Series of M(I)[Co(bpy)3][Mo(CN)8] x nH2O (M(I) = Li (1), K (2), Rb (3), Cs (4); n = 7-8) exhibiting reversible diamagnetic to paramagnetic transition coupled with dehydration-rehydration process.
In this paper we report the synthesis and the structural and magnetic properties of the series of ionic compounds with general formula: M(I)[Co(bpy)(3)][Mo(CN)(8)] x nH(2)O (M(I) = Li, n = 8 (1), M(I) = K, n = 8 (2), M(I) = Rb, n = 8 (3), M(I) = Cs, n = 7.5 (4)). Solids 1-4 are characterized by the optical outer-sphere metal-to-metal charge transfer (MMCT) transition from Mo(IV) center to Co(III) center in the visible region and the Co(III)Mo(IV) <==> Co(II)Mo(V) spin equilibrium strongly dominated by the Co(III)Mo(IV) form. We show a gentle thermal treatment of diamagnetic compounds 1-4 leading to the dehydrated forms 1a-4a, which reveal a significant increase of paramagnetic contribution (from 0.5 to 2% to 30-40%). The rehydration allows to recover the diamagnetic phases 1b-4b of compositions and properties similar to those of 1-4. The irradiation of the dehydrated form 2a within the MMCT band in the Superconducting Quantum Interference Device (SQUID) cavity at T = 10 K causes further increase of the Co(II)Mo(V) contribution giving the metastable phase annealed back to the 2a phase after heating above T = 290 K. The IR, electron paramagnetic resonance (EPR), and X-ray photoelectron spectroscopy (XPS) spectroscopic data along with the magnetic data are interpreted in terms of strong modification of the Co(III)Mo(IV) <==> Co(II)Mo(V) equilibrium occurring in these systems.
Faculty of Chemistry, Jagiellonian University, Ingardena 3, 30-060 Kraków, Poland.
Marcin
M
Kozieł
Robert
R
Podgajny
Rafał
R
Kania
Rémy
R
Lebris
Corine
C
Mathonière
Krzysztof
K
Lewiński
Krzysztof
K
Kruczała
Michał
M
Rams
Christine
C
Labrugère
Azzedine
A
Bousseksou
Barbara
B
Sieklucka