Revealing the early stages of carbamazepine crystallization by cryoTEM and 3D electron diffraction

Broadhurst, E.T.; Xu, H.; Parsons, S.; Nudelman, F.

doi:10.1107/S2052252521010101

research letters

IUCrJ

Volume 8| Part 6| November 2021| Pages 860-866

ISSN: 2052-2525

https://doi.org/10.1107/S2052252521010101

CHEMISTRY | CRYSTENG

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Revealing the early stages of carbamazepine crystallization by cryoTEM and 3D electron diffraction

Edward T. Broadhurst,^a Hongyi Xu,^b ^* Simon Parsons ^a ^* and Fabio Nudelman ^a ^*

^aEaStCHEM School of Chemistry and Centre for Science at Extreme Conditions, The University of Edinburgh, King's Buildings, West Mains Road, Edinburgh EH9 3FJ, United Kingdom, and ^bMaterials and Environmental Chemistry, Stockholm University, Stockholm, SE-106 91, Sweden
^*Correspondence e-mail: hongyi.xu@mmk.su.se, s.parsons@ed.ac.uk, fabio.nudelman@ed.ac.uk

Edited by C.-Y. Su, Sun Yat-Sen University, China (Received 2 June 2021; accepted 28 September 2021; online 30 October 2021)

Time-resolved carbamazepine crystallization from wet ethanol has been monitored using a combination of cryoTEM and 3D electron diffraction. Carbamazepine is shown to crystallize exclusively as a dihydrate after 180 s. When the timescale was reduced to 30 s, three further polymorphs could be identified. At 20 s, the development of early stage carbamazepine dihydrate was observed through phase separation. This work reveals two possible crystallization pathways present in this active pharmaceutical ingredient.

Keywords: crystal nucleation; 3D electron diffraction; polymorphism; cryoTEM; carbamazepine.

CCDC references: 2085759; 2085760; 2085761

1. Introduction

Polymorphism occurs when a material crystallizes into more than one distinct solid form. It is very common in organic chemistry, affecting 74% of a set of pharmaceutical materials in one study for which extensive screening had been carried out (Cruz-Cabeza et al., 2015 ). Polymorphs differ in solubility, bioavailability and processing (e.g. tableting) characteristics, and their evolution during crystal growth and storage is a complex but fundamental question worth many billions of dollars to sectors such as opto-electronics, energy storage and pharmaceuticals (Cruz-Cabeza et al., 2015).

The initial stage of crystal growth, which is stochastic at an atomistic or molecular level (Gladkov, 2008 ), has been observed recently in the nucleation and growth of an NaCl nanocrystal at the tip of a carbon nanotube (Nakamuro et al., 2021 ). This experiment showed an ordered nucleus emerging directly at the point of nucleation. Alternative `non-classical' crystallization pathways involve initial formation of an amorphous particle which grows via the attachment of other particles (De Yoreo et al., 2015 ).

The attaching particles may be ions and ion complexes, droplets or other amorphous or nanocrystalline materials (De Yoreo et al., 2015). Work on aragonite growth, which follows this pathway, has shown that partially aligned nanocrystalline domains spontaneously and simultaneously emerge within the amorphous framework, subsequently maturing to yield a crystal (Walker et al., 2017 ). These pathways have been extensively studied in inorganic minerals (De Yoreo et al., 2015), but information on organic systems is sparse.

In this paper we describe the use of cryo-transmission electron microscopy (cryoTEM) (Dubochet et al., 1988 ) to capture the earliest stages of crystallization of the polymorphic pharmaceutical carbamazepine. Each stage was flash-frozen in liquid ethane at 100 K after crystallization times of 20–180 s. CryoTEM allows real space imaging of crystals and the measurement of diffracted intensities in reciprocal space via tilting of the sample in the electron beam, known as three-dimensional electron diffraction (3D ED) (Wan et al., 2013 ; Huang et al., 2021 ; Gemmi et al., 2019 ; Clabbers & Xu, 2020 ; Jones et al., 2018 ; Gruene et al., 2018 ). Subsequent crystal structure determinations on crystallites measuring only a few hundred nanometres lead to unambiguous polymorph identification (Broadhurst et al., 2020 ). This combination of imaging and diffraction reveals not only short-lived polymorphs, but also the non-classical mechanism of crystal growth in this material (Walker et al., 2017).

Carbamazepine [CBZ, 5H-dibenz(b,f)azepine-5-carboxamide] is a neuralgic drug which is often used as a model for polymorphism studies. There are five unsolvated polymorphs (Table S1 of the supporting information): triclinic form I (Grzesiak et al., 2003 ), trigonal form II (Lowes et al., 1987 ), monoclinic form III (Fernandes et al., 2007 ) and IV (Lang et al., 2002 ) and the most recent polymorph discovered orthorhombic form V (Arlin et al., 2011 ). The relative stability is III > I > V > IV > II (Table S2). In the presence of water, either aqueous solution or wet solvents such as bench ethanol, a dihydrate (CBZDH) is formed (Kahela et al., 1983 ; Kaneniwa et al., 1987 ; Young & Suryanarayanan, 1991 ; Kobayashi et al., 2000 ). CBZDH is usually described as monoclinic, though recent work has defined a disordered orthorhombic model (Sovago et al., 2016 ). Form II also contains cavities which can accommodate solvent (Fabbiani et al., 2007 ; Cabeza et al., 2007 ).

2. Experimental

CBZ was obtained from Alfa Aesar, with a sample purity quoted as ACS reagent grade (≥98.5%); impurities were identified using ICP-MS. Ethanol was obtained from Fisher Chemical at analytical reagent grade (≥99.8%). The characterization of water content was achieved by Karl–Fischer titration, carried out using a Mettler Toledo C30S Coulometric KF titrator equipped with a Mettler Toledo DM 143-SC electrode. Hydranal Coulomat AD was used as the solvent. Details of the ICP-MS and Karl–Fischer titrations are available in the supporting information.

In a typical experiment, a saturated solution of CBZ (0.1125 g) in ethanol (25.6257 g, water content 0.03% by Karl–Fischer titration, Table S3) was filtered under gravity to remove any undissolved CBZ. Fresh solutions were made for each study. Aliquots of 3 µl solution were pipetted onto a cryoTEM grid (Quantifoil R2/2) which had been previously plasma-treated using a PELCO Easiglow discharge cleaning system for 45 s to improve hydrophilicity. The grids were allowed to stand under ambient conditions (298 K, 21% humidity) for periods between 20 and 180 s. The ethanol was removed by pressure-assisted blotting (Zhao et al., 2021 ) at different time-points and the sample immediately vitrified in liquid ethane to arrest further crystallization and protect the crystals from beam and vacuum damage when under the microscope. Fig. S1 of the supporting information summarizes the procedure, in which rapid blotting was accomplished using a disk of filter paper secured with a rubber band over the top of a Büchner flask connected to a water aspirator.

A Tecnai F20 FEG transmission electron microscope operating at 200 kV (λ = 0.02508 Å) equipped with a CMOS TVIPS F816 camera (8k × 8k pixels) was used for imaging and 3D ED in selected area electron diffraction (SAED) mode. A Gatan tomography cryo-transfer holder was used, operating at 100 K. During typical 3D ED data collection, diffraction patterns were collected while rotating the crystal continuously, going from −40 to +20° (Dubochet et al., 1988; Clabbers & Xu, 2020; Broadhurst et al., 2020; Gemmi et al., 2019; Huang et al., 2021). The exposure time (0.2 s) and rotation speed (0.95° s⁻¹) were chosen so that individual diffraction images were integrated over 0.21° of reciprocal space. The estimated dose rate was 2 e Å⁻² s⁻¹, with each collection taking on average 240 s, the total estimated dose per 3D ED data collection was 480 e Å⁻². The diffraction patterns were indexed and integrated with the programs REDp (Wan et al., 2013), XDS (Kabsch, 2010 ) and PETS (Palatinus et al., 2019 ). Details of structure analysis and listings of crystal and refinement data are available in the supporting information.

Samples were also prepared after 3 min and 30 s and measured using powder X-ray diffraction, further details are provided in the supporting information.

3. Results and discussion

After 180 s, crystals with an elongated morphology [Fig. 1(a)] had formed across the entire grid. 3D ED data were collected from seven different crystals (Fig. S2), exhibiting typical monoclinic unit-cell dimensions of a = 10.38, b = 27.79, c = 5.08 Å, β = 102.52°, characteristic of the dihydrate, CBZDH. Data collected from seven crystals were merged to produce a single dataset of 90% completeness, from which the structure of CBZDH was solved and refined (R₁ = 16.31%). The high value of the R factor reflects the neglect of dynamical effects during refinement (Clabbers & Xu, 2020) (Table S4), though the data quality was good enough for the hydrogen atoms to be located in a Fourier difference map (Fig. S3). CBZDH was the only phase observed after a crystallization time of 180 s. It has a distinctive morphology which allowed it to be identified in all other samples, both repeats and at shorter time-points.

