Growth, crystal structure, Hirshfeld surface analysis, DFT studies, physicochemical characterization, and cytotoxicity assays of novel organic triphosphate

A novel organic–inorganic hybrid compound, named (1-phenylpiperazinium) trihydrogen triphosphate, with the formula (C10H15N2)2H3P3O10 has been obtained by low speed of evaporation of a mixture of an alcoholic solution of 1-phenylpiperazine and triphosphoric acid H5P3O10 at room temperature after using the ion exchange chemical procedure. To carry out a detailed crystallographic structure analysis, single-crystal X-ray diffraction has been reported. In the molecular arrangement, the different entities are held together through N–H…O, O–H…O, and C-H…O hydrogen bonds, building up a three-dimensional packing. Powder X-ray diffraction analysis is acquired to confirm the purity of the product. The nature and the proportion of intermolecular interactions were investigated by Hirshfeld surface analysis. In order to support the experimental results, a density functional theory (DFT) calculation was performed, using the Becke-3-parameter-Lee–Yang–Parr (B3LYP) function with LANL2DZ basis set, and the data indicate much agreement between the experimental and the theoretical results. Thus, the physicochemical properties were studied employing a variety of techniques (FTIR, NMR, UV–visible, and photoluminescence). To get an insight of the possible employment of the present material in biology, cell viability assays were performed.


Introduction
The scientific community has been focused more than ever in improvement and development of organic-inorganic hybrid materials due to the growing need for new sophisticated products to allow the access to various spectra of functionalities [1][2][3][4][5][6][7]. These composites become trend owing to their interesting features to gather the excellent merits of both organic and inorganic worlds on the molecular level. Up to date, hybrid solids are subject to many scientific studies due to their low cost, ease of synthesis, structural tenability, and specific physical, chemical, and biological properties. Such materials can be applied in both academic research and technological applications such as optic [8,9], electronic [10], mechanics, sensors, magnetism [11,12], catalysis, and medicine [13,14].
In this context, the main focus was on the hybrid compounds based on phosphates, in particular. Among them, the choice was on the triphosphates, those with the formula of the anion [P 3 O 10 ] 5− . Unsurprisingly, the number of these series of compounds remains limited in comparison with other condensed phosphates because they are chemically unstable in their synthesis. Indeed, the phosphoric chain containing three PO 4 tetrahedra, which are linked together by two internal oxygen atoms, can be destructed and gives either a diphosphate or monophosphate compound. Since their first synthesis, only eight composites have appeared in literature. These include (2-C 2 H 5 C 6 H 4 NH 3 ) 3 10 .2H 2 O [22].
As for the organic materials, the aromatic amines have been widely acted as templates, termed structure directing agents, because of their important characteristics thanks to the presence of delocalized π-electrons. Piperazine derivatives present an important group of aromatic amines, which are composed of a six-member ring containing the two opposing nitrogen. These latter have been used as organic part in various compounds and are able to form a dication in the boat and chair forms. Owing to their excellent biological, pharmacology, and cardiovascular properties, piperazine derivatives are of great significance to the rational design of well-known drugs with various therapeutic uses, such as antimalarial agents [23,24], anti-bacterial agents [25], anti-psychotic agents [26][27][28], anti-hypertension, antifungal [29], anti-inflammation [30], and cytotoxic. Due to the extensive use of these amines in wide variety of medical formulations, researcher efforts have focused in the synthesis of new materials consisting of piperazine derivates to expand their scope of application.
Within this context, we report in this work the synthesis of a novel triphosphate compound, named (1-phenylpiperazinium) trihydrogen triphosphate (C 10 H 15 N 2 ) 2 H 3 P 3 O 10 , through the method of crystallization. In order to reach a fine description of the architecture of the title compound and provide detailed information about the internal lattice of the crystal, a single-crystal X-ray diffraction was used. The optimized geometry was calculated using a method based on the density functional theory (DFT) employing B3LYP/LANL2DZ basis sets. Experimental data and theoretical calculations are compared. Furthermore, Hirshfeld surface analysis is required to elucidate the role of intermolecular contacts. A vibrational study was investigated and discussed. Frontier orbitals, Mulliken charges, and molecular electrostatic potential of the title compound have been calculated. The optical properties have been also well discussed in detail. Additionally, cell viability studies in the presence of the compound were also conducted in order to assess its biocompatibility and lack of cytotoxicity.

