Halogen Bonding Interactions of sym-Triiodotrifluorobenzene with Halide Anions: A Combined Structural and Theoretical Study Sonia Triguero,†,‡ Rosa Llusar,*,‡ Victor Polo,‡ and Marc Fourmigue´*,† Sciences Chimiques de Rennes, UMR 6226 CNRS-UniVersite´ Rennes 1, Equipe MaCSE, Baˆt 10C, Campus de Beaulieu, 35042 Rennes Cedex, France, and Departament de Quı´mica Fı´sica i Analitica, UniVersitat Jaume I, AVda. Sos Baynat s/n, 12080 Castello´, Spain
CRYSTAL GROWTH & DESIGN 2008 VOL. 8, NO. 7 2241–2247
ReceiVed September 5, 2007; ReVised Manuscript ReceiVed April 4, 2008
ABSTRACT: Cocrystallization of 1,3,5-trifluoro-2,4,6-triiodobenzene (sym-TFTIB) with nBu4NX or Ph4PX (X ) Cl-, Br-) afforded the 1:1 complex salts formulated as (sym-TFTIB)(nBu4NCl), (sym-TFTIB)(nBu4NBr), (sym-TFTIB)(Ph4PCl)(H2O)0.5 or (symTFTIB)(Ph4PBr). In all four salts, each halide anion is halogen bonded to three iodine atoms from three different sym-TFTIB molecules, affording a recurrent polymeric two-dimensional anionic network, characterized by short I · · · X distances and linear C-I · · · X but acute I · · · X- · · · I angles (X- ) Cl-, Br-). Topological analysis of the electron localization function (ELF) shows a perfect match between the iodine valence shell electrons, with a “belt”-shape arrangement around the C-I axis, and the spherical halide anions. The lack of covalent character for the halogen bond allows the simultaneous participation of one X- anion in three halogen bonds. Introduction The term halogen bonding describes a C-Hal · · · B interaction where a covalently bonded halogen atom approaches a Lewis base B. An attractive interaction takes places, which finds its origin in the anisotropy of the electron density around the halogen atom, leading to a smaller effective atomic radius along the extended C-Hal bond axis than in the direction perpendicular to this axis. This polar flattened region exhibits an electron deficiency,1 which acts as the direction of maximum electrostatic interaction toward electron-rich (lone pairs) Lewis bases. This interaction, first identified in the gas phase,2 has been recently thoroughly investigated by Resnati,3 Hanks4 and others5 in the crystalline solid state, allowing for the elaboration of extended polymeric network in cocrystallization experiments or for solid state reactivity. It also has an interest for the formation of liquid crystalline phases6 or in enzyme-substrate interactions.7 It was also successfully investigated in the domain of conducting molecular materials along two different routes.8 The first one involved halogenated tetrathiafulvalene molecules; their oxidation to the radical cation state further activates the bonded halogen atom to enter into an halogen bond interaction with counterions of Lewis base character (Br-, [Ag(CN)2]-, etc).9,10 The second route involves neutral halogenated molecules such as diiodoacetylene or 1,4-difluorotetraiodobenzene (Scheme 1) which were shown by Dehnicke to form polymeric networks upon cocrystallization with halide anions as in · · · [I- · · · (I-CtC-I)]∞ · · · .11,12 Such polymeric anionic networks were included by Yamamoto and Kato in electrocrystallization experiments with tetrathiafulvalene derivatives to afford ternary systems incorporating the partially oxidized donor molecules, and the anionic networks composed of halide anions halogen bonded to neutral iodinated molecules.13 In that respect, we were attracted by the 3-fold symmetry of the 1,3,5-trifluoro-2,4,6-triiodobenzene molecule (sym-TFTIB),14 which had not been investigated so far in halogen bonding interactions until the very recent report by van der Boom et al.15 They described that cocrystallization experiments of sym* Corresponding author. E-mail:
[email protected] (M.F.). † Sciences Chimiques de Rennes. ‡ Universitat Jaume I, Castello´.
