Chem 3840 Test 2 – Spring 2009
Answers
March 9th, 2009: 10:00 to 10:50 am
Your name _______________
Instructor: Dr. M. Gerken
Student ID _______________
Time: 50 min
No. of pages: 3+3
Answer all questions on the question sheet in the space provided.
Q1
Q2
Q3
Q4
Total
Percent
11
19
3
9
42
100 %
Question 1 (11 Marks)
Determine the term symbol for the ground state of a carbon atom in the gas phase? What is the overall
multiplicity (degeneracy) of this spectroscopic state?
valence electron configuration of C: 2s2 2px1 2py1 2pz0
maximum MS = Σ ms = ½ - ½ + ½ + ½ =1
S=1
2S +1 = 3
maximum ML = Σ ml = 0 + 0 + 1 + 0 =1
L=1
hence, P term
term symbol: 3P
Multiplicity:
spin = 3
orbital = 2L +1 = 3
overall multiplicity 3x3 = 9
The spectroscopic ground state of atomic carbon is nine-fold degenerate.
1-6
Question 2 (19 Marks)
The two salts, almost colourless [Fe(H2O)6]Cl3 and red K3[Fe(CN)6], contain complexes of iron.
(a) Name these two salts.
[Fe(H2O)6]Cl3 : hexaaquairon(III) chloride
K3[Fe(CN)6]: potassium hexacyanoferrate(III)
(b) What are the valence electron configurations of iron in these two complexes? Briefly explain your
answers.
[Fe(H2O)6]Cl3 :
free ion configuration: 3d5
configuration of iron in the Oh complex: (t2g)3 (eg)2 .i.e. high-spin
The aqua ligand is a rather weak-field ligand, hence the complex is a high-spin complex.
K3[Fe(CN)6]:
free ion configuration: 3d5
configuration of iron in the Oh complex: (t2g)5 (eg)0.i.e. low-spin
The cyano ligand is a strong-field ligand, hence the complex is a low-spin complex.
(c) Use the correct Tanabe-Sugano Diagram to predict the most intense d-d transition for K3[Fe(CN)6].
How many bands do you expect to see in the UV/visible spectrum of this salt.
2
A2g ← 2T2g
2
T1g ← 2T2g
2
Eg ← 2T2g
2
A1g ← 2T2g
The first two transitions have the same energy, hence three spin-allowed d-d transitions are expected.
(d) Why is [Fe(H2O)6]Cl3 almost colourless.
Iron has a high-spin electron configuration in this complex and all d-d transitions are spin-forbidden.
(e) Fe2O3 (octahedral coordination about iron) is intensely red (rust colour). Why is Fe2O3 so intensely
coloured?
The intense coloration of iron in rust is due to a ligand-to-metal charge transfer.
2-6
Question 3 (3 Marks)
Name one synthetic route of distannens. Describe very briefly the synthetic approach.
In general, three major preparative routes have been used to prepare distannenes:
1. Dimerization of carbene analogues (stannylenes)
West et al. used this approach, preparing an intermediate silylene. In the preparation of distannenes and
digermenes, stable stannylenes and germylenes have been prepared in solution, which dimerize in the solid state;
however, those distannenes and digermenes usually dissociate in solution.
2. Cleavage of three-membered rings
The photochemical cleavage of cyclotrisilanes was employed by Masamune. Photolysis and thermolysis of
cyclotristannanes and cyclotrigermanes have been used to prepare the compounds with double bonds between the
heavy group-14 elements.
3. Reductive coupling and elimination reactions
Reaction silicon, germanium and tin organohalides using reducing agents, such as lithium naphthalenide (LiNp)
can lead to cyclic species. Increasing the bulk of the organic ligands on the group-14 element disfavours the
formation of a cycle and leads directly to the formation of the double bonded species. Ligands such as
bis(trimethylsilyl)methyl, 2,4,5-triisopropylphenyl (tip), and 2,6-diisopropylphenyl (dip) are large enough to
allow for the direct reductive formation of the double bond.
Question 4 (9 Marks)
How many possible isomers of the [Co(en)2Cl2]Br exist? Label all possible isomers with the appropriate
formula + geometry descriptors. What types of isomers are they?
trans-[Co(en)2Cl2]Br
cis-[Co(en)2Cl2]Br, which is chiral, hence: cis-Δ-[Co(en)2Cl2]Br
cis-Λ-[Co(en)2Cl2]Br
there are also the ionization isomers, where chlorine and bromine are exchanges as the ligand and anion:
trans-[Co(en)2ClBr]Cl
cis-[Co(en)2ClBr]Cl, which is chiral, hence:
cis-Δ-[Co(en)2ClBr]Cl
cis-Λ-[Co(en)2ClBr]Cl
Six isomers are possible.