Synthesis
Single crystals of (C 10 H 15 N 2 ) 2 H 3 P 3 O 10 were obtained via an acid-base reaction under normal conditions of temperature and pressure. The chemical synthesis of the title compound was carried out in two steps: The triphosphoric acid was first prepared by passing a sodium salt solution of Na 5 P 3 O 10 (a starting material to prepare the organic triphosphates) through an ion exchange resin (Amberlite IR 120), and then an alcoholic solution of 1-phenylpiperazine was added drop by drop to this aqueous solution until a pH = 2.
Schematically the synthesis reaction is: After a few days of slow evaporation at 298 K, colorless transparent crystals appeared in the solution.

X-ray crystallography
The powder X-ray diffraction (PXRD) was performed using Cu-Kα (λ = 1.5406 Å) radiation on a Bruker D8-advance diffractometer; for typical powder patterns, data is collected at 2θ over the range of 0-40°. A tiny single crystal of approximate dimension 0.21 × 0.16 × 0.14 mm 3 was chosen for the diffraction measurement. The data were collected at 293(2) K with an Enraf-Nonius MACH3 four-circle diffractometer, using graphite monochromated Mo-K α radiation (λ = 0.71073 Å). The structure was solved and refined with SHELXT [31] and refined using SHELXL [32]. The drawing of the molecular structure was made with DIAMOND [33]. Further details of the structure analysis are reported in Table S1. The hydrogen bonds are given in Table S2. Hirshfeld surface and their associated two-dimensional fingerprint were plotted with the Crystal Explorer (version 3.1) software [34] which use the CIF files of the desired compound in order to analyze the intermolecular interactions in the crystal.

Computational methods
Gaussian03 program [35] was used for the quantum chemical calculations and the optimized molecular geometries. All the calculation results were visualized with the Gauss-View 4.1 [36]. The structure based on the crystallographic data in the supplementary table was used as starting points at the density functional theory (DFT) with the Becke-threeparameter hybrid exchange functional combined with the Lee-Yang-Parr correlation functional (B3LYP) levels. It is to be noted that the LANL2DZ was used as the basis set. The molecular electrostatic potential (MEP) map, Mulliken population charge, and FTIR spectrum of optimized structure were calculated at the same basis set. The calculated vibration frequencies were scaled using the scaling factor 0.9614 [37]. The absence of imaginary frequencies in the calculated vibrational spectrum confirms that the structure corresponds to minimum energy.

Spectroscopic measurements
A Nicolet IR200 FTIR equipped with a diamond micro-ATR was used to characterize the infrared stretching and bending bands of the (1-phenylpiperazinium) trihydrogen triphosphate in the 4000-400 cm −1 range.
Solid state UV-vis absorption spectra were performed on a Perkin Elmer Lambda 35 spectrophotometer in the range of 200-800 nm.
Emission spectrum was performed using the PerkinElmer LS55 fluorescence spectrometer equipped with a 450-W xenon lamp as the excitation source using solid sample at room temperature.
All NMR experiments were carried out using D 2 O as solvent on a Bruker Avance III spectrometer operating at 400 MHz.

