Solid-state Raman Spectra Research Articles

Discovery of two rotational isomers of 4-methoxystyrene by laser-induced fluorescence in a supersonic jet

The S1–S0 fluorescence excitation spectrum of 4-methoxystyrene seeded into a supersonic free jet shows two 000 bands, corresponding to the cis and trans rotational isomers. Dispersed fluorescence, with excitation in each of these bands, show that some of the resulting ground-state vibration wavenumbers are appreciably different. This confirms the 000 band assignments to different isomers. One prominent vibration has a wavenumber of 373 or 400 cm–1, depending on the isomer involved. These two bands are also observed in the Raman spectrum of the liquid and the fact that the 373 cm–1 band disappears in the solid-state Raman spectrum at 269 K identifies the 000 band of the more stable isomer. Ab initio calculations at the 6-31G* level indicate that the trans isomer is the more stable but by only 77 cm–1. This compares with a possible value of 174 cm–1 derived from experimental data.

Vibrational spectroscopic study of nickel(II) hypophosphite, Ni(H 2PO 2) 2

The vibrational spectrum of nickel(II) hypophosphite is reported for the first time. A comparison between the solid-state Raman spectrum and that of a 0.6 M aqueous solution of nickel(II) hypophosphite with sodium hypophosphite indicates the presence of a bidentate monohypophosphito complex, Ni(H 2PO 2) +, and hypophosphite ions H 2PO − 2 in the solid state, with dissociation into hexa-aquo nickel(II) ions and hypophosphite ions in aqueous solution. This is compared with the behaviour of nickel(II) carboxylates in the solid state and in aqueous solution.

PH dependent raman spectra of nicotinic acid - spectra of aqueous solutions and surface enhanced raman spectra on silver electrodes

Raman spectra of nicotinic acid have been measured in aqueous solutions in the pH-range between 1.0 and 12.5. Raman band assignments between 500 cm−1 and 1750 cm−1 are carried out by referring to the compound's solid state Raman spectrum and to spectra of related molecules. Changes of the Raman spectra with solution pH are correlated to the structure change of the nicotinic acid molecule. The surface enhanced Raman spectra (SERS) of nicotinic acid (NA) on a polycrystalline silver electrode are reported in the range 500–1750 cm−1 as a function of pH and applied potential. The results are presented in order to determine the type of adsorbed species (anion, cation, zwitterion). Therefore the SER spectra are compared with the pH dependent solution spectra of NA. These investigations show – in the presence of a non specifically adsorbing electrolyte (0.1 mol l−1 Na2SO4) – the nicotinate anion as the only surface active species detectable within the pH range of 1.4 to 12.5. A detailed analysis of the SER spectra reveals, that the anion exhibits two different molecular orientations towards the metal electrode, a presumably planar alignment dominating at low and medium pH values and a perpendicular one at low proton concentrations. In the intermediate range both orientations exist side by side. The ratio of planar to perpendicular oriented molecules depends on applied potential and increases with growing cathodic polarisation.

Raman spectra of some complexes containing methyldihalo- and dimethylhalo-sulphonium cations: Isomerism in the dimethyl sulphide-bromine complex

Vibrational assignments for the skeletal modes of some complexes containing CH3SX2+ and (CH3)2SX+ (X = Cl, Br) have been made on the basis of their solid-state Raman spectra and compared with any previous data. The stabilities of the parent CH3SX3 and (CH3)2SX2 compounds are discussed; two isomers of (CH3)2SBr2 were obtained under varying reaction conditions and assigned as ionic [(CH3)2SBr+Br−] and charge-transfer [(CH3)2S → Br2] forms. The transition of the ionic (metastable) form to the more stable charge-transfer form was monitored by differential scanning calorimetry. High-frequency shifts occur in some fundamental modes of (CH3)2SBr+Br− when Br− is replaced with a polyatomic anion, analogous to those seen in halophosphonium complexes; this is rationalized in terms of anion-cation interaction.

Models for organometallic polymers. Zigzag chains of tetrakis(acetate)dimolybdenum units linked by bis(dimethylphosphine)ethane and tetramethylethylenediamine ligands

