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Bridging the gap between solution and solid state studies in Polyoxometalate chemistry: Discovery of [V 1 M 17 ]-based cages. Haralampos N. Miras , a De-Liang Long, a Paul Kögerler, b Daniel Stone, c Eric McInnes, c and Leroy Cronin a* a WestCHEM, Department of Chemistry, The University of Glasgow, Glasgow, G12 8QQ, UK. b AMES Laboratory, Department of Astronomy and Physics, Iowa State University c School of Chemistry, The University of Manchester Email: [email protected] ; Web: www.chem.gla.ac.uk/staff/lee/ Results and Discussion Synthesis of the first mixed-metal (V/Mo and V/W) Dawson-like capsules with the unique composition {M 17 V 3 } is reported. MS studies proved to be crucial in terms of establishing the existence of vanadium-based tetrahedral templates within the Dawson-like shell as well as the vanadium ion disorder over the cage framework. DFT calculations help us postulate the position of the V IV ion: The total energy favours the isomer with V localised in the two outer M 3 cap positions. Results show multiple V IV sites in both W 17 V 3 and Mo 17 V 3 and demonstrates that EPR can be used to reveal Brief Overview-Experimental Approach -Polyoxometalates (POMs) are metal-oxygen clusters of W, Mo, V and represent a class of inorganic materials with unmatched range of structure types and physical properties, with applications in areas as diverse as biology and catalysis. -Significant number of clusters display Dawson type structure with general formula [M 18 O 54 (μ 9 -XO 4 ) 2 ] n- where M = Mo, W or V and X = P, S, As, Sb, e.t.c. -Ability to direct synthesis from smaller building blocks in a predetermined fashion remains a great challenge. -Combination of synthetic approach with solution-based techniques to characterise new clusters enables rapid discovery of new clusters. -Properties like acidicity and redox activity are critically dependent on the nature and the relative positions of the metal cations in the framework as well as the type of heteroanion template incorporated within the cluster framework. -Herein, we present our very recent efforts to expand our approach towards the isolation of new cluster types using ‘encapsulating’ and structure directing organo-cations along with high resolution EPR, CSI and ESI-MS. By combining our synthetic approach with solution based techniques we aim to discover new cluster types which reveal novel architectures. Ultimately the aim is to be able to design new cluster architectures based on POM building blocks. Representations of the iso- structural frameworks found in the structures of the general formula [H 2 VM 17 O 54 (VO 4 ) 2 ] 6- (M = W or Mo). Since the ‘framework’ V IV ion can not be formally located, there are two structurally distinct positions over which it could be disordered; either over the six ‘capping’ M-sites shown by the light green spheres or over the twelve ‘belt’ positions shown by the dark green spheres. - EPR investigation of (n-Bu 4 N) 6 [H 2 W 17 VO 54 (VO 4 ) 2 ] - X-band powder, fluid and frozen solution spectra - Spectra consistent with data => single S = ½ V IV O vanadyl per cluster - Spectrum can be simulated with a single set of g-values, indicating a single cluster position for V IV -Simulation of fluid solution spectrum is consistent with powder and frozen solution spectra - g iso = 1.96 - A iso = 91 G X-band fluid solution spectrum -4 10 5 -2 10 5 0 2 10 5 4 10 5 6 10 5 8 10 5 2500 3000 3500 4000 4500 Experiment Sim ulation Intensity /arbitrary units B /G -2 10 6 -1 10 6 0 1 10 6 2 10 6 3 10 6 4 10 6 5 10 6 6 10 6 2500 3000 3500 4000 4500 Experim ent Sim ulation Intensity /arbitrary units B /G X-band powder spectrum - EPR spectra for (n- Bu 4 N) 6 [H 2 Mo 17 VO 54 (VO 4 ) 2 ] in agreement with data - Single S = ½ V IV O vanadyl per cluster - Multiple V IV sites evident in X-band powder spectrum -Fluid solution simulation gives g iso = 1.945 and A iso = 97 G - Weighted average of parameters for X-band powder simulation gives g av = 1.942 and A av = 103 G - Frozen solution simulation gives g av = 1.943 and A av = 102 G X-band powder spectrum X-band fluid solution spectrum -1 10 7 -5 10 6 0 5 10 6 1 10 7 1.5 10 7 2500 3000 3500 4000 4500 E xperim ent Sim ulation Intensity /arbitrary units B /G -4 10 5 -2 10 5 0 2 10 5 4 10 5 6 10 5 8 10 5 2500 3000 3500 4000 4500 Experim ent Sim ulation Intensity /arbitrary units B /G Positive ion mass spectrum showing the {(TBA) 10- n [H n V 3 W 17 O 62 ]} 2+ in acetonitrile solution. LEFT where n = 2 at m/z ca. 3106 RIGHT where n = 1 m/z ca. 3227. References 1. (a) D.–L. Long, E. Burkholder, L. Cronin, Chem. Soc. Rev., 2007, 36, 105; L. Cronin, (Eds., J. A McCleverty, T. J. Meyer) Comp. Coord. Chem. II, Vol. 7, p.1-57. 2. H.N. Miras, D-L. Long, P. Kögerler, L. Cronin, Dalton Trans., 2008, 214-221 3. H. N. Miras, D-L. Long, P. Kögerler, D. Stone, E. McInnes, L. Cronin, (in preparation)
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