Crystals of the title compound, (C₇H₉N₂O)₃HSO₄SO₄, were prepared by slow evaporation at room temperature of an aqueous solution of sulfuric acid (98wt% from Fluka) and the organic molecule 2-Aminobenzamide (Sigma-Aldrich ) in a 2:3 molar ratio. The corresponding acid-base chemical reaction can be written as follows:

After agitation, the resulting solution was left to slowly evaporate at room temperature until single crystals suitable for X-ray structure analysis formulates and remain stable under normal conditions of temperature and humidity.

The title compound has been studied by various physico-chemical methods: X-ray diffraction, Infrared spectroscopy and Thermal analysis.

The atomic arrangement of the structure of the tris (2-amoniumbenzamide) sulfate (C₇H₉N₂O)₃HSO₄SO₄ was

described by a three-dimensional network of structural units formed by a cluster (HS₂O₈)³⁻ sulfate and three organic cations (C₇H₉N₂O)⁺. Figure 1 shows an ORTEP [9] stereoscopic projection of the crystal packing. The mineral skeleton of this compound is formed by basic and acid groups which are interconnected via a hydrogen bond type O(2)-H∙∙∙O(7), and are organized in isolated clusters (HS₂O₈)³⁻ in the plane (a, c) (Figure 2). The short distance O(2)∙∙∙O(7)= 2.485(3)Å, shows that this hydrogen bond was considered strong. The distance S(1)∙∙∙S(2) being of the order of 4.525(1)Å. Distances and bond angles describing anions () and () are shown in Table 2. S-O distances vary in the range [1.438(3) - 1.506(4)Å]. The review of these distances reveals that the last distance S-O(2) [1.506(4)Å] is the longest, this is due to the location of a proton on

oxygen O(2) of the anion, this characteristic is in line with those observed in the protonated oxoanions [10] -[12] , the mean value of S-O distances and angles O-S-O are: 1.466(3)Å, 109.46(19), 1.473(3)Å, 109.38(20) respectively for the tetrahedra S(1)O4 and S(2)O4. These values are also in good agreement with those observed for similar anionic groups [13] [14] . The oxygen atoms O(1) and O(3) of the tetrahedron are doubly protonated, the HSO₄ have the longest distances [1.456(3), 1.466(3)Å], while O(4) engaged in a single hydrogen bond it is a S-O distance smaller [1.438(3)Å]. The interaction of the sulfuric acid with the organic molecule (C₇H₈N₂O) leads to the protonation of nitrogen grafted on the benzene ring and the formation of three cations (C₇H₉N₂O)⁺ crystallographically independent. Respectively denoted: A{C(1) C(7)}, B{C(8) C(14)} et C{C(15) C(21). Figure 3 shows a projection along the a axis of the atomic arrangement in (C₇H₉N₂O)₃HSO₄SO₄. Main geometrical characteristics of these cations are summarized in Table 3; these organic species are no local symmetry in the structure. Note that the two cations A and C are associated with two hydrogen bonds N(1)-H(1N1)∙∙∙O(10)

and N(5)-H(2N5)∙∙∙O(11) to form a first type of dimmer located in planes z = (2n + 1)/4. A second type of dimmer formed by two B cations that associate through hydrogen bond N(3)-H(2N3)・・・O(9) is situated around the center of inversion (0, 0, 0) (Figure 4, Figure 5).

The work demonstrating the important role of hydrogen bonds, the stability of the structure reveals two types of connections: O-H∙∙∙O and N-H∙∙∙O, the structure studied in this work, contains a single hydrogen bond of first type and the second type seventeen. The only link O(2)-H(O2)∙∙∙O(7) considered high [O(2)-H(O2)∙∙∙O(7) = 2.485(3)Å] [14] , brings the two anionic species as a cluster (HS₂O₈)³⁻. it is noted, among the seventeen hydrogen bonds of the N-H∙∙∙O, six strong for which the distance N∙∙∙O range from 2.621(1)Å to 2.756(1)Å [14] and eleven moderately low [N∙∙∙O > 2.76Å] [15] . The second type of hydrogen bonds connecting the various clusters to generate the three-dimensional network structure.