Biological assays
After in vitro characterization, the new organic triphosphate synthesized was evaluated in experiments with cells. These additional studies were undertaken to assess and to exclude any toxic effect of the compound. For these experiments, RAW 264.7 murine macrophage cell lines were used as model system. The cells were routinely grown in a DMEM (Dulbecco's modified Eagle's medium)/nutrient mixture F-12 ham containing 10% fetal calf serum (FCS) and 1% penicillin/streptomycin purchased from Sigma-Aldrich. The maintenance of the cell culture was carried out according to standard protocols provided by the European Collection of Authenticated Cell Cultures (ECACC). To study the effect of the synthesized compound, cells were seeded in 24-well culture plates at a density of 1.510 6 cells per well and treated with the corresponding concentration of compound (ranging from 100 µM to 10 nM) for 24 h. Then, the medium was gently aspirated and cells were washed with PBS. Then, 200 µL of a solution of an MTT (0.1 mg mL −1 ) in fresh medium was added and the cells were incubated for 45 min at 37 °C. Finally, the medium was aspirated and 200 µL of DMSO was added to measure absorbance of each well at 492 nm using a 96-well multiwell plate reader (Wallac 1420 VIC-TOR2TM, Perkin Elmer). Three independent experiments were carried out.

Results and discussion
Description of the crystal structure X-ray diffraction patterns of the experimental and the simulated studied sample are shown in Fig. 1. Both the peak positions displayed in the measured patterns and the simulated patterns are in good line. This result reveals clearly that the synthesis product is in pure phase. A slight difference in the positions and intensities of some peaks can be observed, which are ascribed to the preferred orientation of the powder samples. It is noted that some of the extra unexpected lines with weak intensities are observed which is certainly due to the presence of some impurities in the powder sample that are absent in the single-crystal state.
An ORTEP plot of (C 10 H 15 N 2 ) 2 H 3 P 3 O 10 is shown in Fig. S1. This structural model in which the asymmetric unit contains one inorganic anion [H 3 P 3 O 10 ] 2− and two organic cations denoted [C 10 H 15 N 2 ] + crystallographically independent. Figure 2 displays the projection of the structure of (1-phenylpiperazinium) trihydrogen triphosphate in the (ac) plane.   The longest ones with average value equal to 1.6227 Ǻ correspond to the two bridging oxygen atoms, the intermediate ones with average value equal to 1.569 Ǻ correspond to the P-OH bonding, and the shortest ones with average value equal to 1.477 Ǻ correspond to the external oxygen atoms. The average values for the P-O distances and O-P-O angles are 1.548 Ǻ and 109.36°, and the O-P-O average angle is always very close to 109°. Such distances and angles are quite similar to those measured in other triphosphate anions [15].
The average values of the distortion indices were calculated using the Baur method [38] which is based on the following formula: The results of the calculation are [DI (OPO) = 0.057; DI (PO) = 0.083; and DI (OO) = 0.068]. Reviewing these values we can conclude that the distortion in the P-O distances is slightly higher than O-O distances. In this structure, the PO 4 group can be regarded as a regular arrangement of oxygen atoms with the phosphorus atom softly displaced from the gravity center. The two crystallographically independent organic cations adopt a chair conformation, which is the most stable conformation. The conformation of the piperazine six-membered ring can be described in terms of Cremer and Pople puckering coordinates [39]. In this crystal structure, the puckering parameters are as follows: QT = 0.5174 Å, q2 = 0.0123 Å, q3 = 0.5172 Å, θ = 1.36°, and ϕ = − 61.79° for the (N2-C10-C9-N1-C7-C8) ring and QT = 0.5432 Å, q2 = 0.0432 Å, q3 = 0.5415 Å, θ = 4.56°, and ϕ = 176.67° for the (N4-C19-C18-N3-C17-C20) ring. DFT calculations were applied on (C 10 H 15 N 2 ) 2 H 3 P 3 O 10 at B3LYP/ LANL2DZ level. The optimized structure of the title compound is illustrated in Fig. 3.
The experimental and theoretical structural parameters of the studied compound are given in Table 2. After a careful comparison, we find that the optimized parameters such as bond lengths, bond angles, and torsion angles are compatible with those determined using single-crystal X-ray diffraction method. The slight minor deviations observed can be explained by the fact that the experimental data is obtained in the solid state in the gaseous phase, whereas in the theoretical methods the molecular interactions are not taken into account. As shown, the optimized parameters (bond lengths, bond angles) are very close with the experimental data (Fig. S3). The calculated geometrical parameters of the anionic entity H 3 P 3 O 10 go in good consistency with those found in other studies especially with methyl triphosphate (− 1) that are predicted by DFT/6-31G* method of computations [40].

