Literature DB >> 28435726

Crystal structure of 2-(aza-niumylmeth-yl)pyridinium bis(hydrogen squarate).

Nina Salamzadeh1, Zeynep Demircioglu1, Ufuk Korkmaz1, Orhan Büyükgüngör1.   

Abstract

The asymmetric unit of the title compound, C6H10N222C4HO4-, comprises two hydrogen squarate (Hsq-; systematic name: 2-hy-droxy-3,4-dioxo-cyclo-butano-late) anions and a 2-(aza-niumylmeth-yl)pyridinium dication. The squaric acid mol-ecules each donate an H atom to the N atoms of the pyridine ring and the amino-methyl units of a 2-(amino-meth-yl)pyridine mol-ecule, forming the 1:2 salt. The Hsq- anions are linked by strong O-H⋯O hydrogen bonds and an N-H⋯O hydrogen bond links the 2-(aza-niumylmeth-yl)pyridinium cation to one of the squaric acid anions. The crystal structure features additional N-H⋯O and O-H⋯O hydrogen bonds, π-π stacking and unusual weak C-O⋯π(ring) inter-actions.

Entities:  

Keywords:  2-(aza­niumylmeth­yl)pyridinium; crystal structure; hydrogen bonding; squaric acid

Year:  2017        PMID: 28435726      PMCID: PMC5382627          DOI: 10.1107/S2056989017004376

Source DB:  PubMed          Journal:  Acta Crystallogr E Crystallogr Commun


Chemical context

Hydrogen bonding is the most common way of generating supra­molecular organic systems in crystal engineering and mol­ecular recognition. Hydrogen-bonded systems generated from organic cations and anions are of special inter­est as they would be expected to form stronger hydrogen bonds than those in neutral mol­ecules (Reetz et al.,1994 ▸; Bertolasi et al., 2001 ▸). Squaric acid (H2C4O4, H2sq), has been of inter­est because of its cyclic structure and potential aromaticity and is used as a building block in crystal engineering due to the simplicity of the cyclic units. It can be found in three forms: uncharged H2sq, the Hsq− monoanion and the sq2− dianion. The mono- and dianions are often produced following deprotonation by amines (Lam & Mak, 2000 ▸; Mathew et al., 2002 ▸). The squarate derivatives are almost flat because of the π-conjugation of their C—C and C—O bonds, and therefore their four oxygen atoms behave as planar (sp 2) electron donors of one or two lone pairs of electrons. Recently, we reported the synthesis and characterization of the same organo­ammonium squarate as the title compound but as a hydrate in the triclinic space group P (Korkmaz & Bulut, 2013 ▸). We report here the unsolvated form of this salt, which crystallizes in the monoclinic space group P21/c.

Structural commentary

2-(Amino­meth­yl) pyridine forms a n class="Chemical">salt with two squaric acid mol­ecules and each mol­ecule of the acid loses one proton. One of these is transferred to the N atom of the pyridine ring, generating the 4-(amino­meth­yl)morpholinium mono-cation. The other from the second acid mol­ecule is engaged in the formation of a homo-conjugated hydrogen squarate anion via a short, symmetric O5—H5A⋯O3 [2.4583 (14) Å] hydrogen bond (Fig. 1 ▸). The electron density associated with this H atom is shared by the O5 and O3 atoms, indicating a large degree of ionic character (Gilli & Gilli, 2000 ▸). Considering the range (2.38–2.50 Å) of Gilli’s classification for such an inter­action, this hydrogen bonding can be referred to as negative charge-assisted hydrogen bonding [(−) CAHB] (Gilli & Gilli, 2009 ▸; Gilli et al., 2001 ▸ ; Becke, 1993 ▸, Lee et al., 1988 ▸) and can be represented as [-O⋯H⋯O-]−.
Figure 1

A view of the asymmetric unit of (I), showing the atom-numbering scheme and 30% probability displacement ellipsoids. Dashed lines indicate hydrogen bonds.

