Jana Chrappová

Synthesis, crystal structure, spectral characterization, and theoretical study of glycolato peroxido complexes of vanadium(V)

We present the crystal structures and spectral characterization of two glycolato peroxido complexes of vanadium(V) with divalent cations. Assignment of their experimental infrared and Raman solid-state spectra was corroborated by gas-phase and periodic density functional calculations. First, the conventional BP86, PBE, and B3LYP exchange–correlation functionals were applied; their long-range-corrected variants LC-BP86 and CAM-B3LYP were subsequently utilized to evaluate their applicability in reproducing the solid-state structures and spectroscopic properties of the [V2O2(O2)2(C2H2O3)2]2− anion. Band assignments are presented in terms of potential energy distribution contributions. The structure of [Zn(H2O)6][V2O2(O2)2(C2H2O3)2]·2H2O obtained in solid state using the PBE functional is in very good agreement with the X-ray single-crystal structure. Computed vibrational frequencies and infrared intensities provided a satisfactory fit for the observed spectrum. 51V NMR chemical shifts were calculated using optimized gas-phase geometries with the GIAO approach employing the B3PW91 functional, and they were correlated with experimentally observed shift measured for the aqueous solutions.

The first transition metal iodato peroxido complex: the synthesis, vibrational spectra and crystal structure from powder diffraction data of K3[V2O2(O2)4(IO3)]·H2O

AbstractThe first transition metal iodato peroxido complex, K3[V2O2(O2)4(IO3)]·H2O (I), was prepared by crystallization from the KVO3 — KIO3 — H2O2 — H2O — ethanol (HNO3) solution. The dinuclear anion is immediately decomposed in aqueous solution; the 51V NMR spectrum exhibits signals corresponding to [VO(O2)2(H2O)]−, [V2O2(OH)(O2)4]3− and H2VO4− species only. The IR and Raman spectra contain all characteristic bands of the VO(O2)2 group and the coordinated IO3− ligand. Based on the positions of bands assigned to the vibrations of the VO(O2)2 groups a pentagonal pyramidal arrangement around the vanadium atoms can be supposed. The crystal structure was solved from X-ray synchrotron powder data by direct space method and refined by energy minimization in the solid state employing a hybrid PBE0 functional. This crystal and molecular structure, has confirmed the presence of hexacoordinated vanadium atoms and revealed asymmetric dinuclear structure of the [V2O2(O2)4(IO3)]3− ion. The coordination spheres of vanadium atoms are different — the IO3− anion is coordinated only to one vanadium center. A thermal analysis of the complex confirmed the presence of water molecules in the crystal structure and revealed a considerable stability of the dehydrated complex.

Order-disorder phase transition in the peroxidovanadium complex NH 4 [VO(O 2 ) 2 (NH 3 )]

Complex NH4[VO(O2)2(NH3)] (1) undergoes an order-disorder phase transition at Tc~258K. This transition is accompanied by change in the space group of the orthorhombic lattice and also by significant structural rearrangements of the constituent molecules, which are pertinent mostly to their NH4+ ions and their ammonia ligands. The low-temperature solid state IR and Raman spectra of 1 were corroborated by solid-state computations that employed Gaussian functions as the basis set. Results of these computations yielded excellent agreement with experimental data. On the curves of temperature dependence of vibrational modes, the phase transition is expressed by an abrupt change of the slope above Tc.

Preparation of Aluminium Hydroxide with Mechanochemical Synthesis in the Middle School Laboratory Lesson

Abstract Mechanochemical reactions proceed if solid reactants combine together by grinding, milling or kneading with no or minimal solvent. It is possible to observe changes: fizzing, foaming, colour changes, water release. This process is manually simple and there are several mechanochemical reactions which can be demonstrated during school laboratory lessons. For high school pupils there exist five possibilities of inorganic synthesis: mechanochemical synthesis, crystallisation, precipitation, filtration and decantation. The preparation of aluminium hydroxide in the school laboratory is described in this paper. Five mechanochemical reaction schemes were tested by pupils in their laboratories. The pupils conducted the experiments and filled in worksheets to accompany the practical. On the basis of their results, a suitable procedure for school use is suggested.