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

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Crystal structure and Hirshfeld surface analysis of a supra­molecular aggregate of 4-formyl-N,N-di­methyl­anilinium bromide with tetra­bromo­methane

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aExcellence Center, Baku State University, Z. Khalilov Str. 23, AZ 1148 Baku, Azerbaijan, bHacettepe University, Department of Physics, 06800 Beytepe-Ankara, Türkiye, cDepartment of Chemistry, Baku State University, Z. Khalilov Str. 23, AZ 1148 Baku, Azerbaijan, dAzerbaijan Medical University, Scientific Research Centre (SRC), A. Kasumzade Str. 14, AZ 1022 Baku, Azerbaijan, eDepartment of Chemistry and Chemical Engineering, Khazar University, Mahsati Str. 41, AZ 1096 Baku, Azerbaijan, and fDepartment of Chemistry, Bahir Dar University, PO Box 79, Bahir Dar, Ethiopia
*Correspondence e-mail: [email protected]

Edited by S. Parkin, University of Kentucky, USA (Received 22 July 2025; accepted 1 August 2025; online 7 August 2025)

The title compound, C9H12NO+·Br·CBr4, consists of one 4-formyl-N,N-di­methyl­benzenaminium bromide and a tetra­bromo­methane mol­ecule. In the crystal, the bromide ions link 4-formyl-N,N-di­methyl­benzenaminium moieties through inter­molecular C—H⋯Br and N—H⋯Br hydrogen bonds, while inter­molecular C—H⋯O hydrogen bonds link 4-formyl-N,N-di­methyl­benzenaminium cations, enclosing R22(18) ring motifs, into a di-periodic network structure. The tetra­bromo­methane mol­ecules fill the spaces between the layers. Neither ππ nor C—H⋯π(ring) inter­actions are observed. A Hirshfeld surface analysis of the crystal structure indicates that the most abundant contacts contributing to the crystal packing are from H⋯Br/Br⋯H (56.0%), Br⋯Br (12.1%), H⋯O/O⋯H (9.7%) and H⋯H (9.5%) inter­actions.

1. Chemical context

Aldehydes are versatile compounds for the synthesis of organic acids, dyes, drugs, perfumes, detergents, soaps, etc. In the synthesis of those compounds the aldehydes undergo many different nucleophilic addition reactions. In order to increase the electrophilicity of the carbon atom at the C=O group of the aldehyde mol­ecule, metal complexes or organocatalysts are commonly used (Ma et al., 2017View full citation, 2021View full citation; Mahmudov & Pombeiro, 2023View full citation). Following crystal engineering principles (Gurbanov et al., 2020View full citation; Mahmoudi et al., 2018View full citation; Velásquez et al., 2019View full citation), weak inter­actions, halogen bonds, and other inter­actions, have been used in the activation of aldehydes towards the synthesis of various classes of organic compounds (Gurbanov et al., 2022View full citation; Sutar & Huber, 2019View full citation). We found that weak inter­actions can be formed with substituents at the aldehyde mol­ecules instead of with the oxygen atom of the C=O group.

[Scheme 1]

Herein, we provide details of the synthesis and an examination of the mol­ecular and crystal structures, together with a Hirshfeld surface analysis, of the title compound (I)[link].

2. Structural commentary

The title compound, (I)[link], consists of one 4-formyl-N,N-di­methyl­benzenaminium bromide unit and a tetra­bromo­methane solvent mol­ecule (Fig. 1[link]). The C—C and C—C—C bond lengths and angles of ring A are in the ranges 1.366 (7) to 1.3998 (10) Å and 118.6 (4) to 121.8 (4)° with average values of 1.388 (8) Å and 120.0 (4)°, respectively. These values are reported as 1.375 Å and 119.9° in p-di­methyl­amino-benzaldehyde hydro­bromide, (II) (Dattagupta & Saha, 1973View full citation). Both of the N—C bonds between the methyl carbon and amino nitro­gen atoms are 1.497 (4) Å, and the corresponding ones in compound (II) are 1.51 (4) and 1.43 (4) Å. The C=O bond length in the aldehyde group is 1.198 (7) Å, and its corresponding value is 1.18 (4) Å in compound (II). The dihedral angle between ring A and the plane of atoms (O1/C4/C8) is 0.00 (2)° while the corresponding value in compound (II) is 1.39°. The C4—C8 [1.467 (7) Å] bond length is in good agreement with the theoretically calculated single-bond lengths between trigonally linked (sp2) carbon atoms: 1.479 Å (Dewar & Schmeising, 1959View full citation) and 1.477 Å (Cruickshank & Sparks, 1960View full citation). The corresponding exocyclic C—C bond length is reported as 1.38 (4) Å in compound (II).

