Supramolecular assembly of guanidinium benzilate and benzylammonium benzilate: structural and spectroscopic (FT-IR, UV–Vis and photoluminescence) analyses

Guanidinium benzilate (GBA) and benzylammonium benzilate (BABA) have been prepared from guanidinium carbonate and benzylamine/benzilic acid (BA). GBA has inter-ionic, intraionic and intermolecular hydrogen bondings giving a three-dimensional supramolecular assembly. The carboxylate ion is present in the resonance form with C–O distances of 1.242 and 1.246 Å in GBA, whereas the C–O distances being 1.262 and 1.245 Å in BABA. In BABA, an inverted dimer with inter-ionic hydrogen bonding exist as a dimer with supramolecular assembly due to intermolecular hydrogen bonding between the ion pairs. So the counter cation decides the resonance form of the carboxylate ion, hydrogen-bonding network and the disposition of the phenyl rings in the benzilate and benzyl moiety. The IR, 1H NMR and 13C NMR spectral data have been interpreted using the crystal structure data and by the comparison between the two similar derivatives. Both the compounds show the formation of the ammonium benzilate or methylammonium benzilate moiety which decompose leaving no residue. Both the compounds exhibit the emission at 442 nm (blue) and 547.2 nm (green) on excitation at 257 nm. Chromaticity indicated excellent emission characteristics of both GBA and BABA which is necessary for OLED applications.


Introduction
Supramolecular chemistry is based on the intermolecular bond, in which species are bound together by non-covalent interactions (Zhou et al. 2021). Supramolecular compounds attracted the interest of researchers due to the tremendous progress in their applications in different fields (Soliman et al. 2020). It underpins the design and development of materials for a vast number of applications (e.g. sensors, nonlinear optics, switches, etc.). It is necessary to obtain atomic-level information to understand self-assembly at a fundamental level where the molecular crystals are the ideal supramolecular entities (Clausen et al. 2010). The formation of multiple hydrogen bonds between complementary organic molecules has recently been exploited in the molecular self-assembly of well-defined artificial supramolecular structures and materials (Ji and Xu 2010). The organic acids and bases are donor and acceptor is good for the multi-component congregation and they exhibited dimer, catemer and bridged synthons in the solid. So they are often chosen as building units for the supramolecular crystal engineering (Gao et al. 2018;Xu et al. 2020).
Benzilic acid is a strong organic acid (pKa = 3.05), comprising carboxylic acid (-COOH) and hydroxy (-OH) groups in its skeleton, which tend to form several supramolecular motifs (Madhankumar et al. 2019). Benzilic acid is used in polymers and medicine as an analytical agent . The structural chemistry and biochemistry of α-hydroxycarboxylic acids, such as benzilic acid (BA), have over the years attracted considerable research interest, which still challenges researchers in the multidisciplinary fields of advanced materials and the manufacture of glycolate pharmaceuticals and hallucinogenic drugs found in methyl derivatives of BA (Halevas et al. 2014). BA rearrangement has been well investigated (Xiao et al. 2015) and BA has the potential to coordinate in different ways as a multifunctional ligand (Gilda and Devarajan 2016). BA crystal was found to be twice that of the standard prototype in the second harmonic generation (SHG) efficiency and it has many nonlinear optics (NLO) (Karnan et al. 2022) applications. Benzilate derivatives of 2-amino-5-bromopyridinium or 2-amino-4-methylpyridinium or 2-aminopyridinium (Gomathi et al. 2021) have been reported.
Guanidinium carbonate [NHC(NH 2 ) 2 ] 2 ·H 2 CO 3 is a strong basic reactant with most organic and inorganic acids and is useful to enhance the physical property due to its structure containing imine group and amino acetal (two amine groups attached to the same carbon atom) functional group (Drozd 2007). Organic guanidine compounds are reviewed, with emphasis on natural products isolation, identification, synthesis and biological activities (Berlinck et al. 2008). The guanidine derivatives act as intermediates in the manufacture of photo chemicals, resins, rubber, fungicides, plastics, resins, rubber and disinfectant industries (Silambarasan et al. 2015). Many synthetic receptors comprising a guanidinium moiety have been designed and studied for their recognition pattern for a wide range of anions (Goswami et al. 2010;Panja et al. 2017). As an amine derivative, benzylamine has the additional rigid phenyl ring and the somewhat flexible CH 2 linker, which can provide more complex non-covalent associations when it is associated with the organic acids (Jin et al. 2015;Wen et al. 2017). Benzylamine is capable of decreasing the surface trap state density in thin films (Duim et al. 2019). Supramolecular assembly of benzylammonium hydrogen fumarate and benzylammonium hydrogen cyclobutane-1,1-dicarboxylate was reported (Ballabh et al. 2002). We hereby report the preparation and growth of benzilic acid derivative crystals. The harvested crystals were analysed by single crystal X-ray diffraction (SXRD), 1 H and 13 C NMR, FT-IR, UV-Vis and photoluminescence spectral analyses.