Figure 1
(a) Low-magnification image of CBZDH crystallized after 3 min on the TEM grid at 100 K showing an elongated morphology. Scale bar = 5 µm. (b) Selected crystal of CBZDH used for collection of 3D ED data. Scale bar = 2 µm. Inset shows a diffraction image from the dataset. (c) Disordered structure of CBZDH.

To probe earlier time points of crystallization, a sample was examined at 100 K after 30 s. At this crystallization stage, no less than four different forms of CBZ were present and identified based on their unit-cell dimensions (Table S5). Alongside CBZDH, which was the dominant form, one crystal of CBZ-III with a somewhat indistinct morphology was identified from its monoclinic unit-cell dimensions a = 7.61, b = 11.30, c = 13.89 Å, β = 92.43° [Fig. 2(a)]. 3D ED data were collected to 52% completeness from this crystallite. Despite the low data completeness, the structure of CBZ-III could be solved and refined (R₁ = 19.68%). Two more monoclinic crystals exhibited unit-cell dimensions of a = 27.15, b = 7.30, c = 14.10 Å, β = 110.30°, corresponding to CBZ-IV [Fig. 2(b)]. Merging of the two 3D ED datasets (66% completeness) enabled the structure to be refined (R₁ = 19.86%). A third crystalline form present in the same sample exhibited rhombohedral unit-cell dimensions of a = 36.24, c = 5.31 Å, α = β = 90°, γ = 120° indicative of CBZ form II [Fig. 2(c)]. Although the quality of data obtained precluded structure solution, the crystal form was unambiguously identified from the unit-cell dimensions.

Figure 2
(a)–(c) Crystals of form III, IV and II, respectively, found in a sample after crystallization for 30 s on a TEM grid. Scale bars = 2 µm. The insets show representative frames from the data collections. (d)–(f) Corresponding 3D ED reciprocal lattice reconstructions all viewed along b*. All images were measured at 100 K.

The identification of forms II, III and IV is the first time that any polymorph other than the dihydrate has been observed in the crystallization of CBZ from (wet) ethanol. The fact that they were only present as tiny fractions of samples otherwise consisting exclusively of the expected dihydrate demonstrates the ability of cryoTEM and 3D ED to identify minor phases and thier potential importance in polymorph discovery. The results obtained after 180 s, which showed the presence only of CBZDH, showed that these minor phases are short-lived and re-dissolve or transform into CBZDH in a matter of minutes.

To obtain bulk measurements of the crystals forming in the solution after 3 min and 30 s of crystallization, powder X-ray diffraction data were collected. At both time points, the only form detected was CBZDH (Figs. S6 and S7). The absence of the other forms at 30 s is possibly due to them being present as crystallites that are too small and too few in numbers to be detected by powder X-ray diffraction. These findings do illustrate the power of ED for phase identification within a small quantity of sample. Further details are provided in the supporting information.

To investigate even earlier stages of the crystallization, samples were examined after 20 s (Fig. 3). No crystals were observed. Instead, dark droplet-like structures ca 150–200 nm in diameter were contained within a thinner film (area I in Fig. 3). Area II shows the droplet-like particles which lack a film of the mother liquor surrounding them and are slightly darker, suggesting that they are further developed particles of CBZ (see below). Areas III and IV show these droplet-like structures coalescing inside and outside the electron-dense film. The absence of Bragg reflections in the diffraction images of these particles showed that they were amorphous, and that the sample had been captured at a pre-crystallization stage.

Figure 3
Images taken at 100 K after crystallization for 20 s and vitrification. Scale bar = 2 µm. I shows the droplet-like structures with a surrounding film of mother liquor and II shows the same structures without the surrounding film. III and IV show these structures coalescing inside and outside the film.

The images showed that CBZDH crystallizes via a non-classical phase separation mechanism that begins with the formation of an initial film which separates into droplet-like structures (areas I and II). The coalescence of these droplet-like structures (areas III and IV) then signals the next stage of crystal growth and development. The time difference between the images in Fig. 3 and those consisting of CBZDH, along with CBZ forms II, III and IV (Fig. 2) is only 10 s, indicating the time scale of the transition from the droplets to crystals.

Pressure-assisted blotting (Zhao et al., 2021) removes most of the mother liquor from the grid. As the image in Fig. 3 shows, some residue remains, but crystallization is completely halted by freezing in liquid ethane 1–2 s after blotting. A further sample was prepared after 20 s of crystallization, blotted and placed into the microscope at room temperature. The TEM vacuum (≃10⁻⁵ Pa) also stops crystallization by removing residual solvent, but the procedure is not as quick as plunge-freezing as it involves insertion of the sample into the microscope in a non-vitrified state, so that crystal growth can continue for a few seconds longer.

Discrete, electron-dense droplet-like structures ca 50–150 nm in size were again present, covering the grid (Fig. 4). The existence of these features after removal of solvent demonstrates that the electron-dense droplets observed in Fig. 3 are probably amorphous CBZ particles. Although they are similar to those observed at 100 K [Fig. 3(b)], they now exhibit `roughened' or `textured' edges [Fig. 4(a)] as a result of solvent removal by the TEM vacuum. The images also show structures with a morphology characteristic of CBZDH [Fig. 4(b)], but the lack of Bragg reflections indicates that they are also non-crystalline. This absence of long-range order can be explained by dehydration of the CBZDH crystals by the high vacuum in the TEM at room temperature. Crystallinity is lost, but with preservation of morphology. The effect can be reproduced by exposing crystalline CBZDH to the TEM vacuum (Fig. S4).

Figure 4
Images taken at room temperature after crystallization for 20 s and no vitrification. (a) Droplet-like features with roughened edges after removal of their surrounding mother liquor by the vacuum in the TEM. (b) Coalescence of the droplet structures producing two crystals of CBZDH, identified from morphology. White boxes labelled I, II and III show magnified areas within the sample. Scale bars = 2 µm.

Three areas of particular interest are highlighted in Fig. 4(b). Area I shows a part of the grid where the initial stages of the coalescence of the droplet-like particles into a pre-crystalline form of CBZ can be seen, this is comparable to what is shown in Fig. 3, areas III and IV. Fissures appearing along the length of this developing crystal are either a feature of vacuum damage as the ethanol is drawn off or that a thin crystal has been interrupted at a fragile stage of its early development. The maturing crystal is visible below this point (II), running from the left of the image down to the bottom. The more mature character of this part of the crystal is demonstrated by its more uniform texture and by the absence of particles around it, due to their incorporation into the insipient structure. The crystal in Fig. 4(b) area III is, by the same criteria, more mature: it is more uniform, with no fissures along its length while its darker colour indicates it is thicker. Finally, there are no roughened droplet-like structures surrounding this crystal, as found in areas I and II.

4. Conclusions

Following the crystallization of CBZ using cryoTEM was made possible by combination of rapid sample preparation, imaging and 3D ED, revealing unprecedented insights into the crystal growth of an organic material. Growth begins with the formation of pre-concentrated areas of CBZ within a film of the mother liquor. Phase-separation into electron-dense, non-crystalline particles is followed by coalescence of the particles. We infer that initial crystallization occurred spontaneously in a matter of 2–3 s in some coalesced particles. Although this stage is not explicitly observed here, it has been captured in the crystallization of aragonite (Walker et al., 2017).

However, the subsequent stage, consisting of a mixture of crystalline CBZDH growing by attachment of amorphous particles, has been captured by arresting growth on exposure to the TEM vacuum. Fig. 4 shows this process occurring at one end of a CBZDH crystal which is mature and fully developed at the other end.

The results establish a non-classical crystallization mechanism for CBZDH, with the whole sample becoming crystalline after only 30 s. While the bulk of the sample at 30 s consists of crystalline CBZDH, the presence of three minor forms (CBZ-II, III and IV) indicates that other crystallization routes are available. Alternative non-classical and classical growth mechanisms have been observed for CaF₂, depending on the identity of ligands used to cap precursor nanocrystals (Mashiach et al., 2021 ). Whether CBZ-II, III and IV develop classically or non-classically is not yet established. Here, they form as isolated crystallites (Fig. 2), lacking proximity to CBZ in other parts of the sample precluding the attachment mechanism by which CBZDH develops as discussed above. These minor forms either transform or re-dissolve, so that by 180 s the entire sample consists of crystalline CBZDH.

Finally, our results highlight the ability of time-resolved cryoTEM, coupled to 3D ED, to reveal transient phases in a crystallization process which are present in amounts too small to be detected by bulk techniques such as powder X-ray diffraction.

5. Related literature

The following references are cited in the supporting information: Coelho (2018 ); Doyle & Turner (1968 ); Himes et al. (1981 ); Kachrimanis & Griesser (2012 ); Lisgarten et al. (1989 ); Sheldrick (2008 ; 2015a ); Thorn et al. (2012 ); Rigaku OD (2016 $[Rigaku OD (2016). CrysAlis PRO. Rigaku Oxford Diffraction Ltd, Yarnton, Oxfordshire, England. ]$ ).