[Figure 1]
Figure 1
The title compound with atom-numbering scheme and 50% probability ellipsoids. Symmetry codes: (i) x, −y + Mathematical equation, z; (ii) x, −y + Mathematical equation, z.

3. Supra­molecular features

In the crystal, inter­molecular C—H⋯Br and N—H⋯Br hydrogen bonds link the bromide ions and the 4-formyl-N,N-di­methyl­benzenaminium moieties (Table 1[link] and Fig. 2[link]a). At the same time, inter­molecular C—H⋯O hydrogen bonds (Table 1[link]) link pairs of mol­ecules through R22(18) hydrogen-bonding motifs, into a di-periodic network structure (Fig. 2[link]a). The tetra­bromo­methane solvent mol­ecules occupy the spaces between the layers (Fig. 2[link]b).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N1—H1N⋯Br4 0.85 2.37 3.221 (4) 175
C6—H6A⋯Br4 0.95 2.91 3.698 (4) 141
C7—H7A⋯O1iii 0.98 2.52 3.424 (5) 153
C7—H7B⋯O1iv 0.98 2.47 3.390 (5) 157
Symmetry codes: (iii) Mathematical equation; (iv) Mathematical equation.
[Figure 2]
Figure 2
(a) A partial packing diagram showing the presence of an R22(18) ring motif (upper right). (b) A packing diagram viewed approximately down the c-axis direction. Inter­molecular C—H⋯Br, N—H⋯Br and C—H⋯O hydrogen bonds are shown as dashed lines. Hydrogen atoms not involved in hydrogen bonds have been omitted for clarity.

4. Hirshfeld surface analysis

For visualizing the inter­molecular inter­actions in (I)[link] a Hirshfeld surface (HS) analysis (Hirshfeld, 1977View full citation; Spackman & Jayatilaka, 2009View full citation) was carried out using Crystal Explorer 17.5 (Spackman et al., 2021View full citation). In the HS plotted over dnorm (Fig. 3[link]), the white regions indicate contacts with distances equal to the sum of van der Waals radii, while the red and blue colours indicate distances shorter (in close contact) or longer (distant contact) than the sum of the van der Waals radii, respectively (Venkatesan et al., 2016View full citation), where the bright-red spots indicate their roles as the respective donors and/or acceptors. There are no ππ stacking inter­actions between aromatic rings in the packing of (I)[link]. Unusually, this is in spite of the presence of juxtaposed red/blue triangular regions in the HS plotted over shape-index (Fig. 4[link]). There are also no C—H⋯π close contacts. According to the two-dimensional fingerprint plots (McKinnon et al., 2007View full citation), the inter­molecular H⋯Br/Br⋯H, Br⋯Br, H⋯O/O⋯H, H⋯H and H⋯C/C⋯H contacts make the most abundant contributions to the HS of 56%, 12.1%, 9.7%, 9.5% and 7.5% respectively (Table 2[link], Fig. 5[link]). All other contact types contribute <5% to the surface. The nearest neighbour coordination environment of a mol­ecule can be determined from the colour patches on the HS based on how close to other mol­ecules they are. These are plotted onto the HS for the H⋯Br/Br⋯H, Br⋯Br, H⋯O/O⋯H and H⋯H inter­actions in Fig. 6[link], showing that van der Waals inter­actions and hydrogen bonding play the major roles in the crystal packing (Hathwar et al., 2015View full citation).

Table 2
Selected interatomic distances (Å)

Br3⋯Br4i 3.3403 (8) H7B⋯O1iv 2.47
H6A⋯Br3ii 2.95 C2⋯H7C 2.83
O1⋯H5A 2.57 C7⋯H2A 2.96
H7A⋯O1iii 2.52 H1N⋯H6A 2.22
Symmetry codes: (i) Mathematical equation; (ii) Mathematical equation; (iii) Mathematical equation; (iv) Mathematical equation.
[Figure 3]
Figure 3
View of the three-dimensional Hirshfeld surface plotted over dnorm.
[Figure 4]
Figure 4
Hirshfeld surface of the title compound plotted over shape-index.
[Figure 5]
Figure 5
Two-dimensional HS-fingerprint plots showing, (a) all inter­actions, and those delineated into (b)H⋯Br/Br⋯H, (c) Br⋯Br, (d) H⋯O/O⋯H, (e) H⋯H, (f) H⋯C/C⋯H inter­actions. The di and de values are the closest inter­nal and external distances (in Å) from given points on the Hirshfeld surface.
[Figure 6]
Figure 6
The Hirshfeld surface representations plotted as fragment patches for (a) H⋯Br/Br⋯H, (b) Br⋯Br, (c) H⋯O/O⋯H and (d) H⋯H inter­actions.

