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  • 1.
    Andersson, Ingegärd
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Gorzsás, András
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Pettersson, Lage
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Speciation in the aqueous H+/H2VO4–/H2O2/picolinate system relevant to diabetes research2004In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 3, p. 421-428Article in journal (Refereed)
    Abstract [en]

    A detailed study of the quaternary aqueous H+/H2VO4/H2O2/picolinate (Pi) system has been performed at 25 °C in 0.150 M Na(Cl) medium using quantitative 51V NMR (500 MHz) and potentiometric data (glass electrode). In the ternary H+/H2VO4/Pi system, six complexes have been found in the pH region 1–10. In the quaternary H+/H2VO4/H2O2/Pisystem, eight additional complexes have been found. Generally, equilibria are fast in both systems. The rate of peroxide decomposition depends on the species in solution. Chemical shifts, compositions and formation constants for the species are given. Equilibrium conditions and the fit of the model to the experimental data are illustrated in distribution diagrams. Possible formation of mixed ligand species with imidazole, lactic acid and citric acid have been investigated and ruled out under the same experimental conditions. Structural proposals are given, based on 13C NMR data and available crystal structures.

  • 2. Aureliano, Manuel
    et al.
    Fraqueza, Gil
    Ohlin, C. Andre
    Ion pumps as biological targets for decavanadate2013In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 42, no 33, p. 11770-11777Article in journal (Refereed)
    Abstract [en]

    The putative applications of poly-, oligo-and mono-oxometalates in biochemistry, biology, pharmacology and medicine are rapidly attracting interest. In particular, these compounds may act as potent ion pump inhibitors and have the potential to play a role in the treatment of e. g. ulcers, cancer and ischemic heart disease. However, the mechanism of action is not completely understood in most cases, and even remains largely unknown in other cases. In the present review we discuss the most recent insights into the interaction between mono-and polyoxometalate ions with ion pumps, with particular focus on the interaction of decavanadate with Ca2+-ATPase. We also compare the proposed mode of action with those of established ion pump inhibitors which are currently in therapeutic use. Of the 18 classes of compounds which are known to act as ion pump inhibitors, the complete mechanism of inhibition is only known for a handful. It has, however, been established that most ion pump inhibitors bind mainly to the E2 ion pump conformation within the membrane domain from the extracellular side and block the cation release. Polyoxometalates such as decavanadate, in contrast, interact with Ca2+-ATPase near the nucleotide binding site domain or at a pocket involving several cytoplasmic domains, and therefore need to cross through the membrane bilayer. In contrast to monomeric vanadate, which only binds to the E2 conformation, decavanadate binds to all protein conformations, i.e. E1, E1P, E2 and E2P. Moreover, the specific interaction of decavanadate with sarcoplasmic reticulum Ca2+-ATPase has been shown to be non-competitive with respect to ATP and induces protein cysteine oxidation with concomitant vanadium reduction which might explain the high inhibitory capacity of V-10 (IC50 = 15 mu M) which is quite similar to the majority of the established therapeutic drugs.

  • 3. Aureliano, Manuel
    et al.
    Ohlin, C. André
    Vieira, Michele O.
    Marques, M. Paula M.
    Casey, William H.
    Batista de Carvalho, Luis A. E.
    Characterization of decavanadate and decaniobate solutions by Raman spectroscopy2016In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 45, no 17, p. 7391-7399Article in journal (Refereed)
    Abstract [en]

    The decaniobate ion, (Nb-10 = [Nb10O28](6-)) being isoelectronic and isostructural with the decavanadate ion (V-10 = [V10O28](6-)), but chemically and electrochemically more inert, has been useful in advancing the understanding of V-10 toxicology and pharmacological activities. In the present study, the solution chemistry of Nb-10 and V-10 between pH 4 and 12 is studied by Raman spectroscopy. The Raman spectra of V-10 show that this vanadate species dominates up to pH 6.45 whereas it remains detectable until pH 8.59, which is an important range for biochemistry. Similarly, Nb-10 is present between pH 5.49 and 9.90 and this species remains detectable in solution up to pH 10.80. V-10 dissociates at most pH values into smaller tetrahedral vanadate oligomers such as V-1 and V-2, whereas Nb-10 dissociates into Nb-6 under mildly (10 > pH > 7.6) or highly alkaline conditions. Solutions of V-10 and Nb-10 are both kinetically stable under basic pH conditions for at least two weeks and at moderate temperature. The Raman method provides a means of establishing speciation in the difficult niobate system and these findings have important consequences for toxicology activities and pharmacological applications of vanadate and niobate polyoxometalates.

