Difluoro-7,7,8,8-tetracyanoquinodimethane (F2- TCNQ) Single Crystals

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1 Supporting Information for Publication Inhibiting Low-Frequency Vibrations Explains Exceptionally High Electron Mobility in 2,5- Difluoro-7,7,8,8-tetracyanoquinodimethane (F2- TCNQ) Single Crystals Ivan Yu. Chernyshov, Mikhail V. Vener,, Elizaveta V. Feldman, Dmitry Yu. Paraschuk, and Andrey Yu. Sosorev,* Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences, Leninskii prosp. 31, Moscow , Russia G.A. Krestov Institute of Solution Chemistry of the Russian Academy of Sciences, Academicheskaya 1, Ivanovo, Russia Faculty of Physics and International Laser Center, M.V. Lomonosov Moscow State University, Moscow , Russia.

2 1. Details of transfer integrals calculation To calculate the transfer integral between the initial and final state wavefunctions, Ji, the direct method employing projection of the monomer wavefunctions on the dimer (DIPRO method) was used as described in Refs. [1,2]. The results for Ji in FnTCNQ crystals are presented in Table S1. In addition, Ji were calculated using the energy-splitting-in-dimer method, 3 and results within 10% correspondence were obtained for symmetrical dimers (i.e. for which the molecules are in equivalent positions) where the latter method is applicable. Table S1. Ji values in Fn-TCNQ crystals. TCNQ Dimer configuration a) Distance between molecular centers, Å Ji, mev Number of the corresponding contacts ff-1 (1/2+x,1/2+y,z) ef-1 (1/2-x,1/2+y,1/2-z) ff-2 (1/2+x,-1/2+y,z) ee-1 (1+x,y,z) ee-2 (1-x,y,1/2-z) ee-3 (-x,y,1/2-z) F2-TCNQ ff-1 (1/2+x,1/2+y,1+z) ff-2 (1/2+x,1/2+y,z) ee-1 (x,y,1+z) ee-2 (1+x,y,1+z) ee-3 (1+x,y,z) F4-TCNQ ef-1 (1/2+x,1/2-y,1-z) ff-1 (x,1+y,z) ef-2 (1/2-x,-y,1/2+z) ef-3 (1-x,1/2+y,1/2-z) a) Edge-to-edge, edge-to-face and face-to-face dimers are denoted as ee, ef an ff respectively.

3 2. Estimation of the electron mobility Within the hopping model, charge mobility is related to diffusion coefficient D via Einstein- N e 1 Smolukhowski formula: D. Diffusion coefficient is D Pk i id kt 6 i 1 2 i, where P i i k i k i is the probability of charge hopping to the nearest neighboring site i (total 14 in our crystals), ki is the transfer rate to this site, and di is the distance between the initial and final sites. We use semiclassical approach to the transfer rate based on the Marcus formula: 4 k i 2 J 2 i 1 4 kt exp E 4 kt 2 (S1) In (S1), ħ is the reduced Planck constant, k is the Boltzman constant, T is the absolute temperature, E is the energy difference between the initial and final states, and is the reorganization energy (Epol).

4 Counts Counts 3. Temperature dependent Raman spectra for single crystals The temperature-dependent Raman spectra for single crystals of TCNQ and F2-TCNQ are shown in Fig. S1. Most of the observed peaks show prominent temperature dependence indicating the impact of the intermolecular interactions on them. Absence of any (temperaturedependent) features for F2-TCNQ spectrum below 50 cm -1 indicate that the small peak at Fig. 1 of the main text is an artifact. 1.0 TCNQ (crystal) 1.0 F2-TCNQ (crystal) C 60 0 C 10 0 C C C C C C 60 0 C 10 0 C C C C C Raman shift (cm -1 ) Raman shift (cm -1 ) Figure S1. Raman spectra for single crystals of TCNQ (left panel) and F2-TCNQ (right panel) in the temperature range C.

