Crystal structure and Hirshfeld surface analysis of the salt 2-iodo­ethyl­ammonium iodide – a possible side product upon synthesis of hybrid perovskites

Petrosova, H.R.; Naumova, D.D.; Golenya, I.A.; Buta, I.; Gural'skiy, I.A.

doi:10.1107/S205698902401034X

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Volume 80| Part 11| November 2024| Pages 1226-1229

https://doi.org/10.1107/S205698902401034X

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Crystal structure and Hirshfeld surface analysis of the salt 2-iodoethylammonium iodide – a possible side product upon synthesis of hybrid perovskites

Hanna R. Petrosova,^a ^* Dina D. Naumova,^a Irina A. Golenya,^a Ildiko Buta ^b and Il'ya A. Gural'skiy ^a

^aDepartment of Chemistry, Taras Shevchenko National University of Kyiv, Volodymyrska St. 64, Kyiv 01601, Ukraine, and ^b"Coriolan Dragulescu" Institute of Chemistry, Mihai Viteazu Bvd. 24, Timisoara 300223, Romania
^*Correspondence e-mail: anna.petrosova@knu.ua

Edited by M. Weil, Vienna University of Technology, Austria (Received 8 October 2024; accepted 23 October 2024; online 31 October 2024)

The title organic–inorganic hybrid salt, C₂H₇IN⁺·I⁻, is isotypic with its bromine analog, C₂H₇BrN⁺·Br⁻ [Semenikhin et al. (2024 ). Acta Cryst. E80, 738–741]. Its asymmetric unit consists of one 2-iodoethylammonium cation and one iodide anion. The NH₃⁺ group of the organic cation forms weak hydrogen bonds with four neighboring iodide anions, leading to the formation of supramolecular layers propagating parallel to the bc plane. Hirshfeld surface analysis reveals that the most important contribution to the crystal packing is from N—H⋯I interactions (63.8%). The crystal under investigation was twinned by a 180° rotation around [001].

Keywords: crystal structure; organic cation; ammonium salt; iodide; hydrogen bonding.

CCDC reference: 2393092

1. Chemical context

Hybrid organic–inorganic perovskites are known for their interesting semiconducting and optical properties, which allow their application in photovoltaic and optoelectronic devices (Younis et al., 2021 ). At the same time, hybrid perovskites create an equally fascinating background for fundamental studies by forming numerous structural motifs of different periodicities.

Even though the structure type perovskite usually refers to inorganic compounds with composition ABX₃ (Li et al., 2017 ), recent developments in this field led to ‘hybrid organic-inorganic perovskites’, which contain discrete or fused [BX₆]ⁿ⁻ octahedral building units of inorganic nature, the charge of which is compensated by organic cations. The corresponding octahedra can be connected to each other in various ways, resulting in frameworks with different periodicity (Han et al., 2021 ).

However, an important issue that demands extra caution upon work with hybrid perovskites is their stability. These materials are very sensitive to water vapor, which can cause their immediate degradation to different products including inorganic salts such as BX₂ and organic salts AX.

Here we report on synthesis and crystal structure of the organic–inorganic hybrid salt 2-iodoethylammonim iodide, C₂H₇IN⁺·I. The 2-iodoethylammonim cation has previously been incorporated into some hybrid perovskites with layered arrangements (Xue et al., 2023 ; Skorokhod et al., 2023 ). In addition, 2-iodoethylammonim can be formed as a result of aziridine ring-opening reaction upon synthesis of aziridinium perovskites (Kucheriv et al., 2023 ; Petrosova et al., 2022 ). Therefore, the reported structural data of the title compound are valuable for phase analysis, since such a phase can be a side product in the synthesis of hybrid perovskites with 2-iodoethylammonium or aziridinium cations.

