Vibronic behaviour of octahedral Cu(II) complexes in Cu(2-benzoylpyridine)₂(NO₃)₂x2H₂O crystal with a weak superexchange coupling. Temperature EPR studies

• Autorzy: Hoffmann S. K. , Goslar J. , Hilczer W. , Goher M. A. S.
• Języki publikacji: EN

Abstrakty

EN

Octahedral [Cu(2-benzoylpyridine)2 (H20)2] complexes in the Cu(2-Bzpy)2-(NO3)2 .2H2O are very dynamical and Cu(II) ions are very weakly coupled as it is shown by the single crystal EPR measurements in the temperature range 4.2-300 K. Rigid lattice limit (9 K) of spin-Hamiltonian parameters are: gx = 2.137, gy = 2.014, gz = 2.306 as determined by decoupling of exchange merged EPR lines. The ground state is predominantly Ix(2) -y(2)) with 8% of the Iz(2)) state. This mixing is produced by zero-point motions in the ground vibrational state and results in g x > gy with strong lowering of the gy-value. The decoupling procedure gave superexchange coupling parameter J = 0.0040 cm(1), which unexpectedly is temperature independent in contrast to other weakly coupled Cu(II) paramagnets. The g-factors show relatively strong temperature variations with gy practically not affected by temperature and a tendency to averaging of the g x and gz with room tem-perature parameters: g x = 2.161, gy = 2.013, gz = 2.285. This is explained as the pseudo Jahn-1eller effect with dynamical transitions between two elongated octahedral axes, i.e. O-Cu-O (x-axis) and H2O-Cu-H2O (z-axis) with N-Cu-N (y-axis) direction ill the in-plane coordination with pyridine nitrogen not affected by vibronic dynamics. The vibronic effect can be described by two-well model in the temperature range 80-150 K only with energy difference between the ground vibronic state in the well being 220 cm-l. At lower temperatures Cu(II) complexes are strongly localized in the deepest potential well, whereas at higher temperatures, the vibronic g-factor averaging is dominated by the other mechanism.

Słowa kluczowe

EN

complex; copper; exchange interaction; EPR spectroscopy

PL

kompleksy; miedź; reakcja wymiany; elektronowy rezonans paramagnetyczny

• Wydawca: Centrum Upowszechniania Nauki PAN
• Czasopismo: Bulletin of the Polish Academy of Sciences. Chemistry
• Rocznik: 2000
• Tom: Vol. 48, No. 4
• Strony: 397--409
• Opis fizyczny: Bibliogr. 18 poz.

Twórcy

autor

Hoffmann S. K.

autor

Goslar J.

autor

Hilczer W.

autor

Goher M. A. S.

• Institute of Molecular Physics, Polish Academy of Sciences, Smoluchowskiego 17, 60-179 Poznań, Poland (Instytut Fizyki Molekularnej PAN),