Supporting information

CCDC references: 2085759; 2085760; 2085761

Crystal structure: contains datablocks CBZDH, CBZIII, CBZIV. DOI: https://doi.org/10.1107/S2052252521010101/yc5034sup1.cif

Supporting information file. DOI: https://doi.org/10.1107/S2052252521010101/yc5034sup2.pdf

Computing details top

For all structures, data collection: TVIPS and TEMspy. Cell refinement: REDp (Wang, 2013) for CBZDH, CBZIV; PETS 2.0 (Palatinus, 2019) for CBZIII. Data reduction: XDS (Kabsch, 2010) for CBZDH, CBZIV; PETS 2.0 (Palatinus, 2019) for CBZIII. For all structures, program(s) used to solve structure: SHELXT 2014/5 (Sheldrick, 2014); program(s) used to refine structure: SHELXL2018/3 (Sheldrick, 2018).

(CBZDH) top

Crystal data top

C₁₅H₁₆N₂O₃	F(000) = 220
M_r = 272.30	D_x = 1.268 Mg m⁻³
Monoclinic, P2₁/c	Electron radiation, λ = 0.02508 Å
a = 10.410 (2) Å	Cell parameters from 2602 reflections
b = 28.117 (6) Å	θ = 0.1–1.8°
c = 5.038 (1) Å	µ = 0.000 mm⁻¹
β = 104.64 (3)°	T = 100 K
V = 1426.8 (5) Å³	Lath, colourless
Z = 4	0.01 × 0.001 × 0.000001 mm

Data collection top

FEI Tecnai F20 @ 200 keV w TVIPS F816 camera. diffractometer	R_int = 0.531
Radiation source: electron	θ_max = 0.9°, θ_min = 0.1°
continuous rotation (3DED) scans	h = −12→12
16902 measured reflections	k = −33→34
2602 independent reflections	l = −6→6
1576 reflections with I > 2σ(I)

Refinement top

Refinement on F²	Hydrogen site location: mixed
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F² > 2σ(F²)] = 0.163	w = 1/[σ²(F_o²) + (0.122P)² + 0.2581P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.433	(Δ/σ)_max = 0.010
S = 1.10	Δρ_max = 0.13 e Å⁻³
2602 reflections	Δρ_min = −0.13 e Å⁻³
196 parameters	Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
181 restraints	Extinction coefficient: 1521 (18)
Primary atom site location: SHELXT 2014/5 (Sheldrick, 2014)

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. electron diffraction data. SFAC from Table 4 of Doyle and Turner (1968).

The structure was solved by dual space methods (Shelxt) and refined using the kinematic approximation in Shelxl. Use of this approximation means that data-fitting statistics (R-factors etc.) are much higher than is usual with X-ray or neutron data.

Disordered structure modelled as 50% occupancy for N and O atoms on C1. H-atoms were located in a difference map and H on aromatic Carbon atoms were free to refine distances (AFIX 44).

Checkcif output with comments:

RINTA01_ALERT_3_A The value of Rint is greater than 0.25 Rint given 0.531 PLAT020_ALERT_3_A The Value of Rint is Greater Than 0.12 ········· 0.531 Report

Data from several crystals were merged to produce a single data set for structure analysis. Variable extinction effects between crystals lead to high Rint values.

PLAT029_ALERT_3_A _diffrn_measured_fraction_theta_full value Low . 0.906 Why?

Only rotation about phi is available and this has led to low completeness.

PLAT924_ALERT_1_A The Reported and Calculated Rho(min) Differ by . 11047.21 eA-3 PLAT925_ALERT_1_A The Reported and Calculated Rho(max) Differ by . 1368.80 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 0.60A From C1 1368.93 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 0.44A From C1 1254.56 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 1.22A From N1 981.49 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 1.74A From N1 861.70 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 1.37A From O1 846.41 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 1.95A From O4 773.90 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 0.58A From O4 741.13 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 2.12A From O3 738.21 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 0.70A From O4 736.89 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 1.86A From O4 704.41 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 1.61A From N2 693.72 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 1.68A From N2 693.72 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 1.31A From C14 693.52 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 2.17A From O2 682.96 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 2.11A From O1 669.09 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 2.05A From O3 635.83 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 1.16A From O4 633.07 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 1.42A From C14 574.73 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 2.10A From O2 498.86 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 0.72A From O3 496.65 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 0.50A From C3 485.80 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 0.63A From O3 484.80 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 1.52A From C3 468.90 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 1.39A From C3 449.98 eA-3 PLAT971_ALERT_2_A Check Calcd Resid. Dens. 1.40A From O3 429.18 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.04A From N1 -11047.34 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 0.99A From O1 -10663.84 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.10A From O4 -6583.34 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.10A From O3 -6480.92 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 0.76A From C1 -608.90 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.81A From O3 -431.95 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.31A From C2 -399.44 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 2.11A From C4 -381.64 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.60A From C13 -378.20 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 0.61A From N1 -373.20 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.27A From O1 -352.78 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.43A From C15 -337.99 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.60A From C12 -329.76 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 0.85A From C8 -299.71 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 2.03A From C6 -289.63 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 0.57A From C15 -286.72 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 0.87A From C13 -285.05 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.29A From C9 -278.88 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.38A From C9 -275.04 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.23A From N1 -261.76 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.67A From O1 -248.56 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.37A From O3 -234.14 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.97A From C8 -232.03 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 1.24A From O2 -218.16 eA-3 PLAT972_ALERT_2_A Check Calcd Resid. Dens. 0.57A From C5 -212.20 eA-3 PLAT975_ALERT_2_A Check Calcd Resid. Dens. 0.58A From O4 741.13 eA-3 PLAT975_ALERT_2_A Check Calcd Resid. Dens. 0.70A From O4 736.89 eA-3 PLAT975_ALERT_2_A Check Calcd Resid. Dens. 0.72A From O3 496.65 eA-3 PLAT975_ALERT_2_A Check Calcd Resid. Dens. 0.63A From O3 484.80 eA-3 PLAT976_ALERT_2_A Check Calcd Resid. Dens. 1.10A From O3 -6480.92 eA-3 PLAT977_ALERT_2_A Check Negative Difference Density on H1A -182.98 eA-3 PLAT977_ALERT_2_A Check Negative Difference Density on H1B -10726.72 eA-3 PLAT977_ALERT_2_A Check Negative Difference Density on H2B -10395.15 eA-3 PLAT977_ALERT_2_A Check Negative Difference Density on H3B -6480.92 eA-3 PLAT977_ALERT_2_A Check Negative Difference Density on H3C -48.09 eA-3 PLAT977_ALERT_2_A Check Negative Difference Density on H4 -46.49 eA-3 PLAT977_ALERT_2_A Check Negative Difference Density on H4B -84.63 eA-3 PLAT977_ALERT_2_A Check Negative Difference Density on H4C -6564.03 eA-3 PLAT977_ALERT_2_A Check Negative Difference Density on H5 -106.26 eA-3 PLAT977_ALERT_2_A Check Negative Difference Density on H9 -184.69 eA-3 PLAT977_ALERT_2_A Check Negative Difference Density on H12 -92.23 eA-3 PLAT977_ALERT_2_A Check Negative Difference Density on H13 -267.55 eA-3

We suspect that Checkcif is using X-ray scattering factors for these calculations. The figures quoted are from Shelxl.

PLAT082_ALERT_2_B High R1 Value ·································. 0.16 Report PLAT084_ALERT_3_B High wR2 Value (i.e. > 0.25) ··················. 0.43 Report

Typical values for electron data without accounting for dynamical effects. No action taken.

PLAT112_ALERT_2_B ADDSYM Detects New (Pseudo) Symm. Elem b 100 %Fit PLAT112_ALERT_2_B ADDSYM Detects New (Pseudo) Symm. Elem m 100 %Fit PLAT113_ALERT_2_B ADDSYM Suggests Possible Pseudo/New Space Group Cmca Check

Structure was solved as both monoclinic and orthorhombic Cmca. Better R1 for our disordered monoclinic structure. Electron data reduction is not good enough to determine which is more correct. A comprehensive study between X-ray and Neutron data has been reported. (see Sovago, Ioana, et al., Acta Cryst B, 72.1, (2016), 39-50)

PLAT340_ALERT_3_B Low Bond Precision on C-C Bonds ··············· 0.01067 Ang. PLAT260_ALERT_2_C Large Average Ueq of Residue Including O3 0.103 Check

Correct.

