Single Crystal Studies Research Articles

High pressure neutron diffraction study of magnetic ordering in erbium

We have studied magnetic ordering in polycrystalline erbium at high pressures up to 32 GPa and low temperatures down to 10 K using neutron diffraction techniques at the Spallation Neutron Source at Oak Ridge National Laboratory, USA. For the hexagonal close-packed (hcp) phase, strong nuclear and magnetic satellite intensities permit a simultaneous refinement of the nuclear and magnetic structures. At 1 GPa of applied pressure, a modulation vector q=γc∗ with γ≈2/7 for the c-axis modulated and cycloidal phases is consistent with prior single-crystal studies at low pressures. At 6.7 GPa in the hcp phase, we find γ≈0.31, indicating a reduction in the period of the magnetic structure with respect to the crystal lattice. The magnetic ordering temperature at 6.7GPa is slightly above 60 K. At 32 GPa in the double hexagonal close-packed phase, the magnetic scattering constrains the magnetic ordering temperature to 25±5 K. Our neutron diffraction study demonstrates that the magnetic ordering persists in the high-pressure double hexagonal close-packed phase of erbiumto the highest pressure of 32 GPa.

A Crystalline 2D Fullerene‐Based Metal Halide Semiconductor for Efficient and Stable Ideal‐bandgap Perovskite Solar Cells

AbstractDespite advances in mixed tin‐lead (Sn‐Pb) perovskite‐based solar cells, achieving both high‐efficiency and long‐term device stability remains a major challenge. Current device deficiencies stem partly from inefficient carrier transport, originating from defects and improper band energy alignment among the device's interfaces. Developing multifunctional interlayer materials simultaneously addressing the above concerns poses an excellent strategy. Herein, through molecular and crystal engineering, an amine‐functionalized C60 mono‐adduct derivative (C60‐2NH3 = bis(2‐aminoethyl) malonate‐C60) is utilized for the synthesis of the first crystalline fullerene‐based 2D metal halide semiconductor, namely (C60‐2NH3)Pb2I6. Single crystal XRD studies elucidated the structure of the new material, while DFT calculations highlighted the strong contribution of C60‐2NH3 to the electronic density of states of the conduction band of (C60‐2NH3)Pb2I6. Utilization of C60‐2NH3 as an interlayer between a FA0.6MA0.4Pb0.7Sn0.3I3 perovskite and a C60 layer offered superior band energy alignment, reduced nonradiative recombination, and enhanced carrier mobility. The corresponding perovskite solar cell (PSC) device achieved a power conversion efficiency (PCE) value of 21.64%, maintaining 90% of its initial efficiency, after being stored under a N2 atmosphere for 2400 h. This work sets the foundation for developing a new family of functional materials, namely Fullerene Metal Halide Semiconductors, targeting applications from photovoltaics to catalysis, transistors, and supercapacitors.

Structural anatomy and thermal transitions of barium feldspars, BaAl2Si2O8

BaAl2Si2O8 (barium feldspar-based) materials are widely used in glass and ceramic industry due to high melting temperature, chemical resistance, low thermal expansion, low dielectric constants and attractive luminescence properties. The durability of barium feldspar ceramics strongly depends on reversible phase transitions between the low-temperature modification (celsian), and series of high-temperature (HT) polymorphs known as 'hexacelsian'. Numerous works have been devoted to the study of the thermal transitions of 'hexacelsian' by X-ray powder diffraction methods and transmission electron microscopy, the use of which provides limited information about structural changes. Here, the crystal structures, thermal properties and phase transitions of HT BaAl2Si2O8 polymorphs are characterized for the first time using in-situ HT X-ray single-crystal structural study (SCXRD), and micro-Raman spectroscopy up to 1000 °C. The crystal structure of α-hexacelsian under ambient conditions is monoclinic (I2/a). The alpha-form undergoes two polymorphic transformations upon heating: into an orthorhombic (Fmmm) β-modification above 300 °C and into a hexagonal (P–62m) γ-modification above 700 °C. These transitions lead to significant changes in the unit-cell volume: an obstacle in the production of BaAl2Si2O8-based ceramics.