  • 4. Boniolo, Manuel
    et al.
    Chernev, Petko
    Cheah, Mun Hon
    Heizmann, Philipp A.
    Huang, Ping
    Shylin, Sergii, I
    Salhi, Nessima
    Hossain, Md Kamal
    Gupta, Arvind K.
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Molecular Biomimetics, Department of Chemistry – Ångström Laboratory, Uppsala University, Sweden.
    Thapper, Anders
    Lundberg, Marcus
    Electronic and geometric structure effects on one-electron oxidation of first-row transition metals in the same ligand framework2021In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 50, no 2, p. 660-674Article in journal (Refereed)
    Abstract [en]

    Developing new transition metal catalysts requires understanding of how both metal and ligand properties determine reactivity. Since metal complexes bearing ligands of the Py5 family (2,6-bis-[(2-pyridyl)methyl] pyridine) have been employed in many fields in the past 20 years, we set out here to understand their redox properties by studying a series of base metal ions (M = Mn, Fe, Co, and Ni) within the Py5OH (pyridine-2,6-diylbis[di-(pyridin-2-yl)methanol]) variant. Both reduced (M-II) and the one-electron oxidized (M-III) species were carefully characterized using a combination of X-ray crystallography, X-ray absorption spectroscopy, cyclic voltammetry, and density-functional theory calculations. The observed metal-ligand interactions and electrochemical properties do not always follow consistent trends along the periodic table. We demonstrate that this observation cannot be explained by only considering orbital and geometric relaxation, and that spin multiplicity changes needed to be included into the DFT calculations to reproduce and understand these trends. In addition, exchange reactions of the sixth ligand coordinated to the metal, were analysed. Finally, by including published data of the extensively characterised Py5OMe (pyridine-2,6-diylbis[di-(pyridin-2-yl)methoxymethane])complexes, the special characteristics of the less common Py5OH ligand were extracted. This comparison highlights the non-innocent effect of the distal OH functionalization on the geometry, and consequently on the electronic structure of the metal complexes. Together, this gives a complete analysis of metal and ligand degrees of freedom for these base metal complexes, while also providing general insights into how to control electrochemical processes of transition metal complexes.

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  • 5.
    Das, Krishna Sundar
    et al.
    School of Chemical Sciences, Indian Association for the Cultivation of Science, Kolkata, India.
    Pal, Baishakhi
    Department of Physics, Jadavpur University, Jadavpur, Kolkata, India.
    Saha, Sayan
    School of Chemical Sciences, Indian Association for the Cultivation of Science, Kolkata, India.
    Akhtar, Sohel
    School of Chemical Sciences, Indian Association for the Cultivation of Science, Kolkata, India.
    De, Avik
    School of Chemical Sciences, Indian Association for the Cultivation of Science, Kolkata, India.
    Ray, Partha Pratim
    Department of Physics, Jadavpur University, Jadavpur, Kolkata, India.
    Mondal, Raju
    School of Chemical Sciences, Indian Association for the Cultivation of Science, Kolkata, India.
    Utilization of counter anions for charge transportation in the electrical device fabrication of Zn(ii) metal–organic frameworks2020In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 49, no 46, p. 17005-17016Article in journal (Refereed)
    Abstract [en]

    The present work reports the fabrication of anion-induced electrical devices with Zn(II) metal–organic frameworks. The essence of our electronic device fabrication is to utilize the anionic species entrapped inside of the three-dimensional network of the MOFs for charge transportation. The idea is to generate MOFs as a host–guest system with encapsulated anions or anion–solvent clusters as guests and a cationic yet insulating three-dimensional framework as the host. Accordingly, we have synthesized two Zn(II) MOFs using a neutral bispyrazole-based ligand, which results in a cationic chassis with substantial void space and porous channels inside the network. For both MOFs, the porous channels are occupied by infinitely hydrogen bonded networks of anions and anion–solvent clusters. This provides an excellent platform for anionic species-induced charge transportation and improved electrical conductivity. Indeed, the impedance spectroscopy data and current density–voltage (J–V) characteristics of the fabricated electrical devices further vindicate our idea. The current–voltage measurements clearly indicate the usefulness of modified host–guest-type MOFs for electronic device fabrication with corroborating conductivity values of 8.71 × 10−5 S m−1 and 5.79 × 10−4 S m−1 for compound 1 and compound 2, respectively.

