NMR Crystallography, Hydrogen Bonding and Optical Properties of

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NMR crystallography, hydrogen bonding and optical properties of a novel 2D hybrid oxyfluorotitanate [Htaz]·(TiOF ) 2

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Marjorie Albino, Monique Body, Christophe Legein, Annie HémonRibaud, Marc Leblanc, Vincent Maisonneuve, and Jerome Lhoste Cryst. Growth Des., Just Accepted Manuscript • DOI: 10.1021/acs.cgd.8b01085 • Publication Date (Web): 25 Sep 2018 Downloaded from http://pubs.acs.org on October 4, 2018

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Crystal Growth & Design

COVER PAGE NMR crystallography, hydrogen bonding and optical properties of a novel 2D hybrid oxyfluorotitanate [H2taz]2·(Ti5O5F12) Marjorie Albino, Monique Body, Christophe Legein,* Annie Hémon-Ribaud, Marc Leblanc, Vincent Maisonneuve and Jérôme Lhoste* Institut des Molécules et Matériaux du Mans (IMMM) - UMR 6283 CNRS, Le Mans Université, Avenue Olivier Messiaen, 72085 Le Mans, Cedex 9, France

We present the structural characterization of a new 2D hybrid oxyfluorotitanate [H2taz]2·(Ti5O5F12) by the use of diffraction experiments (one H atom site is half-fully occupied and two sites have a mixed C and N composition), solid-state NMR spectroscopy and GIPAW calculations on super cells. Moreover hydrogen bonding was probed by deriving a method usually applied to organic solids (calculations on the full crystal structures and on isolated molecules). For this purpose, 1H isotropic chemical shits were also calculated for the [H2taz]+ cations alone to probe hydrogen bonding between inorganic and organic parts and for an isolated [H2taz]+ cation to probe hydrogen bonding between organic cations. Solid state NMR and DFT modelling of NMR parameters of [H2gua]2·(Ti5O5F12) which adopts the same space group (Cmm2) and, considering the inorganic part, the same structure, have been also achieved for the sake of comparison.

Corresponding Authors Christophe Legein and Jérôme Lhoste Institut des Molécules et Matériaux du Mans (IMMM) - UMR 6283 CNRS, Le Mans Université, Avenue Olivier Messiaen, 72085 Le Mans, Cedex 9, France J.L.: +33 2 43 83 35 59; e-mail: [email protected] C.L.: +33 2 43 83 33 49; e-mail: [email protected] http://immm.univ-lemans.fr/fr/index.html

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NMR crystallography, hydrogen bonding and optical properties of a novel 2D hybrid oxyfluorotitanate [H2taz]2·(Ti5O5F12) Marjorie Albino, Monique Body, Christophe Legein,* Annie Hémon-Ribaud, Marc Leblanc, Vincent Maisonneuve and Jérôme Lhoste* Institut des Molécules et Matériaux du Mans (IMMM) - UMR 6283 CNRS, Le Mans Université, Avenue Olivier Messiaen, 72085 Le Mans, Cedex 9, France

ABSTRACT: A new 2D hybrid oxyfluorotitanate [H2taz]2·(Ti5O5F12), wherein [H2taz]+ represents 1,4-diH-1,2,4-triazolium cation ([C2N3H4]+), has been prepared and its structure has been refined from powder X-ray diffraction data. It is built up from ∞(Ti5O5F12)2- inorganic layers separated by [H2taz]+ cations and adopts the same space group (Cmm2) and, considering the inorganic part, the same structure than [H2gua]2·(Ti5O5F12) wherein [H2gua]+ represents guanidinium cation ([C(NH2)3]+). The substitution of [H2gua]+ by [H2taz]+ was aimed at reducing the refractive index, while keeping a high optical band gap. The substitution effect is small but [H2taz]2·(Ti5O5F12) could also allow a high UV protection with a good aesthetic effect. In [H2taz]2·(Ti5O5F12), a fifty per cent site occupancy is attributed to one H atom site and two mirror symmetry related positions have a mixed C and N composition, preventing DFT calculations to be performed for the structural cell and preventing the cation configuration to be determined. Three ordered structures have then been constructed by using a double cell in the


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Cmc21 space group and DFT geometry optimized. The resulting calculated 1H NMR parameters are in good agreement with experimental values for the structure that involves the most stable 1,4-diH+ tautomer. 1H and

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F solid state NMR and DFT modelling of NMR parameters of

[H2gua]2·(Ti5O5F12) have been also achieved for the sake of comparison. Moreover, it is demonstrated that, for hybrid materials, in the same way than for molecular solids, the changes when comparing the 1H chemical shielding values calculated from the full crystal structure, the cations alone and an isolated cation, provide a quantitative way of assessing hydrogen bonding, between organic and inorganic parts and between organic cations, as well as inter cationic ring current effects.

Keywords: hybrid oxyfluorides; solvothermal synthesis; UV filter; photochromic behaviour; 1H and 19F solid state NMR, DFT calculations, hydrogen bonding.


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INTRODUCTION Rutile and anatase titanium oxides constitute the UV filter materials that are most currently used in industries. These inorganic filters have several advantages over organic filters such as a good chemical stability and a convenient optical spectrum for UV protection. Nevertheless, TiO2 phases show a very high refractive index (2.7 for rutile and 2.5 for anatase) leading to a whitening effect of the coatings in the visible region. Consequently, a poor aesthetic effect appears when TiO2 particles are incorporated into organic matrices (plastic, wood...). In order to decrease the refractive index and increase the transparency, several alternative solutions were proposed: (i) adjust the size of TiO2 nanoparticles between 20 and 80 nm,1 (ii) substitute O by F (and OH)2,3 or (iii) develop new Class I hybrid materials in which the organic and inorganic parts are interlinked by weak interactions (hydrogen bonds).4 We adopted this option for the study of the amine-TiF4 system in solvothermal conditions.5 In two recent reviews,6,7 58 Class I hybrids containing cyclic or aliphatic amine cations and fluoride, oxy- or hydroxy-fluoride (eventually hydrated) TiIV anions have been listed. In most cases, the structures are built up from isolated (TiF6)2- octahedral anions8-17 but several hybrids exhibit original polyanions that result from the condensation of TiF62- units by corner sharing: (Ti2F10)2-, (Ti2F11)3-, (Ti4F18)2-, (Ti4F20)4-, (Ti5F23)3- or

∞(Ti2F9)

