Crystal vibration of low temperature phase β-barium metaborate and its multipolar coupling

The Raman and i.r. spectra of the newly synthesized second harmonic generating crystal β-barium metaborate in the low temperature phase are presented with a complete assignment of the external and internal vibrational modes. Emphasis is put on the discussion of the site group effect, the isotope effect and the dynamic coupling between the external and the internal motion of the B₃O³⁻₆ ring and the Ba²⁺ ion. Force constants are also calculated with the prediction that there is one internal vibrational mode of the B₃O³⁻₆ ring at a frequency of 177 cm⁻¹ which is of the order of the frequencies of the lattice modes. Multipolar coupling between the B₃O³⁻₆ rings in this crystal is also analyzed with the generalization of a dipolar coupling theory.     

Raman spectra of lanthanide sesquioxide single crystals: Correlation between A and B-type structures

Structures and Raman spectra of lanthanide sesquioxide single crystals with A-type trigonal structure (La₂O₃, Pr₂O₃, Nd₂O₃, Sm₂O₃) and B-type monoclinic structure (Sm₂O₃, Eu₂O₃, Gd₂O₃) are compared. The B form (C³_2h or $\text{C2}\text{m}\text{, Z = 6}$) derives from the A form (D³_3d or $\text{P}\text{3}\text{m1, Z = 1}$) by a slight lattice deformation, implying a splitting of D_3d and C_3v atomic positions into less symmetrical C_2h and C_s sites. This close structural relationship allows one to relate the Raman active modes of the B-type crystals to vibrations of the A-type crystals and to deduce an interpretation of the complex B-type spectra from those of the simpler A-type spectra. Furthermore, it is shown that the frequency of the modes which mainly involve metal-oxygen stretching motion increases with the lanthanide atomic number in the A and B series. This evolution is interpreted in terms of increasing compactness of the structure.     

Molecular structure of the boron(III) oxide molecule in the SCF approximation

The potential surface for the boron(III) oxide (B₂O₃) ground state has been calculated in restricted HF approximation with a minimal STO—3G basis set. The equilibrium geometry has C_2v symmetry; the corresponding structural parameters are as follows: r(O_i—B₁)= 1.241 Å; r(B_i—O)= 1.341 Å ; ∠B₁QB₂ = 142° and ǒO₁B₁O = 177°. Calculations were also carried out using the SCF-Xα approach for two configurations of B₂O₃ with C_2v and D_∞h symmetry.     

Vibrational analysis of 1,4-diiodobutane

Infrared and Raman spectra were obtained for 1,4-diiodobutane, and normal-coordinate calculations were made using a transferred 48-parameter modified v force field. This compound sometimes crystallizes in the GG' conformation with C₂ symmetry and sometimes in the TG conformation. No evidence was obtained for the presence of the TT (C_2h symmetry) or GG (C_i) conformers, but one or two additional conformers are present that must have a nonplanar chain of carbon atoms.     

Vibrational spectra and structure of gaseous and solid dimethylboric anhydride

The Raman spectra of gaseous, liquid and solid dimethylboric anhydride (CH₃)₂BOB(CH₃)₂ have been recorded from 10–3500 cm^?1. The IR spectra from 4000–30 cm^?1 have also been recorded. The spectra of the gaseous phase have been interpreted in terms of C₂ symmetry implying a bent B-O-B skeleton with the B(CH₃)₂ groups twisted and consistent with a rather larger barrier to internal rotation about the B-O bonds. The spectra of the crystalline state, however, suggest that the molecular symmetry is altered upon solidification. Isotopic substitution of the oxygen atom by ¹⁸O confirmed that the B-O-B skeleton is linear in the solid state, and the spectra have been interpreted in terms of D_2h molecular symmetry.     

