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Intermolecular Spin-Crossover-like Phenomenon Sensitive to Applied External Pressure in Heterospin Crystals
journal contribution
posted on 2020-03-23, 11:33 authored by Kseniya Maryunina, Koyo Yamaguchi, Sadafumi Nishihara, Katsuya Inoue, Gleb Letyagin, Galina Romanenko, Irina Barskaya, Sergey Veber, Matvey Fedin, Artem Bogomyakov, Marina Petrova, Vitaly Morozov, Victor OvcharenkoThe interaction of
Cu(acF6)2 with the stable imino nitroxide
2-(pyridin-3-yl)-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-1-oxyl (ImN-mPy) at a ratio of 2:1 led
to the formation of a new complex [{Cu(acF6)2}2(ImN-mPy)], which can exist in two polymorphic modifications, 1 and 2. The solid phases of both polymorphs
are formed by binuclear molecules, in which the paramagnetic ligand
performs the ditopic function due to the coordination of the imine
N atoms of the imidazoline and pyridine heterocycles; the >N-•O
fragment is not involved in coordination. The intramolecular exchange
interactions in the {Cu2+-NC–N-•O} exchange clusters were found to be ferromagnetic (JCu‑R > +100 cm–1). When the
cooling–heating
cycles are repeated, the χT(T) dependence for 2 acquires a hysteresis with T↓ = 37 K and T↑ = 46 K due
to the appearance of a strong antiferromagnetic intermolecular exchange
between the >N–•O fragments of adjacent molecules.
It
was impossible to trace the structural changes in the solid compound
at T < 50 K because the crystals cracked and lost
their quality during the phase transitions. Coating the crystals with
epoxide resin prevented their decomposition, but completely suppressed
the spin transition. Immersion of the polymorph 2 crystals
in a pressure-transmitting medium Daphne7373, which froze together
with the crystals of the experimental sample at T < 200 K, also suppressed the transition to the low-spin state.
An increase in the external pressure to ∼1.8 kbar led to stabilization
of the strongly coupled low-spin state in the {>N–•O···O•–N <} intermolecular exchange clusters already at room
temperature.
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Intermolecular Spin-Crossover-like Phenomenonχ Tpyridine heterocyclescoordinationfragmentm Pypolymorph 2 crystals50 Kimidazole -1-oxylepoxide resinimine N atomsintramolecular exchange interactionsImNditopic functionHeterospin CrystalsCuphase transitionsexchange clusterspolymorphic modificationsmolecule46 K37 Kroom temperature
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