5 4. Solid-state DFT computations Solid-state DFT computations were performed with the CRYSTAL14 package 5,6 using the B3LYP/6-31G(d,p) approximation. The total energy convergence criteria was set to 10-8 and Hartree for geometry optimization and frequency calculations respectively. The default options were used for the level of accuracy in evaluating the Coulomb and Hartree-Fock exchange series. The Brillouin zone was sampled with a Γ-centered grid with 3x3x3 k-points. The space groups and unit cell parameters of the considered crystals were adopted for solid-state DFT computations with structural relaxations limited to the positional parameters of atoms. This approximation effectively compensates for the appreciable increases in volume that occur between the minimum electronic energy structure and the finite temperature structure 7 and yields a reasonable description of various properties of molecular crystals X-ray coordinates 11 were used as initial guess for geometry optimization. The average root-mean square deviations (RMSD) of intermolecular structural parameters between experimental and theoretical values does not exceed 0.02 Å in the considered solids. This confirms the reliability of the B3LYP/6-31G(d,p) approximation in studies of molecular crystals Frequencies of normal modes were calculated within the harmonic approximation by numerical differentiation of the analytical gradient of the potential energy with respect to atomic position. 15 The D2 semiempirical Grimme dispersion correction was also used in this study. 16 It has practically no impact on the intermolecular distances, the interaction energies and the Elatt values of the considered crystals (compare ΔD values in Tables S2 S4 to those in Tables S5 S7). Note, that the C(H) N distances were used in calculation of root-mean-square deviation of intermolecular distances instead of H N distances due to problems in identifying hydrogen atom positions using X-ray diffraction experiment. The crystallographic cell of the F2-TCNQ crystal was chosen as supercell in order to reveal acoustic vibrations. The computations were carried out for the space group P1.

6 5. Visualization of lowest-frequency vibrational modes Three lowest-frequency vibrational modes according to the Γ-point calculation are shown in Figure S2. For the sake of simplicity, only one of the molecule comprising the unit cell is shown. Figure S2. The three calculated low-frequency vibrations in the TCNQ (left panel), F2-TCNQ (middle panel) and F4-TCNQ (right panel) crystals. Red arrows denote scaled vibrational displacement vectors.

7 6. Description of packing motifs Structurally close Fn-TCNQ molecules form crystals with qualitatively different packing motifs. 11 These differences are illustrated in Figures S3 S5. TCNQ crystallizes in a brickwork motif, in which each molecule interacts with 4 neighbors face-to-face forming π-stacked 2D layers (Figure S3, upper panel). These layers abut in a herringbone-like manner producing wave-like CH N bonded layers (Figure S3, lower panel). The F2-TCNQ crystal consists of the flat layers lying on symmetry planes (Figure S4, upper panel). The molecules of one layer are located opposite the voids of the adjacent layer, thus each molecule interacts with 8 neighbors face-to-face (Figure S4, lower panel). This 3D-brickwork packing motif is unusual for OSC. 17,18 F4-TCNQ crystallize in a classic herringbone motif (Figure S5).

8 Figure S3. Upper panel: brickwork motif in the TCNQ crystal. Lower panel: crystal structure of TCNQ; orange frame highlights layer pictured in the upper panel. Red, green and blue lines denote the unit cell vectors a, b and c, respectively.

9 Figure S4. Upper panel: crystal structure of F2-TCNQ. Lower panel: the relative arrangement of the F2-TCNQ molecule with respect to the molecules of the adjacent layer. Red, green and blue lines denote the unit cell vectors a, b and c, respectively.

10 Figure S5. Upper panel: herringbone motif in the F4-TCNQ crystal. Lower panel: crystal structure of F4-TCNQ; orange frame highlights layer pictured in the upper panel. Red, green and blue lines denote the unit cell vectors a, b and c, respectively.

11 7. Bader analysis of periodic electron density The quantum-topological analysis of the crystalline electron density was performed using the TOPOND14 computer program. 19 The intermolecular interaction energies were estimated by the value of local electronic kinetic energy density, Gb, at the bond critical point: 20 Eint,i,j [kj mol 1 ] = 1124 Gb [atomic units], (S2) where Eint,j,i is the energy of a particular intermolecular (noncovalent) interaction between atoms j and i belonging to different molecules. 21 The electron density features and the energy of determined intermolecular contacts of the considered crystals are given in Tables S2 S7. The lattice energy Elatt was evaluated as: Elatt = ΣiΣj>iEint,i,j. (S3) Taking into account that the root-mean-square deviation (RMSD) of intermolecular distances between experimental and theoretical values does not exceed 0.02 Å in the considered solids, and that the electron density features mainly depend on the interatomic distances, we conclude that the Eq. S2 are well applied to these crystals. The Elatt values are close to the experimental sublimation enthalpy of TCNQ crystal (79.0 kj mol 1 ) 24, which verifies the method for estimating the intermolecular interaction energy.