Hirshfeld surface studies
Surface analysis is a powerful tool in the visualization and exploration of the intermolecular interactions in the crystal structure of compound. The Crystal Explorer 3.1 program which processes structure input files in the CIF format was used to calculate Hirshfeld surfaces [41] and their associated two-dimensional fingerprint plots (2D fingerprint) [42] which summarize and provide relevant information of all the intermolecular interactions in the crystal. The normalized Projection of the crystal structure of (C 10 H 15 N 2 ) 2 H 3 P 3 O 10 in the (ac) plane The italicized values indicate the P-O distances 1.3190 (15) 101.30 (10) 112.17 (12) ( contact distance (d norm ), based on two types of distances defined: d e , the distance from the point to the nearest nucleus external to the surface, and d i , the distance to the nearest nucleus internal to the surface, respectively is calculated via the following expression: where r vdw i is the van der Walls radius of the atom that lies inside the surface of Hirshfeld, while r vdw e is the van der Walls radius of the atom that lies outside of the surface of Hirshfeld.
For describing the surface characteristics of the crystal structure, Hirshfeld surface and two-dimensional fingerprint plots are useful tools using the Crystal Explorer package. Hirshfeld surface of (C 10 H 15 N 2 ) 2 H 3 P 3 O 10 with mapped d norm is portrayed in Fig. 4.
The surface of the three-dimensional d norm was obtained in the range − 0.830 (red) to 1.414 (blue) using a standard (high) surface resolution for the title compound. A redwhite-blue color scheme is used for the analysis of the molecular. The inter-contacts included in hydrogen bonds are represented with the red spots over Hirshfeld surface. The blue fields indicate areas where neighboring atoms are too far away to interact with each other [43][44][45][46][47]  The overall fingerprint plot for the studied compound is shown in Fig. 5a; the examination of decomposed 2D fingerprint plots shows that the O…H/H… O contacts represent the largest relative contribution, amounting to 43.7% in the compound, appearing as two symmetric long spikes (Fig. 5b) Fig. 3 The optimized geometric structure of (C 10 H 15 N 2 ) 2 H 3 P 3 O 10  (Fig. 5c). These contacts appear as a single broad peak at d e = d i ~ 1 Å, and it should be also noted that (d e + d i ) ~ 2 Å, which is longer than the generally accepted van der Waals radius for hydrogen atom. The C … H/H … C contacts cover 12.9% of the total surface and appear as two broad short spikes (Fig. 5d). The H … N/N … H and O … O contacts comprise 2.1% and 1% respectively. These contacts have very little effect on crystal packing (Fig. 5e, f). C … C and P … O/O … P contacts are the less contributed to the Hirshfeld surfaces with a small percentage of 0.3% and 0.2% on the Hirshfeld surface, respectively (Fig. 5g, h). 2D fingerprint (full and decomposed) plot with combination of d e and d i provides summary of intermolecular contacts in the crystal. The breakdown of FP into specific atom…atom contacts in a crystal provides the types of intermolecular contacts experienced by the molecule quantitatively.
Thus, fingerprint graphics and the molecular Hirshfeld surface are a good way to understand the contributions of diverse contacts that assist stabilize molecular structures.

