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of propane-1,3-diaminium squarate dihydrate
aInstitut für Pharmazie, Martin-Luther-Universität Halle-Wittenberg, Wolfgang-Langenbeck-Str. 4, 06120 Halle (Saale), Germany, and bInstitute of Molecular Biology "Roumen Tsanev", Bulgarian Academy of Sciences, Acad. G. Bonchev-Str. Bl. 21, Sofia 1113, Bulgaria
*Correspondence e-mail: ruediger.seidel@pharmazie.uni-halle.de
Propane-1,3-diaminium squarate dihydrate, C3H12N22+·C4O42−·2H2O, results from the proton-transfer reaction of propane-1,3-diamine with squaric acid and subsequent crystallization from aqueous medium. The title compound crystallizes in the tetragonal (space group P4bm) with Z = 2. The squarate dianion belongs to the D4h and contains a crystallographic fourfold axis. The propane-1,3-diaminium dication exhibits a C2v-symmetric all-anti conformation and resides on a special position with mm2 The orientation of the propane-1,3-diaminium ions makes the polar in the c-axis direction. The solid-state supramolecular structure features a triperiodic network of strong hydrogen bonds of the N—H⋯O and O—H⋯O types.
Keywords: propane-1,3-diamine; squaric acid; proton-transfer compound; hydrogen bonding; polar structure; crystal structure.
CCDC reference: 2378952
1. Chemical context
Squaric acid (H2C4O4; 3,4-dihydroxycyclobut-3-ene-1,2-dione) and its derivatives have been widely studied in organic chemistry and materials science (Grus et al., 2021; Laramie et al., 2017
; Wurm & Klok, 2013
; Xia & Wang, 2017
). Squaric acid analogues have also attracted attention in medicinal chemistry (Chasák et al., 2021
; Ruseva et al., 2022
). In structural chemistry, the interest in squaric acid and its mono- and dianions arises mainly from their planar, symmetrical and strained molecular structures and their diverse hydrogen-bonding patterns in the solid state (Allen et al., 2013
; Gilli et al., 2001
). As a strong diprotic organic acid with pKa1 = 0.59 ± 0.09 and pKa2 = 3.48 ± 0.023 at 298 K (as determined by potentiometric titrations; Schwartz & Howard, 1970
), squaric acid readily forms proton-transfer compounds with nitrogen bases and a wide variety of structurally characterized examples can be found in the Cambridge Structural Database (CSD; Groom et al., 2016
). In the present contribution, we describe the of the dihydrate of the proton-transfer compound propane-1,3-diaminium squarate.
2. Structural commentary
Fig. 1 shows the molecular structures of the components of the title compound in the crystal. The squarate dianion exhibits D4h point-group symmetry and contains a crystallographic fourfold rotation axis with the direction [001]. The propane-1,3-diaminium dication adopts a C2v-symmetric all-anti conformation and is located on a special position with mm2 in the The overall orientation of the molecular dications renders the polar in the c-axis direction. The water molecule of crystallization sits on a crystallographic mirror plane perpendicular to the [110] direction.
![]() | Figure 1 Displacement ellipsoid plot (50% probability level) of the title compound. Hydrogen atoms are shown by small spheres of arbitrary radius. Dashed lines represent hydrogen bonds. Symmetry codes: (iv) y, −x, z; (v) −x, −y, z; (vi) −y, x, z; (vii) −x + 1, −y, z; |
3. Supramolecular features
Apart from ion–ion interactions between propane-1,3-diaminium dications and squarate dianions, hydrogen bonding dominates the solid-state structure of the title compound. The protonated amino group joins two squarate ions via N—H⋯O hydrogen bonds. The remaining hydrogen-bond donor site of the aminium group forms an N—H⋯O hydrogen bond to a water molecule (Fig. 2). The water molecule in turn acts as hydrogen-bond acceptor towards two squarate ions, which results in a triperiodic hydrogen-bond network (Fig. 3
). Table 1
lists the corresponding hydrogen-bond parameters, which are characteristic of strong hydrogen bonds (Thakuria et al., 2017
). The centroid–centroid distance between the squarate ions in the [001] direction corresponds to the c lattice parameter. A packing index of 67.8% (Kitajgorodskij, 1973
), as calculated with PLATON (Spek, 2020
), indicates a relatively open structure. This lends support to the view that strong hydrogen bonding governs the structure rather than van der Waals close packing.