N1/C1–C5, C7–C10 and C11–C14 are defined as rings 1, 2 and 3, respectively, with centroids Cg1, Cg2 and Cg3. The dihedral angles between the mean plane of ring 1 and those of rings 2 and 3 are 18.818 (8) and 31.564 (6)°, respectively. The dihedral angle between the two squarate anions is 29.19 (1)°. The angles between the C—C bonds in the Hsq− anions are close to 90°, with the oxygen atoms directed almost along the diagonals. The CC distances in the planar squarate ring systems reflect partial double-bond character for C9—C10, C7—C10, C11—C12 and C11—C14 with distances of 1.4291 (17), 1.4357 (16), 1.4139 (17) and 1.4465 (18) Å, respectively. In contrast C7—C8, C8—C9, C12—C13 and C13—C14 display more single-bond character with distances of 1.4886 (17), 1.4929 (17), 1.4802 (18) and 1.5141 (17) Å, respectively. The Hsq− ion has one C—O bond (C11—O5) at 1.3023 (17) Å, which is significantly longer than a normal single C—O bond. This most likely reflects the involvement in the negative charge-assisted hydrogen bonding mentioned earlier. At 1.3000 (15) Å, the C10—O4 bond is similarly extended. The remaining C—O bonds in both rings display a similar pattern with one obvious C=O double bond in each ring [C8=O2, 1.2268 (15) Å and C13=O7, 1.2141 (17) Å] and the others of inter­mediate length in the range 1.2356 (16) to 1.2658 (15) Å, indicating some delocalization occurring in both rings.

Supra­molecular features

The two hydrogen squarate anions are linked in the asymmetric unit by a short hydrogen-bonding inter­action O5—H5A⋯O3 [2.4583 (14) Å] related to the proton-sharing inter­action discussed earlier. This pair of anions is further linked to the 2-(aza­niumylmeth­yl)pyridinium dication by an N1—H1A⋯O1 hydrogen bond, Fig. 1 ▸, Table 1 ▸. O5—H5A⋯O3, N2—H2B⋯O2i and N2—H2B⋯O5i hydrogen bonds form rings with an (7) graph-set motif while N2—H2C⋯O6i and N2—H2B⋯O5i hydrogen bonds combine to form (7) rings. In addition, heteronuclear N2—H2C⋯O6i, and N2—H2A⋯O8ii and homonuclear O4—H4A⋯O6iii and O5—H5A⋯O3 hydrogen bonds generate a larger (14) ring motif (Fig. 2 ▸, Table 1 ▸). The crystal packing also features unusual weak C7—O1⋯Cg2ii, C7—O1⋯Cg3iv and C13—O7⋯Cg2v inter­actions reinforced by π–π stacking inter­actions. These latter contacts [Cg1· · ·Cg3 = 2.5382 (9) Å, Cg2· ··Cg2ii = 3.5997 (9) Å, Cg2· · ·Cg3iv = 3.6406 (10) Å and Cg3·· ·Cg2v = 3.6406 (10) Å; symmetry codes: (ii) 1 − x, 1 − y, 1 − z; (iv)  − x,  + y,  − z; (v)  − x, − + y,  − z] also contribute to the stabilization of the crystal packing (Fig. 3 ▸).
Table 1

Hydrogen-bond geometry (Å, °)

Cg2 and Cg3 are the centroids of the C7–C10 and C11–C14 rings, respectively.

D—H⋯A D—HH⋯A DA D—H⋯A
N1—H1A⋯O10.93 (2)1.74 (2)2.6598 (15)166.7 (19)
N2—H2B⋯O2i 0.892.052.8565 (16)150
N2—H2B⋯O5i 0.892.563.1613 (17)126
N2—H2C⋯O6i 0.892.022.8765 (16)161
N2—H2A⋯O8ii 0.891.902.7580 (15)162
O4—H4A⋯O6iii 0.99 (2)1.51 (2)2.4993 (14)175 (2)
O5—H5A⋯O31.00 (2)1.46 (2)2.4583 (14)175 (2)
C7—O1⋯Cg2ii 1.25 (1)3.38 (1)3.3226 (14)77 (1)
C7—O1⋯Cg3iv 1.25 (1)3.39 (1)3.3297 (14)76 (1)
C13—O7⋯Cg2v 1.21 (1)3.52 (1)3.4188 (15)75 (1)

Symmetry codes: (i) ; (ii) ; (iii) ; (iv) ; (v) .

