Hydrogen Squarate Research Articles

Diisopropylammonium hydrogen squarate: Synthesis and comprehensive analysis of non-linear optical co-crystal using X-ray, Hirshfeld, mechanical, optical and DFT methods

This research successfully synthesized a single co-crystal of diisopropylammonium hydrogen squarate using prolonged vaporization for crystal growth. Single-crystal X-ray spectrometry confirmed its monoclinic structure, and morphological predictions were made. UV–visible spectroscopy revealed its optical transmittance with a direct optical energy band gap of 3.45 eV. Photoluminescence studies showed a strong violet emission at 402 nm when excited by a 260 nm source. Microhardness study examined the crystal's mechanical attributes portraying the normal indentation size effect followed by a qualitative overview of half-penny crack dynamics. FTIR study aided in the discernment of varied vibrational modes with NH stretching being observed at 3078 cm−1. Thermal examination further revealed the crystal's stability up till 244 °C. Proton and carbon-13 NMR spectra were analyzed to verify the presence of functional groups and the overall molecular integrity. Intermolecular interactions were analyzed using Hirshfeld surface and fingerprint mapping. The Z-scan technique demonstrated the crystal's applicative potential in its third harmonic generation capability. Theoretical calculations with Density Functional Theory (DFT) supported the experimental findings, offering insights into optimized geometries, frontier molecular orbitals, natural population and bond orbital distributions, hyperpolarizability, molecular electrostatic potentials, IR vibrational modes, and UV absorbance profiles.

Growth, Structural, Spectral, Thermal, Optical, Second and Third Order Nonlinear Optical Properties of Imidazolium Hydrogen Squarate (IHS) Single Crystal

Abstract: Imidazolium hydrogen squarate (IHS) crystal has been grown by slow evaporation solution growth technique at room temperature. The lattice parameters of grown crystal were determined using single crystal X-ray diffraction data and compared with powder XRD. Single crystal XRD shows that the crystal crystallizes in monoclinic system with noncentrosymmetric space group Pc. The crystallinity of the grown crystal was confirmed by X-ray powder diffraction analysis. FT-IR and FT-RAMAN analyses qualitatively confirm the various functional groups present in the grown crystal. The 1H and 13C NMR spectra were recorded to establish the molecular structure. Thermal properties of title crystal were studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The UV-Vis-NIR transmission spectrum was recorded to find the band width of optical transmittance window and the lower cutoff wavelength. The optical band gap value of the material is evaluated to be 5.6 eV. The second harmonic generation efficiency was calculated by the Kurtz and Perry powder method using a Q-switched mode locked Nd: YAG laser emitting 1064 nm laser as source. Finally, Z-scan technique was employed to determine the nonlinear refractive index, nonlinear absorption coefficient and third-order NLO susceptibility to find suitability of the grown crystal in photonics and optoelectronics applications. Keywords: Single crystal; Powder XRD; thermal analysis; SHG; Z-scan studies

Interactions of pyridoxine (Vitamin B6) with squaric acid and water. Experimental and theoretical studies

Pyridoxine (Vitamin B6, 3‑hydroxy-4,5-bis(hydroxymethyl)-2-methylpyridine) forms a hydrate adduct with squaric acid (3,4-dihydroxy-3-cyclobuten-1,2‑dione). The proton from squaric acid is transferred to the pyridoxine nitrogen atom. Two hydrogen squarate anions form a centrosymmetric α-dimer, which interacts symmetrically with two pyridoxinium cations and two water molecules, through several hydrogen bonds of the lengths from 2.498(3) to 2.843(3) Å. The molecular structure of the 2:2:2 adduct (dimer) was studied by a single-crystal X-ray diffraction, DFT calculations, FTIR and NMR spectroscopies. Structures of three models of the monomer of pyridoxinium hydrogen squarate monohydrate (1:1:1) were optimized at the APF-D/6–311++G(d,p) level of theory. Their molecular geometries, hydrogen bond distances, IR spectra, natural atomic charges, frontier molecular orbitals (HOMO and LUMO) were analyzed. The quantum theory of atoms in molecule (QTAIM) was used to classify the strength of the hydrogen bonds in the dimer and monomers of the optimized adducts. The studied compound was screened for antifungal activities and showed inhibiting properties against A. niger and P. placenta.

