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Download fileSolvent-Triggered Cis/Trans Isomerism in Cobalt Dioxolene Chemistry: Distinguishing Effects of Packing on Valence Tautomerism
journal contribution
posted on 2016-08-24, 20:29 authored by Anangamohan Panja, Narayan
Ch. Jana, Antonio Bauzá, Antonio Frontera, Corine MathonièreIn this article,
the synthesis and X-ray crystal structures of
two cis/trans isomers of valence tautomeric (VT) cobalt dioxolene
compounds are reported. The cis isomer (1) was isolated
from the polar protic methanol solvent as a kinetic product, whereas
the less polar nonprotic solvent acetone yielded the trans isomer
(2). It should be noted that, although some coordination
polymers involving cobalt bis(dioxolene) with the cis disposition
are known for bridging ancillary ligands, such an arrangement is unprecedented
for mononuclear compounds. A careful study of intermocular interactions
revealed that the methanol solvent does not have much influence on
the crystal growth in 1, whereas acetone forms strong
halogen-bonding interactions that are crucial in the solid-state architecture
of 2. This behavior can likely be used in crystal engineering
to design new organic–inorganic hybrid materials. The energy
difference between the two isomers was examined using DFT calculations,
confirming that the trans form is in the thermodynamic state whereas
the cis isomer is a kinetic product that can be converted into the
trans isomer with time. Finally, both isomers exhibit solvent loss
at elevated temperatures that is accompanied by a change in magnetic
properties, associated with an irreversible valence tautomerism. Our
results highlight the crucial role of the solvents for the isolation
of cis/trans isomers in cobalt dioxolene chemistry, as well as the
distinguishing effects of intermolecular forces and the solid-state
packing on VT behavior.