Figure 2

A view of the N—H⋯O and O—H⋯O inter­actions in the crystal of the title compound (hydrogen bonds are shown as dashed lines; see Table 1 ▸ for numerical details).

Figure 3

A packing diagram showing the C—O⋯π and π–π stacking inter­actions. [Symmetry codes: (ii) −x + 1, −y + 1, −z + 1; (iv) −x + , y + , −z + ; (v) −x + , y − , −z + .] H atoms not involved in the inter­actions have been omitted for clarity.

Database survey

A search of the Cambridge Structural Database (Version 5.38, update February 2017; Groom et al., 2016 ▸) revealed the structures of various organo­ammonium squarates (Georgopoulos et al., 2005 ▸; Wang & Stucky, 1974 ▸; Kanters et al., 1991 ▸; Kolev et al., 2000 ▸; Karle et al., 1996 ▸; Angelova et al.,1996 ▸). In the squarate anion form, the anions are generally linked to amines by N—H⋯O hydrogen bonds (Gilli et al., 2001 ▸; Korkmaz et al., 2011 ▸; Dega-Szafran et al., 2012 ▸). Structures of 2-(amoniometh­yl) pyridinium, di­hydrogen squarate and squaric acid derivatives are also known (Korkmaz et al., 2011 ▸; Korkmaz & Bulut, 2013 ▸, 2014 ▸). Often, the supra­molecular architectures of similar structures have been investigated together with their spectroscopic properties, including their potential non-linear optical (NLO) behaviour (Bosshard et al., 1995 ▸; Kolev et al., 2008 ▸). The literature also reveals that squarenes show photo-chemical, photo-conductive and NLO properties and that they can be used as electron acceptors in photo-sensitive devices (Korkmaz et al., 2016 ▸).

Synthesis and crystallization

All chemical reagents were analytical grade commercial products. The solvent was purified by conventional methods. Squaric acid (H2Sq; 0,46 g, 4 mmol) and 2-(amino­meth­yl)pyridine (0,24 g; 2 mmol) were dissolved in water (25 cm3) to obtain a mixture in the molar ratio 2:1 and the solution was heated to 323 K in a temperature-controlled bath and stirred for one h. The reaction mixture was then slowly cooled to room temperature. The crystals formed were filtered and washed with 10 cm3 of methanol, and dried in air.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2 ▸. All C-bound hydrogen atoms were included in calculated positions with C—H = 0.93 Å (aromatic) and 0.97 Å (methyl­ene) and allowed to ride, with U iso(H) = 1.2U eq(C). The NH3 group (N—H = 0.89 Å) was also allowed to ride in the refinement with U iso(H) = 1.5U eq(N). The O-bound H atoms and N1-bound H atom were located in a difference-Fourier map and refined with U iso(H) = 1.2U eq(O) and U iso(H) = 1.5U eq(N).
Table 2

Experimental details

Crystal data
Chemical formulaC6H10N2 2+·2C4HO4
M r 336.26
Crystal system, space groupMonoclinic, P21/n
Temperature (K)296
a, b, c (Å)7.4653 (7), 15.4548 (14), 12.2095 (12)
β (°)90.073 (4)
V3)1408.7 (2)
Z 4
Radiation typeMo Kα
μ (mm−1)0.13
Crystal size (mm)0.17 × 0.13 × 0.11
 
Data collection
DiffractometerBruker APEXII CCD
Absorption correctionMulti-scan (SADABS; Bruker, 2013)
T min, T max 0.672, 0.746
No. of measured, independent and observed [I > 2σ(I)] reflections70681, 3496, 3090
R int 0.042
(sin θ/λ)max−1)0.668
 
Refinement
R[F 2 > 2σ(F 2)], wR(F 2), S 0.042, 0.118, 1.11
No. of reflections3496
No. of parameters227
H-atom treatmentH-atom parameters not refined
Δρmax, Δρmin (e Å−3)0.26, −0.28

Computer programs: APEX2 and SAINT (Bruker, 2013 ▸), SHELXT2014 (Sheldrick, 2008 ▸), SHELXL2016 (Sheldrick, 2015 ▸), ORTEP-3 for Windows and WinGX (Farrugia, 2012 ▸) and PLATON (Spek, 2009 ▸).