(Figure 1, left).10,18-21 The

maximum dimensionality of the inorganic network is 1D for [Him](Ti2F9) ([Him]+: imidazolium cation) which presents infinite double zigzag chains.10 Nine titanium (IV) hybrids exist with discrete (TiF6-x(OH)x)2-,22,23 or (Ti(H2O)F5)- entities.9,24 Finally, the substitution of fluoride by oxide anions in TiF62- units led to four oxyfluoride hybrids, obtained with the [H2gua]+ guanidinium cation, in which the inorganic networks adopt various dimensionalities (Figure 1, right): 0D-(Ti2OF10)4- dimers,25 1D-∞(TiOF4)2- chains,26,27 and 2D-∞(Ti5O5F12)2- layers.5 The


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latter displays the highest connectivity and enhanced optical properties. The optical band gap energy (3.32 eV) of [H2gua]2·(Ti5O5F12) is very similar to that of TiO2 rutile whereas the refractive index is lower (1.94 vs 2.7) in the visible region.5 Both optical parameters are key requirements for transparent UV filters. Reducing the refractive index while keeping a high optical band gap could be achieved by a substitution of [H2gua]+. In this scope, we successfully elaborated, by solvothermal synthesis, a new 2D hybrid oxyfluorotitanate in which [H2gua]+ cations are replaced by 1,2,4-triazolium cations [H2taz]+. The structure of [H2taz]2·(Ti5O5F12), determined in a noncentrosymmetric space group, using PXRD, is disordered and several ordered models are possible. Then, we used one of the approaches to structure determination, refinement, or selection covered by the term ‘NMR crystallography’.28-33 For DFT calculations on disordered systems a supercell can be constructed or various ordered arrangements of atoms at specified sites within the unit cell can be generated. In this work, experimental and calculated 1

H and

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F NMR parameters are used to select or validate the optimized ordered structures of

[H2taz]2·(Ti5O5F12) in 2c supercells. To reveal to what extent X–H···Y contacts correspond to hydrogen bonding interactions, 1H chemical shifts were also calculated for the [H2taz]+ cations, alone and isolated, and compared to those obtained for the full crystal structure, applying to these ionic solids a method usually applied to organic (molecular) solids by which the strength of hydrogen bonds can be quantified.34-37 [H2taz]+ being aromatic, these calculations also allow to gain insight into ring current effect.36,37-40 For the sake of comparison, the same approach is applied to [H2gua]2·(Ti5O5F12). Additionally, the microstructure, the thermal behavior and the optical properties of [H2taz]2·(Ti5O5F12) are discussed.


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EXPERIMENTAL SECTION Synthesis. The starting chemicals were TiF4 (≥ 99.9%, Alfa Aesar), 1,2,4-triazole (Htaz, 99%, Alfa Aesar) and ethanol (EtOH, 95%). [H2taz]2·(Ti5O5F12) was obtained from a mixture of 1.2386 g TiF4 (10.0 mmol), 0.296 g Htaz (4.3 mmol) and 20 mL EtOH (325.4 mmol). The reactants were introduced in a Teflon vessel (volume = 100 mL) and the mixture was heated to 160°C for 1 h. After this microwave-assisted solvothermal synthesis, the white solid product was filtered, washed with EtOH and dried at RT. Scanning electronic microscopy. The microstructure of the powder was observed using scanning electronic microscopy (SEM, JEOL JSM 6510 LV). Powder X-ray diffraction. PXRD analyses were performed with a PANalytical X’Pert Pro diffractometer with CuKα radiation. For the structural determination, the diagram was recorded at RT in the 2θ = [5-100]° range with a scan time of 2 h. Crystallographic data (excluding structure factors) for the structure of [H2taz]2·(Ti5O5F12) have been deposited at the Cambridge Crystallographic Data Centre (CCDC 1826645) and the cif file is supplied as SI. Temperaturecontrolled X-ray diffractograms were collected under air flow in an Anton Parr XRK 900 high temperature furnace at 10°C intervals from RT to 400°C and at 450°C and 500°C. Each PXRD pattern was recorded in the 2θ = [5-60]° range with a scan time of 10 min. Thermogravimetric analyses. The TGA were carried out with a thermoanalyzer SETARAM TGA 92 under air flow with a heating rate of 1°C.min-1 from RT up to 900°C. Solid state NMR. 1H and 19F solid-state MAS NMR experiments were performed on a Bruker Avance III spectrometer operating at 7.0 T (1H and

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F Larmor frequencies of 300.1 and 282.4

MHz, respectively), using a 1.3 mm CP-MAS probe head. The 1H and

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F MAS spectra were

recorded using a Hahn echo sequence with an interpulse delay equal to one rotor period. For 19F,


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the 90° pulse length was set to 1.25 µs and the recycle delay was set to 120 and 20 s, for [H2taz]2·(Ti5O5F12) and [H2gua]2·(Ti5O5F12), respectively. For 1H, the 90° pulse length was set to 1.25 µs and the recycle delay was set to 90 s and 20 s, for [H2taz]2·(Ti5O5F12) and [H2gua]2·(Ti5O5F12), respectively. 1H and

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F spectra are referenced to TMS and CFCl3,

respectively, and they were fitted by using the DMFit software.41 DFT calculations. Calculations of the 1H and 19F chemical shielding were performed with the CASTEP code,42 using the GIPAW approach.43,44 The Perdew-Burke-Ernzerhof (PBE) functional,45 was employed in the GGA for the exchange correlation energy and ultrasoft pseudopotentials were used to describe core-valence interactions.44 The wave functions were expanded on a plane-wave basis set with a kinetic energy cutoff of 700 eV. The total energy was converged up to change below 1 x 10−8 eV. The Brillouin zone was sampled using a MonkhorstPack grid spacing of 0.04 Å−1 (corresponding to a k-point mesh of 3 × 3 × 4 for [H2taz]2·(Ti5O5F12) and 3 × 3 × 7 for [H2gua]2·(Ti5O5F12). NMR parameters were calculated using “on-the-fly” ultrasoft pseudopotentials provided in CASTEP. Core radii of 0.8, 1.4, 1.5, 1.3, 1.4 and 1.8 a. u. were used for H, C, N, O, F and Ti respectively, with 1s valence orbitals for H, 2s and 2p valence orbitals for C, N, O and F, and 3s, 3p, 4s and 3d valence orbitals for Ti. Computations of the NMR parameters were performed for experimental (EXP) and geometry optimized (APO) structures. APO structures were obtained by minimizing the residual forces (|F|max below 10 meV.Å-1) for all atoms, using the Broyden-Fletcher-Goldfarb-Shanno (BFGS) method and keeping symmetry constraints and fixing cell parameters to experimentally measured values.46 Insight into hydrogen bonding was provided by comparing 1H chemical shielding values calculated for the APO crystal structures of [H2taz]2·(Ti5O5F12) and [H2gua]2·(Ti5O5F12), for the