[email protected] (R.L.);
Scheme 1. Examples of Halogenated Molecules Involved in Halogen Bonding Interaction with Halide Anions
TFTIB with bipyridyl derivatives only afforded two I · · · N halogen bonds per sym-TFTIB molecule, and this reluctance to reach a full “coordination” was attributed to a deactivation of the iodine atoms of sym-TFTIB upon successive interactions with the Lewis bases. Hoping however that sym-TFTIB could favor the formation of extended polymeric networks of 3-fold symmetry with halide anions, we have investigated its cocrystallization with the Cl- and Br- anions, both as nBu4N+ and PPh4+ salts, and we report here the preparation of these four salts and analyze in detail the similarities and differences of their X-ray solid state structures, together with a theoretical investigation using density functional theory (DFT) methods of the halogen bonding in these systems. In order to understand the nature of the halogen bond interactions present in these compounds, a topological analysis of the electron localization function, as defined by Becke and Edgecombe16 and applied to the study of the chemical bond by Silvi and Savin,17 will be carried out in the last part of the article. Results and Discussion Cocrystallization of sym-TFTIB with nBu4NCl, nBu4NBr, PPh4Cl or PPh4Br by slow evaporation of CH2Cl2 solutions afforded in the four cases the 1:1 complex salts, formulated as (sym-TFTIB)(nBu4NBr), (sym(sym-TFTIB)(nBu4NCl), TFTIB)(Ph4PCl)(H2O)0.5 or (sym-TFTIB)(Ph4PBr) respectively. Note that the complex salts surprisingly exhibit a low solubility in CH2Cl2, already indicative of a polymeric structure. Both tetrabutylammonium salts were found to be isostructural, while the two tetraphenylphosphonium salts slightly differ by inclusion of water molecule in the chloride salt. (sym-TFTIB)(nBu4NCl) and (sym-TFTIB)(nBu4NBr) crystallize in the monoclinic system,
10.1021/cg7008489 CCC: $40.75 2008 American Chemical Society Published on Web 06/07/2008
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Figure 1. Projection along a of the unit cell of [nBu4N][(symTFTIB)Br]. Hydrogen atoms have been omitted for clarity.
Figure 3. A detailed view of the polymeric anionic [(sym-TFTIB)Br]network within one single layer. Halogen bonds are indicated with black dotted lines. nBu4N+ cations have been omitted for clarity.
Figure 2. Projection view along b of [nBu4N][(sym-TFTIB)Br], showing the layered nature of the anionic network which develops in the (101) lattice planes (shown in red). Halogen bonds are indicated with black dotted lines. nBu4N+ cations have been omitted for clarity.
Figure 4. A projection along a of the unit cell of [Ph4P][(symTFTIB)Br]. Hydrogen atoms have been omitted for clarity.
space group P21/n with the neutral sym-TFTIB molecule, the n Bu4N+ cation and the halide anion (Cl-, Br-) in general position in the unit cell. A projection view of the unit cell along a is shown in Figure 1, where one observes an intricate structure with interspersed sym-TFTIB neutral molecules, halide anions and nBu4N+ cations. As shown in Figure 2 where the nBu4N+ cations have been removed for clarity, the bromide anions are halogen bonded to three iodine atoms from three different symTFTIB molecules, while in a parallel way each sym-TFTIB molecule is halogen bonded to three different bromide anions, hence the observed 1:1 stoichiometry. As shown in Figure 2, the complex polymeric [(sym-TFTIB)Br]- anionic network is organized into independent layers parallel to the (101) plane. A detailed view of one single layer is shown in Figure 3, where 12-membered cycles involving the I(1), I(2) iodine atoms and two bromide atoms are connected to each others through halogen bonding with the I(3) iodine atoms, allowing for the formation of larger cavities with four sym-TFTIB and four Br- anions, which are actually occupied by the nBu4N+ cations. The cocrystals obtained with the tetraphenylphosphonium salts are almost isostructural and only differ by their formulas as the chloride salt crystallizes with a half water molecule while the bromide is anhydrous. Both salts crystallize in the monoclinic system, space group P21/c with the sym-TFTIB molecule, the tetraphenylphosphonium and the halide in general position, corresponding again to a 1:1 stoichiometry between the symTFTIB molecule and the tetraphenylphosphonium halide. A view of the unit cell of [Ph4P][(sym-TFTIB)Br] shows (Figure 4) that the tetraphenylphosphoniums are associated two by two
Figure 5. A projection view along b of the structure of [Ph4P][(symTFTIB)Br], showing the halogen bonding interactions (dotted lines) forming polymeric anionic [(sym-TFTIB)Br]- layers parallel to the (1j02) lattice planes (Shown in red). To be compared with Figure 2. Ph4P+ cations have been omitted for clarity.