Crystal structure: contains datablock(s) I. DOI: 10.1107/S2056989017004376/sj5524sup1.cif Structure factors: contains datablock(s) I. DOI: 10.1107/S2056989017004376/sj5524Isup2.hkl Click here for additional data file. Supporting information file. DOI: 10.1107/S2056989017004376/sj5524Isup3.cml CCDC reference: 1538918 Additional supporting information: crystallographic information; 3D view; checkCIF report
C6H10N22+·2C4HO4F(000) = 696
Mr = 336.26Dx = 1.586 Mg m3
Monoclinic, P21/nMo Kα radiation, λ = 0.71073 Å
a = 7.4653 (7) ÅCell parameters from 9896 reflections
b = 15.4548 (14) Åθ = 3.0–28.3°
c = 12.2095 (12) ŵ = 0.13 mm1
β = 90.073 (4)°T = 296 K
V = 1408.7 (2) Å3Block, bronze
Z = 40.17 × 0.13 × 0.11 mm
Bruker APEXII CCD diffractometer3090 reflections with I > 2σ(I)
φ and ω scansRint = 0.042
Absorption correction: multi-scan (SADABS; Bruker, 2013)θmax = 28.3°, θmin = 3.0°
Tmin = 0.672, Tmax = 0.746h = −9→9
70681 measured reflectionsk = −20→20
3496 independent reflectionsl = −16→16
Refinement on F20 restraints
Least-squares matrix: fullHydrogen site location: mixed
R[F2 > 2σ(F2)] = 0.042H-atom parameters not refined
wR(F2) = 0.118w = 1/[σ2(Fo2) + (0.0556P)2 + 0.5691P] where P = (Fo2 + 2Fc2)/3
S = 1.11(Δ/σ)max < 0.001
3496 reflectionsΔρmax = 0.26 e Å3
227 parametersΔρmin = −0.28 e Å3
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.
xyzUiso*/Ueq
C10.3472 (2)0.59963 (10)0.10814 (12)0.0377 (3)
H10.3764710.5411810.1110710.045*
C20.2856 (2)0.63543 (13)0.01196 (13)0.0479 (4)
H20.2702450.601292−0.0500690.058*
C30.2473 (2)0.72223 (14)0.00899 (14)0.0507 (4)
H30.2100630.747750−0.0561550.061*
C40.2640 (2)0.77205 (11)0.10321 (14)0.0442 (4)
H40.2365000.8307330.1017000.053*
C50.32152 (18)0.73381 (8)0.19877 (12)0.0305 (3)
C60.3378 (2)0.78078 (10)0.30627 (14)0.0419 (4)
H6A0.4247100.7512930.3520980.050*
H6B0.3812470.8390050.2931040.050*
C70.61186 (16)0.53092 (8)0.38741 (10)0.0245 (2)
C80.59463 (17)0.44771 (8)0.32689 (10)0.0273 (3)
C90.71303 (18)0.40741 (8)0.41129 (10)0.0278 (3)
C100.72538 (16)0.48889 (8)0.46610 (10)0.0247 (2)
C110.64141 (18)0.16148 (8)0.29601 (10)0.0289 (3)
C120.54027 (17)0.10155 (8)0.23404 (10)0.0271 (3)
C130.57553 (18)0.03307 (9)0.31604 (10)0.0293 (3)
C140.67917 (17)0.09946 (8)0.38172 (10)0.0272 (3)
N10.36494 (15)0.64919 (7)0.19743 (9)0.0288 (2)
N20.16375 (17)0.78523 (8)0.36470 (10)0.0346 (3)
H2A0.1778210.8139620.4272900.052*
H2C0.1252600.7318880.3788380.052*
H2B0.0838440.8125010.3229840.052*
O10.54865 (14)0.60498 (6)0.37564 (8)0.0328 (2)
O20.51318 (15)0.42458 (7)0.24462 (8)0.0387 (3)
