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Electron paramagnetic resonance study of Cu(II) in the Cu(II) doped (NH4)2[Zn(NH3)2(CrO4)2] and (NH4)2[Cd(NH3)2(CrO4)2]: Orientational disorder of NH3 and dynamically induced structural change (1992)

Wang, D. M. ; Kovacik, I. ; Reijerse, E. J. ; [et al.]

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 97 (1992), S. 3897-3904

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Electron paramagnetic resonance (EPR) spectra recorded at X band on Cu(II) in the Cu(II) doped single crystals of (NH4)2[Zn(NH3)2(CrO4)2] and (NH4)2[Cd(NH3)2(CrO4)2] showed an unusual temperature dependence in the temperature range between 4.2 and 370 K. This unusual temperature dependence is attributed to the dynamics of NH3 molecules. It is concluded that NH3 undergoes an order–disorder transition. This transition occurs at 282±2 K (T*) for (NH4)2[Zn(NH3)2(CrO4)2] and at 300±5 K for (NH4)2[Cd(NH3)2(CrO4)2]. For temperatures above T* the EPR spectra are found independent of temperature. This observation indicates that the NH3 molecules behave as free rotors rotating about their threefold symmetry axis. As the temperature is lowered, the free rotation gradually becomes hindered which leads at T* to site doubling in the EPR spectra. The hindered rotation simultaneously induces a structural change at T* reducing the local symmetry at the Cu(II) site from C2/m to approximately Cs. In the temperature range between T* and about 80 K, the EPR spectra with the magnetic field perpendicular to the threefold axis of NH3 are temperature dependent, but those with the magnetic field parallel to the threefold axis remain unchanged. This behavior is qualitatively interpreted as being due to the torsional oscillation of NH3. At temperatures lower than 80 K, the NH3 molecules exhibit the torsional oscillation of the lowest state and accordingly, all the EPR spectra become temperature independent.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.462928

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Einfluß der Imidazol- und Benzimidazolliganden auf die strukturellen Eigenschaften von Thiocyanato-Nickel(II)-Komplexen (1991)

Mašlejová, A. ; Kováčik, I.

Weinheim : Wiley-Blackwell

Zeitschrift für anorganische Chemie 604 (1991), S. 151-156

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ISSN: 0044-2313

Keywords: Benzimidazole / imidazole-thiocyanatonickel(II) complexes ; ir,uv/vis spectra ; magnetism ; Chemistry ; Inorganic Chemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Description / Table of Contents: Influence of Imidazole and Benzimidazole Ligands on the Structure Character of Thiocyanatonickel(II) ComplexesComplexes of the type Ni(NCS)2L4 and Ni(NCS)2L2 (for L see Inhaltsübersicht) were prepared. Based on the spectral data a pseudooctahedral stereochemistry was assigned to the complexes of the type Ni(NCS)2L4, while the complexes of the type Ni(NCS)2L2 have a square-planar stereochemistry.

Notes: Komplexverbindungen des Typs Ni(NCS)2L4 (L = Imidazol, 1-Methylimidazol, 2-Methylimidazol, 2-Ethylimidazol, 1,2-Dimethylimidazol oder Benzimidazol) und Ni(NCS)2L2 (L = 2-Methylbenzimidazol bzw. 2-Ethylbenzimidazol) wurden dargestellt. Aufgrund der Spektren wird den Komplexen vom Typ Ni(NCS)2L4 pseudooktaedrische Symmetrie zugesprochen, während die Komplexe des Typs Ni(NCS)2L2 durch quadratisch-planare Anordnung gekennzeichnet werden.

Additional Material: 3 Tab.