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[H2taz]+ and [H2gua]+ cations alone (by removing the inorganic part of the crystal structures) and for isolated [H2taz]+ and [H2gua]+ cations. The calculations of the NMR parameters for the cations alone, in the geometry of the APO crystal structures, were performed under the same conditions than those used for the full crystal structures. The NMR parameters of the isolated cations, in the geometry of the APO crystal structures, were calculated in supercells large enough so as to effectively isolate each cation from external influence. Specifically, one [H2taz]+ or [H2gua]+ cation was placed in a cubic cell with a equal to the orthorhombic cell a parameter of the corresponding titanate structure (> 22 Å). For a fast convergence, these calculations were performed using a single k-point located at (¼ ¼ ¼) in the reciprocal space. The isotropic chemical shielding value is defined as σiso = (σxx + σyy + σzz)/3, σii being the principal components of the shielding tensor defined in the sequence |σzz - σiso| ≥ |σxx - σiso| ≥ |σyy - σiso|. The isotropic chemical shift is defined as δiso ≈ - σiso + σref. The 1H δiso values have been calculated by using σref = 31.0 ppm.47 Calculations of the refractive index were performed using the GGA for the exchange correlation energy, “on-the-fly” ultrasoft pseudopotentials provided in CASTEP and the same core radii as for the NMR parameters calculations. The wave functions were expanded on a plane-wave basis set with a kinetic energy cutoff of 500 eV. The total energy was converged up to change below 1 x 10−8 eV. The Brillouin zone was sampled using a Monkhorst-Pack grid spacing of 0.016 Å−1 (corresponding to a k-point mesh of 7 × 7 × 9 for [H2taz]2·(Ti5O5F12) and 7 × 7 × 17 for [H2gua]2·(Ti5O5F12)). The included conduction bands represent at least 40% of the filled bands, (corresponding to 96 for [H2taz]2·(Ti5O5F12) and 48 for [H2gua]2·(Ti5O5F12)). UV-visible

diffuse

experiments.

The

UV-Vis

diffuse

reflectance

spectrum

of

[H2taz]2·(Ti5O5F12) was recorded at RT from 200 nm to 800 nm with a 0.2 nm step using a


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Shimadzu UV-2700 spectrophotometer. The 100% reflectance was obtained with Halon powder reference. After UV irradiation at 254 nm with a UV-lamp for various durations (0, 10, 60, 960, 1200, 1440 min), the UV-Vis diffuse reflectance spectra were collected. The reflectivity spectra (R) were transformed to absorption α/S spectra using Kubelka-Munk (KM) transformation.48 The optical band gap value was determined from the intersection of the energy axis and the extrapolated line of the linear portion at the absorption threshold. RESULTS AND DISCUSSION Thermal and IR analyses. TGA analysis and temperature-controlled XRPD patterns (Figure 2) show that [H2taz]2·(Ti5O5F12) is stable up to 230°C in air. Above this temperature, [H2taz]2·(Ti5O5F12) decomposes to give rutile TiO2. The experimental and theoretical weight losses are in good agreement (44.1 % and 41.6 %, respectively). The IR spectrum (Figure S1) confirms the presence of the organic entities in the hybrid structure. Crystal structure. The RT PXRD pattern of [H2taz]2·(Ti5O5F12), displayed in Figure 3, is found to be very similar to that of [H2gua]2·(Ti5O5F12)5 (CCDC 1853981) and the indexation of the pattern confirms the analogy of both C centered orthorhombic cells; the presence of a small amount of anatase TiO2 impurity (1.4(1) wt %, I41/amd SG) is detected. SEM image (Figure 3, inset B) shows that the powder is constituted by micrometric platelets with a thickness close to 1 µm. This observation is consistent with a preferential orientation along the [100] direction evidenced during the structural refinement by the Rietveld method of the PXRD pattern (Fullprof software).49 Crystal data of [H2taz]2·(Ti5O5F12) are given in Table 1. A Second Harmonic Generation (SHG) test was negative and consequently was not conclusive to ascertain a noncentrosymmetric SG (at the opposite of the test on [H2gua]2·(Ti5O5F12) for which a very faint signal was observed).


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The starting positions of Ti, O and F atoms were deduced from that of [H2gua]2·(Ti5O5F12) (Cmm2 SG) and converted in centrosymmetric Cmmm SG.5 After refinement of the variable coordinates, the C or N atoms of [H2taz]+ cations were located by Fourier difference and refined with isotropic atomic displacements parameters (ADPs) without any geometry constraints (RB = 0.0434, RF = 0.0504, RP = 0.113 and RwP = 0.112). Very large ADPs affected the C and N atoms and even Ti atoms (Table S1). As a consequence, the noncentrosymmetric Cmm2 SG was selected for two reasons: the opposite Ti-O bonds in TiO2F4 octahedra are not necessarily equal and the cation z coordinate is not constrained to z = ½. The refinements converged to RB = 0.0357, RF = 0.0409, RP = 0.105 and RwP = 0.103 and the ADPs were improved. At this stage of the refinement, the attribution of C or N atoms was not determined (see SI (Table S1 and cif file) and Figure 4); it is not univocal and several solutions can be proposed (Figure 5) after the calculation of the positions of H atoms (HFIX command in SHELX program). The solution represented in Figure 5a must be excluded as a reason of the short C-H···H-C contact (1.3 Å). Similarly, the intermolecular N1-H···H-N1 contact for the solution of Figure 5b is too short (1.3 Å). Consequently, a fifty per cent site occupancy can be attributed to the attached H atom; a carbon atom C1 is located in the symmetry mirror element and a statistical distribution of N2 and C2 atoms is introduced. The ADPs of HN1 and HNC2 were constrained to the corresponding values of N1 and N2 or C2. The interatomic distances and the bond valence sum calculations are in good agreement with the literature values (Table S2). The structure contains two inequivalent Ti sites, Ti1 and Ti2, forming TiO2F44- octahedra (Table S1 and Figure 4). F1 is linked to only one Ti1, F2 bridges one Ti1 and one Ti2, F3 and F4 bridge two Ti1. O1 and O2 atoms bridge two Ti1 and two Ti2, respectively. Short (1.84-1.86 Å) and long (1.94-1.96 Å) Ti-O bond lengths alternate along the c direction (Table S2).