Dual-Channel Imine-Amine Photoisomerization in a Benzoimidazole and Benzothiazole Coupled System: Photophysics and Applications.

A molecule, namely 2-(1H-benzo[d]imidazol-2-yl)-6-(benzo[d]thiazol-2-yl)-4-bromophenol (BIBTB), having a two-way proton transfer unit of thiazole and imidazole moieties was synthesized and characterized by NMR, electrospray ionization mass spectrometry (ESI-MS), and single-crystal diffraction studies. Steady state and time-resolved spectral studies of BIBTB support excited state intramolecular proton transfer (ESIPT), causing imine-amine tautomerization through a two-way 6-membered H-bonded ring, where the N atoms of benzothiazole and the benzoimidazole unit are involved as proton acceptor sites. Interestingly, in a nonpolar and moderately polar solvent, photoisomerization in BIBTB is found to be favored toward the thiazole ring, whereas in a highly polar solvent, it is favored toward the imidazole ring. A spectral comparison of BIBTB with judicially designed molecules 2-(benzo[d]thiazol-2-yl)-4-bromophenol (HBT) and 2-(1H-benzo[d]imidazol-2-yl)-4-bromophenol (BIB) supports these inferences. Theoretical calculation using the Density Functional Theory (DFT) at CAM-B3LYP/6-311+G(d,p) level supports the existence of two low-energy 6-membered hydrogen-bonded planar conformers in the ground state in the gas phase and in solvents of different dielectrics. The potential energy curves (PECs) calculated along the proton transfer (PT) coordinate are found to have a high energy barrier in the ground state and to be barrierless or have a low energy barrier in the excited state for both the forms. The calculated vertical excitation and the emission energy from the relaxed excited and PT states show good correlation with the experimental spectral data. Aggregation of BIBTB in water with red shifted emission was established from X-ray single-crystal structure analysis, solid state emission, and Dynamic Light Scattering (DLS) measurement. The molecule BIBTB also acts as a fluorescence probe for sensing the explosive picric acid in the subnano scale and can be used to determine the proportion of water in dimethyl sulfoxide (DMSO) solvent.

Zn(II), Mn(III), and Co(III) complexes of Schiff base derived from 2‐hydroxy‐1‐naphthaldehyde: Synthesis, spectral surveys, single crystal structure studies, Hirshfeld surface analysis, density functional theory calculation, molecular electrostatic potential, and molecular docking evaluations

A new series of transition metal complexes of bidentate Schiff base compound derived from 2‐hydroxy‐1‐(2‐methoxyethylimino)‐naphthalene (HL) were synthesized and characterized using elemental analysis, Fourier transform infrared spectroscopy (FT‐IR), and UV–vis spectroscopies. X‐ray single crystal structures of Zn(II), Mn(III), and Co(III) complexes (1–4) have also been determined, and it was indicated that these Zn(II) and Co(III) complexes (1, 4) are in an octahedral geometry. Whereas, it was found that the Zn complex (2) is in quite a regular tetrahedral environment. Also, the Mn center in complex (3) is ligated by two azomethine nitrogen atoms, two ligand oxygen atoms, and one Cl atom of metal salt forming five coordinated tetragonal pyramid geometry around the Mn atoms. The cyclic voltammetry of the complexes specifies an irreversible redox behavior for all complexes (1–4). Next, DFT/B3LYP theoretical method was used to determine the optimal geometrical configurations and comparison between experimental and theoretical data, as well as for calculations of molecular electrostatic potential, highest‐occupied molecular orbital (HOMO)‐lowest‐unoccupied molecular orbital (LUMO) energy values of selected compounds. The study of non‐covalent interactions was done by Hirshfeld surface analysis using CrystalExplorer program. Furthermore, molecular docking inspection was carried out to study the binding affinity of the tested complexes towards protein B‐cell lymphorna (PDB ID: 4LXD). Using the results obtained from the molecular docking and the summarized interaction of the binding processes, these structures show the validity of effective inhibition against liver cancer.