|
![]() | Figure 2 Section of the crystal structure of the title compound, viewed approximately along the [010] direction. Dashed lines illustrate hydrogen bonds. Symmetry codes: (i) x + |
![]() | Figure 3 The tetragonal unit cell of the title compound, projected along the c-axis direction. Dashed lines illustrate hydrogen bonds. Colour scheme: C, grey; H, white; N, blue; O, red. |
4. Database survey
The CSD (version 5.43 with September 2022 updates; Groom et al., 2016) contains >400 crystal structures with propane-1,3-diaminium cations and >100 crystal structures with squarate dianions. A structure closely related to the title compound is that of the homologous pentane-1,5-diaminium squarate dihydrate (CSD refcode: JARGAN; Ivanova & Spiteller, 2014
). In contrast to the title compound, the of JARGAN is centrosymmetric, although the pentane-1,5-diaminium cation likewise exhibits a polar (approximately) C2v-symmetric all-anti conformation. A solvent-free of propane-1,3-diaminum bis(hydrogen squarate) has also been published (TURQEC; Mathew et al., 2002
). The propane-1,3-diaminum cations in TURQEC similarly adopt an all-anti conformation with approximate C2v point-group symmetry, but the is centrosymmetric. Worthy of note, a low-temperature determination of the parent free-base propane-1,3-diamine, which is liquid at room temperature, has also been disclosed (QATVUC; Thalladi et al., 2000
).
5. Synthesis and crystallization
Starting materials were obtained from commercial sources and used as received. A solution of propane-1,3-diamine (148 mg, 2 mmol) in 25 mL of ethanol was mixed with a solution of squaric acid (228 mg, 2 mmol) in 40 mL of distilled water. After stirring at 333 K for 4 h, the mixture was left at ambient conditions. After three weeks, colourless crystalline material was collected by filtration and air-dried. Colourless crystals of the title compound suitable for single-crystal X-ray diffraction were grown from methanol/water (1:1) by the slow evaporation method.
6. Refinement
Crystal data, data collection and structure . Hydrogen-atom positions were refined freely, and Uiso(H) values were set 1.2Ueq(C, N, O) to improve the data/parameter ratio. The direction of the polar axis was chosen to give a Flack x parameter, as calculated by Parsons' quotient method (Parsons et al., 2013
), close to zero. In the absence of significant however, the polar axis direction could not be determined reliably in view of the high of the Flack x parameter (Flack & Bernardinelli, 1999
). For this reason, the presence of inversion also cannot be excluded.
|
Supporting information
CCDC reference: 2378952
https://doi.org/10.1107/S2056989024008235/pk2708sup1.cif
contains datablocks I, global. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989024008235/pk2708Isup2.hkl
Supporting information file. DOI: https://doi.org/10.1107/S2056989024008235/pk2708Isup3.cdx
Supporting information file. DOI: https://doi.org/10.1107/S2056989024008235/pk2708Isup4.cml
C3H12N22+·C4O42−·2H2O | Dx = 1.353 Mg m−3 |
Mr = 224.22 | Mo Kα radiation, λ = 0.71073 Å |
Tetragonal, P4bm | Cell parameters from 5992 reflections |
a = 11.2716 (2) Å | θ = 3.6–28.7° |
c = 4.3310 (1) Å | µ = 0.12 mm−1 |
V = 550.25 (2) Å3 | T = 105 K |
Z = 2 | Block, colourless |
F(000) = 240 | 0.23 × 0.16 × 0.11 mm |
Oxford Diffraction Xcalibur2 diffractometer | 745 independent reflections |
Radiation source: fine-focus sealed X-ray tube, Enhance (Mo) X-ray Source | 721 reflections with I > 2σ(I) |
Detector resolution: 8.4171 pixels mm-1 | Rint = 0.027 |
ω scans | θmax = 28.9°, θmin = 3.6° |
Absorption correction: multi-scan [ABSPACK in CrysAlisPro (Rigaku OD, 2023)] | h = −15→15 |