into the so-called inversion centered phenyl embrace motif which is recurrent among many Ph3PR derivatives.18 If we now consider the halogen bonding interactions (dotted lines) and suppress the Ph4P+ cations for clarity, we observe in Figure 5 (see also Figure 6) the formation of halogen bonded layers running here parallel to the (1j02) lattice plane, but highly reminiscent of those described above in Figure 2 for the nBu4N+ salts.
Halogen Bonding of sym-TFTIB with Halide Anions
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Figure 6. A detail view of one polymeric halogen bonded plane [(symTFTIB)Br]-. To be compared with Figure 3. Ph4P+ cations have been omitted for clarity.
The geometrical features of the halogen bonding interactions collected in Table 1 are characterized by I · · · Cl distances in the 3.06-3.28 Å range, the I · · · Br distances in the 3.19-3.39 Å range. These values are to be compared with the contact distances predicted by the anisotropic model for halogen bonding,1 which gives (C-)I · · · Cl and (C-)I · · · Br at 3.54 and 3.60 Å respectively.8 The much shorter distances observed here, combined with the strong linearity, demonstrate the strength of the halogen interactions in these salts. It is also important to note here that the three iodine atoms in sym-TFTIB are actually able to simultaneously participate in halogen bonding interactions, in contrast with the first reported structures of cocrystals involving sym-TFTIB with bispyridines such as 1,4-(4-pyridylethyl-enyl)benzene, trans-1,2-di-(4-pyridyl)ethylene and 4,4′bipyridine.15 In these structures, only two out of the three iodine atoms were engaged in halogen bonding. This behavior had been explained on the basis of DFT calculations by an increased deactivation of the iodine atoms of sym-TFTIB upon successive interactions with one, two or three Lewis bases such as pyridine derivatives. Besides possible packing effects which might play an important role, it is also probable that the halogen interaction with charged species such as Cl- or Br- is stronger than with neutral pyridine derivatives, hence allowing for a complete set of interactions and formation of these recurrent extended halogen bonded layered networks (see below). A similar behavior was observed for example with CBr4,19 which acts as a tetradentate halogen bond donor20 with halide anions from Me4NBr, Et4NI, Et4NBr or Et4NCl while it is bidentate when interacting with diazabicyclooctene21 and monodentate when interacting with quinuclidine.22 An analysis of these structures from the point of view of the halide anion provides a striking “coordination” around the Cl-
or Br- anions. As shown in Figure 7, the 3 iodine atoms are clustered on the same side of the halide anion, which eventually completes its “coordination” by a water molecule, as observed in the PPh4Cl salt. As shown in Figure 7 and Table 1, two acute I · · · Hal · · · I angles (75-90°) characterize these structures while the sum of the three I · · · Hal · · · I angles, an indication of the planarity of the I3Hal system, amounts to 300-320°, relatively far from the 360° characterizing a fully planar motif. Indeed, the halide anion is found to be out of the plane defined by the three iodine atoms by 1.0 to 1.5 Å. This strongly dissymmetric organization contrasts with the polymeric networks identified by Yamamoto and Kato in the conducting salts formed with partially oxidized TTF derivatives, where the halide anions are linked to 2 or 4 iodine atoms, in a symmetric linear or square-planar