PLAT351_ALERT_3_C Long C-H (X0.96,N1.08A) C3 - H3 . 1.12 Ang. PLAT351_ALERT_3_C Long C-H (X0.96,N1.08A) C4 - H4 . 1.12 Ang. PLAT351_ALERT_3_C Long C-H (X0.96,N1.08A) C5 - H5 . 1.12 Ang. PLAT351_ALERT_3_C Long C-H (X0.96,N1.08A) C6 - H6 . 1.12 Ang. PLAT351_ALERT_3_C Long C-H (X0.96,N1.08A) C8 - H8 . 1.12 Ang. PLAT351_ALERT_3_C Long C-H (X0.96,N1.08A) C9 - H9 . 1.12 Ang. PLAT351_ALERT_3_C Long C-H (X0.96,N1.08A) C11 - H11 . 1.12 Ang. PLAT351_ALERT_3_C Long C-H (X0.96,N1.08A) C12 - H12 . 1.12 Ang. PLAT351_ALERT_3_C Long C-H (X0.96,N1.08A) C13 - H13 . 1.12 Ang. PLAT351_ALERT_3_C Long C-H (X0.96,N1.08A) C14 - H14 . 1.12 Ang.

C-H bond lengths are typically longer in ED as the diffraction pattern measured is based on the electrostatic potential, rather than electron density as is the case for X-rays.

PLAT911_ALERT_3_B Missing FCF Refl Between Thmin & STh/L= 0.600 239 Report PLAT913_ALERT_3_B Missing # of Very Strong Reflections in FCF ···. 236 Note PLAT906_ALERT_3_C Large K Value in the Analysis of Variance ······ 79.343 Check PLAT906_ALERT_3_C Large K Value in the Analysis of Variance ······ 11.736 Check PLAT906_ALERT_3_C Large K Value in the Analysis of Variance ······ 4.802 Check PLAT906_ALERT_3_C Large K Value in the Analysis of Variance ······ 3.082 Check

No action taken

ABSMU01_ALERT_1_G Calculation of _exptl_absorpt_correction_mu not performed for this radiation type.

Not usually performed for this radiation type.

PLAT002_ALERT_2_G Number of Distance or Angle Restraints on AtSite 28 Note PLAT007_ALERT_5_G Number of Unrefined Donor-H Atoms ············.. 10 Report PLAT013_ALERT_1_G N.O.K. _shelx_hkl_checksum Found in CIF ······ Please Check

Correct.

PLAT172_ALERT_4_G The CIF-Embedded .res File Contains DFIX Records 2 Report PLAT175_ALERT_4_G The CIF-Embedded .res File Contains SAME Records 1 Report PLAT176_ALERT_4_G The CIF-Embedded .res File Contains SADI Records 1 Report PLAT187_ALERT_4_G The CIF-Embedded .res File Contains RIGU Records 1 Report PLAT300_ALERT_4_G Atom Site Occupancy of O1 Constrained at 0.5 Check PLAT300_ALERT_4_G Atom Site Occupancy of O2 Constrained at 0.5 Check PLAT300_ALERT_4_G Atom Site Occupancy of N1 Constrained at 0.5 Check PLAT300_ALERT_4_G Atom Site Occupancy of N2 Constrained at 0.5 Check PLAT300_ALERT_4_G Atom Site Occupancy of H1A Constrained at 0.5 Check PLAT300_ALERT_4_G Atom Site Occupancy of H1B Constrained at 0.5 Check PLAT300_ALERT_4_G Atom Site Occupancy of H2A Constrained at 0.5 Check PLAT300_ALERT_4_G Atom Site Occupancy of H2B Constrained at 0.5 Check PLAT300_ALERT_4_G Atom Site Occupancy of H3B Constrained at 0.5 Check PLAT300_ALERT_4_G Atom Site Occupancy of H3C Constrained at 0.5 Check PLAT300_ALERT_4_G Atom Site Occupancy of H4B Constrained at 0.5 Check PLAT300_ALERT_4_G Atom Site Occupancy of H4C Constrained at 0.5 Check

Correct. Structure is disordered.

More ···PLAT301_ALERT_3_G Main Residue Disorder ············..(Resd 1 ) 11% Note PLAT309_ALERT_2_G Single Bonded Oxygen (C-O > 1.3 Ang) ·········.. O1 Check PLAT309_ALERT_2_G Single Bonded Oxygen (C-O > 1.3 Ang) ·········.. O2 Check PLAT417_ALERT_2_G Short Inter D-H..H-D H3A ..H4B . 2.06 Ang. -1+x,y,z = 1_455 Check PLAT417_ALERT_2_G Short Inter D-H..H-D H3C ..H4A . 1.91 Ang. -1+x,y,-1+z = 1_454 Check

H-H atom distances can be as short as 1.7 Ang in some crystal structures. (Wood, et al., CrystEngComm, 10 (4), (2008), 368-376).

PLAT802_ALERT_4_G CIF Input Record(s) with more than 80 Characters 119 Info PLAT860_ALERT_3_G Number of Least-Squares Restraints ············. 181 Note PLAT933_ALERT_2_G Number of OMIT Records in Embedded .res File ··· 1 Note

Correct.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
O1	0.3797 (17)	0.0458 (9)	0.585 (6)	0.080 (9)*	0.5
N1	0.6117 (13)	0.0481 (6)	0.645 (4)	0.045 (5)*	0.5
H1A	0.611547	0.015404	0.548038	0.054*	0.5
H1B	0.700411	0.066364	0.718448	0.054*	0.5
O2	0.6187 (16)	0.0452 (8)	0.715 (5)	0.072 (7)*	0.5
N2	0.3870 (13)	0.0467 (6)	0.537 (4)	0.042 (5)*	0.5
H2A	0.387035	0.012821	0.454710	0.051*	0.5
H2B	0.298140	0.065186	0.512382	0.051*	0.5
C1	0.4997 (5)	0.0664 (3)	0.6731 (15)	0.0531 (18)
N3	0.4994 (5)	0.1099 (2)	0.7898 (14)	0.0478 (15)
C2	0.3770 (6)	0.1344 (3)	0.7910 (14)	0.0457 (16)
C3	0.2936 (7)	0.1163 (3)	0.9520 (16)	0.0533 (19)
H3	0.3235 (8)	0.0841 (5)	1.085 (2)	0.064*
C4	0.1684 (7)	0.1406 (3)	0.9401 (16)	0.0549 (19)
H4	0.0996 (12)	0.1270 (4)	1.062 (2)	0.066*
C5	0.1367 (7)	0.1794 (3)	0.7814 (15)	0.0546 (19)
H5	0.0416 (15)	0.1987 (4)	0.7744 (15)	0.066*
C6	0.2189 (6)	0.1958 (3)	0.6281 (16)	0.0515 (19)
H6	0.1868 (7)	0.2276 (5)	0.494 (2)	0.062*
C7	0.3420 (6)	0.1745 (3)	0.6307 (14)	0.0443 (16)
C8	0.4332 (6)	0.1958 (3)	0.4715 (16)	0.052 (2)
H8	0.3833 (9)	0.2134 (4)	0.272 (3)	0.062*
C9	0.5698 (6)	0.1963 (3)	0.5409 (16)	0.053 (2)
H9	0.6210 (9)	0.2140 (4)	0.396 (3)	0.064*
C10	0.6522 (6)	0.1753 (3)	0.7911 (15)	0.0483 (17)
C11	0.7799 (6)	0.1963 (3)	0.9117 (16)	0.0530 (19)
H11	0.8111 (7)	0.2280 (5)	0.808 (2)	0.064*
C12	0.8643 (6)	0.1798 (3)	1.1446 (16)	0.056 (2)
H12	0.9604 (14)	0.1986 (4)	1.234 (2)	0.067*
C13	0.8300 (7)	0.1389 (3)	1.2733 (16)	0.059 (2)
H13	0.8990 (12)	0.1246 (4)	1.464 (3)	0.070*
C14	0.7089 (7)	0.1165 (3)	1.1599 (16)	0.057 (2)
H14	0.6796 (8)	0.0847 (6)	1.264 (2)	0.068*
C15	0.6233 (6)	0.1335 (3)	0.9159 (15)	0.0482 (17)
O3	0.0846 (11)	0.0462 (5)	0.360 (3)	0.103 (3)
H3A	0.032426	0.043833	0.494980	0.154*
H3B	0.190465	0.039852	0.463896	0.154*	0.5
H3C	0.062296	0.018794	0.253949	0.154*	0.5
O4	0.9165 (10)	0.0497 (4)	0.773 (2)	0.089 (3)
H4A	0.957883	0.056583	0.964708	0.134*
H4B	0.922958	0.016429	0.748222	0.134*	0.5
H4C	0.807333	0.053635	0.736194	0.134*	0.5