Preparation and growth of GBA (guanidinium benzilate)
Gunadinium carbonate (0.25 mol) was taken in 20 cm 3 of methanol and benzilic acid (0.5 mol) in 20 cm 3 of methanol was added. The solution was stirred for 0.5 h and filtered. The filtrate is left for evaporation for 27 days. The white crystals (Fig. S1) obtained are filtered and washed with methanol. Yield: 72%.

Preparation and growth of BABA (benzylammonium benzilate crystals)
Benzylamine (99% pure, specific gravity: 0.980) was used. Benzylamine (0.5 mol) in 20 cm 3 of metahnol was dissolved, to which benzilic acid (0.5 mol) in 20 cm 3 methanol was added and stirred for 0.5 h. The solution after keeping for 25 days left the crystals, on slow evaporation. The white crystals (Fig. S1) obtained are washed with methanol and dried. Yield: 68%. Reaction scheme of GBA and BABA is given in Scheme 1.

Characterization techniques
GBA and BABA crystals were subjected to single crystal XRD analysis. The crystals were kept at 296(2) K during data collection using Bruker APEX-II CCD diffractometer equipped with graphite monochromator and with an X-ray source of MoKα radiation (Table 1). The structures were Scheme 1. Preparation of GBA and BABA solved using the SHELXT-2014 (Sheldrick 2014) solution programme and refined using SHELXL2018/3 (Sheldrick 2015) programme using full-matrix least squares on F2 method. Olex2 1.5 (Dolomanov et al. 2009) is used to generate the ORTEP images and crystal packing diagrams. All non-hydrogen atoms were placed by anisotropic displacement parameters and hydrogen atoms were positioned isotropically. Hirshfeld analysis was performed by Crystal Explorer 21.5 programme (Spackman et al. 2021) to estimate the percentage of various interactions in the molecule using CIF file. The Avance III HD Nanobay 400 MHz FT-NMR spectrometer was used to analyse 1 H and 13 C NMR in CD 3 OD (deuterated methanol). FT-IR studies were performed using Perkin Elmer-4700 Spectrum, in the range of 4000-400 cm −1 . UV-Vis spectra were recorded using Perkin Elmer lambda 35 UV-Visible spectrophotometer in the wavelength range of 200-800 nm. PL spectrum was recorded using Jobin Yvon Flurolog-3-11 Spectrofluorometer unit, with a Xenon lamp of 450 W as the source. TG-DTA analysis was performed using NETZSCH NJA-STA 2500 Regulus, with a heating rate of 10 °C/min using an alumina crucible under nitrogen atmosphere.