Synthesis, structural elucidation and characterization of a new organic single crystal Guanidinium adipate monohydrate (GuAM) for nonlinear optical applications

A slow evaporation solution growth process was employed to grow a new organic single crystal Guanidinium adipate monohydrate (GuAM) at room temperature. The structure refinement and cell specifications were elucidated using the X-ray diffraction method. Single crystal XRD study revealed that the grown crystal crystallized in the monoclinic system with unit cell dimensions a = 4.948 (9) Å; b = 16.770 (2) Å; c = 13.554 (2) Å; α and γ = 90.00⁰; β = 95.302⁰ (3), V = 1120.1(3) Å3 and Z = 4. The structure of the crystal was solved by direct method and refined by full matrix least-square method using SHELXL-2018/3 program. The crystalline nature of the sample was evaluated by powder X-ray diffraction (PXRD) study. Fourier transform infrared (FTIR) spectral study was employed to recognize the diverse functional groups present in the synthesized crystal. Optical attributes such as absorbance and emission nature of the GuAM were explored using UV–visible-NIR absorbance study and photoluminescence study respectively. The laser damage threshold value of the formed crystal has been determined by employing an Nd-YAG laser with a wavelength of 1064 nm. The mechanical nature of the GuAM was examined utilizing Vicker's microhardness test and other related parameters were also calculated. TGA-DTA analysis was utilized to estimate the title crystal's thermal stability. The Z-scan technique has been employed to gain insight into the third order nonlinear (NLO) parameters of the GuAM. These findings imply that guanidinium adipate monohydrate (GuAM), a grown single crystal, may be a viable choice for NLO applications.

Dinuclear cadmium(II) complexes with distorted octahedral/monocapped trigonal prism coordination geometries: synthesis, crystal structure, DFT/TD-DFT calculation and photocatalytic degradation of methylene blue

Two Cd(II) complexes [Cd2(L1)2(dca)(NO3)] (1) and [Cd2(L2)2(SCN)(NO3)] (2) (HL1 = 2-methoxy-6-[(2-phenylamino-ethylimino)-methyl]-phenol; and HL2 = 2-[(2-ethylamino-ethylimino)-methyl]-6-methoxy-phenol), have been synthesized and characterized by single crystal structure analysis, IR and mass spectroscopic studies. Both the complexes 1 and 2 possess a triclinic crystal system with space group P1¯. In complex 1, geometry around one metal centre is distorted octahedral and other centre is distorted monocapped trigonal prism, whereas in complex 2, both the metal centres possess distorted octahedral geometries. Strong NH⋅⋅⋅O and weak aromatic CH⋅⋅∙O hydrogen bonding interactions in 1 and strong NH⋅⋅⋅O and NH⋅⋅⋅S hydrogen bonding in 2 results 1D and 2D supramolecular structures, respectively. Experimentally determined electronic spectral data have been compared with the calculated data obtained by DFT and TD-DFT calculation. Photocatalytic abilities of 1 and 2 have been examined by using spectroscopic technique and found that in presence of UV light both the complexes catalytically decomposed methylene blue by 54.0 % and 50.3 %, respectively.

K8CaSi10O25 – Synthesis, in-situ high-temperature single-crystal diffraction and heat capacity

Different sol-gel routes were tested to synthesize polycrystalline material of K8CaSi10O25. The best result in terms of phase purity was obtained using combustion synthesis with glycine as fuel. Single crystals were obtained from the devitrification of a glass. Cyclic single-crystal diffraction studies were carried out within the temperature range of ambient conditions to 873 K with different cooling rates. The crystal structure (space group R3c) at ambient temperature was consistent with previous investigations (a = 11.1135(6) Å, c = 21.9286(14) Å, V = 2345.5(2) Å3). A new high-temperature polymorph was discovered, showing the following crystallographic data at 873 K: space group R3‾m, a = 11.2251(8) Å, c = 11.1789(9) Å, V = 1219.9(2) Å3. On heating, an incommensurately modulated structure was observed between the two aforementioned modifications. The standard third-law entropy was determined from low-temperature Cp’s measured by relaxation calorimetry and amounts to S°(298 K) = 898.7 ± 6.3 J mol−1 K−1.