Infinite zigzag chains of Mo{sub 2}(O{sub 2}CCH{sub 3}){sub 4} units linked by the bidentate ligands 1,2-bis(dimethylphosphino)ethane (dmpe) and tetramethylethylenediamine (tmed) crystallize from solutions of Mo{sub 2}(O{sub 2}CCH{sub 3}){sub 4} (1) dissolved in the respective neat ligand. Single-crystal X-ray structures of the light yellow polymers {sub {infinity}}{sup 1}(Mo{sub 2}(O{sub 2}CCH{sub 3}){sub 4}(dmpe)) and (2) and {sub {infinity}}{sup 1}(Mo{sub 2}(O{sub 2}CCH{sub 3}){sub 4}(tmed)) (3) showed that the compounds were isostructural. Crystal structures for compounds 2 and 3 reported. The ligands dmpe and tmed are coordinated axially through weak Mo-L bonds to relatively unperturbed Mo{sub 2}(O{sub 2}CCH{sub 3}){sub 4} centers. The solid-state Raman spectrum of 3 reveals a small decrease in the Mo-Mo stretching frequency ({nu}{sub Mo-Mo} = 391 cm{sup {minus}1}) relative to 1 ({nu}{sub Mo-Mo} = 405 cm{sup {minus}1}). TGA and powder diffraction studies involving 3 showed that solid-state thermolysis results in the expulsion of tmed at 92{degree}C and the formation of crystalline 1. 25 refs., 3 figs., 6 tabs.

Complexation between molybdenum(VI) and citrate: structural characterisation of a tetrameric complex, K4[(MoO2)4O3(cit)2]·6H2O

The complex anion obtained by crystallisation from an aqueous solution of molybdate and citric acid (H3cit) at pH ca. 3 is of the type (i), [(MoO2)4O3(cit)2]4−, as determined by X-ray analysis of the salt K4[Mo4O11(cit)2]·6H2O. Principal dimensions [ranges or means; estimated standard deviation (e.s.d.) 0.005 A] are: MoO 1.692–1.734; Mo–O(bridging) 1.886–1.948; Mo–O(hydroxy) 1.972(5); Mo–O(carboxylate) (unidentate) 2.185–2.318, (bridging) 2.296–2.333 A. The crystals are triclinic, space group P, a = 8.966(4), b = 12.319(6), c = 15.962(9) A, α = 89.34(4), β = 99.80(4), γ = 107.04(4)°, R = 0.041 for 4 399 observed [I/σ(I) 2.0] reflections. The complex is tetranuclear with the citrato-ligands co-ordinated through the deprotonated hydroxy group and the α-carboxy group to form five-membered chelate rings. One of the oxygens of the β-carboxylate groups bridges between two Mo atoms [Mo(1)–Mo(2) and Mo(3)–Mo(4)] whereas the other oxygen bridges between these dimers. The other β-carboxylate group is not co-ordinated to molybdenum but is protonated. The i.r. and Raman solid-state spectra are in agreement with this structure as well as a study in solution (Raman, 1H and 13C n.m.r. spectroscopy, molecular weight determination).

Electrochemical and spectroscopic studies on tetranuclear [{Re(µ3-X)(CO)3}4](X = Cl, Br, or I) and acetonitrile complexes derived therefrom

The solid-state Raman spectra of the tetranuclear rhenium(I) carbonyl halides [{Re(µ3-X)(CO)3}4](X = Cl, Br, or I) have been recorded and compared with the i.r. spectra recorded previously. In acetonitrile, [{Re(µ3-Cl)(CO)3}4] reacts to form [ReCl(CO)3(NCMe)2]via the intermediacy of [Re2(µ-Cl)2(CO)6(NCMe)2]. This reaction has been followed by cyclic voltammetry and the electrochemical properties of these complexes have been measured in CH2Cl2 and/or MeCN. The related electrochemical properties of [NEt4][Re2(µ-Cl)3(CO)6], fac-[Re(CO)3(NCMe)3]PF6, cis-[ReCl4(NCMe)2], and [ReCl(CO)5] have also been examined.

Vibrational spectrum and force constants of xenon (II) fluoride

The vibrational Raman spectra of xenon (II) fluoride in the solid state and in the vapour at 325 K are reported. From the most precise wavenumbers of ν 2 and ν 3 from the infrared spectrum, and ν 1 from the Raman spectrum, the force constants of bond stretching, bond deformation and stretch—stretch interaction are evaluated using a SVFF approximation. From the solid state Raman spectrum the E g lattice vibration is assigned to the band at 111 cm −1.

Cystine peptides.

NHCH3 (X = Gly 1, Ala 2, Aib 3, Leu 4 and D‐Ala 5), have been investigated by Raman and circular dichroism (CD) spectroscopy. Solid state Raman spectra are consistent with β‐turn conformations in all five peptides. These peptides exhibit similar conformations of the disulfide segment in the solid state with a characteristic disulfide stretching frequency at 519 ± 3 cm‐1, indicative of a trans‐gauche‐gauche arrangement about the Cα—Cβ—S—S—Cβ—Cα bonds. The results correlate well with the solid state conformations determined by X‐ray diffraction for peptides 3 and 4. CD studies in chloroform and dimethylsulfoxide establish solvent dependent conformational changes for peptides 1, 3 and 5. Disulfide chirality has been derived using the quadrant rule. CD results together with previously reported nuclear magnetic resonance (n.m.r.) data suggest a conformational coupling between the peptide backbone and the disulfide segment.