5. Database survey

A substructure search of the Cambridge Structural Database [CSD Version 5.46 (November 2024); Groom, et al., 2016View full citation] using the 4-formyl-N,N-di­methyl­anilinium moiety was carried out, and 49 similar compounds were found. Of these compounds, seven are structurally related. These include: p-di­methyl­amino-benzaldehyde hydro­bromide, C9H12NOBr (CSD refcode MABZAL10; Dattagupta & Saha, 1973View full citation), 4-formyl-N,N-di­methyl­anilinium 4-methyl­benzene­sulfonate monohydrate, C9H12NO+·C7H7O3S·H2O (CSD refcode QAFROH; Jin et al., 2016aView full citation), ammonium 4-formyl-N,N-di­methyl­anilinium naphthalene-1,5-di­sulfonate ammonia, C9H12NO+·C10H6O6S22−·H4N+·H3N (CSD refcode SUYYUI; Jin et al., 2016bView full citation), 4-formyl-N,N-di­methyl­anilinium tetra­fluoro­borate, C9H12NO+·BF4 (CSD refcode VOJMEO; Froschauer et al., 2013View full citation) and 4-formyl-N,N-di­methyl­anilinium 2,4,6-tri­nitro­phenolate, C9H12NO+·C6H2N3O7 (CSD refcodes VUWLIJ: Thakuria et al., 2007View full citation; VUWLIJ01: Jin et al., 2016aView full citation; VUWLIJ02: Prasad, 2016View full citation). It is worth mentioning that the last three entries report different colours for the crystals (brown, colourless and metallic dark red).

6. Synthesis and crystallization

4-(Di­methyl­amino)­benzaldehyde (5 mmol) and tetra­bromo­methane (5 mmol) were dissolved in 25 ml of CHBr3, and left for slow evaporation. Orange crystals (suitable for X-ray analysis) of the product started to form after 1 d at room temperature; they were then filtered off and dried in air. Yield 59% (based on tetra­bromo­methane), orange powder soluble in methanol, ethanol and DMSO. Analysis calculated for C10H12Br5NO (Mr = 561.73): C, 21.38; H, 2.15; N, 2.49. Found: C, 21.36; H, 2.13; N, 2.47. 1H NMR (DMSO-d6), δ: 5.13 (–NHMe2), 9.67 (CHO), 7.70 and 7.68 (2H Ar), 6.80 and 6.78 (2H Ar), 3.05 (6H, 2CH3). 13C NMR (DMSO-d6), −29.2 (CBr4), 43.6 (2CH3), 111.2 (2CAr), 124.4 (CCHO), 133.6 (2CAr), 155.1 (CNMe2), 190.0 (C=O).

7. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 3[link]. The N- and C-bound hydrogen-atom positions were calculated geometrically at distances of 0.85 Å (for NH), 0.95 Å (for CH) and 0.98 Å (for CH3) and refined using a riding model by applying the constraint Uiso = kUeq (C, N), where k = 1.2 for NH and CH hydrogen atoms and k = 1.5 for CH3 hydrogen atoms.

Table 3
Experimental details

Crystal data
Chemical formula C9H12NO+·Br·CBr4
Mr 561.76
Crystal system, space group Orthorhombic, Pnma
Temperature (K) 150
a, b, c (Å) 21.1900 (7), 7.4114 (2), 10.2297 (4)
V3) 1606.55 (9)
Z 4
Radiation type Mo Kα
μ (mm−1) 12.49
Crystal size (mm) 0.32 × 0.18 × 0.12
 
Data collection
Diffractometer Bruker APEXII CCD
Absorption correction Multi-scan (SADABS; Krause et al., 2015View full citation)
Tmin, Tmax 0.086, 0.254
No. of measured, independent and observed [I > 2σ(I)] reflections 9073, 1649, 1462
Rint 0.027
(sin θ/λ)max−1) 0.611
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.026, 0.064, 1.06
No. of reflections 1649
No. of parameters 98
No. of restraints 6
H-atom treatment H-atom parameters constrained
Δρmax, Δρmin (e Å−3) 0.79, −1.21
Computer programs: APEX3 and SAINT (Bruker, 2014View full citation), SHELXT2019/1 (Sheldrick, 2015aView full citation), SHELXL2019/1 (Sheldrick, 2015bView full citation) and SHELXTL (Sheldrick, 2008View full citation).

