Reader in Chemistry
Department of Chemistry, Joseph Black Building,
University of Glasgow, GLASGOW G12 8QQ
Telephone 0141 330 4375; Fax 0141 330 4888; Email email@example.com
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Circular Dichroism in the X-ray region:
The new bright synchrotron source at ESRF
(Grenoble) has made it possible to measure Natural
Circular Dichroism (NCD) in the X-ray region for the first time.
In collaboration with Dr
B Stewart (Paisley), Dr T Prosperi and co-workers (ICMAT-CNR, Rome)
and Dr J Goulon and co-workers (ESRF) we have made the first
measurements of CD in the X-ray region - at the Nd L3
edge on oriented single crystals of Na3Nd(diglycolate)3.2NaBF4.6H2O.
The XNCD spectra
have several interesting aspects including a well-resolved pre-edge feature
and circularly dichroic XANES. We have recently completed measurements
at the K-edge of a chiral transition metal complex, 2[Co(en)3Cl3].NaCl.6H2O.
The most notable feature of these spectra
is the spectacular size
of the 1s -> 3d pre-edge transition.
Circularly polarised luminescence spectroscopy (CPL):
Circularly Polarised Luminescence is the luminescence analogue of CD spectroscopy. As such it probes the chirality of molecules in the excited state. We have one of the few CPL spectrometer in the world and have a number of projects ongoing:
- In collaboration with Professor David Parker (Durham) we are investigating the CPL of a series of lanthanide complexes designed to detect small anions under physiological conditions.
- An investigation of the CPL of chiral polypyridyl complexes.
- The CPL of single crystals of lanthanide and actinide complexes.
Most of our work involves N-functionalising "small" three nitrogen macrocycles such as 1,4,7-triazacyclononane (-aneN3) to produce pendant arm macrocyclic ligands. When -aneN3 is functionalised with pendant alcohol "arms" and is complexed to transition metal ions we produce a series of dimers in which the two halves of the molecule are held together by three hydrogen bridges. The dimers can be symmetric [Co(III), Co(III)], [Cr(III), Cr(III)], mixed valent, [Mn(II), Mn(IV)] (illustrated) or mixed metal [Zn(II), V(IV)].
We have also synthesised monomeric complexes of Mn(IV), V(IV) and Ni(II) by using ligands with "bulky arms" which preclude dimerisation The Ni(II) complex has been the subject of charge density studies (with Dr P R Mallinson).
By expanding the size of the macrocycle ring we can impose unusual geometries on metal complexes for example trigonal prismatic Co(II).
Our most recent work (with Dr L J Farrugia) involves the synthesis of macrocyclic ligands with "soft" donor pendant arms such as thiols, phosphines, alkenes, alkynes and aromatic groups. It is anticipated that these new ligands with form complexes with the heavier transition elements and will enable us to combine macrocyclic chemistry with organometallic chemistry. We have recently devised a general route for the preparation of new phosphine arm ligands based on -aneN3. The structure of the Zn(II) complex of one of these ligands (with a single pendant phosphine arm) is shown on the right.
A series of ligands based on triazacyclononane functionalised with arenes include the three binucleating ligands bis(a,a'-N-1,4,7-triazacyclononane)-o,m and p-xylene. The µ-hydroxy bridged Cu2 dimer formed by the m ligand is shown opposite. The m -xylene unit is held at an angle above the Cu-Cu axis forming a hydrophobic pocket and the OH groups are bent up towards it.
We are also preparing pendant arm ligands based on the more familiar four nitrogen macrocycles cyclam and cyclen. These will be used for complexing and transporting lanthanide and actinide ions.
Complexes with multiple metal-metal bonds:
I am particularly interested in chiral complexes with quadruple metal metal bonds and quadruply bonded species containing amine ligands. Some time ago we synthesised (right) , L-[Mo2Cl4(S,S-dppb)2], the first chiral quadruply bonded complex to be structurally characterised. We have developed a simple theory to explain the circular dichroism spectra of these complexes. We have prepared and characterised the elusive [Mo2(NH3)8]4+ cation containing the "unsupported" [Mo2]4+ core and are keen to develop the chemistry of Mo2 species containing chiral diamine ligands.
In collaboration with Dr
R J Cross and Dr
D Stirling I am investigating the preparation of chiral metal complexes,
for use as supported catalysts in oxidation reactions, particularly enantioselective
sulphoxidation and epoxidation reactions. More details may be obtained
on Dr Cross's Home Page.
We have recently prepared the first series of binaphtholate complexes of first row transition metal ions. The Fe(III) complex is illustrated opposite.