Browsing by Author "Lennie, AR"

Now showing 1 - 2 of 2
  • No Thumbnail Available
    Item
    Detailed investigations of phase transitions and magnetic structure in Fe(iii), Mn(ii), Co(ii) and Ni(ii) 3,4,5-trihydroxybenzoate (gallate) dihydrates by neutron and x-ray diffraction
    (Royal Society of Chemistry, 2011-06-28) Saines, PJ; Yeung, HHM; Hester, JR; Lennie, AR; Cheetham, AK
    The effect of cation valency on the complex structures of divalent and trivalent transition metal gallates has been examined using a combination of neutron and synchrotron X-ray powder diffraction, single-crystal X-ray diffraction and XANES spectroscopy. In the divalent frameworks, M(C7H4O5)[middle dot]2H2O (M = Mn, Co and Ni), it was found that charge balance was achieved via the presence of protons on the meta-hydroxyl groups. It was also established that these compounds undergo a discontinuous phase transition at lower temperatures, which is driven by the position of the extra-framework water molecules in these materials. By contrast, in the trivalent Fe gallate, Fe(C7H3O5)[middle dot]2H2O, it was found that the stronger bonding between the meta-hydroxy oxygen and the cations leads to a weakening of the bond between this oxygen and its proton. This is turn is thought to lead to stronger hydrogen bonding with the extra-framework water. The lattice water is disordered in the Fe(iii) case, which prevents the phase transition found in the M(ii) gallates. Refinement against the neutron diffraction patterns also revealed that the relatively mild microwave synthesis of gallate frameworks in D2O led to an extensive deuteration of the ortho-hydrogen sites on the aromatic ring, which may suggest a more versatile method of deuterating aromatic organics. The antiferromagnetic structure of Co gallate has also been determined. © 2011, Royal Society of Chemistry
  • No Thumbnail Available
    Item
    [Mn-6] under pressure: a combined crystallographic and magnetic study
    (Wiley-VCH Verlag Berlin, 2008-03) Prescimone, A; Milios, CJ; Moggach, S; Warren, JE; Lennie, AR; Sanchez-Benitez, J; Kamenev, KV; Bircher, R; Murrie, M; Parsons, S; Brechin, EK
    Folding under pressure: High-pressure crystallography of an Mn6 single-molecule magnet reveals dramatic changes in the intramolecular geometry of the magnetic core. These structural changes effect the magnetic properties of the molecule: the magnitude of the ferromagnetic exchange between the metals is decreased, and under extreme pressure switches to antiferromagnetic. © 2008, Wiley-VCH Verlag Berlin