Supporting information


Computing details top

4-Formyl-N,N-dimethylanilinium bromide–tetrabromomethane (1/1) top
Crystal data top
C9H12NO+·Br·CBr4Dx = 2.323 Mg m3
Mr = 561.76Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, PnmaCell parameters from 4744 reflections
a = 21.1900 (7) Åθ = 2.8–25.7°
b = 7.4114 (2) ŵ = 12.49 mm1
c = 10.2297 (4) ÅT = 150 K
V = 1606.55 (9) Å3Plate, orange
Z = 40.32 × 0.18 × 0.12 mm
F(000) = 1048
Data collection top
Bruker APEXII CCD
diffractometer
1462 reflections with I > 2σ(I)
φ and ω scansRint = 0.027
Absorption correction: multi-scan
(SADABS; Krause et al., 2015)
θmax = 25.7°, θmin = 2.8°
Tmin = 0.086, Tmax = 0.254h = 2525
9073 measured reflectionsk = 98
1649 independent reflectionsl = 1112
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.026Hydrogen site location: mixed
wR(F2) = 0.064H-atom parameters constrained
S = 1.06 w = 1/[σ2(Fo2) + (0.0299P)2 + 4.3541P]
where P = (Fo2 + 2Fc2)/3
1649 reflections(Δ/σ)max = 0.001
98 parametersΔρmax = 0.79 e Å3
6 restraintsΔρmin = 1.21 e Å3
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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/Ueq
Br10.27771 (2)0.53801 (5)0.91970 (4)0.02322 (12)
Br20.16582 (3)0.7500000.78589 (6)0.03084 (16)
Br30.17920 (2)0.7500001.09645 (6)0.02633 (15)
Br40.39332 (2)0.2500000.88637 (6)0.02293 (15)
O10.53538 (19)0.2500000.1926 (4)0.0295 (9)
N10.54209 (18)0.2500000.8217 (4)0.0160 (9)
H1N0.5023590.2500000.8332310.019*
C10.55221 (17)0.2500000.6801 (5)0.0158 (10)
C20.61354 (18)0.2500000.6293 (5)0.0219 (11)
H2A0.6491200.2500000.6858390.026*
C30.6211 (2)0.2500000.4967 (5)0.0244 (12)
H3A0.6625080.2500000.4609380.029*
C40.5690 (2)0.2500000.4127 (5)0.0195 (11)
C50.5087 (2)0.2500000.4645 (4)0.0247 (12)
H5A0.4731320.2500000.4078060.030*
C60.4998 (2)0.2500000.6000 (4)0.0227 (12)
H6A0.4585580.2500000.6362340.027*
C70.56696 (17)0.4161 (5)0.8872 (3)0.0201 (8)
H7A0.5566970.4121020.9805210.030*
H7B0.5476040.5230400.8476350.030*
H7C0.6128590.4217210.8761620.030*
C80.5776 (3)0.2500000.2704 (5)0.0268 (13)
H8A0.6195810.2500000.2377240.032*
C90.2245 (2)0.7500000.9317 (5)0.0193 (11)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Br10.01931 (18)0.0224 (2)0.0280 (2)0.00397 (14)0.00079 (15)0.00030 (15)
Br20.0245 (3)0.0342 (3)0.0338 (4)0.0000.0135 (2)0.000
Br30.0197 (3)0.0320 (3)0.0273 (3)0.0000.0072 (2)0.000
Br40.0177 (2)0.0244 (3)0.0266 (3)0.0000.0002 (2)0.000
O10.039 (2)0.038 (2)0.012 (2)0.0000.0011 (18)0.000
N10.0140 (19)0.024 (2)0.010 (2)0.0000.0006 (16)0.000
C10.015 (2)0.020 (2)0.012 (3)0.0000.0019 (19)0.000
C20.013 (2)0.036 (3)0.016 (3)0.0000.002 (2)0.000
C30.013 (2)0.038 (3)0.022 (3)0.0000.006 (2)0.000
C40.021 (2)0.025 (3)0.013 (3)0.0000.002 (2)0.000