Growth, mechanical, thermal, electrical, linear, and nonlinear optical studies of urea resorcinol single crystals for NLO applications

Urea Resorcinol (UR) was synthesized and grown using the slow cooling technique to form a possible organic nonlinear optical crystal. Single crystal X-ray diffraction analysis was used to determine the shape and lattice characteristics of the generated UR crystals. The crystallinity was verified using a high-resolution X-ray diffraction examination. The emission and transparency of the formed crystal were revealed by optical studies including photoluminescence and UV–visible-NIR spectrum analyses. Through the use of an optical microscope and the Vickers microhardness tester, its mechanical behavior was investigated and the density of its etch pits was estimated. The investigations were also conducted on the UR crystal's microphysical properties, including its dielectric tensor, dielectric loss, and thermal analysis. An Nd:YAG laser was used to quantify the laser-induced surface damage and the results were connected to the grown crystal's specific heat capacity. By using the Kurtz and Perry technique, the efficiency of second harmonic generation was determined for different UR crystal particle sizes that have good phase matchability, and its SHG output was compared to urea.

Synthesis, characterization, antimicrobial and anti-biofilm studies of Ni(II) complex with Schiff base derived from 2-thiophene carboxaldehyde and phenyl acetic hydrazide

Schiff base titled (Z)-2-phenyl-N'-(thiophen-2-ylmethylene)acetohydrazide (HL) and its Ni (II) complex were obtained by the condensation of 2-thiophene carboxaldehyde and phenyl acetic hydrazide. The ligand (HL) was characterized using elemental analysis, Fourier transform infrared (FTIR), proton nuclear magnetic resonance (1HNMR ), Ultraviolet–visible (UV–Vis.) spectroscopy, and Liquid chromatography–mass spectrometry (LC/MS) methods. Elemental analysis, FTIR, UV–Vis, and X-ray single crystal studies were used to elucidate the structure of the [NiL2] complex. The brown single crystal structure of the Ni(II) complex was elucidated by X-ray diffraction technique, and the complex structure was found to crystallize in a triclinic crystal system with P1¯ space group. With symmetries of 1-x, 1-y, and -z and -x, 1-y, and 1-z, the nickel atoms in the asymmetric unit are positioned on an inversion centre. It was determined that the antimicrobial activity of the newly synthesized HL and [NiL2] compounds was high on clinically important strains and had low minimal inhibitory concentration (MIC) values. In addition, the anti-biofilm activity of the compounds showed 45.14 % and 42.28 % biofilm inhibition, respectively, on the E. coli ATCC 25,922 strain at a concentration of 100 µg/ml, whereas it showed 56.36 % and 42.28 % inhibition, respectively, on the P. aeruginosa ATCC 278533 strain showed an inhibitory effect.

Synthesis of a new hydrazone-based schiff base: Spectroscopy, single crystal, DNA binding and theoretical studies

A new thiosemicarbazide-based Schiff base (TSDHB) was synthesized from thiosemicarbazide and 2,3-dihydroxybenzaldehyde. The prepared thiosemicarbazone was characterized by elemental (CHN), FT-IR, 1H and 13C NMR techniques. Furthermore, the molecular structure was probed using the single-crystal X-ray diffraction (SC-XRD) technique, which confirmed the enol tautomeric form with two independent molecules in asymmetric unit. The dissimilarity between the molecular units was determined by molecular overlay plots. The various intermolecular interactions and solid-state assembly stabilization were explored by Hirshfeld surface analysis. Void analysis was executed to examine the mechanical stability of crystalline units. The bioactivity of thiosemicarbazone was probed with the help of its binding capacity with salmon sperm DNA (SS-DNA) by means of the absorption interaction method. Accompanied by biological activity, optoelectronic properties such as nonlinear optical properties of yielded crystal were also explored through the DFT approach at M06/6–311 G (d,p). For this, various kinds of investigations such as frontier molecular orbital (FMO), UV–Vis, global reactivity parameters (GRPs), transition density matrix (TDM), density of states (DOS), natural population analysis (NPA), and natural bond orbital analysis (NBO) were executed at M06 functional. A good agreement was examined between XRD and DFT findings of molecular geometric parameters. Notably, in comparison with urea, TSDHB demonstrated enhanced nonlinear optical properties (linear polarizability=4.766 × 10−23esu and third-order hyperpolarizability=5.939 × 10−35esu). These findings position TSDHB as a promising candidate for DNA binding as well as for photonic materials due to its unique molecular characteristics and enhanced nonlinear optical behavior.