  • 6.
    De, Avik
    et al.
    School of Chemical Sciences;Indian Association for the Cultivation of Science;Kolkata 700032;India.
    Bala, Sukhen
    Key Laboratory of Bioinorganic and Synthetic Chemistry of Ministry of Education;School of Chemistry;Sun Yat-Sen University;Guangzhou 510275;P. R. China.
    Saha, Sayan
    School of Chemical Sciences;Indian Association for the Cultivation of Science;Kolkata 700032;India.
    Das, Krishna Sundar
    School of Chemical Sciences;Indian Association for the Cultivation of Science;Kolkata 700032;India.
    Akhtar, Sohel
    School of Chemical Sciences;Indian Association for the Cultivation of Science;Kolkata 700032;India.
    Adhikary, Amit
    School of Chemical Sciences;Indian Association for the Cultivation of Science;Kolkata 700032;India.
    Ghosh, Arijit
    Laboratory of Molecular Biology;School of Biological Sciences;Indian Association for the Cultivation of Science;Kolkata 700032;India.
    Huang, Guo-Zhang
    Key Laboratory of Bioinorganic and Synthetic Chemistry of Ministry of Education;School of Chemistry;Sun Yat-Sen University;Guangzhou 510275;P. R. China.
    Chowdhuri, Srijita Paul
    Laboratory of Molecular Biology;School of Biological Sciences;Indian Association for the Cultivation of Science;Kolkata 700032;India.
    Das, Benu Brata
    Laboratory of Molecular Biology;School of Biological Sciences;Indian Association for the Cultivation of Science;Kolkata 700032;India.
    Tong, Ming-Liang
    Key Laboratory of Bioinorganic and Synthetic Chemistry of Ministry of Education;School of Chemistry;Sun Yat-Sen University;Guangzhou 510275;P. R. China.
    Mondal, Raju
    School of Chemical Sciences;Indian Association for the Cultivation of Science;Kolkata 700032;India.
    Lanthanide clusters of phenanthroline containing a pyridine–pyrazole based ligand: magnetism and cell imaging2021In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 50, no 10, p. 3593-3609Article in journal (Refereed)
    Abstract [en]

    In this contribution, we report the synthesis, characterization and luminescence-magnetic properties of Ln-clusters (Ln = Gd3+, Eu3+and Tb3+) using a new pyridine-pyrazole functionalized ligand fitted with a chromophoric phenanthroline backbone. The unorthodox N-rich ligand forms isostructural trinuclear lanthanide complexes with a topology that closely resembles two interdigitating hairpins. The clusters crystallize in chiral space groups and also exhibit chirality for bulk samples, which were further confirmed using solid state CD spectra. Magnetic studies on the complexes reveal their interesting features while the Gd cluster shows a significant cryogenic magnetic cooling behaviour with a moderately high magnetic entropy change of −23.42 J kg−1K−1at 7 T and 2 K. On the other hand, Eu and Tb complexes exhibit interesting fluorescence properties. The compounds were subsequently used as fluorescent probes for the imaging of human breast adenocarcinoma (MCF7) cells. Live cell confocal microscopy images show that the complexes penetrate beyond the usual cytoplasm region and can be useful in imaging the nucleus region of MCF7 cells.

  • 7.
    Driver, Gordon W
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mutikainen, Ilpo
    The complex story of a simple Brønsted acid: Unusual speciation of HBr in an ionic liquid medium2011In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 40, no 41, p. 10801-10803Article in journal (Refereed)
    Abstract [en]

    Crystalline solids, co-existing in equilibrium with the 3-methyl-1H-imidazolium bromohydrogenates(i) ionic liquid, have been characterised by X-ray diffraction analysis. The Brønsted acidic, homo-conjugate [H(2)Br(3)](-) anions presented are discussed in terms of their structure and reactivity, in efforts to advance the understanding of Brønsted acidity in ionic liquid media.

