Geometric isomerism in coordination cages based on tris-chelate vertices: a tool to control both assembly and host/guest chemistry

This 'Perspective' article summarises recent work from the authors' research group on the exploitation of the simple fac / mer geometric isomerism of octahedral metal tris-chelates as a tool to control the chemistry of coordination cages based on bis(pyrazolyl-pyridine) ligands, in tw...

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Published inDalton transactions : an international journal of inorganic chemistry Vol. 45; no. 41; pp. 1696 - 16111
Main Authors Metherell, Alexander J, Ward, Michael D
Format Journal Article
LanguageEnglish
Published England 01.01.2016
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Summary:This 'Perspective' article summarises recent work from the authors' research group on the exploitation of the simple fac / mer geometric isomerism of octahedral metal tris-chelates as a tool to control the chemistry of coordination cages based on bis(pyrazolyl-pyridine) ligands, in two different respects. Firstly this geometric isomerism plays a major role in controlling the guest binding properties of cages because a fac tris-chelate arrangement of pyrazolyl-pyridine chelates around a metal ion vertex results in formation of a convergent set of inwardly-directed C-H protons in a region of high positive electrostatic potential close to a metal cation. This collection of δ + protons therefore provides a charge-assisted hydrogen-bond donor site, which interacts with the electron-rich regions of guest molecules that are of the correct size and shape to occupy the cage cavity, and the strength of this hydrogen-bonding interaction plays a major role in guest recognition in non-aqueous solvents. Secondly the ability to prepare mononuclear complexes with either a fac or mer arrangement of ligands provides an entry into the controlled, stepwise assembly of heterometallic cages based on a combination of kinetically inert and kinetically labile metal ions at different sites. This has allowed introduction of useful physical properties such as redox activity or luminescence, commonly associated with inert metal ions which are not amenable to participation in thermodynamic self-assembly processes, to be incorporated in a predictable way into the superstructures of coordination cages at specific sites. The presence of both fac and mer tris-chelate units as coordination cage vertices allows control of both cage assembly and guest binding properties.
Bibliography:Mike Ward did his BA at Cambridge, studying Natural Sciences (1983-1986). He remained in Cambridge for his PhD (1986-1989) with Ed Constable, studying some early examples of self-assembled helicate complexes. After a post-doc with Jean-Pierre Sauvage in Strasbourg, he was appointed to a lectureship at Bristol in 1990. He moved to Sheffield in 2003 and is currently the Head of Department. Mike's interests are all based around the coordination chemistry of transition metal and lanthanide ions and their multinuclear assemblies. Awards for his research include the RSC Corday Morgan medal for 1999; Sir Edward Frankland Fellowship for 2000-2001; the RSC 'Chemistry of the Transition Metals' award for 2005; and the RSC 'Supramolecular Chemistry' Award for 2016. He has been Chair of the Editorial Board of 'RSC Advances' since the journal started in 2011.
Alex Metherell was born in Bristol and grew up in Maidenhead. After graduating from the University of Sheffield with an MChem in 2011, he remained in Sheffield to study for a PhD (2014) under the supervision of Prof. Michael Ward. Alex is currently undertaking postdoctoral studies within the same group, and his research so far has been based on the synthesis of heterometallic coordination cages and their subsequent applications in host-guest chemistry. In his spare time, Alex enjoys taking walks around the Peak District.
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ISSN:1477-9226
1477-9234
DOI:10.1039/c6dt03041f