Single-crystal Spectra Research Articles

Synthesis, structures and fluorescent properties of two cadmium(II) coordination polymers based on bis(benzimidazole) and different anions

Two new Cd(II) coordination polymers (CPs), {[Cd(BBM)Cl2]·CH3OH}n (1) and [Cd2(BBM)2(isophthalate)2]n (2) (BBM = 2,2-(1,4-butanediyl)bis-1,3- benzimidazole), have been obtained from hydrothermal method and characterized by single-crystal X-ray diffraction, elemental analysis, IR and UV-Vis spectra. The CP 1 displays a one-dimensional (1D) square wave chain structure connected by BBM ligands, whereas CP 2 is a 2D layer network. The structure analysis revealed that the selection of anions with different coordination modes realizes the control of the structure of the cadmium coordination polymer. Weak hydrogen bonds and π···π interactions are the major driving forces in the crystal packing of the two coordination polymers. Hirshfeld surface analysis reveals detailed scrutiny of intermolecular interactions experienced by each complex. In addition, the fluorescence properties of the ligands and CPs 1-2 in the solid-state were studied. The fluorescence peaks of the two Cd(II) CPs were weakened compared to the free ligands, which is attributed to ligand-centered fluorescence. The partial quenching of the aggregates may be due to the π···π stacking and heavy atom effect.

Anisotropic Magnetoabsorption of Light in Cobalt Ferrite and Its Correlation with Magnetostriction

The absorption spectra of a CoFe2O4 ferrite spinal single crystal, which has a giant magnetostriction, demonstrate an absorption edge at 1.18 eV and a fine structure of impurity absorption bands in the IR region. In the Voight geometry, the crystal is shown to exhibit magnetoabsorption, which is related to the field-induced changes in the fundamental absorption edge and impurity absorption bands. The magnetoabsorption (magnetotransmission and magnetoreflection of light) is anisotropic and depends on the magnetic field direction with respect to the crystallographic axes of the crystal. The light magnetoabsorption is found to be related to the magnetostriction of the crystal. The magnetostriction of CoFe2O4 is shown to significantly contribute to its magnetic anisotropy constant, which is accompanied by changes in the electronic spectrum and optical properties when a magnetic field is applied. The high magnetoabsorption in CoFe2O4 in a relatively low magnetic field makes it possible to use this magnetic material for the development of a new trend in spintronics, namely, strain-magnetooptics.

Low-temperature luminescence of ScF3 single crystals under excitation by VUV synchrotron radiation

Photoluminescence and excitation spectra of ScF3 single crystals have been measured under vacuum ultraviolet excitations utilizing undulator synchrotron radiation from 1.5 GeV storage ring of MAX IV synchrotron. The emission peak at 280 nm is explained as emission band of self-trapped excitons in ScF3. This emission is quenched at 50 K and activation energy of thermal quenching was obtained. The excitation spectrum in vacuum ultraviolet spectral range exhibits that the luminescence of self-trapped excitons effectively occurs under direct excitation in the excitonic absorption band, whereas under higher energies this excitation is strongly suppressed, however, multiplication of electronic excitation processes have been successfully identified.

Structural diversity from co-crystal to 1D coordination polymers of 2,6-naphthalenedicarboxylic acid with 4,4′-bipyridine as coligand: structural and computational approach

The co-crystal 2,6-naphthalenedicarboxylic acid (2,6-NDCA) and 4,4′-bipyridine (4,4′-bipy) I and metal (Li+) complex of 2,6-NDCA with 4,4′-bipy i.e. {[Li(2,6-NDC)0.5.(H2O)2] n .4,4′-bipy} II (2,6-NDC = 2,6-naphthalenedicarboxyle) have been characterized by single crystal X-ray diffraction, IR spectra, elemental, and TGA analyses. The co-crystals are stabilized by strong H-bonding between acid–base units whereas the Li+ ion based mixed complex is stabilized by both coordination and H-bonding interactions. During investigation of strong or weak intermolecular interactions, X-ray diffraction analysis and Hirshfeld surface analysis gave rise to comparable results but in the Hirshfeld surface analysis, two-third times more close contacts were observed. Thermogravimetry shows that the complex is stable up to 200 °C after the removal of coordinated water molecules. To get some insights in the chemical reactivity indices, the HOMO-LUMO gap, chemical potential, chemical hardness, and electrophilicity indices for both systems (in gas phase) have been analyzed on the basis of theoretical investigations along with their molecular electrostatic potential surfaces and the total electron density plots; I has been found to be more stable than II which appears to be because of the strong H-bonding interaction(s). The fingerprint plots demonstrate that these weak nonbonding interactions are important for stabilizing the crystal packing.