  • 8. Fraqueza, Gil
    et al.
    Batista de Carvalho, Luis A. E.
    Marques, M. Paula M.
    Maia, Luisa
    Ohlin, C. Andre
    Casey, William H.
    Aureliano, Manuel
    Decavanadate, decaniobate, tungstate and molybdate interactions with sarcoplasmic reticulum Ca2+-ATPase: quercetin prevents cysteine oxidation by vanadate but does not reverse ATPase inhibition2012In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 41, no 41, p. 12749-12758Article in journal (Refereed)
    Abstract [en]

    Recently we demonstrated that the decavanadate (V-10) ion is a stronger Ca2+-ATPase inhibitor than other oxometalates, such as the isoelectronic and isostructural decaniobate ion, and the tungstate and molybdate monomer ions, and that it binds to this protein with a 1 : 1 stoichiometry. The V-10 interaction is not affected by any of the protein conformations that occur during the process of calcium translocation (i.e. E1, E1P, E2 and E2P) (Fraqueza et al., J. Inorg. Biochem., 2012). In the present study, we further explore this subject, and we can now show that the decaniobate ion, [Nb-10 = Nb10O28](6-), is a useful tool in deducing the interaction and the non-competitive Ca2+-ATPase inhibition by the decavanadate ion [V-10 = V10O28](6-). Moreover, decavanadate and vanadate induce protein cysteine oxidation whereas no effects were detected for the decaniobate, tungstate or molybdate ions. The presence of the antioxidant quercetin prevents cysteine oxidation, but not ATPase inhibition, by vanadate or decavanadate. Definitive V(IV) EPR spectra were observed for decavanadate in the presence of sarcoplasmic reticulum Ca2+-ATPase, indicating a vanadate reduction at some stage of the protein interaction. Raman spectroscopy clearly shows that the protein conformation changes that are induced by V-10, Nb-10 and vanadate are different from the ones induced by molybdate and tungstate monomer ions. Here, Mo and W cause changes similar to those by phosphate, yielding changes similar to the E1P protein conformation. The putative reduction of vanadium(V) to vanadium(IV) and the non-competitive binding of the V-10 and Nb-10 decametalates may explain the differences in the Raman spectra compared to those seen in the presence of molybdate or tungstate. Putting it all together, we suggest that the ability of V-10 to inhibit the Ca2+-ATPase may be at least in part due to the process of vanadate reduction and associated protein cysteine oxidation. These results contribute to the understanding and application of these families of mono-and polyoxometalates as effective modulators of many biological processes, particularly those associated with calcium homeostasis.

  • 9.
    Gorzsás, András
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Getty, Kendra
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Andersson, Ingegärd
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Pettersson, Lage
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Speciation in the aqueous H+/H2VO4–/H2O2/citrate system of biomedical interest2004In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 18, p. 2873-2882Article in journal (Refereed)
    Abstract [en]

    The speciation in the quaternary aqueous H+/H2VO4–/H2O2/citrate (Cit3–) and H+/H2VO4–/Cit3–/L-(+)-lactate (Lac–) systems has been determined at 25 °C in the physiological medium of 0.150 M Na(Cl). A combination of 51V NMR integral intensities and chemical shift (Bruker AMX500) as well as potentiometric data (glass electrode) have been collected and evaluated with the computer program LAKE, which is able to treat multimethod data simultaneously. The pKa-values for citric acid have been determined as 2.94, 4.34 and 5.61. Altogether six vanadate–citrate species have been found in the ternary H+/H2VO4–/Cit3– system in the pH region 2–10, only two of which are mononuclear. Reduction of vanadium(V) becomes more pronounced at pH < 2. Solutions, in which reduction occurred to any extent, were excluded from all calculations. In the quaternary H+/H2VO4–/H2O2/Cit3– system, eight complexes have been found in addition to all binary and ternary complexes over the pH region 2–10, including three mononuclear species. Equilibria in general are fast, but the significant and rapid decomposition of peroxide in acidic solutions limited the final model to pH > 4. In the quaternary H+/H2VO4–/Cit3–/Lac– system, two mixed-ligand species have been determined, with the compositions V2CitLac2– and V2CitLac3–(pKa= 5.0). To our knowledge, this is the first time such complexes have been reported for vanadium(V). 51V NMR chemical shifts, compositions and formation constants are given, and equilibrium conditions are illustrated in distribution diagrams as well as the fit of the model to the experimental data. When suitable, structural proposals are given, based on 13C NMR measurements and available literature data of related compounds.

