TY - JOUR

T1 - Pancake-bonding of semiquinone radicals under variable temperature and pressure conditions

AU - Bogdanov, Nikita E.

AU - Milas&garon;inovic, Valentina

AU - Zakharov, Boris A.

AU - Boldyreva, Elena V.

AU - Molc&garon;anov, Kresimir

PY - 2020/4/1

Y1 - 2020/4/1

N2 - The effects of temperature (100-370K) and pressure (0-6GPa) on the non-localized two-electron multicentric covalent bonds ('pancake bonding') in closely bound radical dimers were studied using single-crystal X-ray diffraction on a 4-cyano-N-methylpyridinium salt of 5,6-dichloro-2,3-dicyanosemiquinone radical anion (DDQ) as the sample compound. On cooling, the anisotropic structural compression was accompanied by continuous changes in molecular stacking; the discontinuities in the changes in volume and b and c cell parameters suggest that a phase transition occurs between 210 and 240K. At a pressure of 2.55GPa, distances between radical dimers shortened to 2.9Å, which corresponds to distances observed in extended π-bonded polymers. Increasing pressure further to 6GPa reduced the interplanar separation of the radicals to 2.75Å. This may indicate that the covalent component of the interaction significantly increased, in accordance with the results of DFT calculations reported elsewhere [Molčanov et al. (2019), Cryst. Growth Des. 19, 391-402].

AB - The effects of temperature (100-370K) and pressure (0-6GPa) on the non-localized two-electron multicentric covalent bonds ('pancake bonding') in closely bound radical dimers were studied using single-crystal X-ray diffraction on a 4-cyano-N-methylpyridinium salt of 5,6-dichloro-2,3-dicyanosemiquinone radical anion (DDQ) as the sample compound. On cooling, the anisotropic structural compression was accompanied by continuous changes in molecular stacking; the discontinuities in the changes in volume and b and c cell parameters suggest that a phase transition occurs between 210 and 240K. At a pressure of 2.55GPa, distances between radical dimers shortened to 2.9Å, which corresponds to distances observed in extended π-bonded polymers. Increasing pressure further to 6GPa reduced the interplanar separation of the radicals to 2.75Å. This may indicate that the covalent component of the interaction significantly increased, in accordance with the results of DFT calculations reported elsewhere [Molčanov et al. (2019), Cryst. Growth Des. 19, 391-402].

KW - high pressure

KW - low temperature

KW - multicentric two-electron bonding

KW - pancake bonding

KW - semiquinone radicals

KW - PI-STACKING

KW - DIMER

KW - DISTANCES

KW - LINE

KW - CRYSTALS

KW - SALTS

UR - http://www.scopus.com/inward/record.url?scp=85083077991&partnerID=8YFLogxK

U2 - 10.1107/S2052520620002772

DO - 10.1107/S2052520620002772

M3 - Article

C2 - 32831231

AN - SCOPUS:85083077991

VL - 76

SP - 285

EP - 291

JO - Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials

JF - Acta Crystallographica Section B: Structural Science, Crystal Engineering and Materials

SN - 2052-5192

IS - Pt 2

ER -