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
C1	0.057 (4)	0.045 (4)	0.058 (4)	−0.007 (3)	0.016 (3)	−0.001 (3)
N3	0.041 (3)	0.041 (4)	0.062 (4)	−0.005 (2)	0.013 (2)	0.001 (3)
C2	0.047 (3)	0.041 (4)	0.051 (4)	−0.003 (3)	0.017 (3)	−0.002 (3)
C3	0.056 (4)	0.048 (5)	0.061 (4)	−0.006 (3)	0.025 (3)	0.004 (4)
C4	0.054 (4)	0.058 (5)	0.057 (4)	−0.015 (3)	0.022 (3)	−0.013 (3)
C5	0.043 (4)	0.070 (6)	0.053 (4)	−0.003 (3)	0.016 (3)	−0.001 (3)
C6	0.031 (3)	0.056 (5)	0.064 (4)	0.000 (3)	0.005 (3)	0.008 (3)
C7	0.039 (3)	0.042 (4)	0.053 (3)	0.003 (2)	0.013 (3)	0.000 (3)
C8	0.036 (3)	0.054 (6)	0.067 (4)	0.002 (3)	0.015 (3)	0.008 (4)
C9	0.042 (3)	0.053 (6)	0.065 (4)	−0.002 (3)	0.012 (3)	0.009 (4)
C10	0.031 (3)	0.051 (5)	0.062 (4)	−0.002 (3)	0.009 (2)	−0.001 (3)
C11	0.036 (3)	0.061 (6)	0.061 (4)	−0.004 (3)	0.009 (3)	−0.003 (3)
C12	0.019 (3)	0.082 (6)	0.061 (4)	0.002 (3)	−0.002 (2)	−0.004 (4)
C13	0.038 (3)	0.076 (6)	0.054 (4)	0.014 (3)	−0.002 (3)	−0.003 (4)
C14	0.044 (4)	0.064 (6)	0.054 (4)	0.008 (3)	−0.002 (3)	0.003 (4)
C15	0.035 (3)	0.052 (5)	0.055 (4)	0.005 (2)	0.005 (3)	0.006 (3)
O3	0.101 (7)	0.105 (10)	0.108 (7)	−0.012 (5)	0.037 (6)	0.001 (6)
O4	0.111 (7)	0.066 (7)	0.089 (6)	0.016 (5)	0.022 (5)	0.002 (5)

Geometric parameters (Å, º) top

O1—C1	1.346 (18)	C5—C6	1.369 (10)
N1—C1	1.315 (13)	C6—C7	1.411 (9)
O2—C1	1.343 (18)	C7—C8	1.513 (10)
N2—C1	1.321 (13)	C8—C9	1.376 (8)
C1—N3	1.357 (10)	C9—C10	1.459 (10)
N3—C15	1.447 (9)	C10—C15	1.401 (11)
N3—C2	1.450 (9)	C10—C11	1.442 (9)
C2—C7	1.382 (11)	C11—C12	1.358 (11)
C2—C3	1.423 (10)	C12—C13	1.409 (12)
C3—C4	1.460 (11)	C13—C14	1.396 (11)
C4—C5	1.344 (12)	C14—C15	1.407 (10)

N2—C1—O2	124.0 (11)	C2—C7—C6	117.1 (6)
N1—C1—O1	124.8 (12)	C2—C7—C8	121.6 (6)
N1—C1—N3	119.9 (8)	C6—C7—C8	121.2 (7)
N2—C1—N3	120.2 (8)	C9—C8—C7	128.0 (7)
O2—C1—N3	115.8 (10)	C8—C9—C10	124.0 (7)
O1—C1—N3	115.3 (11)	C15—C10—C11	115.8 (6)
C1—N3—C15	120.3 (6)	C15—C10—C9	125.6 (6)
C1—N3—C2	121.9 (5)	C11—C10—C9	118.4 (7)
C15—N3—C2	117.8 (7)	C12—C11—C10	123.4 (8)
C7—C2—C3	121.1 (6)	C11—C12—C13	119.5 (6)
C7—C2—N3	119.2 (6)	C14—C13—C12	119.1 (6)
C3—C2—N3	119.7 (7)	C13—C14—C15	120.8 (8)
C2—C3—C4	118.5 (7)	C10—C15—C14	121.1 (7)
C5—C4—C3	119.1 (7)	C10—C15—N3	117.2 (6)
C4—C5—C6	120.9 (7)	C14—C15—N3	121.7 (8)
C5—C6—C7	123.3 (7)

(CBZIII) top

Crystal data top

C₁₅H₁₂N₂O	F(000) = 197
M_r = 236.27	D_x = 1.315 Mg m⁻³
Monoclinic, P2₁/n	Electron radiation, λ = 0.02508 Å
a = 7.614 (2) Å	Cell parameters from 1362 reflections
b = 11.302 (2) Å	θ = 0.1–1.8°
c = 13.886 (3) Å	µ = 0.000 mm⁻¹
β = 92.43 (3)°	T = 100 K
V = 1193.9 (5) Å³	Block, colourless
Z = 4	0.002 × 0.001 × 0.001 mm

Data collection top

FEI Tecnai F20 @ 200 keV w TVIPS F816 camera. diffractometer	R_int = 0.258
Radiation source: electron	θ_max = 1.0°, θ_min = 0.1°
continuous rotation (3DED) scans	h = −8→7
2523 measured reflections	k = −12→12
1362 independent reflections	l = −17→16
754 reflections with I > 2σ(I)

Refinement top

Refinement on F²	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F² > 2σ(F²)] = 0.197	w = 1/[σ²(F_o²) + (0.2P)²] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.542	(Δ/σ)_max = 0.003
S = 1.63	Δρ_max = 0.14 e Å⁻³
1362 reflections	Δρ_min = −0.15 e Å⁻³
162 parameters	Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
111 restraints	Extinction coefficient: 5297 (16)
Primary atom site location: SHELXT 2014/5 (Sheldrick, 2014)

Special details top

Refinement. electron diffraction data. SFAC from Table 4 of Doyle and Turner (1968).

Checkcif output with comments:

RINTA01_ALERT_3_A The value of Rint is greater than 0.25 Rint given 0.258 PLAT020_ALERT_3_A The Value of Rint is Greater Than 0.12 ········· 0.258 Report PLAT084_ALERT_3_A High wR2 Value (i.e. > 0.25) ··················. 0.54 Report

Data collected on only one crystal and therefore merging was not possible and as only Phi scan available due to nature of the TEM data collection, this leads to low completeness. Higher R factors expected due to electrons strong interaction.

PLAT082_ALERT_2_B High R1 Value ·································. 0.20 Report

Typical values for electron data without accounting for dynamical effects.

PLAT201_ALERT_2_B Isotropic non-H Atoms in Main Residue(s) ······. 1 Report C14

Due to low completeness (see above) anisotropic refinement was not possible for all atoms. Merging multiple datasets would have improved the statistics but as there was only one crystal of CBZIII, this was not possible.

PLAT340_ALERT_3_B Low Bond Precision on C-C Bonds ··············· 0.0176 Ang.

Merging multiple datasets would have improved the statistics but as there was only one crystal of CBZIII, this was not possible.

PLAT351_ALERT_3_B Long C-H (X0.96,N1.08A) C2 - H2 . 1.18 Ang. PLAT351_ALERT_3_B Long C-H (X0.96,N1.08A) C3 - H3 . 1.18 Ang. PLAT351_ALERT_3_B Long C-H (X0.96,N1.08A) C4 - H4 . 1.18 Ang. PLAT351_ALERT_3_B Long C-H (X0.96,N1.08A) C5 - H5 . 1.18 Ang. PLAT351_ALERT_3_B Long C-H (X0.96,N1.08A) C8 - H8 . 1.18 Ang. PLAT351_ALERT_3_B Long C-H (X0.96,N1.08A) C12 - H12 . 1.18 Ang. PLAT351_ALERT_3_B Long C-H (X0.96,N1.08A) C13 - H13 . 1.18 Ang. PLAT353_ALERT_3_B Long N-H (N0.87,N1.01A) N2 - H2A . 1.17 Ang. PLAT353_ALERT_3_B Long N-H (N0.87,N1.01A) N2 - H2B . 1.17 Ang.

NH and CH distances were constrained to typical electron CH and NH distances from the structure determination of glycine from electron diffraction data. refcode = KUFDOH

PLAT242_ALERT_2_C Low 'MainMol' Ueq as Compared to Neighbors of C14 Check PLAT351_ALERT_3_C Long C-H (X0.96,N1.08A) C10 - H10 . 1.13 Ang. PLAT420_ALERT_2_C D-H Bond Without Acceptor N2 –H2B . Please Check

Correct, no action taken.

ABSMU01_ALERT_1_G Calculation of _exptl_absorpt_correction_mu not performed for this radiation type.

Not usually performed for electron diffraction data.

PLAT007_ALERT_5_G Number of Unrefined Donor-H Atoms ············.. 2 Report PLAT012_ALERT_1_G N.O.K. _shelx_res_checksum Found in CIF ······ Please Check PLAT013_ALERT_1_G No _shelx_hkl_checksum Found in CIF ······ Please Check

Correct.