  • 10.
    Kawde, Anurag
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. European Synchrotron Radiation Facility (ESRF), Grenoble, France.
    Annamalai, Alagappan
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Sellstedt, Anita
    Umeå University, Faculty of Science and Technology, Department of Plant Physiology. Umeå University, Faculty of Science and Technology, Umeå Plant Science Centre (UPSC).
    Glatzel, Pieter
    Wågberg, Thomas
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Messinger, Johannes
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Molecular Biomimetics, Department of Chemistry, Ångström Laboratory, Uppsala University, Sweden.
    A microstructured p-Si photocathode outcompetes Pt as a counter electrode to hematite in photoelectrochemical water-splitting2019In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 48, no 4, p. 1166-1170Article in journal (Refereed)
    Abstract [en]

    Herein, we communicate about an Earth-abundant semiconductor photocathode (p-Si/TiO2/NiOx) as an alternative for the rare and expensive Pt as a counter electrode for overall photoelectrochemical water splitting. The proposed photoelectrochemical (PEC) water-splitting device mimics the "Z"-scheme observed in natural photosynthesis by combining two photoelectrodes in a parallelillumination mode. A nearly 60% increase in the photocurrent density (Jph) for pristine α-Fe2Oand a 77% increase in the applied bias photocurrent efficiency (ABPE) were achieved by replacing the conventionally used Pt cathode with an efficient, cost effective p-Si/TiO2/NiOx photocathode under parallel illumination. The resulting photocurrent density of 1.26 mA cm−2 at 1.23VRHE represents a new record performance for hydrothermally grown pristine α-Fe2O3 nanorod photoanodes in combination with a photocathode, which opens the prospect for further improvement by doping α-Fe2O3 or by its decoration with co-catalysts. Electrochemical impedance spectroscopy measurements suggest that this significant performance increase is due to the enhancement of the space-charge field in α-Fe2O3. 

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  • 11. Ohlin, C. Andre
    et al.
    Brimblecombe, Robin
    Spiccia, Leone
    Casey, William H.
    Oxygen isotopic exchange in an (MnMn3IV)-Mn-III-oxo cubane2009In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 27, p. 5278-5280Article in journal (Refereed)
    Abstract [en]

    The rate and activation parameters for oxygen exchange of the mu(3)-oxo bridges in a manganese tetranuclear cluster with (H2O)-O-18 have been measured by ESI-MS; the observed Delta S double dagger of -146 +/- 22 J K-1 mol(-1) is consistent with the expected associative mechanism of substitution.

  • 12. Ohlin, C. Andre
    et al.
    Rustad, James R.
    Casey, William H.
    The energetics of isomerisation in Keggin-series aluminate cations2014In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 43, no 39, p. 14533-14536Article in journal (Refereed)
    Abstract [en]

    Electronic-structure calculations show that the e-isomer of the polyoxoaluminate ion in the Keggin structure [AlO4-(Al(OH)(2)-(H2O))(12)](7+) is the thermodynamically favoured one. Direct interconversion between the epsilon- and delta-isomers via cap rotation has a prohibitively high energy barrier in vacuo, suggesting that isomerisation in solution either proceeds via a dissolution-precipitation pathway, or that solvation and/or coordination to counterions reduces the barrier significantly. The implications for the formation of the [Al2O8Al28(OH)(56)(H2O)26](18+) ion are discussed.

  • 13. Ohlin, C. Andre
    et al.
    Villa, Eric M.
    Fettinger, James C.
    Casey, William H.
    A new titanoniobate ion-completing the series [Nb10O28](6-), [TiNb9O28](7-) and [Ti2Nb8O28](8-)2009In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, no 15, p. 2677-2678Article in journal (Refereed)
    Abstract [en]

    A new water-soluble polyoxometalate, [TiNb9O28](7-), completes an isostructural and homologous decametalate series from the decaniobate to the dititano-octaniobate ion.

  • 14.
    Ohlin, C. André
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Pascual-Borràs, Magda
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Protonation and water exchange kinetics in sandwich polyoxometalates2018In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 47, no 38, p. 13602-13607Article in journal (Refereed)
    Abstract [en]

    Density functional theory is used to explore the locus and consequences of protonation in [Zn4(HO)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.