IR spectroscopy
The IR spectroscopy has been used due to its usefulness in the determination and the identification of the frequencies of the vibrations on the crystal structure. The theoretical IR spectrum, calculated by using DFT/B3LYP method with LANL2DZ basis set, was made on the optimized geometries of the compound. The scaling factor is taken as 0.9614 to reduce the discrepancy between the experimental frequencies and the computational methods. For visual comparison, the theoretical IR spectrum and the experimental one are schematically illustrated in Fig. 6. The detailed assignments of the scaled calculated and vibrational experimental modes are quoted in Table 3.
The bands appeared in the region of 1300 to 1100 cm −1 , which is an important region for the identification of the stretching vibrations, asymmetric symmetric, of the PO 2 central atomic group. The peaks detected between 1259 and 966 cm −1 are attributed to the stretching vibrations of the PO 3 terminal atomic groups [48]. These vibrations are well observed by DFT calculation in the range 1086 to 959 cm −1 . The stretching P-O-P modes are located in the 896 to 687 cm −1 region [49]. This mode was predicted by DFT calculation at 840 cm −1 . The bands which appear between 600 and 400 correspond to the bending vibrations of the PO 3 terminal groups while the DFT calculation gives these modes between 673 and 577 cm −1 .
The bands which are located in the high-frequency region, those between 3100 and 3000 cm −1 , are generally due to the It is clearly observed that the bands in 2836 to 2250 cm −1 correspond to the stretching vibrations of the -NH 2 + , -CH 2 , and N-H group. The theoretical calculations have predicted the stretching -NH 2 and C-H mode at 3070 cm −1 . It is well known that the wavenumber of the C = C stretching vibration, known as semicircle stretching, is observed normally between 1600 and 1400 cm −1 [50,51]. In this study, the peaks from 1644 to 1325 cm −1 are attributed to the symmetric and asymmetric stretching vibrations ν(C = C), the deformation modes δ(N-H), and ν(O-H) of P-OH groups. The theoretical calculations show that the bands corresponding to the ν(C = C) are detected at 1590 cm −1 . The bands between 1455 and 1333 cm −1 are assigned to -CH 2 deformation modes. The bands situated at 1260 and 1168 cm −1 are due to (C-N) stretching. The peak at 1089 cm −1 is assigned to asymmetric and symmetric C-C stretching modes. Bands detected between 965 and 902 cm −1 are attributed to (C-H) out-of-plane deformation. Bands which appear between 764 and 691 cm −1 are assigned to (C-N) and (C-C) out-of-plane deformation. Finally, those observed at 569 to 496 cm −1 are attributed to the mode of deformation of the group δ (C = C) out of the plane. It is obvious that the theoretical IR spectrum shows a good conformity with the experimental one (Fig. S4).

Frontier molecular orbital analysis
The highest occupied molecular orbital (HOMO), which is the orbital that acts as an electron donor, the lowest unoccupied molecular orbital (LUMO), which is the orbital that acts as electron acceptor, and their electronic band gap are the most important parameters in the field of theoretical quantum chemistry for understanding the chemical reactivity of the molecules and their stability [52][53][54]. The electron distributions of the HOMO-LUMO energy for the synthesized compound computed at the Becke's three-parameter functional and the Lee-Yang-Parr functional (B3LYP) with the basis set LANL2DZ are depicted in Fig. 7.
The HOMO and LUMO energies, the energy gap, and other chemical reactivity descriptors that could be used to predict the chemical stability and reactivity, such as the ionization potential (I), the electron affinity (A), the Fig. 6 Simulated IR spectra of (C 10 H 15 N 2 ) 2 H 3 P 3 O 10 computed at B3LYP/LANL2DZ basis set (red). FTIR spectrum (blue) The slight difference is due to the calculations made in the gas phase, where interactions between molecules are not taken into account. Actually, in crystal structure, each group of the molecule is surrounded with other types of molecule groups via intermolecular interactions.
The large values of the electronic band gaps for (C 10 H 15 N 2 ) 2 H 3 P 3 O 10 favor their hard nature with low chemical reactivity and high stability. The chemical hardness (η) calculated as [− (E HOMO − E LUMO )/2] is found 1.64 eV, and this value reflects that the compound is chemically stable. The softness (σ), which is the reciprocal of the hardness calculated as [− 2(E HOMO − E LUMO )], is found 0.30 eV. The obtained small hardness parameters indicate that the title compound is a hard system which is not prone to chemical reaction and prove also that this compound presents high kinetic stability. The chemical reactivity descriptors used the following equations [55,56]: Absolute electronegativity (χ) and chemical potential (μ)

