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.

 

A collaboration with Changxun Xu and Mats Åström of Linnaeus University with JF Boily and Andrey Shchukarev

You can find the article here

Authored by Merve Yesilbas, Cheng Choo (Nikki) Lee, and Jean-François Boily

We thank the Umeå Core Facility for Electron Microscopy (UCEM) for a great collaboration!

You can find the link here.

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.

 

A collaboration between JF Boily and Glenn Waychunas (LBNL). Paper is here!

A  collaboration with JF Boily and M Zhu (U of Wyoming),  X. Feng (Huazhong Agricultural University), Y. Hu (Canadian Light Source), G. Waychunas (LBNL), J. Kubicki (University of Texas) and X. Wang (U of Wyoming).

Find the paper here

Authored by Merve Yesilbas, Michael Holmboe and JF Boily. We identified vibration spectral signatures of clays with 0, 1 and 2 hydration layers.
You can find the paper here

 

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

We thank the Kempe Foundation for supporting a new venture in the world of isotope geochemistry in the Boily laboratory. More details are to come in 2018.

New paper by M. Lucas (former postdoc) and J.-F. Boily on the local (micron-scale) electrochemical response of inorganic ions at hematite surfaces. Link to article  here!