O30.77376 (16)0.33276 (6)0.42957 (9)0.0409 (3)
O40.80146 (14)0.51691 (6)0.55513 (8)0.0331 (2)
O50.68219 (19)0.24159 (7)0.27431 (9)0.0457 (3)
O60.45452 (15)0.10825 (7)0.14494 (8)0.0380 (3)
O70.54053 (18)−0.04333 (7)0.32469 (10)0.0514 (3)
O80.76167 (16)0.09899 (7)0.46951 (8)0.0400 (3)
H1A0.419 (3)0.6260 (13)0.2598 (17)0.048*
H5A0.725 (3)0.2770 (14)0.3380 (18)0.060*
H4A0.868 (3)0.4687 (15)0.5894 (17)0.060*
U11U22U33U12U13U23
C10.0412 (7)0.0344 (7)0.0375 (8)0.0016 (6)0.0005 (6)−0.0072 (6)
C20.0440 (8)0.0679 (11)0.0320 (7)−0.0028 (8)−0.0042 (6)−0.0111 (7)
C30.0442 (9)0.0732 (12)0.0346 (8)0.0039 (8)−0.0084 (6)0.0176 (8)
C40.0458 (8)0.0362 (8)0.0505 (9)0.0057 (6)−0.0058 (7)0.0159 (7)
C50.0293 (6)0.0253 (6)0.0370 (7)−0.0015 (5)−0.0047 (5)0.0011 (5)
C60.0383 (7)0.0333 (7)0.0540 (9)−0.0031 (6)−0.0126 (7)−0.0137 (6)
C70.0285 (6)0.0245 (6)0.0207 (5)−0.0021 (4)−0.0029 (4)0.0028 (4)
C80.0327 (6)0.0254 (6)0.0237 (6)−0.0010 (5)−0.0045 (5)0.0012 (5)
C90.0344 (6)0.0230 (6)0.0259 (6)−0.0008 (5)−0.0073 (5)−0.0009 (4)
C100.0297 (6)0.0222 (5)0.0223 (5)−0.0007 (4)−0.0045 (4)0.0009 (4)
C110.0364 (6)0.0242 (6)0.0261 (6)0.0020 (5)−0.0054 (5)−0.0052 (5)
C120.0307 (6)0.0257 (6)0.0248 (6)0.0040 (5)−0.0059 (5)−0.0052 (5)
C130.0322 (6)0.0280 (6)0.0276 (6)−0.0013 (5)−0.0061 (5)−0.0020 (5)
C140.0297 (6)0.0287 (6)0.0234 (6)0.0000 (5)−0.0039 (5)−0.0035 (5)
N10.0310 (5)0.0265 (5)0.0287 (5)0.0017 (4)−0.0043 (4)0.0019 (4)
N20.0473 (7)0.0276 (6)0.0288 (6)0.0021 (5)−0.0120 (5)−0.0032 (4)
O10.0431 (5)0.0240 (4)0.0312 (5)0.0049 (4)−0.0081 (4)0.0028 (4)
O20.0505 (6)0.0340 (5)0.0315 (5)−0.0006 (4)−0.0189 (4)−0.0030 (4)
O30.0594 (7)0.0227 (5)0.0405 (6)0.0071 (4)−0.0227 (5)−0.0051 (4)
O40.0452 (5)0.0257 (5)0.0282 (5)0.0014 (4)−0.0150 (4)−0.0028 (4)
O50.0797 (9)0.0227 (5)0.0346 (5)−0.0061 (5)−0.0174 (5)−0.0021 (4)
O60.0520 (6)0.0309 (5)0.0310 (5)0.0043 (4)−0.0204 (4)−0.0050 (4)
O70.0700 (8)0.0309 (6)0.0532 (7)−0.0154 (5)−0.0214 (6)0.0067 (5)
O80.0525 (6)0.0386 (6)0.0290 (5)−0.0023 (5)−0.0171 (4)−0.0034 (4)
C1—N11.3388 (18)C9—O31.2593 (16)
C1—C21.377 (2)C9—C101.4291 (17)
C1—H10.9300C10—O41.3000 (15)
C2—C31.372 (3)C11—O51.3023 (17)
C2—H20.9300C11—C121.4139 (17)
C3—C41.390 (3)C11—C141.4465 (18)
C3—H30.9300C12—O61.2658 (15)
C4—C51.376 (2)C12—C131.4802 (18)
C4—H40.9300C13—O71.2141 (17)
C5—N11.3475 (17)C13—C141.5141 (17)
C5—C61.505 (2)C14—O81.2356 (16)
C6—N21.485 (2)N1—H1A0.93 (2)
C6—H6A0.9700N2—H2A0.8900
C6—H6B0.9700N2—H2C0.8900
C7—O11.2462 (15)N2—H2B0.8900
C7—C101.4357 (16)O3—H5A1.46 (2)
C7—C81.4886 (17)O4—H4A0.99 (2)