Synthesis and characterization of three co-crystals of bis(benzimidazole) derivatives with aromatic dicarboxylic acids

Combination of three aromatic carboxylic acids (5-nitroisophthalic acid (H2nip), 2,6-naphthalenedicarboxylic acid (H2ndc), tetrabromoterephthalic acid (H2tbta)) and flexible bis(benzimidazole) derivatives (1,6-bis(2-methylbenzimidazol-1-yl)hexane (L1), 1,2-bis(2-methylbenzimidazol-1-ylmethyl)benzene (L2), 1,4-bis(2-methylbenzimidazol-1-yl)butane (L3)), three co-crystals [(H2L1)2+·2(Hnip)−·H2O] (1), [(L2)·(H2ndc)] (2) and [(H2L3)2+·(tbta)2−] (3) were synthesized hydrothermally. Single-crystal X-ray diffraction, elemental analysis and IR spectra are employed to characterize 1, 2 and 3. The 2D fingerprint plots and Hirshfeld surfaces of 1, 2 and 3 indicate that the 3D supramolecular network for 1 was generated by N–H···O, O–H···O, C–H··O hydrogen bonds and π−π interactions, the 2D sheet for 2 was produced by O–H···N hydrogen bonds and π−π interactions, and C–H···O hydrogen bonds make structures more stable. For 3, the 2D supramolecular layer was yielded by N–H···O, C–H···O hydrogen bond interactions. Furthermore, thermogravimetric analyses and photoluminescence properties of three compounds were presented.

STUDYING CHARACTERISTIC FEATURES OF THE ELECTRONIC STRUCTURE OF NITROGEN-CONTAINING COMPOUNDS BY ELECTRON PROBE MICRONALYSIS

Primary NKα, OKα, and CKα spectra of single crystals of carbamide, sodium nitrite, sodium nitrate, and ammonium nitrate are recorded by electron probe microanalysis. The spectra of nitrogen in nitrites and nitrates exhibit a structure of resonance levels in the low-energy part of the conduction band. Nitrogen K-edge absorption coefficients for the NKα radiation and the braking background are determined. Polarization spin density of nitrogen and oxygen 2p electrons in NaNO3 is established.

The synthesis of heteroleptic cyanometallate aminopyridine complexes and an investigation into their structural properties with various spectroscopic methods

In this study, three new transition metal(II) complexes consisting of zinc(II), mercury(II) atoms, cyanide group (CN), 3-aminopyridine (3AP) and 4-aminopyridine (4AP) ligand molecules were successfully synthesized in a single crystal form. The formulas of these newly synthesized heteroleptic cyanometalate aminopyridines complexes are given as [Zn(II)(3AP)2(CN)2], [Zn(II)(4AP)2(CN)2] and [Hg(II)(4AP)2(CN)2]. The crystal structures of these heteroleptic cyanometalate complexes were characterized by spectral analysis including single crystal X-ray diffraction techniques, FT-IR, and thermal analysis. The FT-IR and single crystal XRD spectra of these complexes were recorded in the 3750–250 cm−1 wavenumber range and in the region of about 3–29°, respectively. In addition, the thermal analysis curves of these complexes were recorded in the temperature range of 40–850 ℃ using TG, DTG, and DSC methods. The structural properties of these complexes are explained with reference to the changes in their characteristic peaks belonging to 3AP, 4AP ligand molecules and cyanide group in their FT-IR spectra. The most important feature of these new complexes is the presence of NH···N interactions between the H atom of the NH2 group of the 3AP and 4AP ligand molecules and the nitrogen atom of the CN group. These interactions play the most important role in the realization of the three-dimensional structure of the new heteroleptic cyanometalate complexes in crystal form. According to the spectral data of the newly obtained heteroleptic cyanometalate complexes, the complex with 3AP has the orthorhombic crystal system and the space group Pca21, whereas the other two heteroleptic cyanometalate complexes with 4AP have in the monoclinic crystal system and the C2/c space group. The asymmetric unit of [Zn(II)(3AP)2(CN)2] comprises one Zn(II) ion, two cyano groups, and two 3AP ligand molecules; the asymmetric unit of [Zn(II)(4AP)2(CN)2] comprises one Zn(II) ion, one cyano group and one 4AP ligand molecule. Similarly, the asymmetric unit of [Hg(II)(4AP)2(CN)2] comprises one Hg(II) ion, one cyano group and one 4AP ligand molecule.