Synthesis,Crystal Structure,and Characterization of a Novel Metallo‐Organically‐Templated Pentaborate with Mixed Ligands

A novel metallo‐organically templated pentaborate with layered framework, [Cd(TETA)(C₂H₃O₂)][B₅O₆(OH)₄] ( 1 ) (TETA = triethylenetramine), was synthesized under mild solvothermal conditions. The structure was determined by single‐crystal X‐ray diffraction and further characterized by FT‐IR spectroscopy, elemental analysis, thermogravimetric analysis, and photoluminescence spectroscopy. The structure consists of an isolated polyborate anion [B₅O₆(OH)₄]^– and the cadmium complex cation of [Cd(TETA)(C₂H₃O₂)]⁺, which contains both organic amine and organic acid ligands. The [B₅O₆(OH)₄]^– units are connected together by hydrogen bonds, and a 2D sheet‐like framework with rectangle‐like 12‐membered boron rings are formed. The [Cd(TETA)(C₂H₃O₂)]⁺ complex cations are located in the free space between the layers and connect the adjacent borate layers through hydrogen bonds to form a three‐dimensional supramolecular network. The luminescent properties of the compound were studied for the first time in the series of metallo‐organically‐templated pentaborates, and a blue luminescence occurs with an emission maximum at 468 nm upon excitation at 397 nm.     

Structures of 18-crown-6, 15-crown-5 and their metal complexes in methanol solution as studied by Raman spectroscopy

Raman spectra of 18-crown-6, 15-crown-5, and their complexes with Li⁺, Na⁺, K⁺, Cs⁺, Mg²⁺, Ca²⁺ and Ba²⁺ have been investigated in methanol solution. Normal coordinate calculations are presented for the D_3d⁻ and C_i-symmetric structures of 18-crown-6. Analysis of the Raman spectra gives information on the ring conformations of the crown ethers and the stoichiometry of complexation. The uncomplexed ethers adopt diverse conformational states in methanol at room temperature, the D_3d state being the most stable in 18-crown-6 and various states equally stable in 15-crown-5. Most of the cations form 1:1 or 2:1 crown—metal complexes depending on the cation size relative to the hole size of crown. Exceptionally, Cs⁺ forms both 1:1 and 2:1 complexes with 18-crown-6. The ring structures in complexes of 18-crown-6 are not much distorted from the D_3d one, though the distortion is rather large in the 2:1 Cs²⁺ and 1:1 Ca⁺ complexes. Complexes of 15-crown-5 exhibit for types of ring structure depending on the size and charge of the cation. These structures are likely to involve distortion from the gauche or gauche′ conformation about the CC bonds and various conformation about the CO bonds.     

Algebraic symmetry and determination of the “imaginary” crystal field parameters from optical spectra of fn-ions. Hexagonal and trigonal symmetry

Algebraic symmetry of the characteristic equation of the crystal field hamiltonian Ĥ_CF for hexagonal (C₆, C_3h, C_6h) and trigonal (C₃, S₆) symmetry is considered. Explicit dependence of the coefficients a_i of the characteristic equation on the CF parameters is derived by ALTRAN. Magnitudes, signs and/or relative signs of the CF parameters which can be determined from fitting the optical spectra of fⁿ-ions at sites of the above symmetry are established. The algebraic results derived here can facilitate the fitting procedures for any hexagonal and trigonal symmetry. The relevant literature is extensively surveyed. The approach C (complete) to fitting the optical spectra, which yields ambiguous and unreliable results in general, has not been employed to hexagonal (C₆, C_3h, C_6h) symmetry. Some misinterpretations on the approach R (reduced) and A (approximated), which merge for this symmetry, are clarified. Crystal field analysis has been carried out for trigonal (C₃, S₆) symmetry in but a few cases only. The survey has revealed one case of the inappropriate C used for Eu³⁺ in the trigonal (C₃) Eu(DBM)₃ · H₂O system.     

Infrared and Raman spectra of lithium trihorate: Vibrational assignments and a correlation with its nonlinear optical activity

Infrared and polarized single crystal Raman spectra of lithium triborate (LBO; LiB₃O₅) are reported and analysed. All four (A₁, A₂, B₁ and B₂) symmetry species of the C_2v, point group isomorphic to the C_2v⁹(Pna2₁) space group are Raman active in distinct crystal polarization experiments. A complete set of symmetry assignments based on a factor group analysis is presented. The internal and external vibrations are separated on the basis of frequency and the observation that the magnitude of the correlation splitting for the internal modes is very small. A comparison of the internal frequencies of various borate species suggests a correlation between the B-O stretching frequency and the nonlinear optical efficiency of the material.     