Molecular electrostatic potential
The molecular electrostatic potential (MEP) is a powerful descriptor and an effective approach in understanding the intermolecular and intramolecular interactions in the solid states and offers quite accurate information about sites for electrophilic and nucleophilic. In other words, it is able to convey information about the interaction, active sites, and charge distribution of a molecule. Calculation of MEP was conducted at a high theoretical DFT level using B3LYP/ LANL2DZ level of theory and is given in Fig. 8. As you can see in the three-dimensional model of the electrostatic potential map, a color spectrum ranging from red to dark blue, with red as the lowest electrostatic potential energy value indicating the nucleophilic region with rich electrons in the environment, blue-colored region as the highest, is employed to convey the varying intensities of the electrostatic potential energy values and the green color stands for the parts of the molecule where the electrostatic potentials are close to zero (neutral areas). The electrostatic potential increases in the order red < orange < yellow < green < blue. These sites provide information about the region in which the molecules can interact with each other and the hydrogen bonding contacts [57][58][59].  Fig. 7 The electron distribution of the HOMO and LUMO energy levels Table 4 The calculated parameters of (C 10

Mulliken population analysis
Mulliken population method was used to obtain the total atomic charge distributions and to describe the electronic structure, molecular dipole moment, charge transfer mechanism, and polarizability. The Mulliken charges for the molecule were performed with B3LYP/LanL2DZ level of theory in the gas phase. The atomic charges play a key role in the application of quantum mechanical simulations [60]. The charge distribution on atoms is important in explaining donor and acceptor pairs and gaining insight into the overall activity of the compound. Mulliken is highly effective in detecting nucleophilic or electrophilic attacks and regions sensitive to other molecular interactions. The corresponding Mulliken charges are tabulated in Table 5.
From the results, it is clear that all hydrogen atoms in the molecule have a positive charge. Also, all phosphorus atoms P1, P2, and P3 possess positive. It is worthy to mention that the oxygen atoms (O1, O3, O6, O7, and O10) displayed maximum negative charges. Because of these oxygen atoms' environment, all phosphorus atoms have higher Mulliken atomic charge than other positive atoms. The maximum of positive charges of carbon and nitrogen atoms were bonded to oxygen atoms. The results are supported with electrophilic/nucleophilic nature of MEP surface. 13 C NMR spectrum of the title compound is shown in Fig. S5a. Since the organic motif is symmetric and contains ten carbon atoms, each one has its own electronic environment. But as shown from the spectrum, it exhibits only six resonances. According to previous studies [61,62], the carbons observed between 40 and 50 ppm are assigned to the nitrogen-bonded CH 2 groups while the aromatic carbons typically occur between 115 and 150 ppm. It is obvious that the peak at 149 ppm corresponds to the carbon bonded to the strongly attracting nitrogen atom. The 1 H NMR spectrum of the title compound is shown in Fig. S5b; a total often peaks were observed corresponding to fifteen hydrogens. The signals observed at 3.40 ppm and 3.41 ppm are assigned to C(8,10)H 2 and C(7,11)H 2 respectively. At 4.7 ppm, there is a simple signal which is normally the chemical shift of the water proton (as solvent). It is important to note that the range [6-7.5 ppm] is a common zone for aromatic ring protons. The triplet associated with the signals 7.05 ppm, 7.07 ppm, and 7.08 ppm is attributed to C(5)H. However, the 1 H signals of C(1) H and C(3)H appear at 7.11 ppm and 7.13 ppm. Finally, the C(6)H and C(4)H are indeed observed at 7.35 ppm, 7.37 ppm, and 7.39 ppm.