12 8. Intermolecular interactions All intermolecular interactions were divided into three groups: edge-to-edge, edge-to-face and face-to-face (Figures S7 S9). For the purpose the space around the molecule were divided into edge and face regions (Scheme S1). If the vector connecting two interacting atoms were located in face regions of both molecules, then corresponding interaction were classified as face-to-face. Edge-to-face and edge-to-edge interactions were defined in a similar way. Scheme 1. Edge and face regions in Fn-TCNQ molecules. The strongest interactions in the considered crystals are CH N ones. They are responsible for domination of the edge-to-edge interactions in TCNQ. This crystal consists of the non-flat layers, formed by the 1D-ribbons in which molecules are bound by the edge-to-edge CH N bonds forming R2 2 (12) motif 25 (Figure 4). Within the layer, the ribbons interact with each other through the same R2 2 (12) motif formed by the edge-to-edge CH N contacts. The structure of this ribbons does not allow them to lie in the same plane, so the angle between them is 140 degrees. As there are translationally inequivalent molecules, Zred>1. Complete substitution of hydrogen with fluorine atoms leads to the lack of CH N bonds in the F4-TCNQ crystal. This results in formation of the herringbone packing motif, almost complete absence of edge-to-edge interactions and domination of edge-to-face interactions between positively charged π-system and electron-rich nitrogen and fluorine atoms. As a consequence, Zred>1. Conversely, partial

13 substitution of hydrogen by fluorine atoms in F2-TCNQ preserves the CH N-bonded 1Dribbons, but as the number of CH N contacts decreases by half, the ribbons interact through the weak N N contacts. This results in the layer flattening and more than twofold increase of the energy of the face-to-face interactions. All molecules become translationally equivalent that leads to Zred=1. Therefore, we conclude that F2-TCNQ possess Zred=1 because of the balance between edge-to-edge and face-to-face interactions and the absence of edge-to-face interactions. Figure S6. Intralayer interactions in TCNQ (left panel) and F2-TCNQ (right panel). Green frames highlight 1D-ribbons.

14 Figure S7. Intermolecular interactions in the TCNQ crystal. Upper panel: edge-to-edge interactions. Middle panel: edge-to-face interactions. Lower panel: face-to-face interactions.

15 Figure S8. Intermolecular interactions in the F2-TCNQ crystal. Upper panel: edge-to-edge interactions. Lower panel: a quarter of face-to-face interactions.

16 Figure S9. Intermolecular interactions in the F4-TCNQ crystal. Upper panel: edge-to-edge interactions. Middle panel: a quarter of edge-to-face interactions. Lower panel: face-to-face interactions.

17 Table S2. The electron density features and the energy of determined intermolecular contacts in the TCNQ crystal calculated using the B3LYP/6-31G** approximation. Contact D a) thr b) D exp ΔD c) ρ d) 2 ρ e) G f) b E g) int N h) Type i) С3 N1 (1/2+x,-1/2+y,z) ff C2 C6 (1/2-x,1/2-y,1-z) ff H2 N1 (-x,1-y,1-z) ee C6(H2) N1 (-x,1-y,1-z) N1 N1 (-x,1-y,1-z) ee N1 C4 (-1/2+x,1/2+y,z) ff N1 N2 (-x,y,1/2-z) ee H1 N2 (1-x,y,1/2-z) ee C3(H1) N2 (1-x,y,1/2-z) N2 N2 (1-x,y,1/2-z) ee N2 C5 (1/2-x,-1/2+y,1/2-z) ef C6 C6 (1/2-x,3/2-y,1-z) ff a) The theoretical distance value of the corresponding contact, Å. b) The X-Ray distance value of the corresponding contact, Å; Rf = 0.033, T = 180 K. 11 c) The difference between theoretical and experimental distance values of the corresponding contact, Å; the root-mean-squared deviation is Å. d) The electron density value at the bond critical point of the corresponding contact, a.u. e) The value of laplacian of the electron density at the bond critical point of the corresponding contact, a.u. f) The value of positively-defined local electronic kinetic energy density at the bond critical point of the corresponding contact, a.u. g) The energy value of the corresponding contact evaluated using Eq. S2, kj mol 1 ; the lattice energy evaluated using Eq. S3 is 84.5 kj mol 1. h) The number of the corresponding contacts per molecule. i) Type of the intermolecular interaction; edge-to-edge, edge-to-face and face-to-face interactions are denoted as ee, ef and ff respectively.