C8—O21.2268 (15)O5—H5A1.00 (2)
C8—C91.4929 (17)
N1—C1—C2119.82 (15)C10—C9—C889.62 (10)
N1—C1—H1120.1O4—C10—C9135.48 (12)
C2—C1—H1120.1O4—C10—C7131.74 (12)
C3—C2—C1119.01 (15)C9—C10—C792.73 (10)
C3—C2—H2120.5O5—C11—C12129.70 (12)
C1—C2—H2120.5O5—C11—C14137.03 (12)
C2—C3—C4120.09 (15)C12—C11—C1493.24 (11)
C2—C3—H3120.0O6—C12—C11132.49 (13)
C4—C3—H3120.0O6—C12—C13136.82 (12)
C5—C4—C3119.43 (15)C11—C12—C1390.68 (10)
C5—C4—H4120.3O7—C13—C12135.73 (12)
C3—C4—H4120.3O7—C13—C14136.29 (13)
N1—C5—C4118.78 (14)C12—C13—C1487.94 (10)
N1—C5—C6117.37 (12)O8—C14—C11136.71 (12)
C4—C5—C6123.85 (14)O8—C14—C13135.18 (12)
N2—C6—C5111.82 (11)C11—C14—C1388.10 (10)
N2—C6—H6A109.3C1—N1—C5122.79 (12)
C5—C6—H6A109.3C1—N1—H1A119.1 (12)
N2—C6—H6B109.3C5—N1—H1A117.8 (12)
C5—C6—H6B109.3C6—N2—H2A109.5
H6A—C6—H6B107.9C6—N2—H2C109.5
O1—C7—C10135.70 (12)H2A—N2—H2C109.5
O1—C7—C8134.73 (11)C6—N2—H2B109.5
C10—C7—C889.54 (10)H2A—N2—H2B109.5
O2—C8—C7134.48 (12)H2C—N2—H2B109.5
O2—C8—C9137.39 (12)C9—O3—H5A108.5 (9)
C7—C8—C988.12 (9)C10—O4—H4A108.8 (12)
O3—C9—C10134.53 (12)C11—O5—H5A115.9 (12)
O3—C9—C8135.83 (12)
N1—C1—C2—C31.5 (2)O1—C7—C10—C9177.87 (16)
C1—C2—C3—C4−2.5 (3)C8—C7—C10—C9−0.11 (10)
C2—C3—C4—C50.9 (3)O5—C11—C12—O6−4.0 (3)
C3—C4—C5—N11.8 (2)C14—C11—C12—O6177.80 (15)
C3—C4—C5—C6−177.64 (15)O5—C11—C12—C13176.91 (15)
N1—C5—C6—N2−96.31 (15)C14—C11—C12—C13−1.33 (11)
C4—C5—C6—N283.15 (19)O6—C12—C13—O74.0 (3)
O1—C7—C8—O20.6 (3)C11—C12—C13—O7−176.90 (19)
C10—C7—C8—O2178.65 (16)O6—C12—C13—C14−177.79 (17)
O1—C7—C8—C9−177.91 (15)C11—C12—C13—C141.27 (10)
C10—C7—C8—C90.10 (10)O5—C11—C14—O82.2 (3)
O2—C8—C9—O3−0.3 (3)C12—C11—C14—O8−179.74 (17)
C7—C8—C9—O3178.15 (17)O5—C11—C14—C13−176.71 (18)
O2—C8—C9—C10−178.57 (17)C12—C11—C14—C131.30 (10)
C7—C8—C9—C10−0.11 (10)O7—C13—C14—O8−2.1 (3)
O3—C9—C10—O4−0.8 (3)C12—C13—C14—O8179.77 (16)
C8—C9—C10—O4177.53 (16)O7—C13—C14—C11176.91 (19)
O3—C9—C10—C7−178.19 (17)C12—C13—C14—C11−1.24 (10)
C8—C9—C10—C70.11 (10)C2—C1—N1—C51.3 (2)
O1—C7—C10—O40.3 (3)C4—C5—N1—C1−3.0 (2)
C8—C7—C10—O4−177.69 (15)C6—C5—N1—C1176.53 (13)
D—H···AD—HH···AD···AD—H···A
N1—H1A···O10.93 (2)1.74 (2)2.6598 (15)166.7 (19)
N2—H2B···O2i0.892.052.8565 (16)150
N2—H2B···O5i0.892.563.1613 (17)126
N2—H2C···O6i0.892.022.8765 (16)161
N2—H2A···O8ii0.891.902.7580 (15)162
O4—H4A···O6iii0.99 (2)1.51 (2)2.4993 (14)175 (2)
O5—H5A···O31.00 (2)1.46 (2)2.4583 (14)175 (2)
C7—O1···Cg2ii1.25 (1)3.38 (1)3.3226 (14)77 (1)
C7—O1···Cg3iv1.25 (1)3.39 (1)3.3297 (14)76 (1)
C13—O7···Cg2v1.21 (1)3.52 (1)3.4188 (15)75 (1)
  9 in total