Single crystal X-ray diffraction analysis
The guanidinium benzilate (GBA) (Fig. 1) exhibited a shorter C15=N2H at 1.314 Å and C15-N3 and C15-N1 bond lengths being 1.327 Å. The C15-N2 being more basic with sp 2 nitrogen atom got protonated by the carboxylic acid proton. The C2-OH group (C2-O3) was observed at 1.426 Å. The carboxylic C1-O1 and C1-O2 are 1.242 and 1.246 Å indicating the resonance in the COO − group. The C2-C3 and C2-C9 are of the order of 1.531 and 1.532 Å, longer than expected because there is no hyperconjugation or mesomeric interactions that are required for resonance.
In the guanidinium portion, the central carbon atom has sp 2 hybridization with a 120° bond angle indicating a symmetrical plane triangular structure. In the benzilate moiety, the C2 carbon atom has sp 3 hybridization. The O3-C2-C3 angle was found to be 106.79° which is due to the O-H (3) lone pairs will be lying on another phenyl (2) ring side. The O3-C2-C9 was found to be 110.67° higher than 109° due to the interaction between the lone pair of the OH group and the phenyl ring we have assigned the lone pairs more correctly from the bond angle data. It is interesting to note that in the two phenyl rings C8-C3-C4 and C14-C9-C10 have a bond angle around 117.8° which is lower than the expected sp 2 bond angle of 120° due to σ-π repulsion and steric hindrance due to -OH and COO − group. The proposal that the COO − group falls towards the phenyl ring 1 has been supported by the bond angle (122.81°) of C8-C3-C2. The C4-C3-C2 bond angle is 119.5° as expected. So the COO − group is disposed towards the 1 phenyl ring, especially towards the plane of C2-C3-C8-C9. In contrast, the other phenyl ring 2 showed C10-C9-C2 and C14-C9-C2 at 121°. The bond angle measurements have been interpreted to understand the disposition of the groups in the threedimensional space.
The N1-H1A-O3 lone pair (LP) and N2-H2B-O2 (LP) have bond lengths of 2.888 Å and 2.823 Å, respectively, due to inter-ionic hydrogen bonding, that is between the guanidinium ion and benzilate moiety. O3-H3-O2 1 (LP) at 2.814 Å has intermolecular hydrogen bonding with the other unit. N1-H2A-O1 2 and N3-H3A-O1 2 have bond lengths of 2.824 Å and 2.873 Å due to the intermolecular hydrogen bonding between the H2A or H3A of guanidinium of one molecule and carboxylic oxygen O1 (lone pairs) of the second lone pair of the neighbour molecular unit (Table 2) which gives a supramolecular assembly due to intermolecular hydrogen bonding between each molecular moiety. There are two types of hydrogen bondings present: (1) between guanidinium ion and benzilic acid in the same unit that is between the cation and anion (inter-ionic of the same molecule and intramolecular or intraformula (within the formula unit)) and (2) between the guanidinium ion of one unit and benzilic acid carboxylate ion of the second unit (intermolecular).
The hydrogen-bonding interactions, both intermolecular and intramolecular, fix the position of the phenyl rings to have the least intermolecular interactions between the phenyl rings. The stability of the crystal is due to this type of disposition of the phenyl rings one up and one down in different planes along with hydrogen-bonding interactions. It is noteworthy that the COO − is symmetrically resonance stabilized due to the complexity of the cation and enhanced interactions of the COO − group through hydrogen bonding with the cation.
In BABA crystal, it is interesting to note that the C1-O1 and C2-O2 bond lengths are 1.262 and 1.237 Å, respectively. Therefore, the counter cation influences the bond length's of the carboxylate ion. It is interesting to note that there are two units (Z = 2) with each unit as a dimer (BABA) 2 of BABA present in the P-1 unit cell in the triclinic system. This pattern gets repeated throughout the solid state. The first unit and the second unit with the designation of (I) in the dimer suggest that due to molecular interactions and sterical hindrance are the main reasons for such anomaly. The slight difference in the bond lengths, bond angles and torsion angles in the first molecule and second molecule (I) of the same dimer unit may be significant for physical and biological applications. The O2-C1-O1 is 125° with O1-C1-C2 and O2-C1-C2 being equal (117.6°). In BABA the angles around the sp 2 carboxylate carbon are not equal. The equal angles in GBA are due to hydrogen-bonding interaction which fixes the carboxylate ion in the resonance form.
The triclinic unit cell of BABA has two dimeric pairs in the P-1 space (Z = 2) group. The two inverted ion pairs to each other or asymmetric units come closer due to intermolecular hydrogen bonding between the ion pairs. The stability of the molecule is due to the three-dimensional hydrogen-bonding interaction. The orientation and the properties of the molecule depend upon the nature and extent of hydrogen-bonding interactions. In this molecule, the O3-H3 of the first is hydrogen bonded with the second (I) inverted pair unit carboxylate oxygen (O2I) of the other ion-pair molecule unit (Fig. S2) with a distance of 2.698 Å. The O3-H3 of the inverted unit has hydrogen bonding with neighbour yet another ion-pair carboxylate oxygen O2 2 with a bond length of 2.73 Å (D-A). This is responsible for the supramolecular assembly of the compound. The N1-H1B of the first unit has the hydrogen bonding with the carboxylate oxygen (O1I) of the second unit, with a distance of 2.716 Å. N1-H1C of benzylammonium ion of the first unit is involved in hydrogen bonding with O1 of the same unit with a bond distance of 2.77 Å and similarly, in the second unit, N1I-H1IC-O1I has a 2.763 Å. Intraion-pair hydrogen bonding is longer than intermolecular hydrogen bonding (Table 3). It is interesting to note that the BABA exists as a dimer asymmetric unit with strong intermolecular and intramolecular H-bonding (Fig. 2). But this could be called by the new term inter-intramolecular H-bonding. The empirical formula suggests the presence of two BABA units as a single molecular unity. It is unique that the molecule exists as a dimer in the solid state with an opposite orientation. Usually, we observe that acetic acid and benzoic acid exist as a dimer in nitrobenzene solvent, showing a higher (double) molecular weight. But this ion pair now exists as a dimer in the solid state (BABA). The two dimer units of (BABA) are present in the triclinic unit cell.