Specific features of Copper(II) chloride complexes with Caffeine: Synthesis, Structure, DFT calculations

The present article is devoted to the consideration of the interconversions of copper(II) chloride complexes with caffeine (caf) ([CuII2(μ2-Cl)2(caf)2(H2O)2] (1),[CuII3(μ-Cl)6(caf)(H2O)]n (1a), [Cu4(μ2-Cl)6(μ4-O)(caf)4](1b), 2[CuII(caf)Cl2].0.25THF (1c), [CuII(caf)2Cl2] (2)), depending on the synthesis conditions, and to studies on the four-nuclear copper(II) bromide complex with acetamide (AcAm) ([Cu4(μ2-Br)6(μ4-O)(AcAm)4](3)). The results obtained have been confirmed by different methods (powder XRD, single crystal XRD analysis, IR-, ESI-MS-, EPR-spectroscopy, and magnetic properties studies). Two bromide ions in (3) are non-equivalent to the other four and this fact may result in the modification of the exchange integral between bonded copper ions. Single crystal XRD data have been compared with the results of DFT calculations. It has been found that the thermodynamic stability of the complexes grows with an increase in the number of copper atoms and bridging chloride ions and a decrease in the number of water molecules in the formula unit of the compound. The calculation results for complexes with acetamide are in a good correlation with those of caffeine and experimental data.

Structural changes in Rochelle salt on phase transitions revisited in a multi-temperature single-crystal X-ray diffraction study.

Phase transitions in Rochelle salt [sodium potassium L(+)-tartrate tetrahydrate] are revisited in a single-crystal X-ray diffraction multi-temperature study on cooling from 308 to 100 K across the high-temperature paraelectric (PE) ↔ ferroelectric ↔ low-temperature PE phase transition points. The results of structure refinement using three different models (a harmonic with and without disorder, and an anharmonic) were compared. The temperature dependencies of anisotropic displacement parameters (ADPs) and Ueq, which can be calculated directly from ADPs, for the low-temperature PE phase indicate clearly the dynamic nature of disorder of the K1 atoms. The structures of the low-temperature and the high-temperature PE phases are compared for the first time at multiple temperatures for each phase based on diffraction data collected from the same single crystal. The data indicate that the high-temperature and the low-temperature paraelectric phases are probably not two different phases, as was assumed in earlier works, but are structurally the same phase at different temperatures.

Comparative study of composite single crystal and polycrystalline YAG:Ce phosphors for laser-based lighting applications

YAG:Ce, a widely employed phosphor for LED wavelength conversion applications, comes in different forms, including polycrystal (powder), single crystal, and composite single crystal varieties. We investigated Epoch NeoTM, a composite single crystal incorporating Al2O3 as a heat distribution and optical guiding material embedded within its luminescent core. The properties of Epoch Neo were analyzed and compared with those of its polycrystal counterparts in this paper. Multiple characterization techniques like chromaticity points, color temperature, phosphor temperature, and speckle pattern were employed to study the effect of variable laser input power on both polycrystal powder and composite single crystal of YAG:Ce. It was found that under the influence of pumping blue laser high input optical power the composite single crystal phosphor’s performance was significantly better compared to that of the polycrystal.