environment (Scheme 2).13 However, in these conducting salts, it is possible that the layered structures adopted by the oxidized organic cations enforce a layered structure for the anionic polymeric network, which would otherwise adopt a different geometry, as observed here. Indeed, complexes of halide anions (Cl-, Br-, I-) with the ditopic 1,4-diiodotetrafluorobenzene have been reported by Dehnicke to adopt similar organizations around the halide anions (Scheme 3).23 With only two iodine atoms around the halide anion, acute I · · · Hal · · · I angles of 77.24° (Hal ) Cl- in Me4N(p-C6F4I2)Cl) and 74.27° (Hal ) Br- in Me4N(pC6F4I2)Br · CH3CN) were indeed reported. Similarly, in those salts involving three iodine atoms, almost perfect T-shape geometries were found with the sum of the I · · · Hal · · · I angles close to 360°. Density Functional Theory Calculations and Electron Localization Function (ELF) Analysis. The nature of the halogen bond in the sym-TFTIB · X- complex has been investigated from a theoretical perspective and compared with that of the sym-TFTIB · pyridine aggregate, reported recently by van der Boom et al.,15 in order to understand the factors that control the formation of three-dimensional networks only for the symTFTIB · X- system.Inthisregard,ananalysisofthehalogen-halogen interactions in the [(sym-TFTIB)3Cl-] unit, present in the 3-D aggregate, is also included. Because the results obtained for symTFTIB · Cl- are equivalent to those calculated for symTFTIB · Br-, we will focus our discussion in the choride aggregate. The halogen bond complexation energy of symTFTIB · Cl- and sym-TFTIB · pyridine in a gas-phase environment have been calculated as the following energy difference:
∆Ecomplex ) E(sym-TFTIB · A) - E(sym-TFTIB) - E(A) (1) where A stands for Cl- or pyridine. The ∆E complex values yield -26.48 kcal/mol for sym-TFTIB · Cl- and -7.34 kcal/mol for sym-TFTIB · pyridine. Correction of the basis set superposition
Table 1. Geometrical Characteristics of the Halogen Bonding Interactions [nBu4N][(1)Cl]
[nBu4N][(1)Br]
I · · · Hal (Å)
3.1612(8) I(3) 3.1927(8), I(1) 3.2084 (8), I(2)
3.2598(6), I(3) 3.3246(6), I(1) 3.3329(7), I(2)
C-I · · · Hal (deg)
176.67(9), I(3) 166.75(9), I(1) 175.16(10), I(2) 77.74(2), I(1),I(2) 77.30(2), I(2),I(3) 142.09(3), I(1),I(3) 297.13 0.9374(8)
175.78(16), I(3) 166.54(12), I(1) 175.43(14), I(2) 76.65(1) I(1),I(2) 75.99(1), I(2),I(3) 139.68(2), I(1),I(3) 292.32 1.0246(5)
I · · · Hal · · · I (deg) ∑(I · · · Hal · · · I) (deg) dist Hal vs I3 plane (Å)
[Ph4P][(1)Cl][H2O]0.5 3.0659(10), I(2) 3.1078(11), I(1) 3.2784(8), I(3) 3.1103(25), O(1) 173.87(7), I(2) 174.63(6), I(1) 160.53(7), I(3) 82.35(1), I(1),I(3) 90.96(2), I(2),I(3) 144.26(2), I(1),I(2) 317.57 0.9424(8)
[Ph4P][(1)Br] 3.1921(4), I(2) 3.2036(4), I(1) 3.3940(4), I(3) 173.94(6), I(2) 172.91(6), I(1) 159.32(6), I(3) 81.19(1), I(1),I(3) 86.45(1), I(2),I(3) 137.98(1), I(1),I(3) 305.62 1.5218(3)
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Figure 8. Comparison of the ELF plots (isocontour value of 0.8) for the halogen bonds formed by sym-TFTIB · Cl- (a) or by symTFTIB · pyridine (b), and [(sym-TFTIB)3Cl-] unit at the experimental geometry (c).
Scheme 3. Motifs Observed by Dehnicke23 with Halide Anions Interacting with (a) One, (b) Two or (c) Three 1,4-Diiodotetrafluorobenzene Molecules
Figure 7. Detail of the halogen bonding interaction around the Branion (a) in [nBu4N][(sym-TFTIB)Br], (b) in [Ph4P][(sym-TFTIB)Br], and (c) around the Cl- atom in [Ph4P][(sym-TFTIB)Cl][H2O]0.5.
