“Protonation and water exchange kinetics in sandwich polyoxometalates”

in Dalton Transactions, 2018, 47, 13602-13607. Link.

C. André Ohlin, Magda Pascual-Borràs

Abstract: Density functional theory is used to explore the locus and consequences of protonation in [Zn4(H2O)2(PW9O34)2]¹⁰⁻ . The results are used to explain recent observations regarding the contrasting pH effects on the water-ligand exchange in [Mn4(H2O)2(P2W15O56)2]¹⁶⁻ and [Co4(H2O)2(P2W15O56)2]¹⁶⁻ , and the general effect of protonation on solvent exchange in metal oxides is discussed.

Mark Ramabaran has joined the Ohlin group as a PhD student. He will be looking at the solution chemistry of polyoxometalates and their use as models for reactions on extended metal oxide surfaces.

¹⁷O NMR as a Tool in Discrete Metal Oxide Cluster Chemistry

in Annual Reports on NMR Spectroscopy. Link.

C. André Ohlin, William H. Casey

Abstract: This chapter covers recent developments in ¹⁷O NMR spectroscopy as applied to discrete metal oxide clusters, particularly in the context of their use as models in geochemistry and catalysis. Dynamic ¹⁷O NMR methods based on the McConnell–Bloch equations are explored in depth, and recent advances are reviewed. High-pressure NMR methods are also discussed and reviewed, as are recent developments in the use of density functional theory in the computation of ¹⁷O NMR shifts in polyoxometalates. The emphasis of the chapter is on the new developments that promise to reinvigorate ¹⁷O NMR as a central tool in the study of aqueous chemical kinetics, with the most urgent challenges being understanding the rates of isotopic substitution into bridging oxygens in clusters.

Computational Prediction of Mg-Isotope Fractionation Between Aqueous [Mg(OH₂)₆]²⁺ and Brucite

Geochim. Cosmochim. Acta., Accepted. Link.

Christopher A. Colla, W. H. Casey, C. André Ohlin

Abstract: The fractionation factor in the magnesium-isotope fractionation between aqueous solutions of magnesium and brucite remarkably changes sign with increasing temperature, as uncovered by recent experiments.  To understand this behavior, the Reduced Partition Function Ratios and isotopic fractionation factors (Δ^26/24Mg_{brucite-Mg(aq)}) are calculated using molecular models of aqueous [Mg(OH₂)₆]²⁺ and the mineral brucite at increasing levels of density functional theory.  The calculations were carried out on the [Mg(OH₂)₆]²⁺·12H₂O cluster, along with different Pauling-bond-strength-conserving models of the mineral lattice of brucite. Three conclusions were reached: i) all of the calculations overestimate <Mg-O> bond distances in the aqua ion complex relative to Tutton’s salts; ii) the calculations predict that brucite at 298.15 K is always enriched in the heavy isotope, in contrast with experimental observations; iii) the temperature dependencies of Wimpenny et al. (2014) and Li et al. (2014) could only be achieved by fixing the <Mg-O> bond distances in the [Mg(OH₂)₆]²⁺·12H₂O cluster to values close to those observed in crystals that trap the hydrated ion. Read more.

PNacPNacE: (E = Ga, In, Tl) – monomeric group 13 metal(I) heterocycles stabilized by a sterically demanding bis(iminophosphoranyl)methanide

Dalton Trans., 2017, 46, 16872-16877.

Christian P. Sindlinger, Samuel R. Lawrence, Shravan Acharya, C. André Ohlin, Andreas Stasch

Abstract: The salt metathesis reaction of the sterically demanding bis(iminophosphoranyl)methanide alkali metal complexes LM (L – = HC(Ph 2 P=NDip) 2- , Dip = 2,6- i Pr 2 C 6 H 3 ; M = Li, Na, K) with “GaI”, InBr or TlBr afforded the monomeric group 13 metal(I) complexes LE:, E = Ga (1), In (2) and Tl (3), and small quantities of LGaI 2 4 in case of Ga, respectively. The molecular structures of LE: 1-3 from X-ray single crystal diffraction show them to contain puckered six-membered rings with N,N’-chelating methanide ligands and two-coordinated metal(I) centres. Reduction reactions of LAlI 2 5, prepared by iodination of LAlMe 2 , were not successful and no aluminium(I) congener could be prepared so far. DFT studies on LE:, E = Al–Tl, were carried out and support the formulation as an anionic, N,N’-chelating methanide ligand coordinating to group 13 metal(I) cations. The HOMOs of the molecules for E = Al-In show a dominant contribution from a metal-based lone pair that is high in s-character. See http://pubs.rsc.org/en/content/articlelanding/2017/dt/c7dt04048b#!divAbstract

Dr Magdalena Pascual-Borràs has joined the Ohlin group as a postdoc on a Kempe foundation fellowship. She will be looking at the reactivity of discrete metal oxide clusters using experimental and computational techniques.

Dr Rupali Sharma (Ohlin group) has been awarded a PhD by Monash University for her work on the solution chemistry of metal oxides. We wish her all the best in her future endeavours!