Vibrational and luminescent properties of polycrystalline zircon: Effect of structural and impurity defects

Zircon was synthesized by the sol-gel route and subjected to sequential heat treatment. X-ray powder diffraction showed that single-phase zircon was obtained. The impurity content and microstructure of the obtained ceramic were studied by the mass spectrometry and scanning electron microscopy. The contents of Hf ~0.8 ​wt% and Al ~0.2 ​wt% are prevailing, while the presence of other impurity elements does not exceed 0.06 ​wt%. The photo- and cathodoluminescence data indicate the presence of structural and impurity defects. The instability of structural defects during high-temperature annealing was observed. The average value FWHM of the Raman B1g(4) band of asymmetric stretching vibrations of SiO4 tetrahedra lies in the range 2.55–3.15 ​cm-1, which slightly exceeds the minimum value ~1.8–2.0 cm-1 in the spectra of perfect single crystals. The zircon synthesized can be used as a reference sample for spectroscopic studies in mineralogy.

Photoluminescence and scintillation characteristics of β-BaB2O4 single crystal

The photoluminescence (PL) and scintillation emission spectra of β-BaB2O4 single crystal were studied at different temperatures from 9 to 300 K. In PL, intense emission appeared at 430 nm with a sub-peak at 365 nm, and the X-ray-induced scintillation spectrum was close to PL. When we investigated the temperature dependence of PL and scintillation, the PL intensity increased at lower temperature while the scintillation intensity decreased. This tendency can be understood to be due to thermal activation via the trapping phenomenon associated with thermally stimulated luminescence with shallow traps.

In situ NMR Investigation of the Photoresponse of Perovskite Crystal

Summary Hybrid perovskites are outstanding candidates for use in optoelectronic devices. Nonetheless, hybrid perovskites present numerous fundamental issues that are not yet fully understood. This study seeks to address this problem by reporting on the occurrence of ultraslow dynamic orientation changes in the methylammonium (MA) cations and the corresponding changes in the inorganic lattice of MAPbI3 perovskite crystals occurring over a time scale of 100 s under continuous illumination based on in situ single-crystal 2H nuclear magnetic resonance and in situ X-ray diffraction results. The demonstrated ultraslow dynamic changes in MAPbI3 are far slower than elementary molecular motions typically having time scales of femtoseconds and picoseconds and have never been reported previously. The ultraslow dynamic changes have been correlated with the reduction of band gap and the increase of absorption coefficient of MAPbI3, providing the molecular origins of the stabilization process in the photoresponse of the MAPbI3 device.

A methyl viologen-containing cadmium crystalline material with photochromism and methylamine sensing properties

A cadmium crystalline material, namely, (MV)n[Cd(FDC)2]n (H2FDC ​= ​2,5-furandicarboxylic acid; MV ​= ​methyl viologen) has been successfully constructed and fully characterized by single-crystal X-ray structure determination, IR spectra, elemental analyses and powder X-ray diffractions. The compound features a 2D layer structure, in which in situ generated MV2+ cations located in the interlayer. The MV-containing compound offers a type of electron transfer system, which endows the material with reversible photochromism activities originated from photo-induced electron transfer process. Moreover, the material could sense MA vapor with naked-eye colour change in a shorted time.

Synthesis, structure and fluorescent sensing for nitrobenzene of a Zn-based MOF

Nitrobenzene (NB) can cause serious harm to ecosystems and human health. In order to identify and detect NB effectively, a micro-porous Zn-based metal-organic framework (Zn-MOF) material was prepared. Zn-MOF material named [Zn(L)]n was successfully synthesized by solvothermal method, using 1,3,5-tris (3-carboxy-triazole-methylene)-2,4,6-tritoluene (H3L) as organic ligand. Its stucture was characterized by X-ray single-crystal diffraction, elemental analysis, IR spectra and thermogravimetric (TG) analysis. X-ray single-crystal diffraction analysis exhibits that Zn-MOF belongs to the orthorhombic crystal system, space group Pbcn. The central Zn(II) ion exhibits a octahedron {ZnN3O3} coordination geometry. Topological analysis shows that Zn-MOF exhibits a utp uninodal 3-connected 3D 2-interpenetrating framework with the point symbol (103). Furthermore, the fluorescence quenching experimental results show that Zn-MOF is a potential fluorescent material that can selectively and sensitively fluorescent sensing NB.