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However, the short bond lengths are too long to support the occurrence of titanyl bonds. This issue will be discussed after optimization of the atomic positions (see DFT optimization). The structural model in Cmm2 clearly justifies the choice of a non centrosymmetic SG. However, due to the statistical occupation of N2 and C2 atoms, both 1,2-diH+ and 1,4-diH+ tautomers of [H2taz]+ may exist, whereas 1,4-diH+ is known to be the most stable configuration.50,51 The nitrogen-carbon disorder, together with the partial site occupancy of hydrogen HN1 atoms prevents from any periodic DFT calculation to be performed, without constructing a supercell or generating various ordered arrangements of atoms at specified sites within the unit cell.28,29,32 These shortcomings have been overcome by refining the structure in a supercell obtained by doubling the c cell parameter and with the Cmc21 SG. The order can be reached in several ways (Figure 5c, 5d and 5e). Only the solution leading to the most stable 1,4diH+ cation and N-H···N hydrogen bond (Figure 5d) rather than C-H···N hydrogen bond (Figure 5e) provides calculated NMR parameters in agreement with experiment as shown below, at the opposite of the two other configurations (see Table S3). The refinement of the PXRD pattern performed in Cmc21 with the corresponding C, N and H site attributions is given as SI (Figure S2). Strong constraints on the atomic coordinates were applied in order to satisfy the c cell periodicity of Cmm2 (Table S4). Both structural models in Cmm2 and Cmc21 are obviously similar in terms of interatomic distances (Tables S1, S2, S4, S5). It must be mentioned that new reflections should result from the doubling of the c parameter; for the APO structure their calculated intensity is smaller than 0.26 % of the most intense line and, consequently, they cannot be evidenced in the conditions of the diffraction experiments. DFT optimization. The importance of geometry optimization prior to the calculation of NMR parameters is well established,28,29,32 in particular for H atoms which are difficult to locate


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accurately using XRD data. The covalent bond lengths involving H atoms obtained from XRD data are appreciably shorter than those obtained from neutron diffraction data or after DFT optimizations which both provide reliable H positions.52 As expected, appropriate N-H and C-H bond lengths are obtained after optimizations (Tables S5 and S7). However, it is worth noting that the atomic position optimizations lead to significant evolutions of the atomic coordinates and large displacements of even heavy atoms, up to 0.13 and 0.26 Å for Ti, 0.45 and 0.31 Å for O and F, 0.38 and 0.36 Å for C and N and 0.70 and 0.57 Å for H, for [H2taz]2·(Ti5O5F12) and [H2gua]2·(Ti5O5F12), respectively (Tables S4 and S6). Several factors can explain such displacements: the overestimation of bond lengths by GGA with the PBE functional, the difficulty to locate H atoms accurately using XRD data, the limited accuracy of the structural parameters obtained from powder XRD data in a non-centrosymmetric space group and, for [H2taz]2·(Ti5O5F12), the constrained refinement in Cmc21, as well as the disorder of the organic cations for [H2taz]2·(Ti5O5F12) and of the inorganic networks. Indeed, as already observed for [H2gua]2·(Ti5O5F12),5 after APO, the TiO2F44- octahedra exhibit one short (< 1.71 Å), characteristic of a titanyl (Ti=O) bond, and one long (≥ 2.11 Å) Ti-O bond (Tables S5 and S7). It can be assumed that the succession of O=Ti-O bonds along the c axis is not perfectly periodic in the coherent diffraction domains. An inversion to O-Ti=O bonds is likely and results in static positional disorder in the inorganic parts which could be correlated to the disorder of the organic cations. A 2:1 ratio of (O=Ti-O):(O-Ti=O) bonds along the c axis is compatible with the observed Ti-O bond lengths. Geometries of the X–H···Y contacts in [H2taz]2·(Ti5O5F12) are also obviously affected by optimization. They are reported in Tables S8 and S9 for the EXP and Table 2 and Table 3 for the APO structures of [H2taz]2·(Ti5O5F12) and [H2gua]2·(Ti5O5F12), respectively. Only X–H···Y


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contacts with angle larger than 110° and H···Y distances smaller than the sum of H and Y van der Waals radii (H: 1.20 Å; N: 1.55 Å; O: 1.52 Å; F: 1.47 Å) in the APO structures have been retained.53 Enforcing the criterion stating that “the closer the angle is to 180º, the stronger the hydrogen bond and the shorter the H···Y distance”,53 it is expected that the contacts corresponding to hydrogen bonds, strengthened by geometry optimization, are N1a–H···N1b (between the organic cations) and N2a–H···F1b and C2b–H···O1a (between the inorganic and organic parts) in [H2taz]2·(Ti5O5F12) and N2–H2A···F1 and N2–H2B···F1 in [H2gua]2·(Ti5O5F12) (Figure 6). It must be noted that the terminal (non-bridging) F atoms (F1) are more involved in hydrogen bonding in [H2gua]2·(Ti5O5F12) than in [H2taz]2·(Ti5O5F12). This feature impacts the chemical shifts and will be further discussed below. 19

F and 1H solid state NMR. In [H2taz]2·(Ti5O5F12) (Cmm2 SG) and [H2gua]2·(Ti5O5F12), one

terminal F atom (F1, multiplicity 8) and three bridging F atoms (F2, F3 and F4, multiplicities 8, 4 and 4) build the ∞(Ti5O5F12)2- layers. Whereas four NMR lines with relative intensities of 2:2:1:1 are expected on the

19

F NMR spectra (Figure 7), two main, and especially broad,

contributions are observed. Each contribution was fitted with several NMR lines (Figures S3 and S4, Tables S10 and S11; average values in Table 4) and assigned to bridging (δiso ranging from 40 to 40 ppm) and terminal F atoms (δiso ranging from 50 to 120 or 150 ppm) in agreement with their expected relative intensities and with the increase of the chemical shift of the F- anion when the number of surrounding cations decreases. These assignments are also in agreement with the δiso values of terminal F atoms in (C2H5N4)2·TiF6 (76 ppm), anatase Ti0.780.22O1.12(OH)0.48F0.40 (98 ppm),54 K2TiF6 (71.4 ppm),55 a fluorotitanophosphate (78.9 ppm)56 and hybrid hydroxyfluorotitanates (76–82 ppm)22 and with the δiso values of bridging F atoms in anatase Ti0.780.22O1.12(OH)0.48F0.40 (-4 ppm),54 in HTB TiOF2 (Ti1-xxO1-4x(OH,F)4x (-7 to 28 ppm)57


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and in Ti0.900.10O0.60(OH)0.74F1.66 (12-20 ppm).58 No significant sharpening of NMR lines was observed when the MAS frequency was increased from 44 kHz to 64 kHz showing that homonuclear

19

F–19F and heteronuclear

1

H–19F dipolar couplings are already reduced

significantly at 44 kHz. Then, the line-broadening arises mainly from distribution of