2. Structural commentary

The asymmetric unit consists of one organic 2-iodoethylammonium cation and an iodide counter-ion (Fig. 1). The I1—C1 bond length is 2.170 (10) Å, that of C1—C2 is 1.497 (14) Å and of C2—N1 is 1.514 (12) Å. The torsion angle I1—C1—C2—N1 is −65.8 (9)°, indicating that the organic cation adopts a synclinal conformation. It is worth noting, that the organic cation IC₂H₄NH₃⁺ has previously been reported in other crystal structures, but only as a part of hybrid organic–inorganic perovskites (see Database survey). The analysis of these structures reveals that this cation can adopt both synclinal and antiperiplanar conformations inside the inorganic frameworks depending on the strength and orientation of the hydrogen bonds formed (Xue et al., 2023).

Figure 1
The expanded asymmetric unit of the title compound showing hydrogen bonds between the organic cation and iodide anions (dotted lines). Displacement ellipsoids are drawn at the 50% probability level; symmetry codes refer to Table 1

3. Supramolecular features

Each 2-iodoethylammonium cation is connected to four different iodide anions through weak intermolecular N—H⋯I interactions (Fig. 1). Simultaneously, each iodide anion forms hydrogen bonds with four neighboring –NH₃⁺ groups of 2-iodoethylammonium cations, forming infinite supramolecular layers propagating parallel to the bc plane (Fig. 2). A view along the a axis of a single supramolecular layer is given in Fig. 3. Numerical parameters of the hydrogen-bonding interactions are compiled in Table 1.

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A	D—H	H⋯A	D⋯A	D—H⋯A
N1—H1A⋯I2ⁱ	0.84	2.74	3.517 (7)	155
N1—H1B⋯I2	0.84	2.85	3.618 (8)	153
N1—H1C⋯I2ⁱⁱ	0.84	2.96	3.627 (8)	139
N1—H1C⋯I2ⁱⁱⁱ	0.84	3.04	3.600 (8)	127
Symmetry codes: (i) ; (ii) $[x, -y+{\script{3\over 2}}, z-{\script{1\over 2}}]$ ; (iii) $[-x+1, y-{\script{1\over 2}}, -z+{\script{1\over 2}}]$ .

Figure 2
Crystal packing of the title compound in a view approximately along [010] showing infinite supramolecular layers propagating parallel to the bc plane.

Figure 3
A single supramolecular layer viewed along [100].

4. Hirshfeld surface analysis

Hirshfeld surface analysis (Hirshfeld, 1977 ; Spackman & Jayatilaka, 2009 ) was used to visualize and quantify intermolecular interactions in 2-iodoethylammonium iodide using CrystalExplorer (Spackman et al., 2021 ). The Hirshfeld surface plotted over d_norm and the two-dimensional fingerprint plots are given in Fig. 4. The surface shows the four N—H⋯I contacts described above as regions colored in red (Fig. 4a), where the color code denotes contacts with distances equal to the sum of the van der Waals radii as white, while those with shorter and longer distances are represented in red and blue, respectively. The two-dimensional fingerprint plots show that the most important interaction found in the structure is represented by N—H⋯I contacts, which account for 63.8% of all contacts observed in the crystal structure (Fig. 4b). The residual contributions originate from H⋯H interactions.

Figure 4
(a) Hirshfeld surface of the 2-iodoethylammonium cation plotted over d_norm, showing the strongest interactions with I⁻ anions (in red); (b) the two-dimensional fingerprint plots for 2-iodoethylammonium iodide (left) and delineated into N—H⋯I contacts (right).

5. Database survey

A search in the Cambridge Crystallographic Database (CSD, version 5.45, update of September 2024; Groom et al.. 2016 ) for the 2-iodoethylammonium cation revealed the following structures, which all are based on perovskite-type inorganic anions: JIGYEH, JIGYIL, JIGYUX (Skorokhod et al., 2023); SIWHIQ, TEYMIU (Sourisseau et al., 2007 ), TEGROQ (Song et al., 2022 ). The title compound is isotypic with 2-bromoethylammonium bromide (ZOTHAV; Semenikhin et al., 2024).