Scheme 2. Recurrent Motifs Reported by Kato in the Anionic Slabs of BEDT-TTF Salts with Halide Anions and Neutral Iodinated Molecules13
error using the counterpoise method reduces slightly the complexation energy to -26.05 kcal/mol and -6.46 kcal/mol for the chloride and pyridine system, respectively. Although the presence of the charged Cl- may overestimate the interaction for sym-TFTIB · Cl-, these data indicate a stronger halogen bond formation for chloride anion in spite of the superior basicity of pyridine. The optimized intermolecular I · · · Cl- distance is 2.661 Å while the I · · · N interaction distance equals 2.733 Å. A topological analysis of the ELF function calculated for symTFTIB · Cl- and sym-TFTIB · pyridine has been undertaken
focusing our attention into the so-called halogen bonding. Similar analyses have been successfully applied for the characterization of other long-range bonding situations, such as hydrogen bonds24 or 3e-2c bonds.25 If we first concentrate on the interaction between sym-TFTIB with either a Cl- anion or a pyridine molecule, the motifs shown in Figure 8 reveal that the iodine lone pair electrons are arranged in a “belt” shape around the axis defined by the C-I σ-bond. This “hole” in the iodine atom electron-pairing distribution allows the pyridine nitrogen or the chloride lone pairs to approach the iodine core basin, forming a halogen bond. Therefore, this type of interaction can be distinguished using ELF from other long-range interactions, such as hydrogen or 3e-2c bonds, where the valence basins of the two moieties are on the line connecting both nuclei. This ELF topology for the halogen bond corresponds to a nucleophile-electrophile interaction, in agreement with previous studies using other theoretical methods.26,27 Although similar features can be identified in the ELF topology of symTFTIB · Cl- and sym-TFTIB · pyridine, differences are found in the shape of the V(Cl) or V(N) lone pairs pointing toward the iodine nuclei. An inspection of the shape of V(N) shows it to be more compact, that is closer to the N atom, leading to a worse matching with the “hole” of the V(I) basin. Hence, the halogen bond between C-I · · · Cl- presents a better fitting of the ELF basins than that of C-I · · · N. On the other hand, the hydrogen ELF basins of pyridine, V(H,C), are repelled by the V(I) basins. It is worth noting that V(F) and V(I) basins of sym-
Halogen Bonding of sym-TFTIB with Halide Anions
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Figure 9. Plot of the electrostatic potential onto isodensity surfaces (0.08) for the [(sym-TFTIB)3Cl-] unit.
TFTIB have a very different shape; the V(F) basins are more compact and do not present the “hole” like V(I) basins (see Figure 8a), therefore, the existence of such a “hole” seems to be distinctive for halogen bond formation. Calculation of the integrated electronic density for each basin shows that inactivated C-I bonds present populations for the disynaptic basin connecting C and I atoms (V(C,I)) of 1.64 e and the iodine valence (V(I)) of 9.35 e. Upon complexation, there is a transference of ∼0.40 e from V(I) to V(C,I) due to the Pauli (exchange) repulsion between the valence electrons of iodine and chlorine anion. This increment of the electronic charge of the C-I bond can lead to a small destabilization of the sym-TFTIB molecule as it was observed by van der Boom et al.15 This fact combined with the weaker complexation energy of pyridine, due to the lower geometrical fit between the V(I) and V(N) lone pairs, might explain the reluctance of sym-TFTIB to coordinate three pyridine molecules. The ELF topology for the motif with three sym-TFTIB molecules interacting with one Cl- anion is shown in Figure 8c. A slight polarization of the V(Cl) basin can be observed together with deformation of the V(I) due to the proximity of other V(I). Inspection of integrated basin electron populations reveals the effect of activation of C-I bonds upon formation of the halogen bond. The enlargement of I · · · Cl distances in the crystal structure leads