1.  Ammonium hydrogen squarate-water (3/2)

Authors: 
Journal:  Acta Crystallogr C       Date:  2000-01       Impact factor: 1.172

2.  A short history of SHELX.

Authors:  George M Sheldrick
Journal:  Acta Crystallogr A       Date:  2007-12-21       Impact factor: 2.290

3.  Development of the Colle-Salvetti correlation-energy formula into a functional of the electron density.

Authors: 
Journal:  Phys Rev B Condens Matter       Date:  1988-01-15

4.  Associations of squaric acid and its anions as multiform building blocks of hydrogen-bonded molecular crystals.

Authors:  G Gilli; V Bertolasi; P Gilli; V Ferretti
Journal:  Acta Crystallogr B       Date:  2001-11-29

5.  General rules for the packing of hydrogen-bonded crystals as derived from the analysis of squaric acid anions: aminoaromatic nitrogen base co-crystals.

Authors:  V Bertolasi; P Gilli; V Ferretti; G Gilli
Journal:  Acta Crystallogr B       Date:  2001-07-25

6.  Synthesis, an experimental and quantum chemical computational study of a new nonlinear optical material: 2-picolinium hydrogensquarate.

Authors:  Ufuk Korkmaz; Ahmet Bulut
Journal:  Spectrochim Acta A Mol Biomol Spectrosc       Date:  2014-04-20       Impact factor: 4.098

7.  Crystal structure refinement with SHELXL.

Authors:  George M Sheldrick
Journal:  Acta Crystallogr C Struct Chem       Date:  2015-01-01       Impact factor: 1.172

8.  Structure validation in chemical crystallography.

Authors:  Anthony L Spek
Journal:  Acta Crystallogr D Biol Crystallogr       Date:  2009-01-20

9.  The Cambridge Structural Database.

Authors:  Colin R Groom; Ian J Bruno; Matthew P Lightfoot; Suzanna C Ward
Journal:  Acta Crystallogr B Struct Sci Cryst Eng Mater       Date:  2016-04-01
  9 in total

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