trans-[Co(en)2Cl2]Br and cis-[Co(en)2Cl2]Br are geometric isomers
cis-Δ-[Co(en)2Cl2]Br and cis-Λ-[Co(en)2Cl2]Br are optical isomers
the [Co(en)2ClBr]Cl isomers are ionization isomers
3-6
DATA SHEET
Spectrochemical series:
{small orbital splitting, } I < Br < S < SCN- < Cl- < NO3- < F- < C2O42- < H2O < NCS- < CH3CN <
NH3 < en < bipy < phen < NO2- < PPh3 < CN- < CO {large orbital splitting, }
-
1
2-
Chem 3840 Standard Periodic Table
Electronegativities are given in [ ]
1.0079
1H
-
18
4.0026
2He
hydrogen
[2.1]
6.941
2
13
14
15
16
17
helium
9.0122
10.811
12.011
14.0067
15.9994
18.9984
20.1797
3Li
4Be
5B
6C
7N
8O
9F
10Ne
boron
[2.0]
26.9815
carbon
[2.5]
28.0855
nitrogen
[3.0]
30.9738
oxygen
[3.5]
32.066
fluorine
[4.0]
35.4527
neon
39.948
13Al
14Si
16S
17Cl
18Ar
silicon
[1.8]
72.61
15P
phosphorus
chlorine
[3.0]
79.904
argon
[2.1]
74.9216
sulfur
[2.5]
78.96
32Ge
germanium
33As
34Se
35Br
36Kr
lithium berrylium
[1.0]
[1.5]
22.9898 24.3050
11Na
sodium
[1.0]
39.0983
19K
12Mg
magnesium
[1.2]
40.078
3
4
5
6
7
8
9
10
11
44.9559
47.88
50.9415
51.9961
54.9380
55.847
58.9332
58.693
63.546
65.39
aluminum
[1.5]
69.723
20Ca
21Sc
22Ti
23V
24Cr
25Mn
26Fe
27Co
28Ni
29Cu
30Zn
31Ga
iron
[1.7]
101.07
cobalt
[1.7]
102.906
nickel
[1.8]
106.42
copper
[1.8]
107.868
zinc
[1.6]
112.411
gallium
[1.7]
114.82
44Ru
45Rh
46Pd
47Ag
48Cd
49In
potassium calcium
[0.9]
[1.0]
85.4678
87.62
37Rb
38Sr
rubidium strontium
[0.9]
[1.0]
132.905 137.327
55Cs
56Ba
cesium
[0.8]
(223)
barium
[1.0]
(226.025)
87Fr
88Ra
francium
[0.8]
radium
[1.0]
scandium titanium vanadium chromium manganese
[1.6]
[1.3]
[1.4]
[1.5]
[1.6]
88.9059 91.224 92.9064
95.94
(98)
39Y
40Zr
41Nb
yttrium zirconium niobium
[1.3]
[1.4]
[1.5]
178.49 180.948
La-Lu
72Hf
73Ta
hafnnium tantalum
[1.3]
[1.4]
(261)
(262)
Ac-Lr
104Rf
rutherfordium
105Db
42Mo
43Tc
molybdenum technetium
[1.6]
183.85
ruthenium rhodium palladium silver cadmium indium
[1.6]
[1.7]
[1.7]
[1.8]
[1.8]
[1.6]
[1.6]
186.207
190.2
192.22
195.08 196.967 200.59 204.383
75Re
76Os
77Ir
78Pt
79Au
80Hg
81Tl
82Pb
osmium
[1.9]
(269)
iridium
[1.9]
(268)
platinum
[1.8]
(271)
gold
[1.9]
mercury
[1.7]
thallium
[1.6]
lead
[1.7]
106Sg
107Bh
108Hs
109Mt
158.925
162.50
164.930
66Dy
67Ho
dysprosium holmium
144.24
(145)
hassium meitnerium
150.36
140.908
59Pr
151.965
157.25
65Tb
lanthanum cerium
(227.028) (232.038) (231.036) (238.029) (237.048)
60Nd
61Pm
62Sm
63Eu
64Gd
praesodymium neodymium promethium samarium europium gadolinium
protactinium
93Np
51Sb
selenium bromine
[2.4]
[2.8]
127.60 126.905
52Te
antimony tellurium
[1.9]
[2.1]
208.980
(210)
83Bi
84Po
(244)
(243)
(247)
terbium
(247)
94Pu
95Am
96Cm
97Bk
uranium neptunium plutonium americium curium
4-6
(251)
(252)
83.80
krypton
[2.9]
131.29
53I
54Xe
iodine
[2.5]
(210)
xenon
[2.3]
(222)
85At
86Rn
bismuth polonium
[1.8]
[1.9]
astatine
[2.1]
radon
167.26
168.934
173.04
174.967
68Er
69Tm
70Yb
71Lu
110Ds
58Ce
92U
arsenic
[2.1]
121.757
darmstadtium
140.115
actinium9 thorium
tin
[1.8]
207.19
rhenium
[1.7]
(264)
dubnium seaborgium bohrium
91Pa
50Sn
74W
57La
90Th
[1.9]
118.710
tungsten
[1.5]
(266)
138.906
89Ac
12
erbium
(257)
thulium ytterbium lutetium
(258)
(259)
(262)
98Cf
99Es
100Fm 101Md
102No
103Lr
berkelium californium einsteinium fermium mendelevium nobelium lawrencium
5-6
6-6