19

F

chemical shift values highlighting variations of the local structure of the F atoms in relation with a positional disorder in the inorganic and organic parts. For a X–H···Y hydrogen bond, the shorter the H···Y distance, the smaller the 1H shielding and the larger the 1H chemical shift and for a X–H···F hydrogen bond,59-61 the shorter the H···F distance, the larger the 19F shielding and the smaller the 19F chemical shift.62 The average larger 19

F δiso values of the terminal F1 atom in [H2taz]2·(Ti5O5F12) compared with [H2gua]2·(Ti5O5F12)

(102 ppm and 92 ppm) are then related to fewer and moreover weaker X–H···F1 hydrogen bonds with larger distances between the F1 atoms and the H and X atoms and smaller X–H···F1 angles (Tables S5, 2, 3 and S7) and also to the (slightly) shorter F1–Ti bond lengths (1.859 and 1.868 Å vs 1.869 Å) in [H2taz]2·(Ti5O5F12). The 1H NMR spectra of [H2taz]2·(Ti5O5F12) and [H2gua]2·(Ti5O5F12) present also broad contributions (Figure 8) but significant improvements in line-broadening, especially (from 550 Hz to 420 Hz) in the case of [H2gua]2·(Ti5O5F12), were observed when the MAS frequency was increased from 44 kHz to 64 kHz. This shows that homonuclear 1H–1H dipolar couplings are not averaged out completely by MAS at 44 kHz. The 1H NMR spectrum of [H2taz]2·(Ti5O5F12) presents two main contributions which have been fitted with one (δiso = 9.35 ppm) and three (δiso ranging from 12 to 17 ppm, average value in Table 5) NMR lines and assigned to HC and HN, respectively, according to their range of δiso values and relative intensities (Figure S5, Table S12). Indeed, [H2taz]+ contains 50% of HC and 50% of HN, the HC δiso value is in agreement


14

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with those of HC in 1H-1,2,4-triazole in solution (~ 8.4 ppm) and in Zn3Al2F12·[HAmTAZ]6 (with HAmTAZ: 3-amino-1,2,4-triazole, 7.7 ppm)63 and the HN δiso range is in agreement with the value observed in Zn3Al2F12·[HAmTAZ]6 (13.8 ppm).63 These two contributions account for 90% of the integrated intensity and unidentified impurities giving 1H NMR signals between -0.8 and 7.0 ppm account for the remaining 10% (Table S12). The

1

H NMR spectrum of

[H2gua]2·(Ti5O5F12) (Figure S6) presents one main and broad contribution accounting for 97.4% of the integrated intensity. Impurities giving 1H NMR signals at 1.2 and 3.5 ppm and identified as ethanol account for the remaining 2.6% (Table S13). The main contribution has been fitted with two NMR lines (δiso = 6.4 and 6.5 ppm) assigned to the H atoms of the [H2gua]+ cations, in agreement with their δiso values close to the values in solution, depending on the solvent and ranging from 6.63 to 7.07 ppm.64 In conclusion, due to positional disorder, 1H and 19F MAS NMR spectra of [H2taz]2·(Ti5O5F12) and [H2gua]2·(Ti5O5F12) present broad contributions and then do not allow to confirm the number and the relative multiplicities of the H and F sites. This will prevent complete assignments of the NMR parameters from DFT modelling. However, these calculations remain valuable to assess the accuracy of the structural models. 1

H NMR parameters modeling. As expected, considering the large optimization effects, EXP

and APO structures provide dissimilar 1H (Table 5 and Table S14) and 19F (Table 4 and Table S15) σiso values for [H2taz]2·(Ti5O5F12). The agreement between the experimental and calculated 1

H δiso values (Table 5) is good considering the APO structures. It confirms that, in

[H2taz]2·(Ti5O5F12), 1,4-diH+ is the only tautomer of [H2taz]+ and that N-H···N (Figure 5d) rather than C-H···N (Figure 5e) hydrogen bonds occur. It also shows the accuracy of the APO


15


Page 16 of 51

structures, at least regarding the C-H and N-H bonds of the organic cations and the geometry of the hydrogen bonds. 1

H chemical shifts were also calculated for the cations alone (by removing the inorganic part of

the crystal structures) and for isolated [H2taz]+ and [H2gua]+ cations (Table 5 and Figure 9 and Figure S7). [H2taz]+ cation being aromatic, intermolecular ring current effects on 1H chemical shifts could have to be considered in [H2taz]2·(Ti5O5F12). The ring current in aromatic systems causes proton deshielding in the plane of the aromatic ring and proton shielding above or below the plane of the aromatic ring. Its effects vary with r, the distance between the aromatic ring and the H atom, as a function of r-3. Indeed, insights into these effects in organic solids can be provided by applying the same approach that is used for hydrogen bonds.38,39 It should be remembered that one given cation (in the (001) plane approximately) is surrounded by two neighboring cations along [010] and two other cations above and below the plane, along [001]. The distances between the H atoms of the cation and the nearest neighboring cations are large, except for HN1a which is hydrogen-bonded to N1b of the nearest neighboring cation located in the same (001) plane (Figure 4 and Figure 6, Table 2). An increase of the 1H δiso value of HN1a is expected from isolated cation to cations alone, assuming that the effects of the next nearest neighboring cations can be neglected. Then, the observed increase of its 1H δiso value confirms the occurrence of the N1a–H···N1b hydrogen bond and its large magnitude (2.59 ppm) suggests ring current effects from the nearest neighboring cation located in the same (001) plane. Significant shielding changes for the three other H atoms of the [H2taz]+ cations are not expected since they are not involved in hydrogen bonds with the neighboring cations and since the nearest neighboring cations of these H atoms have slight and opposite ring current effects. Accordingly,


16

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from isolated cation to cations alone, only small changes of their 1H δiso values (Table 5 and Figure 9), possibly also related to changes in electrostatic interactions, are observed. From cations alone to crystal, the 1H δiso value of HN1a remains constant (Table 5 and Figure 9) confirming that this H atom is only involved in one hydrogen bond with the N1b atom of its neighboring cation. The significant increases of the 1H δiso values of HC2b and HN2a (1.67 and 1.58 ppm, respectively) ascertain that these H atoms are involved in hydrogen bonds with the inorganic part. The geometries of the contacts involving HC1, with small C-H···F angles and large C···F and H···F distances, are unfavorable (Table 2);53 its δiso value increases slightly (0.29 ppm) from cations alone to crystal confirming the weakness of these interactions. For [H2gua]2·(Ti5O5F12), the change of the 1H δiso values from isolated cation to cations alone (Table 5 and Figure S7) is small for three H atoms of the [H2gua]+ cations, in relation with changes in electrostatic interactions. It ascertains the absence of hydrogen bond between the [H2gua]+ cations, as expected for H1 and H2A, and as it could be inferred for H2B from the unfavorable geometry of the N2–H2B···N2 contact (Table 3). Significant 1H δiso increases are observed from cations alone to crystal for H2A and H2B (1.45 and 1.92 ppm, respectively) confirming hydrogen bonding with the inorganic part for these two H atoms. On the other hand, the slight 1H δiso increase for H1 (0.12 ppm) is in agreement with unfavorable N···Y and H···Y distances of the contacts in which H1 is involved. 19

