Seminar Series

NMR Study of Selected Metal Ion-Ligand Systems: Equilibrium, Structure and Dynamics

Speaker

Imre Toth

Institute

University of Debrecen Hungary

Time & Place

Wed, 02 Nov 2016 12:00:00 NZDT in Rutherford Room 531

All are welcome

Abstract

According to our knowledge the NMR Spectroscopy is the most widely used experimental method in chemistry research including the field of metal-complexes. Using the vastly different NMR technics (often developed for organic chemistry) many questions raised in preparation and characterisation of metal-ligand coordination compounds can be answered. Several aspects of such kind of science are: equilibrium constants, the stoichiometry of species including solvation, constitution, i.e. binding mode and denticity of a ligand, isomers, rate of the formation, ligand exchange reactions, fluxionality etc. Selected examples mainly from our own experimental work done in the last decade are going to be presented. Without the technical details we try to show the advantages and limitations of the multinuclear 1D and 2D NMR spectroscopy in coordination chemistry. Although NMR does not usually have the precision of potentiometric measurements in order to determine the stability constants, it can provide an important independent check on their accuracy, e.g. Al(III) − F− system.1 Combination of the two methods can provide complete speciation of very complicated systems, e.g. Mo(VI) − H+ − H2O2 − SO4 2− − PO4 3− system.2 High resolution NMR spectroscopy is superior to study the structure of complexes in solution, but there is an obvious need to take into account the intra molecular isomerisation / fluxionality of the complexes, because a fast rearrangement of the donor atoms (including the water) in the inner sphere might virtually increase the symmetry. Examples of metal-metal bonded cyanides, (CN)5Pt-Tl(CN)n n− (n=0,1,2,3)3 for symmetry, whilst Al(III)-citrate, 4 M(edta)− (M = Al, Ga and In)5 and lantanide(III)-macrocycle complexes7 for fluxionality will be mentioned. Ligand exchange reactions can also be studied by NMR using the line shape analysis (T2 time scale) or the magnetisation transfer methods (T1 time scale, selective MT or 2D EXSY). Selected examples include U(VI)- carbonate5 and Tl(III) – cyanide6 systems.

Biography

References

1. A. Bodor, I. Tóth, I. Bányai, Z. Szabó and G. T. Hefter: 19F NMR Study of the Equilibria and Dynamics of the Al3+/F– System. Inorganic Chemistry 2000, 39, 2530-2537

2. F. Taube, I. Andersson, S. Angus-Dunne, A. Bodor, I. Tóth and L. Pettersson: Equilibria and Dynamics of some Aqueous Peroxomolybdophosphate Catalysts: A Potentiometric and 31P NMR Spectroscopic Study. Dalton Transactions, 2003, 2512-2518.

3. M. Maliarik, K. Berg, J. Glaser, M. Sandström and I. Tóth: New Class of Oligonuclear Platinum-Thallium Compounds with a Direct Metal-Metal Bond. 2. Structural Characterization of the Complexes. Inorganic Chemistry 1998, 37, 2910–2919

4. A. Bodor, I. Bányai, L. Zékány, I. Tóth: Slow dynamics of aluminium-citrate complexes studied by 1 H- and 13C-NMR Spectroscopy. Coordination Chemistry Reviews, 2002, 228, 163–173

5. I. Bányai, J. Glaser, K. Micskei, I.Tóth and L. Zékány: Kinetic Behaviour of Carbonate Ligands with Different Coordination Modes: Equilibrium Dynamics for Uranyl(2+) Carbonato Complexes in Aqueous Solution. A 13 C and 17O NMR Study. Inorganic Chemistry 1995, 34, 3785-3796

6. I. Bányai, J. Glaser, I. Tóth: Cyanide Exchange on Tl(CN)4¯ in Aqueous Solution Studied by 205Tl and 13C NMR Spectroscopy. European Journal of Inorganic Chemistry 2001, 1709-1717

7. M. Purgel, Z. Baranyai, A. de Blas, T. Rodrı´guez-Blas, I. Bányai, C. Platas-Iglesias, I. Tóth: An NMR and DFT nvestigation on the Conformational Properties of Lanthanide(III)1,4,7,10-Tetraazacyclododecane-1,4,7,10-tetraacetate Analogues Containing Methylenephosphonate Pendant Arms. Inorg. Chemistry 2010, 49, 4370–4382