First-principles molecular-dynamics simulations for neutralp-chloranil and its radical anion

Abstract

The neutral p-chloranil ͑2,3,5,6-tetrachloro-p-benzoquinone͒ and its radical anion have been extensively studied using the Car-Parrinello projector augmented wave method, which is an all-electron electronic structure method for first-principles molecular dynamics based on the local density approximation of density functional theory. Frequencies and eigenmodes are derived by fitting a system of harmonic oscillators to the moleculardynamics trajectories. The dependence of the bond lengths and vibrational frequencies on the molecular ionicity is discussed, and the electron affinity, Coulomb repulsion, and the spin-splitting parameter of p-chloranil are also derived. ͓S0163-1829͑96͒05318-0͔

Stabilisation of tetrabromo- and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals

“…(KBr 4 Q˙ Me 2 CO). Puckering was also observed in the room temperature structure of KCl 4 Q˙ Me 2 CO 27 which occurs due to sterical hindrance of chlorine substituents.Bond lengths in anions (Tables 213,14,41,42 and 3 43 ) agree well with theoretically predicted values; [12][13][14]35,36 geometry of the semiquinone radical anion is more similar to a quinone than to a hydroquinone. In aromatic hydroquinone rings, all C-C bonds are nearly equal, whereas in quinoid rings, well-defined single and double C-C bonds occur.…”

“…In NaBr4Q˙ and RbBr4Q˙ the rings are planar within experimental error, but in acetone solvates they are slightly puckered. Cremer-Pople ring puckering parameters τ 40 [12][13][14]35,36 geometry of the semiquinone radical anion is more similar to a quinone than to a hydroquinone. In aromatic hydroquinone rings, all C-C bonds are nearly equal, whereas in quinoid rings, well-defined single and double C-C bonds occur.…”

“…(2011), "Stabilisation of tetrabromo-and tetrachlorosemiquinone (bromanil and chloranil) anion radicals in crystals", CrystEngComm, Vol. 13,No.16, 1973 23 using a film method (Weissenberg camera). However, due to an extremely weak diffraction of poor crystals the authors could only determine unit cells of two polymorphs at room temperature.…”

“…During the last fifty years perhalogenosemiquinones were studied by various techniques: EPR, 4-6 UV/Vis 7 and IR/Raman spectroscopy [8][9][10][11] and computational methods. [12][13][14][15] Several charge-transfer systems involving tetrachloro-1,4-benzoquinone (Cl4Q) [16][17][18][19][20] and tetrabromo-1,4-benzoquinone (Br4Q), 21,22 where radical anions can be stabilised under appropriate conditions, have also been designed. A crystallographic study of tetrachlorosemiquinone radical anion-in its well-known potassium salt3-was attempted in a Rudjer Bo_skovi_c Institute, Bijeni_cka 54, HR-10000 Zagreb, Croatia.…”

Local response to light excitation in the charge-ordered phase of(EDO−TTF)2SbF6

“…The increase of the number of Raman active modes comes from the cell doubling, resulting in a doubling of phonon branches, whereas slight softening is observed between 100 and 170 K in the I phase for most of the modes. In molecular solids, such low frequency modes are attributed to intermolecular vibrations or librations mode, as well as intramolecular modes of boatinglike nature [23,[26][27][28][29][30]. …”