F NMR parameters modeling. Because the F atoms are not closely located in, nor above or

below, the plane of the aromatic rings, ring current effects on 19F chemical shifts are supposed to be weak in [H2taz]2·(Ti5O5F12). Due to the increase of the F-Ti bond lengths for the bridging F atoms in both compounds (Tables S5 and S7), their optimization (Table 4 and Table S15). The

19

19

F σiso values are larger after geometry

F σiso values of the bridging F atoms can also be


17


Page 18 of 51

compared with each other in each APO structure. At first sight, this comparison is somewhat confusing since in each compound they are in the sequence F4 < F2 < F3 whereas the F-Ti bond lengths are in the sequence F3 < F2 < F4. Indeed, F2, F3 and F4 atoms bridge two Ti atoms but differ in two ways; F2 atoms bridge Ti1 and Ti2 whereas F3 and F4 bridge two Ti2 atoms and the F2-Ti and F3-Ti bonds are rather perpendicular to the F1-Ti bonds whereas the F4-Ti bonds are quite opposite to the F1-Ti bonds. This shows that the F-Ti bond lengths and the

19

F σiso

values of these bridging F atoms essentially depend on their position relative to non-bridging F atoms. A comparable situation was encountered for terminal F (Ft) in NbF5 and TaF5; the σiso values and Ft-M (M = Nb, Ta) bond lengths depend on their positions relative to the bridging FM bonds.65 For the terminal F atoms in [H2taz]2·(Ti5O5F12), changes in their

19

F σiso values

cannot be related so easily to changes in the F-Ti bond lengths since they are closer and hydrogen-bonded to the organic cations are then more sensitive to changes in the positions of these organic cations during optimization. The average

19

F experimental δiso values and

calculated σiso values (from APO structures, Table 4), for bridging and terminal F atoms, of [H2taz]2·(Ti5O5F12) and [H2gua]2·(Ti5O5F12) are represented on Figure 10. Experimental and calculated values correlate almost linearly. Whereas the linear regressions previously established on numerous metal fluorides (alkali, alkaline earth, rare earth, column 13 metal and tantalum fluorides)65-67 have slopes (-0.8) that differ from the theoretical value -1, an error caused by the GGA to the exchange-correlation functional,68 the value of the slope for [H2taz]2·(Ti5O5F12) and [H2gua]2·(Ti5O5F12) is -0.97. This value (based on limited data and requiring to be ascertained) remains quite unusual for 19F. However, a value close to -1 was already observed for NbF5.65 In addition to the nature of the organic cation, [H2taz]2·(Ti5O5F12) and [H2taz]2·(Ti5O5F12) differ essentially by the number of hydrogen bonds involving terminal F atoms. In one [H2gua]+


18

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cation, four H atoms are hydrogen-bonded to F1 atoms whereas in one [H2taz]+ cation, only one H atom is hydrogen-bonded to a terminal F atom (Table 2 and Table 3). This denser network of hydrogen bonds involving terminal F atoms in [H2gua]2·(Ti5O5F12) induces smaller

19

F δiso

values and larger calculated 19F σiso values (Table 4) for these F atoms. Optical properties. The evolution, as a function of the energy radiation, of the calculated refractive indices (n) of [H2gua]2·(Ti5O5F12) and [H2taz]2·(Ti5O5F12) (Figure 11) is very similar. As expected, due to the larger weight proportion of the organic part in [H2taz]2·(Ti5O5F12), its calculated refractive index is smaller in the low energy range. For instance, at 2.1 eV (590 nm), the refractive indices of [H2gua]2·(Ti5O5F12) and [H2taz]2·(Ti5O5F12) are equal to 1.94 and 1.92 respectively. Nevertheless, the relative difference (-1 %) of the indices is quite small, which could be due to the increase of the density (1.6 %), the molar weight increase (2.95 %) being not compensated by the cell volume increase (1.4 %). The UV-Vis diffuse reflectance spectra of [H2taz]2·(Ti5O5F12), after application of the Kubelka-Munk transformation, are displayed in Figure 12. The band gap at RT, 3.30 eV, appears to be almost the same as the band gap of [H2gua]2·(Ti5O5F12). Finally, the ability to reduce Ti4+ to Ti3+ under UV excitation has been evaluated in both materials. The color modification is very similar. CONCLUSION The structure of [H2taz]2·(Ti5O5F12) has been refined from PXRD data in the same SG (Cmm2) as [H2gua]2·(Ti5O5F12) which adopts the same structure for the inorganic part. One H atom site is half-fully occupied and two mirror symmetry related positions have a mixed carbon and nitrogen composition, preventing DFT calculations for the structural cell ; moreover, the occurrence of the less stable tautomer of [H2taz]+ is not excluded. The ordered crystal structure of


19


Page 20 of 51

[H2taz]2·(Ti5O5F12) has then been refined by using a double cell in the Cmc21 SG. DFT geometry optimizations of the structures of [H2taz]2·(Ti5O5F12) and [H2gua]2·(Ti5O5F12) lead to large displacements of even heavy atoms. Positional disorder in both the organic cations and inorganic networks is highlighted. Due to this disorder,

1

H and

19

F MAS NMR spectra of

[H2taz]2·(Ti5O5F12) and [H2gua]2·(Ti5O5F12) present broad contributions and then do not allow to confirm the number and the relative multiplicities of the H and F sites. The best agreement between experimental and calculated 1H NMR parameters confirms that 1,4-diH+ is the only tautomer in [H2taz]2·(Ti5O5F12). Moreover, insights into hydrogen bonding is provided by deriving a method usually applied to organic solids. For this purpose, 1H isotropic chemical shifts have been also calculated for the cations alone and for the isolated cations and compared to those obtained for the full crystal structures, to probe hydrogen bonding between inorganic and organic parts and between organic cations. These calculations reveal hydrogen bonding for three of the four H sites of [H2taz]2·(Ti5O5F12) in which [H2taz]+ cations are N-H···N hydrogen-bonded to each other. They also reveal hydrogen bonding for two of the three H sites of [H2gua]2·(Ti5O5F12) and suggest inter cationic ring current effect for one H site of [H2taz]2·(Ti5O5F12). In addition to the nature of the organic cation, both compounds differ essentially by the number of hydrogen bonds involving terminal F atoms; they are more numerous in [H2gua]2·(Ti5O5F12) in agreement with the smaller

19

F δiso values. Finally, the

substitution of [H2gua]+ by [H2taz]+ reduces slightly the refractive index, while keeping a high optical band gap.