Low frequency Raman spectra of barium borate glasses in the system (BaCl2)y[(BaO)x(B2O3)1-y-x]1-y for various x and y

Low frequency Raman spectra of glasses of the types (BaO)_x·(B₂O₃)_1−x and (BaCl₂)_y·[(BaO)_x·(B₂O₃)₁-_y-_x]₁-_y have been reported. The temperature reduced Raman spectra show peaks at 67, 116 and 140 cm⁻¹ for the binary glass. The bands at 116 and 140 cm⁻¹ are ascribed to the librational motions of the borate groups and the 67 cm⁻¹ band arises because of the limited structural correlation range (SCR) of the glass network, causing a maximum of the frequency dependent Raman coupling coefficient. Due to addition of BaO in v-B₂O₃, the oxygen are mostly incorporated in the formation of BO₄ units; however large Ba²⁺ ions also enhance the number of non-bridging oxygen at higher concentrations of dopant. These barium ions as well as chlorine ions are accomodated in the interstitial vacancies of the glass network which leads to an expansion of the network structure.     

Vibrational spectra of the trans-trans and trans-cis conformers of dimethyl fumarate

Infrared and Raman spectra of dimethyl fumarate (DMFU) have been recorded in the temperature range 12–390 K. The solid state spectra are consistent with the trans-trans conformation. However, in the liquid phase (melt or solution in CCl₄) and in the vapour phase, additional infrared and Raman bands were observed due to the presence of the trans-cis conformer. For the trans-trans conformer the observed spectra have been assigned on the basis of a C_2h molecular symmetry. A normal coordinate analysis of trans-trans DMFU has been carried out using a modified Urey- Bradley force field to assist in the assignment. Observed frequencies for the trans-cis conformer have been assigned on the basis of a structure of C_s symmetry.     

Étude par spectrométrie de vibration de la structure des composés de coordination de l'acétonitrile avec les halogénures d'aluminium AlCl3 et AlBr3

Infrared and Raman spectra of the three definite coordination compounds formed between CH₃CN or CD₃CN and AlX₃ (X = CI or Br) have been recorded and discussed. All the compounds are ionic and contain AIX₄^? anions. The cation is (AI(CH₃CN)₆]^3? for the AlX₃-1.5 CH₃CN and AlX₃-2 CH₃CN. In the first case, the cation is highly symmetrical and the spectra are consistent with the O_h point group. In the second case, the cation is distorted and the symmetry type may be lower than D_3d or D_4h. The frequencies are correlated with the nature of the halogen. The cations of the 1-1 compounds contain one or two halogen atoms. The vibrational spectra of AlBr₃-CH₃CN are consistent with a [Al(CH₃CN)₂Br₂]^* - AlBr₄^? structure but are more difficult to interpret for the AlCl₃-CH₃CN complex.     

Two scandium–biuret complexes: [Sc(C2H5N3O2)(H2O)5]Cl3·H2O and [Sc(C2H5N3O2)4](NO3)3

The scandium(III) cations in the structures of pentaaqua(biuret‐κ²O,O′)scandium(III) trichloride monohydrate, [Sc(C₂H₅N₃O₂)(H₂O)₅]Cl₃·H₂O, (I), and tetrakis(biuret‐κ²O,O′)scandium(III) trinitrate, [Sc(C₂H₅N₃O₂)₄](NO₃)₃, (II), are found to adopt very different coordinations with the same biuret ligand. The roles of hydrogen bonding and the counter‐ion in the establishment of the structures are described. In (I), the Sc³⁺ cation adopts a fairly regular pentagonal bipyramidal coordination geometry arising from one O,O′‐bidentate biuret molecule and five water molecules. A dense network of N—H...Cl, O—H...O and O—H...Cl hydrogen bonds help to establish the packing, resulting in dimeric associations of two cations and two water molecules. In (II), the Sc³⁺ cation (site symmetry 2) adopts a slightly squashed square‐antiprismatic geometry arising from four O,O′‐bidentate biuret molecules. A network of N—H...O hydrogen bonds help to establish the packing, which features [010] chains of cations. One of the nitrate ions is disordered about an inversion centre. Both structures form three‐dimensional hydrogen‐bond networks.     

