Single crystals of the charge-transfer salt picene/2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane have been grown using physical vapor transport. The crystal structure was determined using single-crystal X-ray diffraction. It was found that the crystals grow in a 1:1 molecular ratio and adopt a monoclinic structure with alternate stacking. Both Xray data and Raman measurements show that the grown crystals are of good quality. From structure and infrared data, the charge transfer between acceptor and donor molecules was estimated to be approximately 0.14−0.19 electron. Transport measurements indicate a nonmetallic ground state with an activation energy of 0.6 eV. The supporting density functional theory calculations on molecular model systems as well as on crystalline structures confirm the amount of charge transfer and provide first insights into the electronic structure of the new material.
Two new coronene charge transfer
complexes with F4-TCNQ
of 2:1 and 1:1:1 (solvate with acetonitrile, MeCN) stoichiometry were
obtained using crystal growth procedures from the solution and vapor
phase. It was shown that mobility of coronene molecules in crystals
is more affected by the asymmetry of its surrounding than by the composition
and degree of charge transfer and interstack interactions. The combination
of X-ray diffraction and electrochemistry in the solid state and a
time-resolved one in solution allowed us to clarify the nucleation
in solution showing that the formation of 2:1 coronene/F4-TCNQ complexes is thermodynamically preferable. The X-ray single
crystal data for pristine coronene showed the crystal structure to
be the same as at ambient temperature, raising doubt about the previously
reported phase transitions at 140–180 K.
A series of diverse binuclear and mononuclear cyclometalated palladium(ii) complexes of different structure was investigated by electrochemical techniques combined with density functional theory (DFT) calculations. The studies including cyclic and differential pulse voltammetry, X-ray structure analysis and quantum chemical calculations revealed a regularity of the complexes oxidation potential on the metal-metal distance in the complexes: the larger Pd-Pd distance, the higher oxidation potentials. The reduction potentials feature unusually high negative values while no correlation depending on the structure could be observed. These results are in a good agreement with the electron density distribution in the complexes. Additionally, ESR data obtained for the complexes upon oxidation is reported.
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