to a smaller hole in the V(I), however, the other ELF topological features of the halogen bond remain the same as for sym-TFTIB · Cl-. The attractive interaction between halogen atoms, which are usually viewed as having partial negative charges, can be also elegantly explained in terms of the electrostatic potentials V(r) on the halogen isodensity surfaces. In Figure 9, the V(r) is shown for the chlorine anion interacting with three sym-TFTIB molecules at the X-ray geometry. Electrostatic interactions can be observed between the negative potential on the surface of the Cl- anion and the positive potentials on the outer part of C-I σ-bonds, in agreement with the σ-hole concept defined by Clark et al.28 On the other hand, it appears that, due to the noncovalent character of this halogen bond, the variation of the angle I · · · Cl- · · · I presents a flat potential energy surface. Indeed, DFT calculations of two sym-TFTIB molecules bonded by a chlorine anion yielded an energy penalty of 2.88 kcal/mol for a variation of the I · · · Cl- · · · I angle from the ideal value of 120° to 77°, which is the angle observed in the X-ray structure (see Supporting Information). Hence, crystal packing effects can easily overcome this barrier. Therefore, we can conclude that
the acute I · · · X- · · · I angles observed by Dehnicke and ourselves are not due to any polarization effects of the halide anion upon entering into a halogen bond but most probably find their origin in favored intermolecular dispersion interactions between the iodine atoms of sym-TFTIB molecules and other long-range interactions involved in the crystal structure. Summary and Conclusions We have shown here that contrariwise to a first report on the halogen bonding of the sym-TFTIB molecule with pyridine derivatives,15 the three iodine atoms are able to engage in halogen bonding interactions with stronger halogen bond acceptors such as halide anions, affording a recurrent twodimensional motif in their nBu4N+ or Ph4P+ salts. Topological analysis of the electron localization function (ELF) has shown the perfect adaptation between the “belt”-like electron-pairing distribution of the iodine atom with the spherical distribution of the halide anion, while the acute I · · · Cl- · · · I angles observed in the structures are not related to any distortion of the halide electronic density or to any intermolecular bonding I · · · I interaction but rather to favored intermolecular dispersion forces of van der Waals type. Experimental Section Syntheses. The compound 1,3,5-trifluoro-2,4,6-triiodobenzene (symTFTIB) was prepared according to a literature method29 from commercial 1,3,5-trifluorobenzene. The other reactants and solvents were obtained from commercial sources and used as received. (sym-TFTIB)(nBu4NCl). (nBu4N)Cl (0.017 g, 0.06 mmol) was added to a solution of sym-TFTIB (0.02, 0.04 mmol) in 5 mL of CH2Cl2. After slow evaporation, transparent crystals appeared. Crystals were washed with MeOH affording the title compound (sym-TFTIB)(nBu4N)Cl (0.011 g, 35%). Anal. Calcd for C22H36ClF3I3N: C, 33.55; H, 4.61; N, 1.78. Found: C 33.59; H, 4.60; N, 1.68. (sym-TFTIB)(nBu4NBr). nBu4NBr (0.019 g, 0.06 mmol) was added to a solution of sym-TFTIB (0.02 g, 0.04 mmol) in 5 mL of CH2Cl2. After slow evaporation, transparent crystals appeared. Crystals were washed with MeOH affording the desired compound (sym-TFTIB)(nBu4N)Br (0.025 g, 74%). Anal. Calcd for C22H36BrF3I3N: C, 31.75; H, 4.36; N, 1.68. Found: C, 31.87; H, 4.26;N, 1.71. (sym-TFTIB)(Ph4PCl)(H2O)x (0.25 < x < 0.5). Ph4PCl (0.019 g, 0.06 mmol) was added to a solution of sym-TFTIB (0.02 g, 0.04 mmol) in 5 mL of CH2Cl2. After slow evaporation, transparent crystals appeared. Crystals were washed with MeOH to afford (symTFTIB)(PPh4)Cl, as water solvate (0.015 g, 42%). Anal. Calcd for C30H20ClF3I3P(H2O): C, 39.92; H, 2.46. Found: C, 40.56; H, 2.35,
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Table 2. Crystallographic Data salt formula fw cryst syst space group a/Å b/Å c/Å β/deg V/Å3 Z dcalc/Mg m-3 temp/K µ/mm-1 θ-range/deg meas refls indep refls Rint I > 2σ(I) refls abs corr Tmax, Tmin refined params R(F), I > 2σ(I) wR(F2), all ∆F (e Å-3)