6. Synthesis and crystallization

All reagents were purchased from UkrOrgSynthez Ltd. and used as received. Aziridine (50 µl) was added to aqueous HI (57% w/w, 300 µl) and was left to crystallize at room temperature. Colorless crystals were harvested after one day and protected under Paratone^®oil.

7. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. The crystal under investigation was twinned by a 180° rotation around [001] and the intensity data processed into a HKLF5-type file; the twin components refined to a ratio of 0.617 (2):0.383 (2). Hydrogen atoms were placed at calculated positions with U_iso(H) = 1.2U_eq(C) and U_iso(H) = 1.5U_eq(N).

Table 2
Experimental details

Crystal data
Chemical formula	C₂H₇IN⁺·I⁻
M_r	298.89
Crystal system, space group	Monoclinic, P2₁/c
Temperature (K)	100
a, b, c (Å)	8.3073 (7), 8.8800 (6), 9.3838 (7)
β (°)	102.004 (7)
V (Å³)	677.10 (9)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	9.16
Crystal size (mm)	0.31 × 0.15 × 0.07

Data collection
Diffractometer	XtaLAB Synergy, Dualflex, HyPix
Absorption correction	Analytical (CrysAlis PRO; Rigaku OD, 2023 $[Rigaku OD (2023). CrysAlis PRO. Rigaku Oxford Diffraction, Yarnton, England.]$ )
T_min, T_max	0.157, 0.573
No. of measured, independent and observed [I > 2σ(I)] reflections	2744, 2744, 2535
(sin θ/λ)_max (Å⁻¹)	0.712

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.051, 0.159, 1.12
No. of reflections	2744
No. of parameters	49
H-atom treatment	H atoms treated by a mixture of independent and constrained refinement
Δρ_max, Δρ_min (e Å⁻³)	2.07, −1.68
Computer programs: CrysAlis PRO (Rigaku OD, 2023 $[Rigaku OD (2023). CrysAlis PRO. Rigaku Oxford Diffraction, Yarnton, England.]$ ), SHELXT (Sheldrick, 2015a ), SHELXL (Sheldrick, 2015b ), OLEX2 (Dolomanov et al., 2009 ) and publCIF (Westrip, 2010 ).

Supporting information

CCDC reference: 2393092

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S205698902401034X/wm5738sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S205698902401034X/wm5738Isup2.hkl

Supporting information file. DOI: https://doi.org/10.1107/S205698902401034X/wm5738Isup3.cml

checkCIF report

Computing details top

2-Iodoethylammonium iodide top

Crystal data top

C₂H₇IN⁺·I⁻	F(000) = 528
M_r = 298.89	D_x = 2.932 Mg m⁻³
Monoclinic, P2₁/c	Mo Kα radiation, λ = 0.71073 Å
a = 8.3073 (7) Å	Cell parameters from 3490 reflections
b = 8.8800 (6) Å	θ = 3.2–30.3°
c = 9.3838 (7) Å	µ = 9.16 mm⁻¹
β = 102.004 (7)°	T = 100 K
V = 677.10 (9) Å³	Plate, clear intense colourless
Z = 4	0.31 × 0.14 × 0.07 mm

Data collection top

XtaLAB Synergy, Dualflex, HyPix diffractometer	2744 independent reflections
Detector resolution: 10.0000 pixels mm^-1	2535 reflections with I > 2σ(I)
ω scans	θ_max = 30.4°, θ_min = 2.5°
Absorption correction: analytical (CrysAlisPro; Rigaku OD, 2023)	h = −11→10
T_min = 0.157, T_max = 0.573	k = −11→11
2744 measured reflections	l = −10→12

Refinement top

Refinement on F²	0 restraints
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F² > 2σ(F²)] = 0.051	H atoms treated by a mixture of independent and constrained refinement
wR(F²) = 0.159	w = 1/[σ²(F_o²) + (0.1098P)² + 4.1089P] where P = (F_o² + 2F_c²)/3
S = 1.12	(Δ/σ)_max < 0.001
2744 reflections	Δρ_max = 2.07 e Å⁻³
49 parameters	Δρ_min = −1.68 e Å⁻³

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. Refined as a 2-component twin.