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  • 15. Pilgrim, C. D.
    et al.
    Callahan, J. R.
    Colla, C. A.
    Ohlin, André
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Mason, H. E.
    Casey, W. H.
    27Al MQMAS of the δ-Al13-Keggin†2017In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 46, no 7, p. 2249-2254Article in journal (Refereed)
    Abstract [en]

    One-dimensional 27Al, 23Na Magic-Angle-Spinning (MAS) NMR and 27Al Multiple-Quantum Magic-Angle-Spinning NMR (MQMAS) measurements are reported for the [small delta]-isomer of the Al13 Keggin structure at high spinning speed and 14.1 T field. Values for the CQ and [small eta] parameters are on the same scale as those seen in other isomers of the Al13 structure. Density functional theory (DFT) calculations are performed for comparison to the experimental fits using the B3PW91/6-31+G* and PBE0/6-31+G* levels of theory, with the Polarizable Continuum Model (PCM).

  • 16.
    Rambaran, Mark
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Gorzsás, András
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Holmboe, Michael
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Ohlin, C. André
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Polyoxoniobates as molecular building blocks in thin films2021In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 50, no 44, p. 16030-16038Article in journal (Refereed)
    Abstract [en]

    Niobium oxide thin films have been prepared by spin-coating aqueous solutions of tetramethylammonium salts of the isostructural polyoxometalate clusters [Nb10O28]6−, [TiNb9O28]7− and [Ti2Nb8O28]8− onto silicon wafers, and annealing them. The [Nb10O28]6− cluster yields films of Nb2O5 in the orthorhombic and monoclinic crystal phases when annealed at 800 °C and 1000 °C, respectively, whereas the [TiNb9O28]7− and [Ti2Nb8O28]8− clusters yield the monoclinic crystal phases of Ti2Nb12O29 and TiNb2O7 (titanium–niobium oxides) in different ratios. We also demonstrate a protocol for depositing successive layers of metal oxide films. Finally, we explore factors affecting the roughness of the films.

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  • 17. Sharma, Rupali
    et al.
    Zhang, Jie
    Ohlin, C. Andre
    pH-Dependent solution dynamics of a manganese(II)polyoxometalate, [Mn-4(H2O)(2)(P2W15O56)(2)](16-), and [Mn(H2O)(6)](2+)2015In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 44, no 44, p. 19068-19071Article in journal (Refereed)
    Abstract [en]

    The aqueous reaction dynamics of the manganese(II)-functionalised Wells-Dawson polyoxometalate [Mn-4(H2O)(2)(P2W15O56)(2)](16-) has been determined as a function of pH using variable temperature O-17 NMR, and compared with that of the well-studied monomeric manganese(II) hexa-aqua ion, [Mn(H2O)(6)](2+). While the rate of aquo-ligand exchange on the hexa-aqua ion remains independent of pH in the range 3.2-6.0, the rate of water exchange of the polyoxometalate ion varies by a factor of fifteen, from 1.98 x 10(7) s(-1) at pH 3.2 to 1.3 x 10(6) s(-1) at pH 6.0. This decrease in the rate of exchange correlates with the deprotonation of the polyoxometalate framework.

  • 18.
    Shimizu, Kenichi
    et al.
    Umeå University, Faculty of Science and Technology, Department of Chemistry. Physical and Theoretical Chemistry Laboratory, Department of Chemistry, University of Oxford, UK.
    Driver, Gordon W.
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Lucas, Marie
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Sparrman, Tobias
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Boily, Jean-Francois
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Bifluoride ([HF2](-)) formation at the fluoridated aluminium hydroxide/water interface2016In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 45, no 22, p. 9045-9050Article in journal (Refereed)
    Abstract [en]