Hirshfeld analysis
Hirshfeld surfaces play an important role in revealing a piece of valuable information on intermolecular as well as intramolecular interactions which are closer to van der Waal's radii between nearest neighbours of the molecules (Madhankumar et al. 2020). The hydrogen donor and acceptor interactions through dark red spots are indicated by d e and d i surfaces. The three-dimensional representation of inter and intramolecular contacts was identified from different colour codes which are red, white and blue which represent strong, neutral and weak interactions, respectively, involved in the stability of crystal structure (Madhankumar et al. 2019). The crystallography information file (CIF) was utilized to analyse the type of inter and intramolecular interactions present in the molecules which was visualized by Hirshfeld analysis and it confirms the presence of the non-covalent van der Waals interactions (Clausen et al. 2010). The normalized contact distances "d norm" were calculated using the formula (McKinnon et al. 2007).
The fingerprint plots (Fig. 3) of atom-atom interactions indicated that the intermolecular and intramolecular interactions of GBA were observed between H…H (49.2%), O…H (19.2%), and C…H (26%), and N…H (5.2%). The stability of the material was emphasized by strong interactions between carboxylate oxygen of COO − and the hydrogen of NH 2 + of guanidinium ion. Hirshfield's analysis agrees with the X-ray structure that the intermolecular and intramolecular H-bonding exists in GBA to a greater extent of O-H (19.29%). Further H-H intramolecular interaction is greater in BABA, H-H (61.6%) as expected because the molecule has three benzene rings compared to GBA (H-H: 49.2%) and further BABA exist as a dimer in the solid state as one formula unit. In BABA, many H-H interactions can be present as a set of two molecules as a dimer is squeezed in the triclinic system (P-1). The O-H interactions in BABA are lesser than in GBA, as supported by X-ray data. Hirshfeld interactions of BABA were observed between C…C (1.7%), O…H (14.6%), C…H (21.4%), and H…H (61.6%). The Hirshfeld analysis of BABA and along with the interactions fingerprint plots (Fig. 4) showed that BABA has more surface area and more cages, more reactive or binding sites as a drug. As a drug, it can lock different enzymes extending molecular interaction and to bring out necessary physiological or pathological effects. It is interesting to note that the volume of BABA (1824.8Å 3 ) is greater than GBA (716.3 Å). Hirshfield analysis and X-ray data complement each other.  The 1 H NMR spectrum of GBA (Fig. 5) has a peak at 4.94 ppm due to the NH protons. The peaks at 7.49-7.51 ppm are due to H 10 , H 11 , H 8 and H 9 (Fig. 5) protons which are split by H 12 , H 13, H 14, and H 15 protons. It is expected to have the splitting of H 10 , H 11 , H 8, and H 9 protons to be doublet because the four protons feel a different chemical environment and so a multiplet signal is observed. The peaks at 7.25-7.30 ppm are due to H 12 , H 13 , H 14 H 15 protons which are observed as triplets due to the splitting by H 10 , H 11 , H 17 and also due to H 8 , H 9 and H 16 . A triplet of the triplet is expected theoretically, therefore, a multiplet signal is attributed to these protons (9 peaks). A total of 14 peaks infer that each phenyl proton feels different chemical environment due to sp 3 (C 3 ) atom and crystal structure. The peaks at around 3.33 ppm are due to CH 3 OH in CD 3 OD.