C50.022 (3)0.042 (3)0.011 (3)0.0000.003 (2)0.000
C60.014 (2)0.041 (3)0.013 (3)0.0000.000 (2)0.000
C70.0262 (17)0.0209 (19)0.0132 (19)0.0021 (15)0.0019 (15)0.0029 (15)
C80.027 (3)0.036 (3)0.018 (3)0.0000.008 (2)0.000
C90.013 (2)0.022 (3)0.022 (3)0.0000.001 (2)0.000
Geometric parameters (Å, º) top
Br1—C91.937 (3)C3—C41.3998 (10)
Br2—C91.942 (5)C3—H3A0.9500
Br3—C91.940 (5)C4—C51.384 (7)
O1—C81.198 (7)C4—C81.467 (7)
N1—C11.464 (6)C5—C61.3995 (10)
N1—C7i1.497 (4)C5—H5A0.9500
N1—C71.497 (4)C6—H6A0.9500
N1—H1N0.8501C7—H7A0.9800
C1—C61.379 (6)C7—H7B0.9800
C1—C21.3997 (10)C7—H7C0.9800
C2—C31.366 (7)C8—H8A0.9500
C2—H2A0.9500
Br3···Br4ii3.3403 (8)H7B···O1v2.47
H6A···Br3iii2.95C2···H7C2.83
O1···H5A2.57C7···H2A2.96
H7A···O1iv2.52H1N···H6A2.22
C1—N1—C7i113.0 (2)C6—C5—H5A119.9
C1—N1—C7113.0 (2)C1—C6—C5118.8 (4)
C7i—N1—C7110.6 (4)C1—C6—H6A120.6
C1—N1—H1N106.4C5—C6—H6A120.6
C7i—N1—H1N106.7N1—C7—H7A109.5
C7—N1—H1N106.6N1—C7—H7B109.5
C6—C1—C2121.8 (4)H7A—C7—H7B109.5
C6—C1—N1118.0 (3)N1—C7—H7C109.5
C2—C1—N1120.2 (4)H7A—C7—H7C109.5
C3—C2—C1118.6 (4)H7B—C7—H7C109.5
C3—C2—H2A120.7O1—C8—C4124.5 (5)
C1—C2—H2A120.7O1—C8—H8A117.7
C2—C3—C4121.1 (4)C4—C8—H8A117.7
C2—C3—H3A119.4Br1—C9—Br1vi108.4 (2)
C4—C3—H3A119.4Br1—C9—Br3110.07 (18)
C5—C4—C3119.6 (4)Br1vi—C9—Br3110.07 (18)
C5—C4—C8119.6 (4)Br1—C9—Br2108.90 (18)
C3—C4—C8120.8 (5)Br1vi—C9—Br2108.90 (18)
C4—C5—C6120.2 (4)Br3—C9—Br2110.5 (2)
C4—C5—H5A119.9
C7i—N1—C1—C6116.7 (3)C2—C3—C4—C8180.000 (1)
C7—N1—C1—C6116.7 (3)C3—C4—C5—C60.000 (1)
C7i—N1—C1—C263.3 (3)C8—C4—C5—C6180.000 (1)
C7—N1—C1—C263.3 (3)C2—C1—C6—C50.000 (1)
C6—C1—C2—C30.000 (1)N1—C1—C6—C5180.000 (1)
N1—C1—C2—C3180.000 (1)C4—C5—C6—C10.000 (1)
C1—C2—C3—C40.000 (1)C5—C4—C8—O10.000 (1)
C2—C3—C4—C50.000 (1)C3—C4—C8—O1180.000 (1)
Symmetry codes: (i) x, y+1/2, z; (ii) x+1/2, y+1, z+1/2; (iii) x+1/2, y1/2, z1/2; (iv) x, y, z+1; (v) x+1, y+1, z+1; (vi) x, y+3/2, z.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N1—H1N···Br40.852.373.221 (4)175
C6—H6A···Br40.952.913.698 (4)141
C7—H7A···O1iv0.982.523.424 (5)153
C7—H7B···O1v0.982.473.390 (5)157
Symmetry codes: (iv) x, y, z+1; (v) x+1, y+1, z+1.
 

Acknowledgements

This work has been supported by the Baku State University, Azerbaijan Medical University and Khazar University. TH is also grateful to Hacettepe University Scientific Research Project Unit (grant No. 013 D04 602 004). The authors' contributions are as follows. Conceptualization, AVG, TH and ANB; synthesis, AVG and GZM; X-ray analysis, AVG; writing (review and editing of the manuscript) AVG and TH; funding acquisition, AVG, GZM, KIH and TAJ; supervision, AVG, TH and ANB.

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