Synthesis, crystal structure, linear properties and DFT analysis of L-Tartarate hydrogen squarate (LTS): A nonlinear optical single crystal

A novel organic non-linear single crystal of L-Tartarate hydrogen squarate (LTS) has been synthesized and successfully grown from aqueous solution by slow evaporation solution growth method. In the present investigation the title compound of L-Tartaric acid with squaric acid has been synthesized by using double distilled water as the solvent. The prepared concentrated solution was placed in an undisturbed condition and then the solution was periodically inspected. The good quality single crystals have been harvested in a time span of 40 days. Then the grown crystal was characterized by single crystal XRD, FTIR, UV–vis-NIR, and SHG. The optimized geometry, vibrational frequencies, Mulliken charge distribution, frontier molecular orbitals (FMOs), and associated energies of the ground state and the first single excited state were calculated using density functional theory (DFT) and time-dependant DFT calculations using the B3LYP/6- 311G method. Vibrational frequencies calculated in the gaseous phase compared with experimental values measured in the solid state and showed good agreement with each other. The observed results from the characterization analyses show its suitability for NLO applications when compared with some of the existing organic crystals. The relative second harmonic generation of this grown crystal was found to be 0.9 times than that of KDP crystal.

Synthesis, optical, vibrational spectroscopy, experimental and theoretical investigation of nonlinear optical properties of L-argininium hydrogen squarate

Single crystals of L-Argininium Hydrogen Squarate (LAHSQ) were obtained from slow evaporation solution growth method using deionised water (1:1) as a solvent. The molecular structure and vibrational spectrum of LAHSQ single crystal has been investigated by Density Functional Theory (DFT) method. Single crystal X-ray Diffraction (SXRD) analysis has been used to identify the structure, cell-parameters and space group of the LAHSQ grown singe crystal. It revealed that the present crystal structure is triclinic system with P1 space group. The molecular structure was analysed by identifying the functional groups from FT-IR spectra were calculated and the results are compared to the experimental data, exhibited a good overall agreement. HOMO-LUMO energy gap was found to be 3.1789 eV. The Kurtz-Perry powder technique has been used to found the Second Harmonic Generation (SHG) of LAHSQ crystal. Theory (DFT) calculations have been worked under solvation model to know the geometrical and electronic structural characters like frontier molecular orbital analysis (FMO), Mulliken population analysis, dipole moment, polarizability, and hyperpolarizability of the crystal. All these results agree that the LAHSQ crystal is appropriate for NLO applications.

Unimolecular Dissociation of Hydrogen Squarate (HC4O4-) and the Squarate Radical Anion (C4O4•-) in the Gas Phase and the Relationship to CO Cyclooligomerization.

The unimolecular dissociation of hydrogen squarate and the squarate radical anion has been studied by electrospray ionization mass spectrometry (including collisionally induced dissociation) and quantum chemical calculations, providing consistent reaction models. In both cases, consecutive decarbonylations are observed as the dominating fragmentations. The reverse of these reactions corresponds to the successive cyclooligomerization of CO, which constitutes the most atom-efficient route to the cyclic oxocarbons. The reaction models indicate moderate barriers for CO addition to HCnOn- and CnOn•-, respectively, being larger for the former than for the latter. Cyclooligomerization leading to a neutral product is endothermic, while the analogous one-electron reductive coupling is exothermic. The analysis shows that the addition of an electron is essential for cyclooligomerization to give the cyclic four-CO squarate structure.

Functionalization of poly(epichlorohydrin) using sodium hydrogen squarate: cytotoxicity and compatibility in blends with chitosan

Polymeric blends between chitosan and poly(epichlorohydrin) (PECH) modified with sodium hydrogen squarate were prepared by the casting method, using formic acid (85%) as the solvent. The compatibility of the blends was studied by different methods, such as Fourier transform infrared spectroscopy, Raman spectroscopy, and thermogravimetric analyses. Cytotoxicity assays were also performed by the direct contact method to assess the feasibility of using these materials in veterinary devices. Based on the analysis results, we concluded that these polymers are compatible due to the interaction between the NH3+ chitosan groups and CO− groups of the modified poly(epichlorohydrin), as well the hydrogen bond between the chlorine atom of the modified poly(epichlorohydrin) and the hydrogens of the chitosan methyl group. It is important to highlight that electrostatic interactions are also responsible for the non-toxicity of these materials in bovine fibroblast cells, which indicates the feasibility of their use in veterinary devices for cattle.