(sym-TFTIB)(nBu4NCl)
(sym-TFTIB)(nBu4NBr)
(sym-TFTIB)(PPh4Cl)(H2O)0.5
(sym-TFTIB)(PPh4Br)
C22H36ClF3I3N 787.67 monoclinic P21/n 11.6713(5) 12.0414(6) 20.2722(9) 93.8338(10) 2842.7(2) 4 1.840 100 3.422 3.53-27.53 41727 6524 0.0743 5411 multiscan 1.0, 0.724226 271 0.0308 0.0719 -1.435, +1.139
C22H36BrF3I3N 832.13 monoclinic P21/n 10.9800(5) 12.6270(6) 20.8445(9) 94.2620(10) 2882.0(2) 4 1.918 100 4.669 1.89-27.50 23665 6612 0.0394 5750 multiscan 1.0, 0.738747 271 0.0373 0.1132 -1.14, +2.25
C30H22ClF3I3OP 902.60 monoclinic P21/c 10.153(2) 17.118(3) 17.657(4) 105.26(3) 2960.5(10) 4 2.025 100 3.354 1.69-27.56 30080 6805 0.0459 6336 multiscan 1.0, 0.593775 350 0.0220 0.0584 -0.851, +0.811
C30H20BrF3I3P 929.04 monoclinic P21/c 10.3344(12) 16.9073(19) 17.618(2) 105.194(6) 2970.6(6) 4 2.077 100 4.593 1.70, 32.10 46480 10376 0.0417 8865 multiscan 1.0, 0.516301 343 0.0241 0.0696 -1.523, +1.608
corresponding to a partly dehydrated compound since the calculated composition for C30H20ClF3I3P(H2O)0.25 gives C 40.53; H 2.32. X-ray structure refinement afforded x ≈ 0.5. (sym-TFTIB)(Ph4PBr). PPh4Br (0.019 g, 0.06 mmol) was added to a solution of sym-TFTIB (0.02 g, 0.04 mmol) in 5 mL of CH2Cl2. After slow evaporation, transparent crystals appeared. Crystals were washed with MeOH affording (sym-TFTIB)(Ph4PBr) (0.026 g, 70%). Anal. Calcd for C30H20BrF3I3P: C, 38.78; H, 2.17. Found: C, 38.46; H, 2.19. Crystallography. Data were collected on an APEXII, Bruker-AXS diffractometer with CCD detector and graphite-monochromated Mo KR radiation (λ ) 0.71073 Å) at 100 K. Structures were solved by direct methods (SHELXS-97) and refined (SHELXL-97)30 by full-matrix least-squares methods, as implemented in the WinGX software package.31 Absorption corrections (SADABS) were applied. Hydrogen atoms were introduced at calculated positions (riding model), included in structure factor calculations, and these were not refined. Crystallographic data are summarized in Table 2. Theoretical Methods. All calculations have been carried out by means of the GAUSSIAN03 package.32 The DFT calculations employ the PBE1PBE exchange-correlation potential approach33 in combination with the 6-311G(d) basis set34 for all atoms. The basis set superposition errors (BSSE) was corrected by the counterpoise method35 in the halogen bond energies. Calculations on model systems formed by one sym-TFTIB and Cl- or pyridine have been fully optimized without symmetry constraints. Due to crystal environment and the presence of charged species, it is not straightforward to perform molecular calculations to investigate the changes in the electronic structure. In order to get the best approximation to modeling of halogen bonds, the system formed by Cl- coordinated to three sym-TFTIB monomers has been considered at the experimentally measured geometrical parameters. ELF topological analysis has been carried out using the TopMod program developed by Silvi et al.36 using a cubic grid with a step size of 0.2. Graphical representations of ELF and electrostatic potential surfaces have been done using the MOLEKEL program.37
Acknowledgment. This work was supported through a joint action program by the Spanish Ministerio de Educacio´n y Ciencia (MEC, Grant HF-2005-0146) and the French Ministry of Foreign Affairs (PHC Picasso No. 11445PL). Other financial support from the Spanish MEC (Grants CTQ2005-09270-C0201 and CTQ2006-15447-C02-01) and Generalitat Valenciana (Grants GV2007/106 and QACOMP/2007/286) is also acknowledged. V.P. gratefully acknowledges support from the MEC for a JdC research contract. The authors are grateful to the Servei d’Informatica, Universitat Jaume I, for generous allotment of
computer time, and to the Centre de Diffractome´trie X (CDIFX, Rennes, Dr. T. Roisnel) for the X-ray data collections. Supporting Information Available: CIFs. This material is available free of charge via the Internet at http://pubs.acs.org.
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