    This study uncovers bifluoride-type (difluorohydrogenate(I); [HF2](-)) species formed at mineral/water interfaces. Bifluoride forms at equivalent to Al-F surface sites resulting from the partial fluoridation of gibbsite (gamma-Al(OH3)) and bayerite (alpha-Al(OH3)) particles exposed to aqueous solutions of 50 mM NaF. Fluoride removal from these solutions is proton-promoted and results in a strongly self-buffered suspensions at circumneutral pH, proceeds at a F : H consumption ratio of 2 : 1, and with recorded losses of up to 17 mM fluoride (58 F nm(-2)). These loadings exceed crystallographic site densities by a factor of 3-4, yet the reactions have no resolvable impact on particle size, shape and mineralogy. X-ray photoelectron spectroscopy (XPS) of frozen (-155 degrees C) wet mineral pastes revealed coexisting surface F- and HF0 species. Electron energy loss features pointed to multilayer distribution of these species at the mineral/water interface. XPS also uncovered a distinct form of Na+ involved in binding fluoride-bearing species. XPS and solid state magic angle spinning F-19 nuclear magnetic resonance measurements showed that these fluoride species were highly comparable to a sodium-bifluoride (NaHF2) reference. First layer surface species are represented as =Al-F-H-F-Al= and =Al-F-Na-F-Al=, and may form multi-layered species into the mineral/water interface. These results consequently point to a potentially overlooked inorganic fluorine species in a technologically relevant mineral/water interfacial systems.

  • 19. Sindlinger, Christian P.
    et al.
    Lawrence, Samuel R.
    Acharya, Shravan
    Ohlin, C. André
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Stasch, Andreas
    PNacPNacE: (E = Ga, In, Tl) - monomeric group 13 metal(I) heterocycles stabilized by a sterically demanding bis(iminophosphoranyl)methanide2017In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 46, no 48, p. 16872-16877Article in journal (Refereed)
    Abstract [en]

    The salt metathesis reaction of the sterically demanding bis(iminophosphoranyl)methanide alkali metal complexes LM (L-=HC(Ph(2)PvNDip)(2)(-), Dip=2,6-(Pr2C6H3)-Pr-i; 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) in moderate yields, and small quantities of LGaI2 4 in the 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 LAlI2 5, prepared by iodination of LAlMe2, 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.

  • 20. Son, Jung-Ho
    et al.
    Ohlin, C. Andre
    Casey, William H.
    A new class of soluble and stable transition-metal-substituted polyoxoniobate: [Cr-2(OH)(4)Nb10O30](8-)2012In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 41, no 41, p. 12674-12677Article in journal (Refereed)
    Abstract [en]

    Hydrothermal synthesis of [Cr-2(III)(OH)(4)Nb10O30](8-) in gram-scale quantities leads to a new polyoxometalate ion composed of two CrNb6O19 Lindqvist-type units that are fused via shared faces. The two Cr-III atoms are located in the centre of the molecule and are bridged by two mu(4)-O atoms. Electronic transitions are calculated using density functional theory and compare well with the measured UV-Vis spectra.

  • 21. Son, Jung-Ho
    et al.
    Ohlin, C. Andre
    Casey, William H.
    Highly soluble iron- and nickel-substituted decaniobates with tetramethylammonium countercations2013In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 42, no 21, p. 7529-7533Article in journal (Refereed)
    Abstract [en]

    Iron- and nickel-substituted decaniobates, [(H2FeNb9O28)-Nb-III](6-) and [(H3NiNb9O28)-Nb-II](6-) were hydrothermally synthesized as tetramethylammonium salts and the structures were determined by X-ray crystallography. The highly soluble title compounds were characterized by ESI-MS, FT-IR and UV-Vis titration.

  • 22.
    Soroka, Inna L.
    et al.
    KTH Royal Inst Technol, Sch Chem Sci & Engn, Stockholm, Sweden.
    Shchukarev, Andrey
    Umeå University, Faculty of Science and Technology, Department of Chemistry.
    Jonsson, Mats
    KTH Royal Inst Technol, Sch Chem Sci & Engn, Stockholm, Sweden.
    Tarakina, Nadezda V.
    The University of Würzburg, Würzburg, Germany.
    Korzhavyi, Pavel A.
    KTH Royal Inst Technol, Dept Mat Sci & Engn, Stockholm, Sweden.
    Cuprous hydroxide in a solid form: does it exist?2013In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 42, no 26, p. 9585-9594Article in journal (Refereed)
    Abstract [en]

    Experimental studies have been performed to obtain the unknown cuprous hydroxide compound, which has recently been predicted theoretically (P. A. Korzhavyi et. al., Proc. Natl. Acad. Sci. U. S. A., 2012, 109, 686-689) to be metastable in a solid form. The reduction of Cu2+ with ferrous ethylenediamine tetraacetate (EDTA) results in the formation of a yellow powder precipitate whose composition corresponds to CuOH x H2O as probed by Fourier Transform Infrared Spectroscopy (FTIR) and cryogenic X-ray Photoelectron Spectroscopy (XPS). A similar compound has been found on the surface of Cu-CuH powder stored in water, as detected by XPS. The reduction of Cu2+ to Cu+ with free radicals in aqueous solutions results in a Cu2O precipitate as the final product, while the formation of the yellow cuprous hydroxide colloids may be an intermediate step. Our studies reveal that cuprous hydroxide does exist in a solid form and most likely has a hydrated form, CuOH x H2O.

