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H Fuess

Publications and source records attributed to H Fuess.

10 recordsLinked to original sources
PubMed2001

Strong cooperativeness in the mononuclear iron(II) derivative exhibiting an abrupt spin transition above 400 K.

The spin crossover system, [Fe(bzimpy)(2)](ClO(4))(2).0.25H(2)O, was reinvestigated above room temperature (bzimpy = 2,6-bis(benzimidazol-2-yl)pyridine). The system exhibits an abrupt low-spin to high-spin transition at T(c) = 403 K. Liberation of a fractional amount of water does not affect the spin crossover: the system is perfectly reversible with a hysteresis width of DeltaT = 12 K. The existence of the hysteresis at such high temperature determines that the lowest limit of the solid-state cooperativity parameter is J/k > 403 K despite long iron(II) separations (10 A). The high cooperativeness has been assigned to a perfect pi-stacking of the benzimidazole rings in the crystal lattice at a distance as short as 3.6 A. Variable-temperature IR data and the heat capacity measurements match well the magnetic data. The thermodynamic properties are DeltaH = 17 kJ mol(-)(1), DeltaS = 43 J K(-)(1) mol(-)(1), so that the entropy of the spin transition shows a considerable contribution from the molecular vibrations. A theoretical model has been applied in fitting the magnetic data along the whole hysteresis path. A statistical distribution of the cooperativity parameter led to the feature that angled walls of the hysteresis loop are well reproduced.

Journal Article↗
PubMed2001

(Bis(N,N-dimethylformamide)[mu-N,N'-bis(salicylidene)-1,3-propanediaminato]nickel(II))dibromozinc(II).

The title compound, [NiZnBr2(C3H7NO)2(C17H16N2O2)], is a heterodinuclear nickel complex. The Ni atom has an irregular octahedral environment involving two O and two N atoms from the bis(salicylidene)-1,3-propanediaminate ligand in the equatorial plane, and two O atoms from the dimethylformamide groups. The Zn-O-Ni, O-Zn-O, Ni-O-Zn and O-Ni-O angles in the bridged plane are 100.1 (2), 79.9 (2), 100.4 (2) and 78.89 (17) degrees, respectively. The Ni...Zn distance is 3.0738 (19) A

Journal Article↗
PubMed2000

Selective imidazolidine ring opening during complex formation of iron(III), copper(II), and zinc(II) with a multidentate ligand obtained from 2-pyridinecarboxaldehyde N-oxide and triethylenetetramine.

The condensation of 2-pyridinecarboxaldehyde N-oxide and triethylenetetramine yields a product with two imidazolidine rings, as proven by a solid-state X-ray structure analysis as well as by NMR solution spectra. This ligand, L1, undergoes a ring-opening reaction on complex formation with Cu(II), yielding [CuL2]2+ where L2 functions as a pentadentate ligand, containing only one imidazolidine ring. On complexation with Zn(II) and Fe(III), both rings are opened and the complexes [ZnL3]2+ and [FeL3]3+ with a hexadentate L3 ligand are formed. The recrystallization of [ZnL3]2+ from DMSO solution results in the complex [ZnL1(DMSO)2]2+ in which L1 behaves as a tetradentate ligand. Thus L1, L2, and L3 are structural isomers with two, one, or no imidazolidine rings, as confirmed by X-ray structure analyses. The intramolecular ring formation is the result of the nucleophilic addition of the N(amino) group to the electrophilic sp2-hybridized -HC delta+=N site. Owing to the absence of the chelate effect on the sp3-hybridized carbon atom belonging to the imidazolidine ring, the ring opening is facilitated and readily observed upon complex formation with Cu(II), Zn(II), and Fe(III).

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PubMed2000

Rietveld analysis of electron powder diffraction data from nanocrystalline anatase, TiO2

The structure of nanocrystalline anatase (TiO2) was successfully refined from electron powder diffraction data using the Rietveld technique. A polycrystalline sample (average crystal size about 70 A) was characterised by selected area electron diffraction in a conventional transmission electron microscope operated at 300 kV. Radially integrated intensities were extracted from digitised photographic films and used in the course of structure refinements by a standard program for Rietveld analysis. The structure was refined in space group I4(1)/amd (#141) with lattice parameters a = 3.7710(9) A and c = 9.430(2) A. The reliability factors of the refinement are Rwp = 5.2% and R(B) = 2.6%. The close agreement of the refined structural parameters with previous results obtained from neutron diffraction on coarse-grained powders proves the applicability of the method for characterising nanocrystalline powders. The present study shows that Rietveld analysis on electron powder data is a good compliment to the existing methods for accurate structural investigations on nanocrystalline materials and thin films.

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PubMed2000

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Journal Article↗
PubMed1999

The crystal structure of Tm5Re2O12.

The crystal structure of Tm(5)Re(2)O(12), pentathulium dirhenium dodecaoxide, was determined by synchrotron diffraction on a reticular merohedral twin, revealing space group C2/m with a = 12.3717 (7), b = 5.6744 (3), c = 7.4805 (4) Å, beta = 107.816 (2) degrees and Z = 2. Distorted ReO(6) octahedra form chains with alternating rhenium-rhenium distances of 2.455 (1) and 3.219 (1) Å. Early reports on Ln(2)ReO(5) compounds are critically reviewed in the light of our results for Tm(5)Re(2)O(12).

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