18 Table S3. The electron density features and the energy of determined intermolecular contacts in the F2-TCNQ crystal calculated using the B3LYP/6-31G** approximation. Contact D a) thr b) D exp ΔD c) ρ d) 2 ρ e) G f) b E g) int N h) Type i) N1 N1 (3/2-x,-1/2+y,1-z) ff N2 C1 (1/2+x,-1/2+y,z) ff N1 N1 (1-x,y,1-z) ee N2 N2 (2-x,y,1-z) ee N2 C6 (3/2-x,-1/2+y,-z) ff F1 F1 (3/2-x,-1/2+y,-z) ff H1 N1 (x,y,-1+z) ee C6(H1) N1 (x,y,-1+z) N1 N2 (2-x,y,1-z) ee a) The theoretical distance value of the corresponding contact, Å. b) The X-Ray distance value of the corresponding contact, Å; Rf = 0.035, T = 180 K. 11 c) The difference between theoretical and experimental distance values of the corresponding contact, Å; the root-mean-squared deviation is Å. d) The electron density value at the bond critical point of the corresponding contact, a.u. e) The value of laplacian of the electron density at the bond critical point of the corresponding contact, a.u. f) The value of positively-defined local electronic kinetic energy density at the bond critical point of the corresponding contact, a.u. g) The energy value of the corresponding contact evaluated using Eq. S2, kj mol 1 ; the lattice energy evaluated using Eq. S3 is 83.4 kj mol 1. h) The number of the corresponding contacts per molecule. i) Type of the intermolecular interaction; edge-to-edge, edge-to-face and face-to-face interactions are denoted as ee, ef and ff respectively.

19 Table S4. The electron density features and the energy of determined intermolecular contacts in the F4-TCNQ crystal calculated using the B3LYP/6-31G** approximation. Contact D a) thr b) D exp ΔD c) ρ d) 2 ρ e) G f) b E g) int N h) Type i) F1 F2 (1/2-x,1/2+y,z) ef N2 F1 (x,-1/2-y,-1/2+z) ef N2 F1 (1/2+x,-1/2-y,1-z) ef N1 C2 (1/2-x,-1/2+y,z) ef N1 N2 (1-x,-1/2+y,1/2-z) ee N1 N1 (1-x,-1-y,1-z) ff N2 C1 (1/2+x,y,1/2-z) N2 N1 (1/2+x,y,1/2-z) ef N2 C5 (x,-1/2-y,-1/2+z) ef N1 C6 (1-x,-1-y,1-z) ff a) The theoretical distance value of the corresponding contact, Å. b) The X-Ray distance value of the corresponding contact, Å; Rf = 0.031, T = 180 K. 11 c) The difference between theoretical and experimental distance values of the corresponding contact, Å; the root-mean-squared deviation is Å. d) The electron density value at the bond critical point of the corresponding contact, a.u. e) The value of laplacian of the electron density at the bond critical point of the corresponding contact, a.u. f) The value of positively-defined local electronic kinetic energy density at the bond critical point of the corresponding contact, a.u. g) The energy value of the corresponding contact evaluated using Eq. S2, kj mol 1 ; the lattice energy evaluated using Eq. S3 is 89.9 kj mol 1. h) The number of the corresponding contacts per molecule. i) Type of the intermolecular interaction; edge-to-edge, edge-to-face and face-to-face interactions are denoted as ee, ef and ff respectively.

20 Table S5. The electron density features and the energy of determined intermolecular contacts in the TCNQ crystal calculated using the B3LYP-D2/6-31G** approximation. Contact D a) thr b) D exp ΔD c) ρ d) 2 ρ e) G f) b E g) int N h) Type i) С3 N1 (1/2+x,-1/2+y,z) ff C2 C6 (1/2-x,1/2-y,1-z) ff H2 N1 (-x,1-y,1-z) ee C6(H2) N1 (-x,1-y,1-z) N1 N1 (-x,1-y,1-z) ee N1 C4 (-1/2+x,1/2+y,z) ff N1 N2 (-x,y,1/2-z) ee H1 N2 (1-x,y,1/2-z) ee C3(H1) N2 (1-x,y,1/2-z) N2 N2 (1-x,y,1/2-z) ee N2 C5 (1/2-x,-1/2+y,1/2-z) ef C6 C6 (1/2-x,3/2-y,1-z) ff a) The theoretical distance value of the corresponding contact, Å. b) The X-Ray distance value of the corresponding contact, Å; Rf = 0.033, T = 180 K. 11 c) The difference between theoretical and experimental distance values of the corresponding contact, Å; the root-mean-squared deviation is Å. d) The electron density value at the bond critical point of the corresponding contact, a.u. e) The value of laplacian of the electron density at the bond critical point of the corresponding contact, a.u. f) The value of positively-defined local electronic kinetic energy density at the bond critical point of the corresponding contact, a.u. g) The energy value of the corresponding contact evaluated using Eq. S2, kj mol 1 ; the lattice energy evaluated using Eq. S3 is 81.4 kj mol 1. h) The number of the corresponding contacts per molecule. i) Type of the intermolecular interaction; edge-to-edge, edge-to-face and face-to-face interactions are denoted as ee, ef and ff respectively.