  • 23.
    Taube, Fabian
    et al.
    Umeå University, Faculty of Science and Technology, Chemistry.
    Andersson, Ingegärd
    Umeå University, Faculty of Science and Technology, Chemistry.
    Angus-Dunne, Sarah
    Bodor, Andrea
    Tóth, Imre
    Pettersson, Lage
    Umeå University, Faculty of Science and Technology, Chemistry.
    Equilibria and dynamics of some aqueous peroxomolybdophosphate catalysts: a potentiometric and 31P NMR spectroscopic study2003In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, p. 2512-2518Article in journal (Refereed)
    Abstract [en]

    The equilibrium speciation in the pH++qMoO42–+rH2O2+sH2PO4–+tSO42–(H+)p(MoO42–)q(H2O2)r(H2PO4–)s(SO42–)tp–2q–s–2t system in 0.300 M Na2(SO4) medium at 25 °C and [H2O2]tot/[Mo]tot > 2 has been determined from potentiometric data and 31P NMR integral and chemical shift data in the range 1.0 pH 9.0, 2.0 [MoO42–]tot/mM 293, 32 [H2O2]tot/mM 640, 2 [H2PO4–]tot/mM 60 and 200 [SO42–]tot/mM 380. Species with the following compositions were obtained: MoX2P3–(0,1,2,1,0), MoX2P2–(1,1,2,1,0), MoX2P–(2,1,2,1,0), Mo2X4P3–(2,2,4,1,0), Mo2X4P2–(3,2,4,1,0), Mo3X6P3–(4,3,6,1,0), Mo3X6P2–(5,3,6,1,0) and Mo4X8P3–(6,4,8,1,0). The numbers and charges of molybdenum (Mo), peroxide (X), phosphate (P) and sulfate (S) in each species are given in the abbreviated formula MoqXrPsStp–2q–s–2t. The numbers in parentheses refer to the values of p, q, r, s and t in the formula above. The following formation constants with 3 were obtained; log0,1,2,1,0= 5.16 ± 0.09, log1,1,2,1,0= 12.73 ± 0.02 (pKa= 7.63), log2,1,2,1,0= 16.14 ± 0.03 (pKa= 3.42), log2,2,4,1,0= 25.03 (± 0.04), log3,2,4,1,0= 29.54 ± 0.02 (pKa= 4.51), log4,3,6,1,0= 42.30 ± 0.03, log5,3,6,1,0= 44.06 ± 0.08 (pKa= 1.76), log6,4,8,1,0= 57.30 ± 0.07. pKa values for H3PO4 and H2PO4– were determined to 2.00 and 6.48, respectively. Chemical exchange processes were detected by 31P NMR 2D EXSY and selective magnetisation transfer experiments between the complexes. An averaged lifetime, (X2Mo–OP) 30 ms, can be estimated for the MoX2P and Mo2X4P species at pH = 5.5 and 5 °C.

  • 24.
    Åkerstedt, Josefin
    et al.
    Inorganic Chemistry, Royal Institute of Technology, Stockholm, Sweden.
    Zaffaroni, Riccardo
    University of Milano Bicocca, Milano, Italy.
    Kloo, Lars
    Inorganic Chemistry, Royal Institute of Technology, Stockholm, Sweden.
    Dichloromethane as solvent for the synthesis of polycationic clusters at room temperature: a link to standard organometallic chemistry2010In: Dalton Transactions, ISSN 1477-9226, E-ISSN 1477-9234, Vol. 39, no 35, p. 8132-8134Article in journal (Refereed)
    Abstract [en]

    Dichloromethane (DCM), CH2Cl2 has been identified as an alternative reaction medium for room-temperature synthesis of subvalent homopolyatomic clusters of the group 15 element bismuth.

1 - 24 of 24
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