20

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ACKNOWLEDGMENT MB and CL acknowledge Corentin Jacquemoz for his help in recording NMR spectra. The computations presented in this work have been carried out at the Centre Régional de Calcul Intensif des Pays de la Loire (CCIPL), financed by the French Research Ministry, the Région Pays de la Loire, and Nantes University. CCIPL is thanked for the CASTEP licenses financial support. ASSOCIATED CONTENT Supporting information The Supporting Information is available free of charge on the ACS Publications website at DOI: CIF files of the EXP (Cmm2 (CCDC 1826645) and Cmc21 SG) and APO (Cmc21 SG) structures of [H2taz]2·(Ti5O5F12) and of the EXP (CCDC 1853981) and APO structures of [H2gua]2·(Ti5O5F12). IR spectrum and Rietveld refinement (Cmc21 SG) of [H2taz]2·(Ti5O5F12), fractional atomic coordinates from EXP and APO structures and corresponding atomic displacements, selected interatomic distances from EXP and APO structures, geometries of the X–H···Y contacts in the EXP structures of [H2taz]2·(Ti5O5F12) (Cmc21 SG) and [H2gua]2·(Ti5O5F12), experimental and fitted 1H and

19

F MAS NMR spectra, parameters of the fits, and assignment of the NMR lines,

calculated 1H σiso and δiso and

19

F σiso values from the EXP structure of [H2taz]2·(Ti5O5F12),

calculated 1H σiso and δiso values from the APO structures of [H2taz]2·(Ti5O5F12) (Cmc21 SG) containing 1,2-diH+ cations and 1,4-diH+ cations with C-H···N hydrogen bond, experimental 1H


21


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MAS NMR spectra and calculated 1H individual resonances of the cations in the APO crystal structures and of the cations alone and isolated (PDF) AUTHOR INFORMATION Corresponding Authors * E-mail: (J.L.) [email protected] * E-mail: (C.L.) [email protected] ORCID Marjorie Albino: 0000-0002-9785-5368 Monique Body: 0000-0002-5895-3731 Christophe Legein: 0000-0001-7426-8817 Marc Leblanc: 0000-0001-7958-0359 Vincent Maisonneuve: 0000-0003-0570-953X Jérôme Lhoste: 0000-0002-4570-6459


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Figure 1. Titanium (IV) fluoride or oxyfluoride anions, eventually hydrated, encountered in Class I hybrids containing cyclic or aliphatic amine cations. F, O and H atoms are represented in green, red and white, respectively.


23


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Figure 2. TGA analysis and temperature-controlled XRPD patterns of [H2taz]2·(Ti5O5F12) under air atmosphere.


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Figure 3. Rietveld refinement (Cmm2 SG) of the PXRD pattern of [H2taz]2·(Ti5O5F12); (a) experimental (in black) and calculated (in red) patterns; (b) Bragg positions of (above) [H2taz]2·(Ti5O5F12) and (below) TiO2 anatase (I41/amd SG, 1.4(1) wt. %); (c) difference between experimental and calculated patterns. The inset (A) shows a zoom of a selected 2 θ range and the inset (B) shows the microstructure of the powder (SEM image).


25


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Figure 4. Projection on the (001) plane of the structure of [H2taz]2·(Ti5O5F12). The [H2taz]+ cations are displayed in agreement with the structure refined in the Cmc21 SG. H, C, N, O, F and Ti atoms are represented in light grey, black, blue, red, green and grey, respectively. Ti1O2F4 and Ti2O2F4 octahedra are represented in grey and blue respectively.


26

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Figure 5. Configurations and intermolecular H···H contact or hydrogen bonding of 1,2,4triazolium cations: (a) 1,2-diH+ cations and (b) C/N disorder in Cmm2; (c) 1,2-diH+ and 1,4-diH+ cations in Cmc21 with (d) N-H···N or (e) C-H···N hydrogen bonds. H, C and N atoms are represented in light grey, black and blue, respectively. H···H and H···N distances (in Å) are indicated.


27


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Figure 6. Views of the APO structures of (a) [H2taz]2·(Ti5O5F12) and (b) [H2gua]2·(Ti5O5F12) in which X–H···Y (X = N, C; Y = F, O, N) contacts, with angle larger than 110° and H···Y distances smaller than the sum of H and Y van der Waals radii, are represented by dashed lines. H, C, N, O, F and Ti atoms are represented in light grey, black, blue, red, green and grey, respectively.


28

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Figure 7. 19F MAS (64 kHz) NMR spectra of [H2taz]2·(Ti5O5F12) and [H2gua]2·(Ti5O5F12). The stars indicate spinning sidebands.


29


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Figure 8. 1H MAS (64 kHz) NMR spectra of [H2taz]2·(Ti5O5F12) and [H2gua]2·(Ti5O5F12).


30

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Figure 9. Experimental 1H MAS (64 kHz) NMR spectrum of [H2taz]2·(Ti5O5F12) and GIPAW calculated 1H individual resonances (line widths arbitrarily fixed and assumed to be equal, color of the corresponding atom symbol in the inset) of the cations [H2taz]+ in the APO crystal structure of [H2taz]2·(Ti5O5F12) (Cmc21 SG), of the cations [H2taz]+ alone and isolated. 1H calculated δiso values are given in Table 5.


31


Figure 10.

19

Page 32 of 51

F experimental average δiso values (Tables S10 and S11) as a function of average

calculated σiso values (from APO structures, Table 4), for bridging and terminal F atoms, of [H2taz]2·(Ti5O5F12) (in black) and [H2taz]2·(Ti5O5F12) (in red). The dash line represents the linear regression whose equation is given.


32

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Figure 11. Calculated refractive indices of [H2taz]2·(Ti5O5F12) (in blue) and [H2gua]2·(Ti5O5F12) (in black). The vertical dashed lines delimit the visible (VIS) wavelength range (IR: infrared; UV: ultraviolet).


33


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Figure 12. Evolution of UV-Vis diffuse spectra (after Kubelka-Munk transformation) of [H2taz]2·(Ti5O5F12) irradiated under UV lamp (254 nm) for various durations (0, 10, 60, 960, 1200, 1440 min). The inset shows the optical band gap determined at 0 min.


