COLLEGE OF ENGINEERING & PHYSICAL SCIENCES
SCHOOL OF CHEMISTRY
Year 3 Degree of MSci/BSc with Honours
Chemistry
Chemistry with Industrial Experience
Chemistry with Business Management
Chemistry with Pharmacology
Chemistry with a Modern Language
Degree of B.A./BSc Liberal Arts & Sciences
LH Inorganic IIIa / 03 33983
January Examinations 2021
Time Allowed: 3 hours
1. (a) Explain why the rate of substitution of Cl– with pyridine (py) at T = 25°C in trans-[(PEt3)2Pt(H)Cl] is kobs = 4.7 × 10–2 s–1, whereas for trans-[(PEt3)2Pt(CH3)Cl] the rate is kobs = 6.0 × 10–4 s–1 . (3 marks)
(b) Kinetic data obtained for the reaction of trans-[PtCl2(py)2] with NH3 in methanol solvent are as follows:
(i) Show that the data are consistent with the rate expression:
rate = kobs [PtCl2(py)2] = {k1 + k2 [NH3]}[PtCl2(py)2]
and determine the rate constants k1 and k2. (4 marks)
(ii) Describe clearly the mechanism that explains the rate law and explain how the above observations can be accounted for within this description.
Discuss the relative magnitude of k1 and k2, and the expected sign and magnitude of relevant thermodynamic activation parameters that can aid in elucidation of the mechanism. (5 marks)
2. Stille developed transmetallation reactions involving tin reagents for a number of
useful synthetic procedures, including the palladium(0)-catalysed alkylation of acid halides to ketones:
(a) Using the reaction between acetyl chloride and tetra-(n-butyl)tin to illustrate,
construct a possible catalytic cycle for the above reaction, identifying clearly the key fundamental reactions that are involved in the different stages of the catalytic cycle, i.e. assembly, modification and expulsion. Ensure you sketch clearly the coordination environment around the central palladium atom at each stage, and note any changes in the oxidation state and number of valence electrons for the palladium atom. (8 marks)
(b) Explain why, when the reaction is attempted using 1-chlorobutane instead of acetyl chloride as the starting reagent, a mixture of one alkene and two alkanes can be obtained as products. Identify the alkene and alkanes produced. (4 marks)
3. (a) (i) Determine the Russell–Saunders term symbol for the Cr(III) ion and, using
the Tanabe–Sugano diagram below, deduce all of the spin allowed transitions.
(3 marks)
(ii) Suggest which of these transitions will give broad peaks and explain why. (3 marks)
(iii) Peaks within the UV–Vis spectrum of this compound will likely be further broadened and asymmetric. Please explain why the peaks are expected to be asymmetric. (2 marks)
(b) Highlight two structural characteristics all Fe(II) spin crossover active
complexes display as the temperature is changed that can be observed using a single crystal X-ray diffractometer. What difference will they show at 100 K vs room temperature if the spin crossover temperature is 150 K? (4 marks)
4. (a) The figure below shows three cycles of the magnetic susceptibility
measurements of an iron-containing spin crossover coordination polymer.
Explain how the bridging ligands linking the metals lead to the magnetic
properties observed and outline the application(s) that a complex of this type may display. (7 marks)
(b) Other ligands, such as that given below, do not rely on covalent interactions between adjacent complexes, but use supramolecular interactions instead to form 1D coordination polymers.
Describe the types of non-covalent interactions the ligand above will display as part of a metal complex. (2 marks)
(c) The magnetic data on the iron complex in part (b)(ii) is shown below:
Describe the change in effective magnetic moment, μeff, over the temperature range shown, explain how the non-covalent interactions led to these properties, and give an application for this system. (3 marks)