Weak hydrogen bonds in solid hydroxides and hydrates

Polaronic structure of excess electrons and holes for a series of bulk iron oxides

With the use of a gap-optimized hybrid functional and large supercells, it is found that while the electron hole polaron generally localises onto a single iron site, the electron polaron localises across two iron sites of the same spin layer.

Hydrogen Bonding in Amorphous Alkaline Earth Carbonates

Amorphous intermediates play a crucial role during the crystallization of alkaline earth carbonates. We synthesized amorphous carbonates of magnesium, calcium, strontium, and barium from methanolic solution. The local environment of water and the strength of hydrogen bonding in these hydrated modifications were probed with Fourier transform IR spectroscopy, ¹H NMR spectroscopy, and heteronuclear correlation experiments. Temperature-dependent spin-lattice (T1) relaxation experiments provided information about the water motion in the amorphous materials. The Pearson hardness of the respective divalent metal cation predominantly determines the strength of the internal hydrogen-bonding network. Amorphous magnesium carbonate deviates from the remaining carbonates, as it contains additional hydroxide ions, which act as strong hydrogen-bond acceptors. Amorphous calcium carbonate exhibits the weakest hydrogen bonds of all alkaline earth carbonates. Our study provides a coherent picture of the hydrogen bonding situation in these transient species and thereby contributes to a deeper understanding of the crystallization process of carbonates.

Neutron and X-ray single-crystal structure determination of Be(IO3)2 · 4H2O

The crystal structure of Be(IO3)2 · 4H2O has been determined by both neutron and X-ray single-crystal studies (Pccn, Z = 4, a = 1581.0(6) pm, b = 650.66(10) pm and c = 877.5(2) pm, R = 4.20% and 2.50%) on the basis of 402 and 1063 reflections, respectively, and synchrotron X-ray powder diffraction. The layered structure is built up of tetrahedral Be(H2O)4 2+ units linked to adjacent iodate ions by hydrogen bonds. The shortest interionic I…I and I…O distances are with 360.1 pm and 276.8 pm unusually small, the intraionic bond lengths resemble those of other iodate hydrates. The four crystallographically different hydrogen bonds (rH…o: 159.6 pm, 166.0 pm, 167.0 pm and 178.4 pm), which are the strongest bonds known so far of salt hydrates, as also established by the wavenumbers of the uncoupled OD stretching modes, are discussed in connection with the bond valences of the intramolecular OH bonds and the great synergetic effect of Be2+ ions.

Vibrational analysis of iron and zinc phosphate conversion coating constituents

The FT-MIR/FT-FIR and NIR-FT-Raman spectra of orthorhombic alpha-Zn3(PO4)2 x 4H2O (alpha-hopeite) and monoclinic Zn2Fe(PO4)2 x 4H2O (phosphophyllite), including deuterated samples, have been measured in the polycrystalline state at room temperature and below. The distribution of vibrational levels was related to the results of complete unit-cell group analyses. The number of uncoupled OD stretching modes of alpha-hopeite (isotopically dilute samples) strongly exceeds that expected from the number of hydrogen positions of the structure reported. In contrast, unequivocal assignment of the four hydrogen bonds of phosphophyllite has been performed. The distortion of the phosphate tetrahedra, as revealed from both site group and unit-cell group splitting of the PO stretching modes, is found to be almost equal in both compounds, in accordance with the identical tetrahedral linkage scheme.