Crystal Growth, Structure, and Transport Properties of the Charge-Transfer Salt Picene/2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane

Abstract

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.

Crystal growth of new charge-transfer salts based on π-conjugated donor molecules

“…For picene/TCNQ and picene/TCNQ-F 2 the same space groups P 2 1 /n are revealed as for picene/TCNQ-F 4 reported in Ref. 11 and no disorder of the aromatic donor occurs in this set. Instead of the donor, the acceptor in the picene/TCNQ-F 2 structure is disordered.…”

“…= 228 • C meaning both compounds were intact and TCNQ was not decomposed in this temperature regime. The melting point for the complex phenanthrene/TCNQ lies in between the melting points for the single compounds, which looks reasonable and is in good agreement to the different crystal growth areas for acceptor, CT complex and donor [11,22,18] and is also apparent in Figure 2. Sublimation points could not be detected by DTA but are stronger depending on pressure than melting points.…”

“…11. A structural indication for charge transfer in theses materials is, that short- Table 2: Structural parameters for the new charge transfer salts phenanthrene/TCNQ-F 2 , phenanthrene/TCNQ-F 4 , picene/TCNQ and picene/TCNQ-F 2 together with the known phenanthrene/TCNQ [10] and picene/TCNQ-F 4 [11]. The value of charge transfer obtained from structural changes in the acceptor molecule is shown in the last column.…”

“…The charge transfer process in crystals based on these three compounds is of interest, as the reproducibility of these samples is still under debate [9] and only few experimental studies have been reported. In this paper, we expand the sets of charge transfer (CT) salts based on aromatic donor molecules as reported for phenanthrene/TCNQ [10] and picene/TCNQ-F 4 [11] and present the crystal structures of new charge transfer salts phenanthrene/TCNQ-F x (x=2, 4) and picene/TCNQ-F x (x=0, 2). With respect to the weak donor ability of phenanthrene and picene (HOMO: 6.1 eV, 5.5 eV [12]) and the strong acceptors TCNQ, TCNQ-F 2 and TCNQ-F 4 (LUMO: 4.2 eV, 4.55 eV and 5.24 eV [13]) neutral CT are expected.…”

An Investigation into the Polymorphism and Crystallization of Levetiracetam and the Stability of its Solid Form

“…The solid phase diversity of active pharmaceutical ingredients (APIs), including pharmaceutical polymorphs, pseudo polymorphs (solvates and hydrates), salts, co‐crystals, and amorphous solids, has become one of the most investigated areas in contemporary drug research because of the unique physicochemical properties, efficacy, and toxic side effects existing in different solid forms of drugs . Pharmaceutical solid form screening has rapidly developed into a general approach to improve the physicochemical properties of drugs, which can remarkably affect the solubility, bioavailability, hygroscopicity, melting point, stability, compressibility, and other performance characteristics of pharmaceutical products .…”