34

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Table 1. Crystallographic data of [H2taz]2·(Ti5O5F12). Formula

Ti5O5F12C4N6H8

Molecular weight (g.mol-1)

687.5

Crystal system

Orthorhombic

SG

Cmm2

a (Å)

22.7233(7)

b (Å)

10.2103(3)

c (Å)

3.7940(1)

V (Å3)

880.26(4)

Z

2

ρcalc. (g.cm-3)

2.594

Wavelength (Å)

1.54056

2θ range (°)

5-100

Refl. unique

623

Refined parameters

103

Rp/Rwp

0.105/0.103

RB/Rf

0.036/0.041


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Table 2. Geometries (Å, °) of the X–H···Y (X = N, C; Y = F, O, N) contacts with angle larger than 110° and H···Y distances smaller than the sum of H and Y van der Waals radii (in italic those corresponding to hydrogen bonding interactions) in the APO (Cmc21 SG) structure of [H2taz]2·(Ti5O5F12). X–H···Y

X–H

H···Y

X···Y

X–H···Y

N1a–H···N1b

1.045

1.906

2.949

175.4

N2a–H···F1b

1.027

1.945

2.677

125.6

N2a–H···F2a

1.027

2.632

3.337

129.3

C1–H···F3

1.081

2.500

3.334

133.1

C1–H···F3

1.081

2.566

3.310

125.3

C2b–H···F2b

1.087

2.493

3.284

128.7

C2b–H···O1a

1.087

2.099

3.096

151.1

Table 3. Geometries (Å, °) of the N–H···Y (Y = F, O) contacts with angle larger than 110° and H···Y distances smaller than the sum of H and Y van der Waals radii (in italic those corresponding to hydrogen bonding interactions) in the APO structure of [H2gua]2·(Ti5O5F12). N–H···Y

N–H

H···Y

N···Y

N–H···Y

N1–H1···O1

1.016

2.456

3.547

168.3

N1–H1···F2

1.016

2.286

2.963

122.9

N1–H1···F2

1.016

2.570

3.100

112.2

N2–H2A···F1

1.022

1.919

2.832

147.0

N2–H2B···F1

1.018

1.867

2.726

140.0


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Table 4. 19F calculated σiso (ppm) values from the APO structures of [H2taz]2·(Ti5O5F12) (Cmc21 SG) and [H2gua]2·(Ti5O5F12) and average calculated σiso values for the terminal and bridging F atoms.

19

F average experimental δiso values (ppm) for the terminal and bridging F atoms of

[H2taz]2·(Ti5O5F12) and [H2gua]2·(Ti5O5F12). [H2taz]2·(Ti5O5F12)

[H2gua]2·(Ti5O5F12)

F1a

-54.5

F1

F1b

-32.8

-43.6

-15.9

101.9

92.0

F2a

80.0

F2b

80.4

F3

-15.9

F2

68.9

84.2

F3

71.2

F4a

56.8

F4

60.6

F4b

61.0

75.9

67.4

-4.1

-4.0


37


Table 5.

1

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H average experimental δiso values (δiso,exp, ppm) of [H2taz]2·(Ti5O5F12) and

[H2gua]2·(Ti5O5F12) and 1H calculated σiso (ppm) and δiso (δiso,cal, ppm) values for the cations [H2taz]+ and [H2gua]+ in the APO crystal structures of [H2taz]2·(Ti5O5F12) (Cmc21 SG) and [H2gua]2·(Ti5O5F12), respectively, and for the [H2taz]+ and [H2gua]+·cations alone and isolated. Cations alone to APO crystal structure (∆(δiso,cal)1) and isolated cation to cations alone (∆(δiso,cal)2) 1H chemical shift changes. Average calculated δiso values in the APO crystal structure of [H2gua]2·(Ti5O5F12) and for HC and HN in the APO crystal structure of [H2taz]2·(Ti5O5F12). δiso,exp σiso

δiso,cala σiso

δiso,cala ∆(δiso,cal)1b σiso

δiso,cala ∆(δiso,cal)2c

[H2taz]+

APO structure

Cations alone

HC1

22.37

8.63

22.66

8.34

0.29

22.26

8.74

-0.40

HC2b

20.26

10.74

21.93

9.07

1.67

21.60

9.40

-0.33

9.4

Isolated cation

9.7

HN2a

18.51

12.49

20.09

10.91

1.58

19.36

11.64

-0.73

HN1a

16.95

14.05

16.96

14.04

0.01

19.55

11.45

2.59

13.5

13.3

[H2gua]+

APO structure

Cations alone

H1

25.29

5.71

25.41

5.59

0.12

25.99

5.01

0.58

H2A

24.83

6.17

26.28

4.72

1.45

26.09

4.91

-0.19

H2B

24.84

6.16

26.76

4.24

1.92

26.27

4.73

-0.49

6.4

Isolated cation

6.0

a

σiso values have been converted into δiso values by using δiso = - σiso + σref with σref = 31.0 ppm;47 b∆(δiso,cal)1 = δiso,cal (crystal) - δiso,cal (alone); c∆(δiso,cal)2 = δiso,cal (alone) - δiso,cal (isolated).


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ABBREVIATIONS DFT, Density Functional Theory, GIPAW, Gauge Including Projector Augmented Wave; GGA, Generalized Gradient Approximation; NMR, Nuclear Magnetic Resonance; MAS, Magic Angle Spinning; CP-MAS, Cross Polarization-Magic Angle Spinning; SG, Space Group, XRD, X-Ray Diffraction; PXRD, Powder X-Ray Diffraction; TGA, thermogravimetric analyses; RT, room temperature


39


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For Table of Contents Use Only Manuscript title. NMR crystallography, hydrogen bonding and optical properties of a novel 2D hybrid oxyfluorotitanate [H2taz]2·(Ti5O5F12) Author list. Marjorie Albino, Monique Body, Christophe Legein,* Annie Hémon-Ribaud, Marc Leblanc, Vincent Maisonneuve and Jérôme Lhoste* TOC graphic.

Synopsis. A new hybrid oxyfluorotitanate [H2taz]2·(Ti5O5F12) is structurally characterized by powder XRD and solid-state NMR. One H site is half-fully occupied and two sites have a mixed C and N composition. GIPAW calculations of the 1H chemical shieldings in a supercell of the ordered structure, of the cations alone and of the isolated cation establish the hydrogen bonding scheme.


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A new hybrid oxyfluorotitanate [H2taz]2∙(Ti5O5F12) is structurally characterized by powder XRD and solidstate NMR. One H site is half-fully occupied and two sites have a mixed C and N composition. GIPAW calculations of the 1H chemical shieldings in a supercell of the ordered structure, of the cations alone and of the isolated cation establish the hydrogen bonding scheme. 263x136mm (72 x 72 DPI)


NMR Crystallography, Hydrogen Bonding and Optical Properties of

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