Linking Wheels for use in Quantum Information Processing

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Abstract

Heterometallic Cr7Ni-containing wheels have been identified as potential qubits for use inquantum information processing. The work described in this thesis details attempts toform a variety of multi-qubit systems for the purposes of better understanding theinteractions occurring between the wheels and also forming potential 2-qubit quantumgates using redox/photo-active links.Mono-substituted wheels of type [Pr2NH2][Cr7MF8(O2CCMe3)15(L)], where L is acarboxylate with a pendant coordinating group, have been synthesised for use as bulkyligands in coordination chemistry with metal complexes. Various carboxylates have beensubstituted into the wheels and the products reacted with first row transition metalcomplexes in order to extend the series of linked-wheel systems. Many of these novelcomplexes have been characterised by X-ray crystallography, and in certain cases EPRstudies have been undertaken to probe the strength of interactions occurring via differentbridging units.The first well-established substituted wheel, [Pr2NH2][Cr7NiF8(O2CCMe3)15(O2CPy)] (Py= pyridine), has also been used in reactions with second and third row transition metalcentres to show its ability to act as a ligand under more harsh conditions. In addition, thedisubstituted product [Pr2NH2][Cr7NiF8(O2CCMe3)14(O2CPy)2] has been reacted with acopper complex in order to form a polymeric structure.Purple wheels of type [Cr7NiF3(O2CCMe3)15(EtGu)(H2O)] have been linked through avariety of extended organic molecules containing a minimum of two pendent pyridylgroups. Use of a ligand containing four pyridyl groups, 2,2´:4,4´´:4´,4´´´-quaterpyridyl(qpy) produced a three-wheel-containing system, creating an interesting modification ofthe wheel backbone not seen before.A series of transition metal complexes, containing qpy and its extended derivative bbpe,has been synthesised in order to form linked-wheel systems. While none of these systemshas to date yielded a crystal structure, a significant amount of evidence has been collectedto confirm successful formation of the desired products. UV-vis spectroscopic andelectrochemical measurements show that these compounds are photo and/or redox-active,and preliminary luminescence studies indicate that the presence of the wheels quenches theemission from metal-to-ligand charge-transfer excited states.A series of mixed-wheel systems has been synthesised by reacting four different monosubstituted green wheels with four purple wheels (Cr7M, where M = Ni, Co, Mn or Zn). Atotal of fourteen novel systems has been formed, with two of the attempted reactionsfailing to occur. EPR studies on Cr7Ni-Cr7Ni linked systems show that the strongestinteraction occurs when using isonicotinate as a link, with 4-pyridazinecarboxylate givingthe weakest coupling. Studies have also been undertaken on Cr7Ni-Cr7Mn and Cr7Ni-Cr7Zn systems, with the former showing interactions and the latter showing none.Initial work to link wheels together indirectly via their templates was ultimatelyunsuccessful, but a variety of potential linker molecules were synthesised and aredescribed.

Keyword(s)

Cr7Ni Wheels; Photoswitchability; Redox activity; Transition Metals

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