Tmin = 0.928, Tmax = 1.000 | k = −15→14 |
11463 measured reflections | l = −5→5 |
Refinement on F2 | Secondary atom site location: difference Fourier map |
Least-squares matrix: full | Hydrogen site location: difference Fourier map |
R[F2 > 2σ(F2)] = 0.027 | Only H-atom coordinates refined |
wR(F2) = 0.070 | w = 1/[σ2(Fo2) + (0.045P)2 + 0.0625P] where P = (Fo2 + 2Fc2)/3 |
S = 1.09 | (Δ/σ)max < 0.001 |
745 reflections | Δρmax = 0.38 e Å−3 |
54 parameters | Δρmin = −0.13 e Å−3 |
1 restraint | Absolute structure: Flack x determined using 298 quotients [(I+)-(I-)]/[(I+)+(I-)] (Parsons et al., 2013) |
Primary atom site location: structure-invariant direct methods | Absolute structure parameter: 0.1 (5) |
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. |
x | y | z | Uiso*/Ueq | ||
C1 | 0.00512 (11) | 0.09200 (10) | 0.0161 (4) | 0.0143 (3) | |
C2 | 0.42195 (10) | 0.07805 (10) | 0.5294 (5) | 0.0137 (4) | |
H2 | 0.4703 (15) | 0.1281 (16) | 0.407 (5) | 0.016* | |
C3 | 0.500000 | 0.000000 | 0.7310 (7) | 0.0129 (5) | |
H3 | 0.5480 (17) | 0.0480 (17) | 0.851 (6) | 0.015* | |
N1 | 0.34377 (9) | 0.15623 (9) | 0.7173 (4) | 0.0126 (3) | |
H1A | 0.3011 (18) | 0.1989 (18) | 0.601 (7) | 0.015* | |
H1B | 0.3902 (15) | 0.2026 (15) | 0.834 (5) | 0.015* | |
O1 | 0.01160 (8) | 0.20294 (8) | 0.0165 (3) | 0.0188 (3) | |
O2 | 0.21736 (10) | 0.28264 (10) | 0.2827 (4) | 0.0244 (4) | |
H2A | 0.1556 (18) | 0.2608 (18) | 0.191 (5) | 0.029* |
U11 | U22 | U33 | U12 | U13 | U23 | |
C1 | 0.0114 (5) | 0.0119 (6) | 0.0196 (5) | 0.0002 (4) | −0.0025 (5) | 0.0017 (7) |
C2 | 0.0144 (5) | 0.0144 (5) | 0.0123 (7) | 0.0006 (6) | −0.0005 (6) | 0.0005 (6) |
C3 | 0.0132 (7) | 0.0132 (7) | 0.0124 (11) | 0.0005 (9) | 0.000 | 0.000 |
N1 | 0.0117 (5) | 0.0117 (5) | 0.0144 (6) | 0.0004 (5) | −0.0013 (5) | 0.0013 (5) |
O1 | 0.0149 (4) | 0.0098 (4) | 0.0316 (5) | −0.0004 (3) | −0.0064 (5) | 0.0014 (5) |
O2 | 0.0197 (5) | 0.0197 (5) | 0.0337 (9) | −0.0071 (6) | −0.0117 (5) | 0.0117 (5) |
C1—O1 | 1.2527 (14) | C3—H3 | 0.92 (3) |
C1—C1i | 1.4687 (15) | C3—H3iv | 0.92 (3) |
C1—C1ii | 1.4687 (15) | N1—H1A | 0.85 (3) |
C2—N1 | 1.488 (2) | N1—H1B | 0.896 (19) |
C2—C3 | 1.520 (3) | N1—H1Biii | 0.896 (19) |
C2—H2 | 0.946 (19) | O2—H2A | 0.84 (2) |
C2—H2iii | 0.946 (19) | O2—H2Aiii | 0.84 (2) |
O1—C1—C1i | 135.16 (13) | C2iv—C3—H3 | 108.8 (8) |
O1—C1—C1ii | 134.84 (13) | C2—C3—H3iv | 108.8 (8) |
C1i—C1—C1ii | 89.999 (1) | C2iv—C3—H3iv | 108.8 (8) |
N1—C2—C3 | 111.80 (18) | H3—C3—H3iv | 112 (3) |
N1—C2—H2 | 107.1 (11) | C2—N1—H1A | 110 (2) |
C3—C2—H2 | 109.4 (11) | C2—N1—H1B | 108.0 (11) |
N1—C2—H2iii | 107.1 (11) | H1A—N1—H1B | 109.7 (14) |
C3—C2—H2iii | 109.4 (11) | C2—N1—H1Biii | 108.0 (11) |
H2—C2—H2iii | 112 (2) | H1A—N1—H1Biii | 109.7 (14) |
C2—C3—C2iv | 109.9 (2) | H1B—N1—H1Biii | 111 (2) |
C2—C3—H3 | 108.8 (8) | H2A—O2—H2Aiii | 105 (3) |
N1—C2—C3—C2iv | 180.000 (1) |
Symmetry codes: (i) −y, x, z; (ii) y, −x, z; (iii) −y+1/2, −x+1/2, z; (iv) −x+1, −y, z. |
D—H···A | D—H | H···A | D···A | D—H···A |
C2—H2···O1v | 0.946 (19) | 2.590 (19) | 3.4712 (18) | 155.1 (14) |
N1—H1A···O2 | 0.85 (3) | 1.92 (3) | 2.758 (2) | 171 (3) |
N1—H1B···O1vi | 0.896 (19) | 1.905 (18) | 2.7887 (12) | 168.4 (17) |
O2—H2A···O1 | 0.84 (2) | 1.91 (2) | 2.7413 (13) | 175 (2) |
Symmetry codes: (v) x+1/2, −y+1/2, z; (vi) x+1/2, −y+1/2, z+1. |
Acknowledgements
We are grateful to the late Professor William S. Sheldrick for his support of this research. We acknowledge the financial support of the Open Access Publication Fund of the Martin-Luther-Universität Halle-Wittenberg.
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