphere with
NO2 inner sphere ligand)
d) +2
[Ar]3d7
cis-
Stereoisomerism
- geometric
trans-
e)
+2
[Kr]4d8
Stereoisomerism
- geometric
f)
+2
[Ar]3d7
trans-
Stereoisomerism
- geometric
-
- optical
-
g)
+3
[Ar]3d5
-
Stereoisomerism - optical
-
h) +3
[Ar]3d3
fac-
mer-
Stereoisomerism
- geometric
2. Reaction (1) shows the conversion between linkage isomers (the scheme is written to highlight
how the ligand bonds to the metal) whereas reaction (2) does not. Rationalise these observations.
Where dien is a nitrogen donor, tridentate ligand with formula: H2NCH2CH2NHCH2CH2NH2 and
Et4dien is the more hindered derivative: (C2H5)2NCH2CH2NHCH2CH2N(C2H5)2
Pt is a soft acid so in the absence of any other driver would prefer to bond to the ligand via
the ‘softer’ S donor hence [Pt(SCN)4]. However, the SCN ligand has a bent geometry when
bonded via S, and an increase in steric hindrance brought about by the sterically hindered
Et4dien forces it to the N-bonded case, which has linear geometry (an example of linkage
isomerism). The dien ligand is less bulky so does not force the isomerisation to occur. You
may also want to talk about why the Et4dien binds in preference to 2x SCN ligands, i.e.
chelate effect.
3. Predict the equilibrium position for the following reactions. Explain your reasoning and outline
the driving force(s) for the reaction
i) [RuCl3(OH2)3] + 3NaCN
ii) [Pd(NH3)2(OH2)2]2+ + 2 PMe3
i) Students should identify that NaCN is to deliver CN-. Substitution of CN- for Cl- is
strongly favoured by CFSE, i.e. CN- is much stronger field ligand. Coulombic interactions
may reduce Kf (i.e. getting CN- past ‘negatively charged’ ligands. Therefore probably on
balance we would expect substitution of Cl- with CN-.
ii) Expect to lie towards products i.e. [Pd(NH3)2(PMe3)2] + 2 H2O. Phosphine is softer than
aqua ligand, which is harder than ammine (Pd is soft) therefore will form a favourable softsoft metal-ligand complex. Sterics are a factor (Phosphine is larger than aqua ligand) but
given no other major steric constraints around the metal this is not likely to be a significant
factor. Phosphine is stronger field ligand than aqua therefore CFSE favourable for
substitution.
Note, in both cases suseccive substitutions are expected to get harder/more disfavoured (i.e.
decreasing Kf) due to statistical reasons