New Lines in High Resolution IR Luminescence Spectra of SiC Single Crystals of the 4H and 6H Polytypes

We have studied high-resolution low-temperature IR luminescence and absorption spectra of undoped high-quality SiC single crystals of the 4H and 6H hexagonal modifications. Narrow lines with a width of smaller than 0.2 cm–1 have been revealed, with some of which being observed for the first time. We have found that some of the lines in the 4H and 6H modifications have similar structures; however, the lines in SiC-4H are shifted to the high-energy part of the spectrum by ~180 cm–1. For the most intense quartet in the range of 1.3 µm, we have succeeded in constructing the energy structure of levels for both the 4H modification and the 6H modification based on their luminescence and absorption spectra.

Magneto-optical properties of wider gap semiconductors ZnMnTe and ZnMnSe films prepared by MBE

The II-VI based magnetic semiconductors with a direct and wide optical bandgap are expected to show high potential for optical applications utilizing short wavelength laser diodes (LDs), such as 532-nm green and 475-nm blue LDs. We have confirmed that the Faraday rotation θF in the ZnMnTe and ZnMnSe films deposited on quartz glass (QG) and sapphire (SA) substrates by using molecular beam epitaxy (MBE) is large near the absorption edge. This paper reports the magneto-optical properties of ZnMnTe and ZnMnSe films synthesized on the QG and SA substrates, and shows the result of a direct Faraday rotation observation successfully made for the ZnMnTe films under 1.28-kHz alternating magnetic fields. The optical absorption characteristics of the ZnMnTe films grown on the SA substrates by MBE are discussed by comparing them with the optical absorption properties and photoluminescence spectra of the II-VI ZnTe parent single crystals.

Two d10 coordination polymers based on 4-(4H-1,2,4-triazol-4-yl)benzenesulfonic acid ligand: Syntheses, structures, photoluminescence, and sensing property

Two novel 3D coordination polymer [Cd(L)(NO3)] (1) and [Zn2(L)4(H2O)9‧5H2O] (2) were synthesized by diffusion method with 4-(4H-1,2,4-triazol-4-yl)benzenesulfonic acid (HL) and Cd(NO3)2·4H2O. And the complexes were characterized by single-crystal X-ray diffractometer, FT-IR spectra, elemental analyses, thermogravimetric analyses (TGA) and power X-ray diffractometer (PXRD), meanwhile solid fluorescent property of 1 and 2 have also been investigated. In complex 1, the deprotonated ligand L connected with Cd(II) metal each other to give a 3D structure, the neighboring 3D network can be connected by the CH‧‧‧π to form a final two-fold interpenetrating supramolecular 3D structure, while 2 is 3D structure formed by non-covalent interaction. The fluorescence of complex 1 shows a remarkable red-shift in the luminescence of ligand HL, while 2 performs a 22 nm blue-shift, with respect to the free molecule. Furthermore, 1 can efficiently detect acetone molecules.

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.

Electron paramagnetic resonance study of the paramagnetic center in gamma-irradiated tetrahydrophthalic anhydride single crystal

Electron Paramagnetic Resonance (EPR) analysis of gamma-irradiated tetrahydrophthalic anhydride (C8H8O3) single crystals was performed at 120 K. The single crystals were exposed to 60Co-gamma source at room temperature. The EPR spectra of gamma-irradiated single crystals of tetrahydrophthalic anhydride (THPA) were recorded at 10-degree intervals for different orientations of crystals in a magnetic field. Detailed examination of THPA single crystals by EPR spectroscopy method showed the presence of two carbon-centered THPA anion radicals. Both radicals were determined to have the same structure. The anion radicals observed in gamma-irradiated THPA single crystal were created by the scission of the carbon–oxygen double bond. The g values of the radiation damage centers observed in the THPA single crystal and the hyperfine structure constants of the free electron with nearby protons were obtained. Highlights Single crystals of tetrahydrophthalic anhydride were exposed to gamma radiation. Radiation damage centers in single crystals of tetrahydrophthalic anhydride were determined by EPR spectroscopy method. The presence of two anion radicals in single crystals of tetrahydrophthalic anhydride was determined. The formation mechanism of the paramagnetic centers in the tetrahydrophthalic anhydride is similar to that of succinic anhydride.