The small peak at 4.68 ppm is due to -OH proton. Generally, it is expected to be broad. But it is interesting that present case the -OH group hides in the aromatic packet with no H-bonding. The IR spectrum also showed a sharp peak due to ν (OH). The peaks at 7.22-7.23 ppm are due to H 16 and H 17 which is observed as a triplet due to the agreement of two protons in the integration ratio of (2:2:1) which matches with the assignments. In the benzilate portion, the inductive effect only operates through COO − and no mesomeric or hyperconjugation effect. The COO − and OH groups have −I effect and therefore the assignment of the protons is based on this fact. Since H 16 and H 17 are far away they are observed at lower 'δ' values.
The guanidinium sp 2 carbon has a less intense peak at 158.63 ppm and the weak signal is probably due to the nuclear overhauser effect (NOE). In pure guanidine, this sp 2 carbon appeared at 153.7 ppm, so the protonation of C=NH 2 + increased the 13 C NMR chemical shift. In the benzilic acid portion, the C 3 and C 2 carbon atoms appear Fig. 6 13 C NMR spectrum of GBA in CD 3 OD at 81.89 and 178.56 ppm, respectively. The tertiary carbon atom shows low intensity due to the NOE effect. The C 4 and C 5 carbon atoms due to the high inductive effect of the COO − and OH group have 13 C NMR peaks at 144.99 ppm. The inductive effect decreases as the distance increases. The C 14 and C 15 ; C 12 , C 13 , C 10 and C 11 ; C 6 , C 7 , C 8 and C 9 set of carbons showed signals at 126.62,127.25 and 127.56 ppm, respectively (Fig. 6), due to phenyl carbons.
The proton NMR spectrum of BABA indicated an extensive splitting pattern in the benzilate anion (Govindasamy et al. 2020) portion when compared to the benzilate anionic portion of GBA (Fig. 7). The splitting can be explained due to the coupling of adjacent protons but also due to a slightly different chemical environment in the second unit (I) in the triclinic unit cell (Z = 2). A comparison of the 1 H NMR spectrum of BABA with GBA indicated that the peaks at 7.41 and 7.43 ppm as the hydrogen from H 6 to H 10 are due to the phenyl group of benzylammonium cation which indicated splitting due to adjacent protons in the benzylammonium moiety. A total of 25 aromatic proton peaks are observed due to benzilic and benzyl ammonium groups. This further indicated the chemically distinguishable protons due to sp 3 carbon and stereographic arrangement. A short peak at 4.68 ppm is attributed to the O-H proton as it is submerged in between aromatic rings. The peaks at 4.95 are due to -NH 3 protons and 4.06 ppm is due to the CH 2 group of the benzyl ammonium group.
The peaks around 48.0 ppm are due to carbon atom of CD 3 OD. The carboxylate C 8 carbon showed a peak at 178.19 ppm whereas, in GBA, it is at 178.56 ppm. The additional peak at 42.86 ppm of C 1 carbon is attributed (Fig. 8) to the CH 2 carbon of the benzylammonium group. The peak at 133.27 is attributed to the C 2 carbon of the cation. This assignment could be made as the 13 C NMR spectrum was compared with that of GBA. The C 20 and C 21 ; C 16 , C 17 , C 18 and C 19 ; C 12 , C 13 , C 14 and C 15 showed signals at 126.52, 127.19 and 127.60 ppm due to benzilate moiety. The C 8 and C 9 carbon atoms appear at 178.19 and 81.74 ppm, respectively. The peaks at 128.62 and 128.77 are due to the rest of the phenyl carbon atoms of the benzylammonium part of the compound of C 2 to C 7 . Therefore, by taking two similar derivatives, the NMR peaks could be assigned accurately by inclusion and exclusion methods.