UV-vis absorption
The solid state UV-vis absorption spectrum of the entitled compound, measured at room temperature in the range 200-800 nm, is presented in Fig. S6. As can be seen, two distinct peaks with different intensities and wavelength are observed in the absorption spectrum. The intense peak around 294 nm can be ascribed to the π-π* transition of the aromatic ring of the phenyl group, whereas the weak band near 409 nm probably may originate from the n-π* transition of the triphosphoric anion. The determination of the optical band gap (E g ), which is a pivotal parameter for describing the solid state materials, can be evaluated based on the model proposed by Tauc [63] by plotting (αhυ) 2 versus hυ (α is the absorption coefficient and hυ is the energy of the incident photon where h represents the Planck's constant and υ is the frequency of vibration). The absorption edge is offered by the extrapolation of the curve until the energy axis. As shown in Fig. S7, the value of the optical band gap is 2.82 eV, which proves that the studied compound is a semiconductor and could be used for optical applications in far UV and optoelectronics [64]. The band gap between HOMO and LUMO calculated with DFT was found to be 3.27 eV which is very close in value to the optical band gap (2.82 eV).

Solid state photoluminescence property
Photoluminescence referred to as PL is a nondestructive method which is widely used to identify the luminescence property of the crystalline material. To further understand and study the optical properties of (C 10 H 15 N 2 ) 2 .H 3 P 3 O 10 , the photoluminescence was recorded in the solid state at room temperature over a spectral range from 360 to 470 nm and the spectrum is shown in Fig. S8. The emission spectrum at an excitation wavelength choosing at λ ex = 294 nm presents one band of luminescence located around 351 nm. This luminescence originates from the intraligand π-π* of the transition of the 1-phenylpiperazinium cation. In order to determine fluorescence quantum yield of the title compound, pyrene (quantum yield ϕ r = 0.32 in cyclohexane) was used as a reference. The fluorescence quantum yield [65] can be calculated from the following equation [66]: where the subscripts s and r stand for sample and reference, respectively. ϕ r denotes the fluorescence quantum yield of reference. I stand for the integrated area under the emission curves. A is the absorbance at a particular excitation wavelength. is the refractive index of the medium. The absorbance of the dye at the excitation wavelength was always kept ∼0.1. The fluorescence quantum yield of 1-phenylpiperazinium trihydrogen triphosphate using the relative method was determined to be 0.60. This value claims that the synthesized compound is significantly high luminescent.

Viability assays
As depicted in Fig. 9, experiments with cells were performed by measuring cell viability in the presence of a wide range of concentrations of (C 10 H 15 N 2 ) 2 H 3 P 3 O 10 (from 10 nM to 100 μM) upon incubation for 24 h. Remarkably, no significant cytotoxic effect was observed even at high concentrations in the micro molar range and cell viability remained around 100% in all cases. These results point out that this hybrid material has no short-term cytotoxicity and is biocompatible under the conditions studied, which opens the possibility for its use in biological contexts.

Conclusion
In this work, we have successfully synthesized a novel organic triphosphate. This is noteworthy since such family remained limited in comparison with other condensed phosphates. Our discovery has been characterized by using different physicochemical techniques. The crystal structure can be described as quasi infinite layers of anions and between them are inserted the organic cations to be built, via a variety of interactions, a three-dimensional network. The Hirshfeld surface analysis reveals the percentage of intermolecular contacts of the obtained products. The geometrical parameters, collected within the framework of DFT calculations by using B3LYP methods with LANL2DZ basis set, are well correlated with the experimental results. Detailed IR studies were carried out; as can be seen, there is a good conformity between the experimental results and the theoretical ones. Moreover, NMR spectra were acquired and the results are in line with the crystallographic data. Finally, the performance of the new organic triphosphate compound in a cellular context was also tested. Remarkably, the compound was not toxic even at concentrations as high as 100 μM, which suggests its biocompatibility. Overall, we hope these results could inspire future works in the development of organic phosphates and other hybrid compounds.