PLAT187_ALERT_4_G The CIF-Embedded .res File Contains RIGU Records 1 Report PLAT333_ALERT_2_G Large Aver C6-Ring C-C Dist C9 -C14 . 1.42 Ang. PLAT802_ALERT_4_G CIF Input Record(s) with more than 80 Characters 28 Info PLAT860_ALERT_3_G Number of Least-Squares Restraints ············. 111 Note PLAT933_ALERT_2_G Number of OMIT Records in Embedded .res File ··· 4 Note PLAT941_ALERT_3_G Average HKL Measurement Multiplicity ·········.. 1.9 Low

No action taken.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
O1	−0.0112 (12)	0.1241 (9)	0.4088 (6)	0.044 (2)
N1	0.2040 (14)	0.2620 (11)	0.4372 (8)	0.053 (3)
N2	0.1827 (15)	0.1003 (11)	0.5354 (9)	0.057 (3)
H2A	0.115005	0.012087	0.557050	0.068*
H2B	0.304468	0.135417	0.580833	0.068*
C1	0.1671 (15)	0.3301 (11)	0.3459 (8)	0.047 (3)
C2	0.0077 (16)	0.3888 (14)	0.3276 (10)	0.060 (4)
H2	−0.100055	0.384959	0.386563	0.072*
C3	−0.0289 (16)	0.4500 (11)	0.2449 (9)	0.053 (3)
H3	−0.162934	0.502430	0.234126	0.064*
C4	0.0948 (17)	0.4505 (14)	0.1719 (10)	0.059 (3)
H4	0.064555	0.494685	0.095712	0.071*
C5	0.2587 (15)	0.3942 (10)	0.1961 (8)	0.044 (3)
H5	0.369949	0.398813	0.139183	0.053*
C6	0.2961 (16)	0.3349 (12)	0.2813 (9)	0.051 (3)
C7	0.4690 (17)	0.2774 (15)	0.2962 (9)	0.064 (4)
H7	0.522 (5)	0.242 (3)	0.230 (5)	0.077*
C8	0.5739 (17)	0.2596 (11)	0.3748 (9)	0.051 (3)
H8	0.706935	0.206853	0.367254	0.062*
C9	0.5274 (16)	0.3047 (12)	0.4716 (8)	0.051 (3)
C10	0.6608 (16)	0.3320 (11)	0.5383 (8)	0.048 (3)
H10	0.801 (8)	0.3131 (14)	0.5204 (13)	0.057*
C11	0.6257 (18)	0.3842 (13)	0.6305 (10)	0.056 (3)
H11	0.730 (8)	0.414 (2)	0.678 (4)	0.067*
C12	0.4515 (15)	0.3939 (11)	0.6553 (10)	0.053 (3)
H12	0.420599	0.432417	0.732074	0.064*
C13	0.3090 (18)	0.3594 (13)	0.5922 (9)	0.057 (3)
H13	0.162324	0.368866	0.616227	0.068*
C14	0.3451 (13)	0.3126 (10)	0.4986 (7)	0.037 (2)*
C15	0.1190 (16)	0.1631 (12)	0.4563 (8)	0.049 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.051 (5)	0.048 (7)	0.034 (4)	−0.006 (3)	0.005 (3)	0.007 (3)
N1	0.053 (6)	0.051 (8)	0.054 (5)	−0.003 (4)	0.001 (4)	0.013 (4)
N2	0.052 (7)	0.054 (8)	0.064 (6)	−0.012 (4)	−0.003 (4)	0.013 (5)
C1	0.060 (6)	0.033 (8)	0.049 (5)	0.002 (4)	0.018 (4)	0.001 (4)
C2	0.049 (7)	0.070 (11)	0.062 (7)	0.002 (5)	0.019 (5)	0.031 (6)
C3	0.059 (7)	0.042 (9)	0.061 (7)	0.008 (5)	0.016 (5)	0.012 (6)
C4	0.062 (7)	0.060 (12)	0.056 (7)	0.003 (5)	0.011 (5)	0.005 (6)
C5	0.064 (6)	0.027 (8)	0.043 (5)	−0.009 (4)	0.018 (4)	0.002 (4)
C6	0.058 (6)	0.047 (9)	0.050 (5)	−0.015 (4)	0.011 (4)	0.010 (5)
C7	0.053 (7)	0.097 (14)	0.043 (5)	−0.003 (5)	0.015 (4)	0.013 (6)
C8	0.073 (8)	0.030 (8)	0.051 (5)	0.006 (4)	0.003 (4)	−0.006 (4)
C9	0.061 (7)	0.049 (9)	0.044 (5)	0.011 (4)	0.001 (4)	−0.004 (5)
C10	0.067 (8)	0.026 (8)	0.049 (5)	−0.012 (4)	0.003 (4)	0.013 (4)
C11	0.066 (7)	0.049 (10)	0.052 (6)	−0.003 (4)	−0.003 (5)	−0.005 (5)
C12	0.066 (7)	0.029 (9)	0.064 (7)	−0.005 (4)	−0.011 (5)	0.004 (5)
C13	0.064 (7)	0.053 (9)	0.053 (7)	−0.027 (5)	0.003 (5)	0.012 (6)
C15	0.059 (7)	0.048 (8)	0.039 (5)	−0.006 (4)	0.002 (4)	−0.005 (4)

Geometric parameters (Å, º) top

O1—C15	1.248 (15)	C5—H5	1.1840
N1—C15	1.324 (16)	C6—C7	1.475 (19)
N1—C14	1.460 (15)	C7—C8	1.339 (18)
N1—C1	1.500 (15)	C7—H7	1.09 (8)
N2—C15	1.379 (17)	C8—C9	1.495 (16)
N2—H2A	1.1680	C8—H8	1.1840
N2—H2B	1.1680	C9—C10	1.380 (18)
C1—C6	1.359 (14)	C9—C14	1.456 (15)
C1—C2	1.397 (18)	C10—C11	1.444 (18)
C2—C3	1.360 (17)	C10—H10	1.13 (6)
C2—H2	1.1840	C11—C12	1.389 (17)
C3—C4	1.412 (17)	C11—H11	1.06 (8)
C3—H3	1.1840	C12—C13	1.420 (17)
C4—C5	1.428 (19)	C12—H12	1.1840
C4—H4	1.1840	C13—C14	1.440 (17)
C5—C6	1.378 (17)	C13—H13	1.1840

C15—N1—C14	124.6 (10)	C6—C7—H7	113.6
C15—N1—C1	121.8 (11)	C7—C8—C9	121.7 (11)
C14—N1—C1	113.5 (9)	C7—C8—H8	119.1
C15—N2—H2A	120.0	C9—C8—H8	119.1
C15—N2—H2B	120.0	C10—C9—C14	119.7 (11)
H2A—N2—H2B	120.0	C10—C9—C8	119.0 (10)
C6—C1—C2	120.5 (12)	C14—C9—C8	121.1 (11)
C6—C1—N1	117.6 (10)	C9—C10—C11	121.8 (11)
C2—C1—N1	121.8 (9)	C9—C10—H10	119.1
C3—C2—C1	122.7 (10)	C11—C10—H10	119.1
C3—C2—H2	118.7	C12—C11—C10	117.8 (12)
C1—C2—H2	118.7	C12—C11—H11	121.1
C2—C3—C4	119.3 (11)	C10—C11—H11	121.1
C2—C3—H3	120.4	C11—C12—C13	122.5 (13)
C4—C3—H3	120.4	C11—C12—H12	118.7
C3—C4—C5	115.6 (12)	C13—C12—H12	118.7
C3—C4—H4	122.2	C12—C13—C14	119.2 (12)
C5—C4—H4	122.2	C12—C13—H13	120.4
C6—C5—C4	124.4 (10)	C14—C13—H13	120.4
C6—C5—H5	117.8	C13—C14—C9	118.4 (10)
C4—C5—H5	117.8	C13—C14—N1	120.5 (9)
C1—C6—C5	117.2 (12)	C9—C14—N1	120.8 (10)
C1—C6—C7	123.7 (12)	O1—C15—N1	125.2 (12)
C5—C6—C7	119.1 (10)	O1—C15—N2	119.0 (11)
C8—C7—C6	132.7 (12)	N1—C15—N2	115.8 (11)
C8—C7—H7	113.6