Excitonic and electronic transitions in Me-Sb2Se3 structures.

The optical anisotropy of the Sb2Se3 crystals was investigated at 300 and 11 K. Excitonic features of four excitons (A, B, C, and D) were observed in the optical spectra of the Sb2Se3 single crystals and in the photoelectric spectra of the Me–Sb2Se3 structures. The exciton parameters, such as the ground (n = 1) and excited (n = 2) state positions and the binding energy (Ry), were determined. The effective mass of the electrons at the bottom of the conduction band (mc* = 0.67m0) as well as the holes at the four top valence bands (mv1* = 3.32m0, mv2* = 3.83m0, mv3* = 3.23m0 and mv4* = 3.23m0) were calculated in the Г-point of the Brillouin zone. The magnitude of the valence band splitting V1–V2 due to the spin–orbit interaction (Δso = 35 meV) and the crystal field (Δcf = 13 meV) were estimated in the Brillouin zone center. The energy splitting between the bands V3–V4 was 191 meV. The identified features were discussed based on both the theoretically calculated energy band structure and the excitonic band symmetry in the Brillouin zone (k = 0) for crystals with an orthorhombic symmetry (Рnma). The photoelectric properties of the Me–Sb2S3 structures were investigated in the spectral range 1–1.8 eV under E||c and E⟂c polarization conditions and at different applied voltages.

The Influence of Defects on the Absorption of Terahertz Radiation in a CdSiP2 Single Crystal

The transmission and reflection spectra of a CdSiP2 single crystal are measured in the temperature interval from 80 to 300 K using the terahertz (THz) pulsed and infrared Fourier spectroscopy methods. A significant influence of postgrowth defects on the absorption in the THz frequency range is revealed. This absorption is found to depend weakly on temperature compared to that observed previously for other chalcopyrite crystal with substantially lower concentration of defects. Upon cooling, intrinsic absorption mechanisms are minimized, and the contribution of defects to absorption is separated.

Synthese, structure of three Zn-MOFs and potential sensor material for tetracycline antibiotic in water: {[Zn(bdc)(4,4′-bidpe)]·H2O}n

Recently, enough attention has been paid to the pollution and damage of antibiotics in water. Zn-metal organic frameworks (Zn-MOFs), as a novel kind of sensing material, have been tentatively developed a highly effective candidate to detect antibiotics in water. A series of Zn-MOFs material named {[Zn (bdc)(4,4′-bidpe)]·H2O}n (1), {[Zn3 (bdc)2 (tib)2(HCOO)2]·4(H2O)·0.5(CH2Cl2)}n (2), [Zn (bdc)(bidpa)]n (3) were successfully constructed under the condition of solvothermal, using 4,4′-bis(imidazolyl)diphenyl ether (4,4′-bidpe), 1,3,5-tirs (1-imidazolyl)benzene (tib), 4,4′-bis(imidazolyl)diphenyl amino (4,4′-bidpa) and 1,4-benzenedicarboxylate (H2bdc). Three complexes were characterized by X-ray single-crystal diffraction, elemental analysis, IR spectra and thermogravimetric (TG) analysis. Complex 1 has a three-dimensional (3D) framework that crystallizes in the triclinic system, Pī space group. Complex 2 crystallizes in the monoclinic system, C2/c space group featuring a 3-nodal (3,3,4)-connected network with point symbol of 2{83}2{86}{8.102}. Complex 3 belongs to the tetragonal system, I41/acd space group with two-fold interpenetrating architecture. A linear pH sensing of complex 1 (I ​= ​1035.2 pH ​+ ​726.9) between the fluorescence intensity and pH values was achieved through the fluorescence quenching experiment in the acidic condition. The fluorescence quenching experimental results showed that complex 1 exhibits sensitive response to TC with detection limit of 3.72 ​× ​10−7 ​M based on its effective spectral overlap and adsorption preconcentration with tetracycline (TC).