Preparation and spectral properties of europium hydrogen squarate microcrystals

A simple scheme for preparation of europium hydrogen squarate octahydrate microcrystals, Eu(HSq)3·8H2O is demonstrated. The microcrystalline powders obtained have a potential application as non-centrosymmetric and UV radiation – protective hybrid optical material. The site-symmetry of the Eu – ion is C2V or lower, obtained from diffuse reflectance spectra. The formation of europium hydrogen squarate is supported by IR – spectroscopy, UV–vis spectroscopy, chemical analysis and X-ray diffraction. A detailed analysis of the UV–vis and IR spectra of the micropowders prepared is presented.

X-ray, dielectric, piezoelectric and optical analyses of a new nonlinear optical 8-hydroxyquinolinium hydrogen squarate crystal

The 1:1 complex of 8-hydroxyquinoline with squaric acid has been characterized using single-crystal X-ray diffraction, UV–vis spectroscopy, density functional theory (DFT) calculations, and photoluminescence, dielectric, piezoelectric and second-harmonic generation (SHG) studies. The title compound (8-hydroxyquinolinium hydrogen squarate; HQS) contains one protonated 8-hydroxyquinoline cation (C9H8NO+) and one hydrogen squarate mono-anion (C4HO4 −). All the intermolecular hydrogen-bonding interactions present in the HQS crystal structure are analyzed by three-dimensional molecular Hirshfeld surface analysis and their relative contributions are determined from two-dimensional fingerprint plots. The structure of C9H8NO+·C4HO4 − molecular complex has been optimized at the DFT/B3LYP/6-31G(d,p) level. The UV–vis spectroscopic data calculated by time-dependent density functional theory are compared with the experimental data. The LUMO+1, LUMO, HOMO and HOMO−1 energy values, their shapes and energy gaps are calculated using the B3LYP/6-31G(d,p) level of theory. The HQS material exhibits high SHG output (2.6 times of that of potassium dihydrogen phosphate), high photoluminescence emission centred at 474 nm and a piezoelectric charge coefficient of 3 pC N−1. Henceforth, HQS can serve as an alternative potential candidate for multifunctional nonlinear optically active and piezoelectric crystals.

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

The asymmetric unit of the title compound, C6H10N22+·2C4HO4-, 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.

Tautomers of N-ethyl-3-oxopyridinium and its adduct with squaric acid studied by X-ray, Raman, FTIR, NMR and DFT methods

The molecular complex of N-ethyl-3-hydroxypyridinium hydrogen squarate has been obtained and characterized by single-crystal X-ray diffraction, B3LYP/6-311++G(d,p) calculations, Raman, FTIR and NMR spectra. The complex is built of OH⋯O hydrogen-bonded dimer involving two anions and two cations. In order to establish a tautomeric equilibrium between 3-phenolic and 3-pyridone forms in N-ethyl-3-oxopyridinium unit in the complex, additionally N-ethyl-3-oxopyridinium has been studied by the same experimental and theoretical methods. The potential energy distributions (PED) have been used to assign the vibrational spectra. Charge delocalization has been analyzed using the Natural Bond Orbital (NBO) method.

N,N-Dibutylanilinium hydrogen squarate

The title molecular salt, C14H24N+·C4HO4 − [systematic name: N,N-dibutylbenzenaminium 2-hydroxy-3,4-dioxocyclobut-1-en-1-olate], is composed of a protonated N,N-dibutylaniline cation with a hydrogen squarate monoanion (common names). The disparate bond lengths within the squarate anion suggest delocalization of the negative charge over only part of the squarate moiety. In the crystal, the squarate anions are linked by pairs of O—H...O hydrogen bonds, forming inversion dimers with an R 2 2(10) ring motif. The dimers are linked to the cations on either side by N—H...O hydrogen bonds, and weak C—H...O hydrogen bonds. These cation–anion–anion–cation units are linked by further C—H...O hydrogen bonds, forming layers parallel to (102).