C15—N1—C1—C6	−113.1 (15)	C14—C9—C10—C11	−8.7 (18)
C14—N1—C1—C6	64.5 (15)	C8—C9—C10—C11	175.3 (13)
C15—N1—C1—C2	68.1 (19)	C9—C10—C11—C12	7.3 (18)
C14—N1—C1—C2	−114.4 (14)	C10—C11—C12—C13	−2.7 (19)
C6—C1—C2—C3	2 (2)	C11—C12—C13—C14	0 (2)
N1—C1—C2—C3	−179.4 (14)	C12—C13—C14—C9	−1.1 (18)
C1—C2—C3—C4	3 (3)	C12—C13—C14—N1	171.9 (11)
C2—C3—C4—C5	−6 (2)	C10—C9—C14—C13	5.5 (18)
C3—C4—C5—C6	4 (2)	C8—C9—C14—C13	−178.6 (12)
C2—C1—C6—C5	−3 (2)	C10—C9—C14—N1	−167.5 (11)
N1—C1—C6—C5	177.8 (12)	C8—C9—C14—N1	8.4 (17)
C2—C1—C6—C7	178.8 (15)	C15—N1—C14—C13	−67.4 (18)
N1—C1—C6—C7	0 (2)	C1—N1—C14—C13	115.2 (12)
C4—C5—C6—C1	0 (2)	C15—N1—C14—C9	105.5 (14)
C4—C5—C6—C7	178.2 (13)	C1—N1—C14—C9	−72.0 (14)
C1—C6—C7—C8	−36 (3)	C14—N1—C15—O1	173.7 (10)
C5—C6—C7—C8	146.6 (16)	C1—N1—C15—O1	−9 (2)
C6—C7—C8—C9	−2 (3)	C14—N1—C15—N2	−6.3 (19)
C7—C8—C9—C10	−151.6 (14)	C1—N1—C15—N2	170.9 (10)
C7—C8—C9—C14	32.5 (19)

(CBZIV) top

Crystal data top

C₁₅H₁₂N₂O	F(000) = 394
M_r = 236.27	D_x = 1.198 Mg m⁻³
Monoclinic, C2/c	Electron radiation, λ = 0.02508 Å
a = 27.150 (5) Å	Cell parameters from 1645 reflections
b = 7.3000 (15) Å	θ = 0.1–1.8°
c = 14.100 (3) Å	µ = 0.000 mm⁻¹
β = 110.30 (3)°	T = 100 K
V = 2621.0 (10) Å³	Block, colourless
Z = 8	0.002 × 0.001 × 0.00003 mm

Data collection top

FEI Tecnai F20 @ 200 keV w TVIPS F816 camera. diffractometer	R_int = 0.230
Radiation source: electron	θ_max = 0.9°, θ_min = 0.1°
continuous rotation (3DED) scans	h = −32→31
4267 measured reflections	k = −6→7
1645 independent reflections	l = −16→16
738 reflections with I > 2σ(I)

Refinement top

Refinement on F²	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H atoms treated by a mixture of independent and constrained refinement
R[F² > 2σ(F²)] = 0.199	w = 1/[σ²(F_o²) + (0.2P)²] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.481	(Δ/σ)_max < 0.001
S = 1.21	Δρ_max = 0.14 e Å⁻³
1645 reflections	Δρ_min = −0.17 e Å⁻³
171 parameters	Extinction correction: SHELXL-2018/3 (Sheldrick 2018), Fc^*=kFc[1+0.001xFc²λ³/sin(2θ)]^-1/4
144 restraints	Extinction coefficient: 361 (46)
Primary atom site location: SHELXT 2014/5 (Sheldrick, 2014)

Special details top

Refinement. electron diffraction data. SFAC from Table 4 of Doyle and Turner (1968).

The structure was refined using starting atomic coordinates from CBMZPN12 and refined using the kinematic approximation in Shelxl. Use of this approximation means that data-fitting statistics (R-factors etc.) are much higher than is usual with X-ray or neutron data.

Checkcif output with comments:

PLAT084_ALERT_3_A High wR2 Value (i.e. > 0.25) ··················. 0.48 Report

Typical values for electron data without accounting for dynamical effects.

RINTA01_ALERT_3_B The value of Rint is greater than 0.18 Rint given 0.230 PLAT020_ALERT_3_B The Value of Rint is Greater Than 0.12 ········· 0.230 Report PLAT082_ALERT_2_B High R1 Value ·································. 0.20 Report

Typical values for electron data without accounting for dynamical effects.

PLAT340_ALERT_3_B Low Bond Precision on C-C Bonds ··············· 0.01513 Ang.

Merging multiple datasets would have improved the statistics but as there were only two crystals of CBZIV, this was not possible.

PLAT351_ALERT_3_B Long C-H (X0.96,N1.08A) C6 - H6 . 1.17 Ang. PLAT351_ALERT_3_B Long C-H (X0.96,N1.08A) C8 - H8 . 1.17 Ang. PLAT351_ALERT_3_B Long C-H (X0.96,N1.08A) C9 - H9 . 1.17 Ang. PLAT351_ALERT_3_B Long C-H (X0.96,N1.08A) C11 - H11 . 1.17 Ang. PLAT351_ALERT_3_B Long C-H (X0.96,N1.08A) C12 - H12 . 1.17 Ang.

CH distances were constrained to typical electron CH distances from the structure determination of glycine from electron diffraction data. refcode = KUFDOH

PLAT213_ALERT_2_C Atom C12 has ADP max/min Ratio ···.. 3.2 prolat

Due to low completeness (see above) anisotropic refinement was not possible for all atoms. Merging multiple datasets would have improved the statistics but as there was only two crystals of CBZIV, this was not possible.

PLAT250_ALERT_2_C Large U3/U1 Ratio for Average U(i,j) Tensor ···. 2.5 Note PLAT351_ALERT_3_C Long C-H (X0.96,N1.08A) C3 - H3 . 1.14 Ang. PLAT351_ALERT_3_C Long C-H (X0.96,N1.08A) C4 - H4 . 1.16 Ang. PLAT351_ALERT_3_C Long C-H (X0.96,N1.08A) C5 - H5 . 1.16 Ang. PLAT420_ALERT_2_C D-H Bond Without Acceptor N1 –H1B . Please Check

Correct, no action taken.

ABSMU01_ALERT_1_G Calculation of _exptl_absorpt_correction_mu not performed for this radiation type.

Not usually performed for electron diffraction data.

PLAT013_ALERT_1_G No _shelx_hkl_checksum Found in CIF ······ Please Check

Correct.

PLAT128_ALERT_4_G Alternate Setting for Input Space Group C2/c I2/a Note PLAT180_ALERT_4_G Check Cell Rounding: # of Values Ending with 0 = 4 Note PLAT187_ALERT_4_G The CIF-Embedded .res File Contains RIGU Records 1 Report PLAT333_ALERT_2_G Large Aver C6-Ring C-C Dist C10 -C15 . 1.43 Ang. PLAT802_ALERT_4_G CIF Input Record(s) with more than 80 Characters 23 Info PLAT860_ALERT_3_G Number of Least-Squares Restraints ············. 144 Note PLAT941_ALERT_3_G Average HKL Measurement Multiplicity ·········.. 2.6 Low