Fourier-transform infrared spectroscopy (FT-IR)
The GBA has a sharp peak at 3500 cm −1 due to the υ (O-H) group. The presence (Fig. 9) of guanidine is evident that ν (N-H) was observed at 3464 cm −1 and 3345 cm −1 . The band at 1550 cm −1 is due to ν (C=N) of guanidine moiety. The peak at 1666 cm −1 is due to the δ (NH 2 ) bending mode (Deepa and Philominathan 2016). The presence of the ν (C=O) group gives a stretching frequency of around 1673 cm −1 (Baraniraj and Philominathan 2009).

3
The stretching vibrations of the aromatic ring skeleton are observed by the fingerprint region.
The peaks in BABA 3464 (sharp) and 3343 (broad) cm −1 are due to ν (O-H) and ν (N-H) and a sharp peak (Fig. 9) at 2986 cm −1 is due to ν (C-H). The fingerprint region for phenyl and benzyl groups has been observed for BABA . The peak at 1720 cm −1 is due to ν (C=O) of the carboxylate ion. In comparison with the IR spectrum of GBA, which has ν (C=O) at 1673 cm −1 where COO − is in the resonance form.

UV visible absorption analysis
The observed peaks around 257 nm for GBA and BABA (Fig. 10) are due to π-π*. From the transmittance spectra, the cutoff wavelengths are 202 and 214 nm for GBA and BABA crystals, respectively, which are considered for the calculation of band gap. The molar absorptivity coefficient (α) measures the strength of the chromophore and is directly responsible for the observed sensitivity using a UV-Visible detector. The optical absorption coefficient α, is related to the absorbance A, by the relation: where t is the path length and hυ is the photon energy. The energy band gaps are 6.22 and 5.86 eV for GBA and BABA, respectively.

Photoluminescence spectroscopic analysis
The material relaxes radiatively from the higher excited state to lower vibrational energy states from which it deexcites to emit the light is called photoluminescence. The intensity of PL is most likely dependent on crystallinity and complex chemical nature. The radiative recombination may occur in the PL spectrum by the different energy states available between the valence band and conduction band (Sathya et al. 2018). More precisely it depends upon the vibrational and electronic energy levels. The molecule should undergo vibrational relaxation to exhibit photoluminescence behaviour. The emission spectra for the GBA and BABA (Fig. 11) have two fluorescence emission peaks at 442 nm (blue) and 547.2 nm (green) on excitation at 257 nm. The small energy gap of 2.28 eV corresponding to the photoluminescence band maximum at 547.2 nm depends on the condensation degree and the packing between individual layers (Gibot et al. 2015). The GBA and BABA emit green light which can find OLED applications. The highly intense peaks confirm structural perfections and good crystalline nature of the synthesized crystal. The crystal could be employed in luminescence devices as indicated by these emission peaks (Gomathi et al. 2021). A green LED can be used for many purposes in lighting, treating dilated capillaries, sagging skin around the eyes, under-eye circles, hyperpigmentation and sunspots. Blue LED light has been proven to have powerful antibacterial properties that can kill acne-causing bacteria. Thus, molecular interaction, steric effect, H-bonding and distance between the units (Z = 2) in the triclinic unit cell manifest the π-π* electronic and vibrational energy levels of the benzylammonium benzilate (BABA).