Crystallographic and Spectroscopic Snapshots of Multi‐Stimuli‐Responsive Dinuclear Cobalt Metal−Organic Frameworks

AbstractInvestigating the reversible structural transformation of stimuli‐responsive metal–organic frameworks (MOFs) through single‐crystal diffraction and establishing a structure–property relationship pose a significant challenge. Herein, the controllable synthesis of Co‐MOF‐1 and Co‐MOF‐2 by incorporating water into the solvothermal synthesis process is presented. In comparison to the trinuclear [Co3(COO)8]2− clusters found in Co‐MOF‐1, Co‐MOF‐2 presents a variable dinuclear [Co2(COO)4(H2O)5] cluster. Single crystal diffraction studies, utilizing synchrotron radiation, confirm the reversible two‐step transformation. The presence of various organic solvents induces the single‐crystal‐to‐single‐crystal (SC‐to‐SC) transformation of Co‐MOF‐2. This transformation is initiated by the cleavage of three coordinated water molecules and subsequent coordination of carboxylates in the ligand, resulting in solvatochromic behavior. Further, the reversible stimuli‐responsive behavior can also be rapidly induced under the stimuli of heat, vacuum, and X‐rays. This study successfully demonstrates the crystallographic and spectroscopic snapshots of dynamic coordination bonds in MOFs and contributes to a deeper understanding of the structure–property relationship.

Fluorescent 2-carbonyl carbazole ketones: Photophysical properties, molecular structure and selective detection of Fe3+ ion

Owing to the diverse implication of carbazole scaffolds in medicinal chemistry, photoelectronic materials and chromophores, the molecules containing the carbazole motif have attracted significant attention over the years. In this work, the vibronic contributions to carbazole structures could facilely change the solvatochromic effect, absorption wavelength, emission wavelength, and Stokes shifts of six 2-carbonyl carbazole ketones fluorophores. Among them, the structure of 1-(1-methyl-9H-carbazol-2-yl)ethanone (3a) were confirmed from single crystal XRD studies. The ratiometric detection of Fe(III) ion of 2-carbonyl carbazole ketone 3a were investigated. Furthermore, it was speculated that chemosensor 3a toward the recognition of Fe3+ cation was dependent on its rigid structure and good coplanarity of the conjugated system, strong intramolecular charge-transfer of 3a.

Borosilicate-Based Framework: Synthesis, Single-Crystal Structure Study, and Physical Properties.

Herein, we report the synthesis, crystal structure, and optical properties of a metal-free three-dimensional (3D) inorganic covalent framework ((H2en)[Si(B4O9)], named CityU-11, where H2en is the abbreviation for ethanediamine). With the assistance of a tiny amount of F- ions and the selection of SiO2 as Si sources, single crystals of CityU-11 can be successfully prepared under solvothermal conditions. The precise structure information on CityU-11 has been disclosed through both single-crystal X-ray diffraction (SCXRD) and low-dose high-resolution transmission electron microscopy (LD-HRTEM). The SCXRD results showed that CityU-11 crystallized in the noncentrosymmetric space group of Pnn2, while LD-HRTEM suggested that CityU-11 possessed almost the same interplanar distances of 0.6 nm for both (200) and (020) crystal planes, which finely matched with the double peaks of 2θ = 15° in the pattern of its powder X-ray diffraction (PXRD). CityU-11 also displayed an interesting optical property with a moderate birefringence of 0.0258@550 nm.

Acoustic shock wave-induced ordered to disordered switchable phase transitions: A case study of ferroelectric triglycine sulphate single crystal for the application of molecular switches

Highly efficient switchable materials for external stimuli have impressive applications in the development of precious sensor devices. However, most of the materials do not possess effective switchable structural features such that finding potential switchable materials is one of the critical research tasks for materials science researchers. In the present research perspective, we demonstrate successive switchable phase transitions occurring between the order to disorder states in the ferroelectric triglycine sulphate (TGS) single crystal along the (011) plane with respect to the number of shock pulses (0,1 and 2 counts) and the observed results are evaluated by the diffraction, spectroscopic, microscopic and thermal approaches. The observed switchable phase transitions occur due to the shock wave-induced inter-conversion of planar configuration to the non-planar configuration of Glycine molecules, particularly GII and GIII. The ratio of the normalized Raman bands Sym-CH2/Asym-CH2 is found to be 2.0 and 2.5 for the respective order to disorder states such that these values are identified to be well-matched with the literature reports. In addition to that, the SEM images authenticate that, during the amorphous to crystalline phase transitions, the appearance of well-defined (011) plane on the surface is ensured due to the dynamic recrystallization. To the best of our knowledge, to date, it is probably the first report for the phase switching of order to disorder states of TGS sample by the impact of acoustical shock waves and because of its efficient switchability, it can be strongly suggested for the application of molecular switches.