No action taken.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq
O1	0.0722 (3)	−0.0037 (14)	0.0362 (6)	0.059 (2)
N1	0.0148 (3)	0.1824 (17)	−0.0823 (6)	0.069 (3)
H1A	−0.0165 (15)	0.125 (3)	−0.0742 (7)	0.083*
H1B	0.0105 (4)	0.284 (5)	−0.131 (2)	0.083*
N2	0.1068 (3)	0.2281 (15)	−0.0352 (6)	0.055 (3)
C1	0.0640 (3)	0.1218 (18)	−0.0260 (6)	0.052 (3)
C2	0.1603 (3)	0.1682 (16)	0.0148 (6)	0.050 (3)
C3	0.1847 (3)	0.2063 (16)	0.1172 (6)	0.054 (3)
H3	0.1638 (9)	0.291 (4)	0.1592 (18)	0.065*
C4	0.2359 (3)	0.1383 (18)	0.1683 (7)	0.061 (3)
H4	0.2568 (10)	0.174 (2)	0.253 (4)	0.073*
C5	0.2626 (4)	0.0260 (17)	0.1176 (8)	0.062 (3)
H5	0.3035 (19)	−0.037 (3)	0.161 (2)	0.074*
C6	0.2381 (3)	−0.0046 (16)	0.0147 (8)	0.060 (3)
H6	0.260427	−0.086806	−0.028840	0.072*
C7	0.1859 (3)	0.0615 (14)	−0.0402 (6)	0.047 (2)
C8	0.1643 (4)	0.0228 (18)	−0.1493 (8)	0.066 (3)
H8	0.178685	−0.109848	−0.178091	0.079*
C9	0.1274 (4)	0.135 (2)	−0.2220 (6)	0.072 (3)
H9	0.1123 (9)	0.076 (4)	−0.304 (4)	0.086*
C10	0.1049 (3)	0.3155 (18)	−0.2095 (5)	0.063 (3)
C11	0.0911 (4)	0.451 (2)	−0.2879 (8)	0.083 (4)
H11	0.094695	0.414017	−0.365774	0.099*
C12	0.0734 (4)	0.626 (2)	−0.2752 (7)	0.078 (3)
H12	0.062721	0.728121	−0.343207	0.093*
C13	0.0677 (4)	0.687 (2)	−0.1821 (8)	0.083 (4)
H13	0.0553 (11)	0.817 (10)	−0.1727 (11)	0.100*
C14	0.0807 (4)	0.5501 (17)	−0.1035 (7)	0.066 (3)
H14	0.0775 (4)	0.585 (3)	−0.032 (4)	0.079*
C15	0.0978 (3)	0.3695 (18)	−0.1171 (6)	0.056 (3)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
O1	0.049 (4)	0.080 (7)	0.047 (4)	0.001 (3)	0.015 (3)	0.031 (4)
N1	0.046 (4)	0.093 (10)	0.057 (5)	−0.009 (4)	0.006 (3)	0.048 (6)
N2	0.050 (3)	0.075 (8)	0.040 (4)	−0.003 (3)	0.017 (2)	0.028 (4)
C1	0.045 (4)	0.068 (8)	0.042 (4)	−0.005 (4)	0.013 (3)	0.023 (5)
C2	0.057 (4)	0.056 (9)	0.036 (4)	−0.004 (4)	0.017 (3)	0.010 (4)
C3	0.051 (4)	0.077 (11)	0.034 (4)	0.000 (4)	0.013 (3)	0.003 (5)
C4	0.061 (5)	0.065 (10)	0.056 (5)	0.000 (5)	0.020 (4)	0.008 (6)
C5	0.063 (5)	0.058 (9)	0.065 (5)	−0.007 (5)	0.022 (4)	0.001 (6)
C6	0.066 (5)	0.057 (10)	0.068 (5)	−0.014 (4)	0.037 (4)	−0.007 (5)
C7	0.080 (5)	0.020 (8)	0.045 (4)	−0.017 (4)	0.027 (3)	−0.003 (4)
C8	0.094 (7)	0.055 (10)	0.053 (5)	−0.019 (4)	0.030 (4)	−0.029 (5)
C9	0.098 (7)	0.084 (9)	0.027 (4)	−0.041 (5)	0.015 (4)	−0.023 (5)
C10	0.084 (6)	0.079 (9)	0.020 (4)	−0.028 (5)	0.009 (3)	0.000 (4)
C11	0.107 (8)	0.099 (10)	0.035 (5)	−0.043 (6)	0.014 (5)	0.010 (6)
C12	0.091 (7)	0.086 (10)	0.046 (5)	−0.032 (6)	0.011 (4)	0.040 (6)
C13	0.105 (8)	0.074 (10)	0.060 (5)	−0.025 (6)	0.016 (5)	0.029 (6)
C14	0.088 (6)	0.068 (8)	0.037 (5)	−0.009 (5)	0.016 (4)	0.013 (5)
C15	0.074 (5)	0.066 (8)	0.027 (4)	−0.013 (4)	0.018 (3)	0.017 (4)

Geometric parameters (Å, º) top

O1—C1	1.234 (13)	C6—H6	1.1680
N1—C1	1.368 (12)	C7—C8	1.471 (13)
N1—H1A	0.99 (4)	C8—C9	1.417 (17)
N1—H1B	0.99 (4)	C8—H8	1.1680
N2—C1	1.440 (12)	C9—C10	1.491 (18)
N2—C2	1.445 (11)	C9—H9	1.16 (6)
N2—C15	1.505 (13)	C10—C11	1.435 (15)
C2—C3	1.393 (11)	C10—C15	1.436 (12)
C2—C7	1.437 (13)	C11—C12	1.396 (19)
C3—C4	1.415 (12)	C11—H11	1.1680
C3—H3	1.13 (4)	C12—C13	1.444 (16)
C4—C5	1.438 (16)	C12—H12	1.1680
C4—H4	1.16 (5)	C13—C14	1.442 (15)
C5—C6	1.389 (14)	C13—H13	1.03 (7)
C5—H5	1.16 (5)	C14—C15	1.432 (16)
C6—C7	1.440 (14)	C14—H14	1.08 (6)

C1—N1—H1A	120.0	C6—C7—C8	117.2 (8)
C1—N1—H1B	120.0	C9—C8—C7	124.8 (11)
H1A—N1—H1B	120.0	C9—C8—H8	117.6
C1—N2—C2	120.0 (10)	C7—C8—H8	117.6
C1—N2—C15	121.2 (7)	C8—C9—C10	129.8 (8)
C2—N2—C15	116.7 (7)	C8—C9—H9	115.1
O1—C1—N1	123.6 (8)	C10—C9—H9	115.1
O1—C1—N2	120.7 (8)	C11—C10—C15	115.3 (13)
N1—C1—N2	115.4 (11)	C11—C10—C9	122.0 (10)
C3—C2—C7	121.5 (8)	C15—C10—C9	122.7 (10)
C3—C2—N2	118.7 (8)	C12—C11—C10	122.9 (11)
C7—C2—N2	119.7 (8)	C12—C11—H11	118.6
C2—C3—C4	119.2 (9)	C10—C11—H11	118.6
C2—C3—H3	120.4	C11—C12—C13	123.2 (11)
C4—C3—H3	120.4	C11—C12—H12	118.4
C3—C4—C5	121.5 (9)	C13—C12—H12	118.4
C3—C4—H4	119.3	C14—C13—C12	114.2 (13)
C5—C4—H4	119.3	C14—C13—H13	122.9
C6—C5—C4	118.0 (9)	C12—C13—H13	122.9
C6—C5—H5	121.0	C15—C14—C13	122.6 (10)
C4—C5—H5	121.0	C15—C14—H14	118.7
C5—C6—C7	122.2 (8)	C13—C14—H14	118.7
C5—C6—H6	118.9	C14—C15—C10	121.7 (10)
C7—C6—H6	118.9	C14—C15—N2	120.1 (8)
C2—C7—C6	117.5 (7)	C10—C15—N2	118.1 (11)
C2—C7—C8	125.2 (8)

C2—N2—C1—O1	11.4 (16)	C6—C7—C8—C9	−150.8 (10)
C15—N2—C1—O1	174.2 (11)	C7—C8—C9—C10	4.6 (16)
C2—N2—C1—N1	−175.2 (9)	C8—C9—C10—C11	147.0 (10)
C15—N2—C1—N1	−12.4 (15)	C8—C9—C10—C15	−30.1 (15)
C1—N2—C2—C3	−81.1 (13)	C15—C10—C11—C12	1.9 (13)
C15—N2—C2—C3	115.4 (11)	C9—C10—C11—C12	−175.4 (9)
C1—N2—C2—C7	95.0 (12)	C10—C11—C12—C13	0.3 (15)
C15—N2—C2—C7	−68.5 (13)	C11—C12—C13—C14	−1.3 (13)
C7—C2—C3—C4	0.0 (16)	C12—C13—C14—C15	−0.1 (13)
N2—C2—C3—C4	176.1 (10)	C13—C14—C15—C10	2.4 (14)
C2—C3—C4—C5	−2.0 (16)	C13—C14—C15—N2	−175.2 (8)
C3—C4—C5—C6	4.1 (16)	C11—C10—C15—C14	−3.2 (12)
C4—C5—C6—C7	−4.3 (16)	C9—C10—C15—C14	174.1 (8)
C3—C2—C7—C6	−0.1 (15)	C11—C10—C15—N2	174.4 (7)
N2—C2—C7—C6	−176.2 (10)	C9—C10—C15—N2	−8.3 (11)
C3—C2—C7—C8	−176.7 (10)	C1—N2—C15—C14	83.4 (13)
N2—C2—C7—C8	7.3 (15)	C2—N2—C15—C14	−113.3 (10)
C5—C6—C7—C2	2.4 (15)	C1—N2—C15—C10	−94.2 (12)
C5—C6—C7—C8	179.2 (9)	C2—N2—C15—C10	69.1 (11)
C2—C7—C8—C9	25.8 (15)

Acknowledgements

We would like to thank Maarten Tuijtel for help in the preliminary work setting up the 3D ED experiments and Lorna Eades for help with the ICP experiments. We would also like to thank Prof Xiaodong Zou (Department of Materials and Environmental Chemistry, Stockholm University, Sweden) for helpful discussions regarding the manuscript. ETB, SP and FN conceived the project. ETB undertook experimental work, assisted by HX. ETB analysed the data, both crystallographic and imaging under guidance of SP and FN. All authors were responsible for writing the manuscript.

Funding information

The following funding is acknowledged: Engineering and Physical Sciences Research Council (grant No. EP-M506515-1 awarded to ETB); Wellcome Trust (grant No. WT087658).

References

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IUCrJ

Volume 8| Part 6| November 2021| Pages 860-866

ISSN: 2052-2525

https://doi.org/10.1107/S2052252521010101

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research letters\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Revealing the early stages of carbamazepine crystallization by cryoTEM and 3D electron diffraction

1. Introduction

2. Experimental

3. Results and discussion

4. Conclusions

5. Related literature

Supporting information

Acknowledgements

Funding information

References

research letters