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

	x	y	z	U_iso*/U_eq
I2	0.63381 (7)	0.78334 (6)	0.53313 (6)	0.0165 (2)
I1	0.19546 (8)	0.89307 (7)	0.17832 (7)	0.0224 (2)
N1	0.3819 (10)	0.5459 (8)	0.2618 (8)	0.0176 (15)
H1A	0.412 (3)	0.471 (7)	0.314 (7)	0.026*
H1B	0.417 (3)	0.624 (7)	0.307 (8)	0.026*
H1C	0.419 (3)	0.540 (8)	0.186 (6)	0.026*
C2	0.1958 (12)	0.5506 (11)	0.2219 (10)	0.0200 (18)
H2A	0.153639	0.449803	0.187631	0.024*
H2B	0.152455	0.575673	0.309573	0.024*
C1	0.1349 (13)	0.6643 (12)	0.1053 (10)	0.024 (2)
H1D	0.013934	0.654792	0.073950	0.028*
H1E	0.183992	0.642845	0.019956	0.028*

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
I2	0.0214 (4)	0.0135 (4)	0.0150 (4)	−0.00033 (17)	0.0051 (3)	0.00083 (17)
I1	0.0189 (4)	0.0192 (4)	0.0301 (4)	0.0035 (2)	0.0068 (3)	0.0037 (2)
N1	0.022 (4)	0.013 (3)	0.019 (4)	−0.002 (3)	0.006 (3)	0.001 (3)
C2	0.020 (4)	0.020 (5)	0.020 (5)	−0.001 (3)	0.003 (4)	0.003 (3)
C1	0.024 (5)	0.029 (5)	0.017 (4)	0.004 (4)	0.001 (4)	−0.005 (4)

Geometric parameters (Å, º) top

I1—C1	2.170 (10)	C2—H2A	0.9900
N1—H1A	0.84 (6)	C2—H2B	0.9900
N1—H1B	0.84 (6)	C2—C1	1.497 (14)
N1—H1C	0.84 (6)	C1—H1D	0.9900
N1—C2	1.514 (12)	C1—H1E	0.9900

H1A—N1—H1B	109.5	C1—C2—N1	111.9 (8)
H1A—N1—H1C	109.5	C1—C2—H2A	109.2
H1B—N1—H1C	109.5	C1—C2—H2B	109.2
C2—N1—H1A	109.5	I1—C1—H1D	109.1
C2—N1—H1B	109.5	I1—C1—H1E	109.1
C2—N1—H1C	109.5	C2—C1—I1	112.3 (6)
N1—C2—H2A	109.2	C2—C1—H1D	109.1
N1—C2—H2B	109.2	C2—C1—H1E	109.1
H2A—C2—H2B	107.9	H1D—C1—H1E	107.9

N1—C2—C1—I1	−65.8 (9)

Hydrogen-bond geometry (Å, º) top

D—H···A	D—H	H···A	D···A	D—H···A
N1—H1A···I2ⁱ	0.84	2.74	3.517 (7)	155
N1—H1B···I2	0.84	2.85	3.618 (8)	153
N1—H1C···I2ⁱⁱ	0.84	2.96	3.627 (8)	139
N1—H1C···I2ⁱⁱⁱ	0.84	3.04	3.600 (8)	127

Symmetry codes: (i) −x+1, −y+1, −z+1; (ii) x, −y+3/2, z−1/2; (iii) −x+1, y−1/2, −z+1/2.

Funding information

Funding for this research was provided by: Ministry of Education and Science of Ukraine (grant Nos. 24BF037-02 and 24BF037-01M).

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