Luminescent 8-hydroxyquinoline derived tin(IV) complexes

Four different 8-hydroxyquinoline derivative-based tin(IV) complexes [(nBu)2Sn(Cl-Q-CHO)2] (1), [{(nBu)4Sn2(Q-COO)2}2] (2), [Ph2Sn(Cl)(Q-CHO)] (3) and [Ph2Sn(Cl)(Q-CH{OMe}2)] (4) (Cl-Q-CHO = 5‑chloro-8-hydroxyquinolin-7-carbaldehyde; Q-COO− = 8-hydroxyquinolin-2-carboxylate; Q-CHO = 8-hydroxyquinolin-2-carbaldehyde and Q-CH{OMe}2 = 2-(dimethoxy methyl)quinolin-8-ol) have been synthesized and characterized by elemental analysis, spectroscopy (FT-IR, Mass, UV–Vis, photoluminescence, 1H, 13C and 119Sn NMR) and thermogravimetric analysis. Complexes 1 and 4 have also been characterized by single-crystal diffraction studies and the bulk purity established by powder X-ray diffraction studies. Photophysical studies were conducted in a variety of solvents to demonstrate the effect on excitation and emission on the polarity of the solvent. All the new complexes show higher luminescence in a polar solvent resulting in the stabilization of the excited states. Complex 1 shows a high quantum yield of 97% in chloroform. Further, the photophysical results were substantiated through DFT calculations.

Mono-cyclopentyl substituted [1,3,4]thiadiazole thione tautomer: study of the spectroscopic, geometric, thermal, and biological properties

Regarding the importance of thiol-thione tautomer structure and the existence of hydrogen bonding in thione tautomer structure and its effect on geometric, physicochemical, and biological properties, mono-cyclopentyl-substituted bismuthiol was synthesized via a telescopic process in a green medium. The pure product was characterized by physical and spectroscopic techniques. The suitable crystals for single crystal study were obtained after trying different solvents and mixed solvents, and long clear needle-like crystals could be isolated from a mixture of n-hexane and ethyl acetate (volume ratio of 8:2). The FTIR spectra of bismuthiol, 2,5-bis-cyclopentylsulfanyl-[1,3,4]thiadiazole, and 5-cyclopentylsulfanyl-3H-[1,3,4]thiadiazole-2-thione were studied to define the characteristic wavenumbers of thiol and thione structures. A possible hyper-conjugative interaction between the S–H and π bond of C=N, the existence of C=S and C–N–H. and stability of thione structure was demonstrated for the new product, which supports our prediction of thione or thiol structure using the study of IR spectra. Furthermore, the influence of change in 1,3,4-thiadiazol ring and the presence N–H functional group of thione structure on the transition phases and thermal stability of bismuthiol, bis-cyclopentyl-substituted, and mono-cyclopentyl-substituted bismuthiol were investigated using TGA/DTA and DSC profile analysis. The SwissADME tool was employed to predict the biocheminformatic information of bismuthiol, bis- and mono-cyclopentyl-substituted bismuthiols, which displayed high potential of all 1,3,4-thiadizole derivatives in pharmaceutical and medicine areas. Finally, an in vitro antibacterial activity of the mono- and bis-cyclopentyl substituted bismuthiol against the gram-negative (Escherichia coli ATCC 25922) and gram-positive (Staphylococcus aureus ATCC 25923) bacterial species was conducted by the disk diffusion method with cefazolin as a blank antibiotic. The results showed superior antibacterial efficiency of both derivatives.