Hexakis[3‐(aminocarbonyl)pyridinium] decavanadate(V) dihydrate

The structure of the title compound, (C₆H₇N₂O)₆[V₁₀O₂₈]·2H₂O, at 120 (2) K has monoclinic (C2/c) symmetry. The asymmetric unit consists of one half‐decavanadate anion of C_i symmetry, three cations and one water molecule. Each water molecule is hydrogen bonded to two decavanadate anions, thus forming a one‐dimensional chain of anions. The three‐dimensional supramolecular structure is formed by a network of N—H...O, O—H...O and C—H...O hydrogen bonds, in which the cations, anions and water molecules are involved, and by nonparallel‐displaced π‐stacking interactions between pyridine rings. As a result of hydrogen bonding, the carboxamide groups of the cations are somewhat twisted from the pyridine ring plane.     

Vibrational spectra and IR dichroism of poly(tetramethyl-p-silphenylene-siloxane) and its chain structure

Raman spectra of poly(tetramethyl-p-silphenylene-siloxane) were investigated in solution with depolarization ratios and in the solid state. Polarized infrared (IR) spectra were studied on oriented polymer samples. Assignments of the vibrational bands are given and IR dichroic and Raman data are in agreement with tetragonal P4₁ space group symmetry. These data provide information on the arrangement of the Si? C₆H₄? Si groups in the unit cell. On the basis of vibrational spectra the dynamic interaction between adjacent benzene rings is negligibly small and the rings preserve their local D_2h Pseudosymmetry.     

Stretching vibrations of CH bonds in spectra of dicarbaclosododecaboranes (p-, m-, and o-carboranes)

Parameters of bands corresponding to stretching vibrations of C-H bonds in spectra of o-, m-, and p-isomers of the icosahedral carborane B₁₀H₁₀C₂H₂ have been measured with high accuracy. The stretching vibrations of C-H bonds in spectra of o- and m-carborane (12), molecules which have C_2v point group symmetry, are demonstrated to appear the same as in the spectrum of the p-isomer with D_5d symmetry. The frequencies of Raman and IR lines practically coincide. This indicates the absence of interaction of the stretching vibrations of the two C-H bonds even in the o-carborane molecule.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 10, pp. 2263–2267, October, 1989.     

The structure of the dithionite ion

The Raman spectra of aqueous and solid sodium dithionite have been recorded. Differences in the location, intensity, and number of observed bands are attributed to conformational changes in the dithionite ion. The structure of the aqueous ion is non-planar with a C_2h symmetry with an SS bond distance estimated to be 0.220–0.226 nm, as opposed to the dithionite structure in the Na₂S₂O₄·2H₂O salt which is known to have C_2ν structure with a bond distance of 0.2389 nm. The Raman spectra of aqueous dithionite are assigned to A_g (SO) = 997 cm^?1; B_g (SO) at 912 cm^?1, B_g SO₂ twist at 324 cm^?1. The remaining bands are a strong A_g, the SO₂ wag, the SO₂ scissor, and the SS stretch at 584, 461, and 232 cm^?1, respectively, but due to coupling all three motions are expected to exhibit substantial SS character. The variation of the spectra of the solid and aqueous sodium dithionite indicate strong environmental effect on the structure of the anion.     

Long-range magnetic ordering in Ba2CoS3: A neutron diffraction study

Neutron powder diffraction has been used to determine the magnetic structure of the quasi-one-dimensional compound Ba₂CoS₃, which contains linear [001] chains of vertex-sharing CoS₄ tetrahedra, spaced apart by Ba²⁺ cations. At 1.5 K the Co²⁺ cations in the chains are antiferromagnetically ordered with an ordered magnetic moment of 1.97(4) μ_B per cation aligned along [100]. Each Co²⁺ cation is ferromagnetically aligned with four cation in neighbouring chains and antiferromagnetically aligned with two others.     

Molecular reorientation of liquid benzene. Anisotropic Raman scattering of the CH and CD stretching modes in the deuterated molecules

The anisotropic Raman spectra of the CH and CD stretching modes in seven deuterated benzenes of D_6h, D_3h, D_2h and C_2h symmetry are reported. The reorientational linewidths are interpreted within the model of anisotropic rotational diffusion. The data are consistent with NMR relaxation studies. The study covers the temperature range between T/T_c = 0.49 and T/T_c = 0.97.     

Raman and infrared spectra of lanthanum molybdate

The infrared and Raman spectra of gel-grown lanthanum molybdate were recorded. Group theoretical analysis was carried out and a vibrational assignment proposed based on C_2h symmetry. Factor group and site effects are discussed.