Chromaticity
Chromaticity is an objective specification of the quality of a colour regardless of its luminescence. Chromaticity consists of two independent parameters, often specified as hue and colourfulness, where excitation of the latter is alternatively called saturation, chroma, intensity or purity. Photoluminescence colour tuning (PLCT) and control of emission chromaticity are critical for the continued development of functional organic and hybrid materials (Price et al. 2021). To determine emission line colours from the energy disbursement of the light emitted in the PL spectrum, the CIE 1931 colour chromaticity diagram is used (Dhavamurthy et al. 2022). The chromaticity of GBA crystal coordinates (x,y) was found to be x = 0.2779, y = 0.3630 and for BABA crystal x = 0.2533, y = 0.3429 (Fig. 12) have been determined from the tristimulus values using the following expression, The chromaticity coordinates (x,y) are calculated from the emission intensities of the GBA and BABA. The correlated colour temperature (CCT) is as follows, 6) CCT = −449 n 3 + 3525 n 2 − 6823 n + 5520.33 is the inverse slope (isotemperature line) and x e = 0.332, y e = 0.186. The calculated CCT values of GBA and BABA crystals are 3751.63 K and 2928.53 K. From the CCT values, we can determine two major regions of natural white light, namely warm-white (≤ 3700 K), neutral or pure white (7) Where, n = x − x e y − y e (between 3700 to 5000 K) and cool-white (≥ 5000 K) (Mariyappan et al. 2017). Thus, GBA and BABA compounds exhibited an emission at the pure-white and warm-white regions.

TG-DTA of GBA
The compound is stable up to 90 °C and decomposes in three stages giving nil residue at the end. Loss of NH 4 + ion, giving rise to NH 2 CN (cyanaamide) and benzilic acid was observed in the first stage (Fig. 13). The second stage involves the decomposition of benzilic acid and NH 2 CN giving (NH 4 ) 2 CO 3 as the intermediate phase which decomposes rapidly to NH 3 and CO 2 leaving nil residue (Table 4).

TG-DTA of BABA
The compound decomposes and is thermally not stable. As observed in GBA, the loss of NH 3 was observed at 157.36 °C as an endothermic peak (Fig. 14). The compound decomposes in two stages leading to nil residue (Table 5).

Conclusion
The present study investigated extensively the crystal and molecular structures of guanidinium benzilate (GBA) and benzylammonium benzilate (BABA). GBA shows interionic that is between cation and anion and intermolecular (between two molecules) hydrogen-bonding interactions which gives a three-dimensional supramolecular hydrogen-bonded structure. But BABA exists as a dimer and with two such dimers present in the P-1 triclinic unit cell (Z = 2) with supramolecular assembly. The bond length data indicated the resonance structure for COO − in GBA and the non-resonating structure in BABA. The bond angles and the torsion angle data indicated that the two phenyl rings of benzilate anion are disposed of in different planes with different orientations concerning each other, concerning the lone pair of OH oxygen atom and the COO − group. The counter cation plays an important role in the deciding extent of resonance in carboxylate ions and the three-dimensional disposition of two phenyl rings. Therefore, the nature and extent of hydrogen bonding between the cation and anion and intermolecular hydrogen bonding play a significant role in the orientation of the groups in the molecule. The crystal structure data combined with the comparison of two derivatives have given a fair interpretation for IR, 1 H NMR and 13 C NMR spectral data. It could be noted that there is no mesomeric or resonance or hyperconjugation effect as indicated by bond length measurements in benzilate anion. The inductive effect is used to interpret 1 HNMR and 13 C NMR and spectral data. The thermal analyses indicated that the compounds decompose to give NH 3 gas leading to the formation of ammonium benzilate or methylammonium benzilate and subsequently decomposes to give nil residue. Both the compounds exhibit a blue emission (442 nm) and green emission (547.2 nm) on excitation at 257 nm and so they may be used in OLED applications.