21 Table S6. The electron density features and the energy of determined intermolecular contacts in the F2-TCNQ crystal calculated using the B3LYP-D2/6-31G** approximation. Contact D a) thr b) D exp ΔD c) ρ d) 2 ρ e) G f) b E g) int N h) Type i) N1 N1 (3/2-x,-1/2+y,1-z) ff N2 C1 (1/2+x,-1/2+y,z) ff N1 N1 (1-x,y,1-z) ee N2 N2 (2-x,y,1-z) ee N2 C6 (3/2-x,-1/2+y,-z) ff F1 F1 (3/2-x,-1/2+y,-z) ff H1 N1 (x,y,-1+z) ee C6(H1) N1 (x,y,-1+z) N1 N2 (2-x,y,1-z) ee a) The theoretical distance value of the corresponding contact, Å. b) The X-Ray distance value of the corresponding contact, Å; Rf = 0.035, T = 180 K. 11 c) The difference between theoretical and experimental distance values of the corresponding contact, Å; the root-mean-squared deviation is Å. d) The electron density value at the bond critical point of the corresponding contact, a.u. e) The value of laplacian of the electron density at the bond critical point of the corresponding contact, a.u. f) The value of positively-defined local electronic kinetic energy density at the bond critical point of the corresponding contact, a.u. g) The energy value of the corresponding contact evaluated using Eq. S2, kj mol 1 ; the lattice energy evaluated using Eq. S3 is 83.1 kj mol 1. h) The number of the corresponding contacts per molecule. i) Type of the intermolecular interaction; edge-to-edge, edge-to-face and face-to-face interactions are denoted as ee, ef and ff respectively.

22 Table S7. The electron density features and the energy of determined intermolecular contacts in the F4-TCNQ crystal calculated using the B3LYP-D2/6-31G** approximation. Contact D a) thr b) D exp ΔD c) ρ d) 2 ρ e) G f) b E g) int N h) Type i) F1 F2 (1/2-x,1/2+y,z) ef N2 F1 (x,-1/2-y,-1/2+z) ef N2 F1 (1/2+x,-1/2-y,1-z) ef N1 C2 (1/2-x,-1/2+y,z) ef N1 N2 (1-x,-1/2+y,1/2-z) ee N1 N1 (1-x,-1-y,1-z) ff N2 C1 (1/2+x,y,1/2-z) ef N2 N1 (1/2+x,y,1/2-z) N2 C5 (x,-1/2-y,-1/2+z) ef N1 C6 (1-x,-1-y,1-z) ff a) The theoretical distance value of the corresponding contact, Å. b) The X-Ray distance value of the corresponding contact, Å; Rf = 0.031, T = 180 K. 11 c) The difference between theoretical and experimental distance values of the corresponding contact, Å; the root-mean-squared deviation is Å. d) The electron density value at the bond critical point of the corresponding contact, a.u. e) The value of laplacian of the electron density at the bond critical point of the corresponding contact, a.u. f) The value of positively-defined local electronic kinetic energy density at the bond critical point of the corresponding contact, a.u. g) The energy value of the corresponding contact evaluated using Eq. S2, kj mol 1 ; the lattice energy evaluated using Eq. S3 is 94.2 kj mol 1. h) The number of the corresponding contacts per molecule. i) Type of the intermolecular interaction; edge-to-edge, edge-to-face and face-to-face interactions are denoted as ee, ef and ff respectively.

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Supporting Information

Supporting Information Three Polymorphic Forms of Ciprofloxacin Maleate: Formation Pathways, Crystal Structures, Calculations and Thermodynamic Stability Aspects Artem O. Surov a, Andrei V. Churakov b,