The characteristics of the different hydrogen bonds are given in Table 4. As a result, the two types of hydrogen bonds, O-H∙∙∙O and N-H-O, contribute to the cohesion in the network of the present crystal structure.

The thermal study was conducted using a thermoanalyzer type Setaram TG-ATD92. The thermogram (TG- DTA) of Figure 6 is registered under an air atmosphere using a mass of 19.8 mg sample placed in a platinum crucible and heated from ambient to 400˚C.

The TG curve shows no mass loss in the area, room temperature 200˚C. However it shows a significant loss from 200˚C up. The DTA curve shows two endothermic peaks less intense at 98˚C and 110˚C which is attributed to two transitions likely stage since at this temperature was noticed no mass loss. Note that the observed thermal phenomena in differential thermal analysis are many and varied. The majority of these peaks are endothermic such as melting, evaporation, sublimation, dehydration. The remaining peaks are exothermic such as adsorption, crystallization and decomposition; however, the last two phenomena can also be endothermic. The DTA curve shows a succession of exothermic and endothermic peaks between 200˚C and 400˚C can be explained by the decomposition of the molecule. The endothermic peak observed at 199˚C is attributed to the melting of the anhydrous compound.

^aSymmetry operators: i) −x, y − 1/2, −z + 1/2; ii) −x, y + 1/2, −z + 1/2; iii) x − 1, y, z; iv) x, −y + 3/2, z + 1/2; v) −x, −y + 1, −z + 1; vi) x − 1, −y + 3/2, z − 1/2; vii) −x + 1, y − 1/2, −z + 1/2.

The literature study, conducted over several sulfates [16] [17] shows that specific frequencies of vibration of the free ion SO₄, in its ideal Td symmetry are ν₁ = 981 cm⁻¹, ν₂ = 451 cm⁻¹, ν₃ = 1104 cm⁻¹ and ν₄ = 614 cm⁻¹ [18] . Frequently encountered in structures, SO₄ tetrahedron are often distorted have low symmetry sites. The lifting of degeneracy and activity of inactive modes, in the ideal symmetry, multiply the number of bands in the infrared spectrum. The IR spectrum of compound (C₇H₉N₂O)₃HSO₄SO₄ is reported in Figure 7.

An attempt to assign frequencies to different stretching vibrations and deformation of the organic cation is performed based on previous work [19] [20] . Bands observed in the region 2562 - 3375 cm⁻¹ are assigned to symmetric and asymmetric vibrations of valence ν(NH₃), ν(NH₂), ν(CH) and ν(OH). The bands between 1538 - 1681 cm⁻¹ are attributed to deformation vibrations of bonds (NH₃) and (NH₂) as well as vibrations of valences ν(C=C) and ν(CN). Vibration symmetrical and asymmetrical deformation δ_s(CH) and δ_as(CH), occur in the area from 1276 to 1499 cm⁻¹. The deformation vibrations rocking type: ρ(NH₃), ρ(NH₂) and ρ(CH) appear in the 721 - 965 cm⁻¹ region. The twists τ(NH₃) and τ(NH₂) appear in 514 - 560 cm⁻¹ bands. Finally, the bands 1926 - 2369 cm⁻¹ domains are assigned to overtones and combination bands. The frequency bands in the region 410 - 484 cm⁻¹ are attributed to the symmetric deformation vibration of δ_s(SO₄). The asymmetric deformation symmetry δ_as(SO₄) was observed in the area 602 - 671 cm⁻¹. While that connected to the symmetry of valence SO₄ group is presented by the band 992 cm⁻¹. Bands observed in the 992 - 1186 cm⁻¹, on asymmetrical valence vibration ν_s(SO₄)δ_as(SO₄) region.

Crystallographic data for the structural analysis have been deposited at the Cambridge Crystallographic Data Centre, CCDC No 1000722. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge, CB2 IEZ, UK (fax: +44-1226-336033; e-mail: deposit@ccdc.cam).