A combined crystallographic and theoretical study of weak intermolecular interactions in crystalline squaric acid esters and amides

We report the synthesis and X-ray solid state structures of five squaric acid derivatives, i.e. a zwitterionic compound, namely 3-hydroxy-4-(2-pyridin-2-yl-ethylamino)cyclobut-3-ene-1,2-dione (1), a squaramide monoester, 3-ethoxy-4-(2-pyridin-2-yl-ethylamino)cyclobut-3-ene-1,2-dione (2), two differently solvated (EtOH and DMSO/water) disquaramides 3,4-bis((4-hydroxyphenethyl)amino)cyclobut-3-ene-1,2-dione (3 and 4, respectively), and a mixed hydrogen squarate and disquarate 2-(2-aminoethyl)pyridinium salt (5). All compounds form interesting supramolecular assemblies in the solid state that have been analyzed using high level DFT calculations and Bader's theory of “atoms-in-molecules”. An intricate combination of ion-pair and H-bonding interactions along with π–π stacking and anion–π contacts of the cyclobutenedione rings is crucial for the formation of the supramolecular assemblies in the solid state.

Structural, vibrational and DFT studies of di-(pipecolinium acid) squarate

A racemic mixture of (R)- and (S)-pipecolic acid (piperidine-2-carboxylic acid, P2C) forms a stable crystalline complex with squaric acid (3,4-dihydroxy-3-cyclobutene-1,2-dione, H2SQ), at the 2:1 ratio (1). The crystals are built of two pipecolic acid cations (P2C+H) and squarate dianion (SQ2−). Complex 1 has been characterized by single-crystal X-ray analysis, Raman, FTIR and 13C CP MAS spectroscopy. The title complex crystallizes in monoclinic C2/c space group with Z=4 and Z’=0.5. In the crystal structure two types of C2-symmetric complexes with different chirality are identified as [(R)-P2C+H]2SQ2− and [(S)-P2C+H]2SQ2−. The molecules are linked through the COOH⋯O–C of 2.587(1) Å and two N+H⋯O–C hydrogen bonds of 2.756(1) and 2.759(1) Å. In the optimized structure, at the B3LYP/6–311++G(d,p) level of theory, pipecolic acid zwitterion and cation interact with the hydrogen squarate anion. Charge delocalization has been analysed using the Natural Bond Orbital (NBO) method. Solid-state Raman, FTIR and 13C CP MAS spectra have been measured. The potential energy distributions (PED) have been used to assign the vibrational spectra. The crystal and optimized structures have been compared.

Growth, structural, optical and thermal properties of an organic NLO material: l-Argininium hydrogen squarate

l-Argininium hydrogen squarate (LAHS) is an organic nonlinear optical material grown by slow evaporation solution growth technique. The crystal structure was confirmed by single crystal X-ray diffraction analysis and the crystal system is identified as triclinic system. The thermal stability and decomposition process were studied by thermogravimetric analysis (TGA) and differential thermal analysis (DTA). The crystal is stable up to 238°C. The optical transparency range and lower cut-off wavelength of grown crystal have been identified by UV–vis–NIR spectroscopy method. The existence of second harmonic generation (SHG) signal was observed using Nd:YAG laser with fundamental wavelength of 1064nm. The SHG efficiency is compared with potassium di-hydrogen phosphate (KDP) and urea.

Structural and spectroscopic properties of piperidinium-4-carboxylic acid hydrogen squarate

The 1:1 complex of protonated piperidine-4-carboxylic acid (P4C+H) with hydrogen squarate anion (HSQ−) was prepared and characterized by a single-crystal X-ray diffraction, B3LYP/6-311++G(d,p) calculations, FTIR and NMR spectroscopies. The crystals are orthorhombic, Pbcn space group. The molecules are linked through the OH⋯O hydrogen bonds of 2.723(1) and 2.574(1)Å formed between P4C+H and HSQ−, and between HSQ− anions linked into a β-chain, respectively. The hydrogen squarate anion is surrounded by four P4C+H cations which are involved in the N+H⋯O hydrogen bonds of the lengths from 2.815(1) to 3.183(2)Å. The potential energy distributions (PED), calculated for the optimized structure of the title complex at B3LYP/6-311++G(d,p) level of theory, were used for the assignments of IR bands in the experimental and calculated spectra. The FTIR spectrum was consistent with the X-ray results. The theoretical and experimental IR spectra have been compared. The NMR spectra in an aqueous solution and in the solid-state have been studied.

