Y1S Computational Experiment Assessment – Questions preview
Question 1
Question 5
Which is more stable, the cis or trans square planar structure of NiCl2(PH3)2 at:
For each of [NiCl4]2-, NiCl2(PH3)2 and NiCl2(dHpe), is the tetrahedral or square
planar structure more stable?
the 3-21G level?
the 6-21G(d) level?
Question 6
Question 2
What is the energy difference between the cis and trans structures of NiCl2(PH3)2
at the 3-21G level?
Give your answer as a magnitude (ie. no sign) and as an integer (to the nearest
kJmol-1).
What is the energy difference between the square planar structure and the
tetrahedral structure for [NiCl4]2- at the 6-31G(d) level?
Question 7
What is the energy difference between the lower energy square planar structure
and the tetrahedral structure for NiCl2(PH3)2 at the 6-31G(d) level?
Question 3
What is the energy difference between the cis and trans structures of NiCl2(PH3)2
at the 6-31G(d) level?
Question 8
What is the energy difference between the square planar structure and the
tetrahedral structure for NiCl2(dHpe) at the 6-31G(d) level?
Question 4
Considering your answers to the preceding questions, compare the 3-21G and 631G(d) levels of calculation.
Question 9
Question 12
Processes with energy barriers of 80 kJmol-1 or less will occur spontaneously at
room temperature, such barriers are thermally accessible.
Considering your answers to the preceding questions, indicate whether the
difference between the experimental and computational bond lengths is
systematic and/or significant.
Assuming activation energies of approx. 30 kJmol-1 for the conversion from
square planar to tetrahedral, for which complex(es) would you expect both the
square planar and tetrahedral structures to exist in equilibrium in solution at
room temperature?
Question 13
Is there a significant difference in the computed Ni-Cl bond lengths between the
cis square planar structures of NiCl2(PH3)2 and NiCl2(dHpe)?
Question 10
For a given structure, it is common to observe in bond lengths from different
experimental crystal structures small variations which are not significant in the
study of the molecule's structure. An example is the Ni-Cl bond lengths in
NiCl2(PPh3)2.
Question 14
For each structure of NiCl2(PH3)2 indicate whether the Ni-Cl and Ni-P stretching
modes are well resolved or mixed (not well resolved).
What is the variation in Ni-Cl bond lengths across the crystal structures reported
in the articles below?
Give your answer to 2 decimal places.

B. Corain, B. Longato, R. Angeletti, G. Valle; Inorg. Chim. Acta; 1985; 104;
15

S. Batsanov, J. A. K. Howard; Acta Cryst.; 2001; E57; m308

J. Sletten, J. A. Kovacs; Journal of Crystallographic and Spectroscopic
Research; 1993; 23(3); 239 (now J. Chem. Crystallogr.)
Question 15
Compare the Ni-Cl/Ni-P combined totally symmetric mode in NiCl2(PH3)2 to that in
NiCl2(dHpe). What does the difference in frequency indicate?
Question 16
For the trans square planar NiCl2(PH3)2 complex, what type of vibrations are the
modes in the following frequency ranges:
Between 2500 and 2600 cm-1 ?
Question 11
Between 1000 and 1150 cm-1 ?
Compare the Ni-Cl and Ni-P bond lengths in the experimental crystal structures of
NiCl2(PPh3)2 with the computed structure of NiCl2(PH3)2.
Below 100 cm-1 ?
Question 17
Question 23
What is the energy of the LUMO for trans square planar NiCl2(PH3)2?
What is the energy of MO48 for trans square planar NiCl2(PH3)2?
You should consider the sign, as well as the magnitude, of the energy. Give your
answer in au and to 3 decimal places.
Question 24
What is the energy of MO47 for trans square planar NiCl2(PH3)2?
Question 18
What is the nature of the LUMO of trans square planar NiCl2(PH3)2?
Question 25
What is the energy of the MO46 for trans square planar NiCl2(PH3)2?
Question 19
Which MO is the bonding counterpart of the LUMO, formed from the same metal
and ligand orbitals?
Question 26
For trans square planar NiCl2(PH3)2 identify which metal d orbital is contributing to
each of the following MOs:
Question 20
What is the energy of the HOMO for trans square planar NiCl2(PH3)2?
MO48
MO47
MO46
Question 21
Question 27
What is the nature of the HOMO of trans square planar NiCl2(PH3)2?
Considering your answers to the preceding questions, do the computed relative
energies of the d orbitals match what you would expect based on crystal field
theory?
Question 22
Which MO is the counterpart of the HOMO, formed from the same metal and
ligand orbitals?
(Ie. is the order the same?)
Question 28
Question 32
What is the nature of MO45?
Given the HOMO-LUMO energy gaps you have just calculated, what colour (if any)
would you expect to observe for each of the complexes below?
Trans square planar NiCl2(PH3)2
Cis square planar NiCl2(PH3)2
Tetrahedral NiCl2(PH3)2
Question 29
What is the computed HOMO-LUMO energy gap for trans square planar
NiCl2(PH3)2?
Give your answer as an integer in kJmol-1.
You should assume:


Question 30
a broad absorption band with significant absorption at up to 80 nm from
the maximum
red/orange light 700-600 nm; yellow 600-550 nm; green 550-500 nm;
blue/violet 500-350 nm
What is the computed HOMO-LUMO energy gap for cis square planar NiCl2(PH3)2?
Question 33
Question 31
What is the computed beta HOMO-LUMO energy gap for tetrahedral NiCl2(PH3)2?
Review all your computational results, and consider your answers to the previous
question and what you know about the actual colour of NiCl2(PPh3)2 (see lab
manual, experiment 1, if you have not yet synthesised this compound yourself).
Crystal field theory holds that the HOMO-LUMO energy gap determines the
colour of a compound and can be used to predict its UV-vis absorption profile.
How does the computational work you have carried out on NiCl2(PH3)2 indicate
that this is not the case for such complexes?