The solid state structure of pyridinium hydrogen squarate

The solvothermal reaction of (PyH)[MoOBr4] (PyH+ = pyridinium cation, C5H5NH+) with squaric acid (H2Sq = 3,4-dihydroxy-3-cyclobutene-1,2-dione, H2C4O4) in pyridine has inadvertently afforded apart from a dinuclear molybdenum(V) complex with a coordinated squarato dianion another product, a simple pyridinium salt of hydrogen squarate, (PyH)(HSq) (HSq– = hydrogen squarate, HC4O4–). The salt crystallizes in the monoclinic space group P 21/c with a = 10.1061(9) Å, b = 11.0436(10) Å, c = 7.4497(7) Å and β = 103.188(2)°. Its solid state structure consists of infinite chains made of HSq– ions linked via strong O–H···O– hydrogen bonds. The corresponding O···O contacts are 2.5604(13) Å. The countercations, protonated pyridine molecules, are attached to these chains via N+–H···O– hydrogen bonds. The X-ray structure analysis has revealed stacking arrangements of both ions with short interplanar spacings. Weak intermolecular interactions of the π···π type between ions of the same charge and of the C–H···O type between the oppositely charged ions were shown to play an important role in their packing.

Theoretical investigation on vibrational spectra, first order hyperpolarizability and NBO analysis of 4-Phenylpyridinium hydrogen squarate

The vibrational frequencies of 4-Phenylpyridinium hydrogen squarate (4PHS) in the ground state have been investigated by using B3LYP/6-311++G(d,p) level. The analysis of molecular structure, natural bond orbitals and frontier molecular orbitals was also performed. The IR spectra were obtained and interpreted by means of potential energies distributions (PEDs) using MOLVIB program. NBO analysis proved the presence of C–H⋯O and N–H⋯O hydrogen bonding interactions, which is consistent with the analysis of molecular structure. The dipole moments and first-order hyperpolarizability (βtot) are calculated and are 5.856 D and 4.72×10−30esu, respectively. The high βtot value and the low HOMO–LUMO energy gap (4.062eV) are responsible for the optical and electron-transfer properties of 4PHS molecule. The photoresponse-related results indicate that 4PHS molecule is an excellent organic candidate of photon-responsive materials.

3-Phenylpyridinium hydrogen squarate: Experimental and computational study of a nonlinear optical material

The detailed investigation of an organic nonlinear optical (NLO) squarate salt of 3-phenylpyridinium hydrogen squarate (1), C11H10N+·C4HO4−, was reported in this study. The XRD data indicates that the crystal structure of the title compound is in the triclinic P-1 space group. In the asymmetric unit, the 3-phenylpyridine molecule is protonated by one hydrogen atom donation of squaric acid molecule, forming the salt (1). The X-ray analysis shows that the crystal packing has hydrogen bonding ring pattern of D22(10) (α-dimer) through NH···O interactions. The structural and vibrational properties of the compound were also studied by computational methods of ab initio at DFT/B3LYP/6-31++G(d,p) (2) and HF/6-31++G(d,p) (3) levels of theory. The calculation results on the basis of two models for both the optimized molecular structure and vibrational properties for the 1 are presented and compared with the experimental results. Non-linear optical properties (NLO) of the title compound together with the molecular electrostatic potential (MEP), electronic absorption spectrum, frontier molecular orbitals (FMOs) and conformational flexibility were also studied at the 2 level and the results were reported. In order to evaluate the suitability for NLO applications thermal analysis (TG, DTA and DTG) data of 1 were also obtained.

2-Pyridinium propanol hydrogen squarate: Experimental and computational study of a nonlinear optical material

The experimental and theoretical investigation of a novel organic nonlinear optical (NLO) squarate salt of 2-pyridinium propanol hydrogen squarate (1), C8H12ON+·C4HO4-, were reported in this study. The crystal structure of the title compound was found to crystallize in the triclinic P-1 space group. In the asymmetric unit each squaric acid molecules have donated one H atom to the pyridines N1 and N2 atoms of a 2-pyridine propanol molecule, forming the salt (1). The X-ray analysis clearly indicated that the crystal packing has shown the hydrogen bonding ring pattern of D22(10) (α-dimer) through NH⋯O interactions. The structural and vibrational properties of the compound were also studied by computational methods of ab initio performed on the compound at DFT/B3LYP/6-31++G(d,p) (2) and HF/6-31++G(d,p) (3) level of theory. The calculation results on the basis of two models for both the optimized molecular structure and vibrational properties for the 1 are presented and compared with the X-ray analysis result. The molecular electrostatic potential (MEP), electronic absorption spectra, frontier molecular orbitals (FMOs), conformational flexibility and non-linear optical properties (NLO) of the title compound were also studied at the 2 level and the results are reported. In order to evaluate the suitability for NLO applications thermal analysis (TG, DTA and DTG) data of 1 were also obtained.