Structural investigations of zirconium tetra-acetate and the group IVB tetra-acetates

Solid-state i.r., Raman, 1H and 13C NMR spectra are reported for solid zirconium tetra-acetate and for the group IVB tetra-acetates (M  Si, Ge, Sn or Pb). The types of acetate co-ordination have been identified: Zr(OAc) 4 has a polymeric eight-co-ordinate structure and contains both bridging and bidentate acetate groups; Si(OAc) 4 and Ge(OAc) 4 contain only unidentate acetates to give four-co-ordinate structures while Sn(OAc) 4 and Pb(OAc) 4 contain only bidentate acetate groups to give eight-co-ordinate monomeric structures. The solid-state Raman and 13C NMR spectra are reported for the first time.

Low wavenumberRaman bands (300?50cm?1) for four isotopically substituted lithium hydrogen oxalate monohydrates LiXC2O4�X 2O

The solid stateRaman spectra (300−50 cm−1) of lithium hydrogen oxalate monohydrate have been investigated for four isotopically substituted compounds,6LiHC2O4·H2O,7LiHC2O4·H2O,6LiDC2O4·D2O and7LiDC2O4·D2O. The observed spectral data have been discussed on the basis of the factor group analysis by considering the H/D and6Li/7Li isotope effects on the fundamental lattice vibrations.

Raman spectroscopic evidence for colinear arrangement in the solid state of thermochromic distibanes

The IR and Raman spectra of the compounds (CH 3) 2SbSb(CH 3) 2 (I), [(CH 3) 3Si] 2SbSb[Si(CH 3) 3] 2 (II), [(CH 3) 3Si] 2AsAs[Si(CH 3) 3] 2 (III) and (C 6H 5) 2SbSb(C 6H 5) 2 (IV) have been studied in the liquid and solid states. Given assignments for I to III are based on normal coordinate analyses, and force constants are reported. The solid state Raman spectra of I and II exhibit strong lines near 50 cm −1, which are assigned to the longitudinal acoustic mode of an infinite linear chain of Sb atoms. Intermolecular Sb…Sb force constants, 0.125 and 0.18 N cm −1, are determined for I and II respectively.

Neutral complexes of the indium dihalides

The neutral complexes In2X4•2L (X = Cl, Br, I; L = 1,4-dioxan, tetrahydropyran, tetrahydrofuran, tetrahydrothiophene), In2X4•2L (X = Br, I; L = dimethylsulphide), In2X4•4L (X = Cl, Br, I; L = piperidine, piperazine, morpholine), and In2X4•4L (X = Br, I; L = pyridine, dimethylsulphoxide) have been prepared. Solid state Raman spectra indicate that the compounds contain indium–indium bonds.

The vibrational spectra and conformational structure of 2,2,3,3-tetrachlorobutane

Abstract Infrared spectra (4000–250 cm−1) of CH3Cl2CCCl2CH3 were obtained over a range of temperature extending between + 180°C (about 5°C above the melting point) and − 170°C, together with the solid state Raman spectrum (4000–300 cm−1) of the same compound under ambient conditions. In contrast to the behaviour of structurally related molecules having rotational isomers in the liquid state, no redistribution of the intensities of the absorption bands which usually accompanies molecular configuration inter-conversion occurred over the interval of temperature contemplated. The spectra were used in conjunction with normal coordinate treatment, assuming Urey—Bradley force constants and structural parameters, to establish that the substance exists in two geometrical isomers, trans (C2h and gauche (C2), both in the liquid and solid state.

Raman Spectra of Zn(CD3(CN)2X2(X=C1, Br and I)

Abstract The solid state Raman spectra of complexes of Zn(CD3 CN)2X2, where X is Cl, Br and I, are reported in the frequency region from 4000 to 27 cm−1. The observed frequencies are assigned by comparison with those of Zn(CH3CN)2X2. The isotopic effects on fundamental vibrations are discussed by applying the Teller-Redlich product rule.

Raman Spectra of Zn(CH3CN)2X2(X[dbnd]C1, Br and I)

Abstract The solid state Raman spectra of ZnX2 complexes, where X is Cl, Br and I, with CH3CN are reported in the frequency region 4000 to 27 cm−1. The observed frequencies are assigned assuming C2v molecular symmetry and C3v localized symmetry for ligand. The Zn-X stretching vibrations are discussed using G matrix elements.

A laser-Raman study of some mercury(II) nitrite compounds

Raman spectra are reported for solutions of mercury(II) perchlorate in the presence of various concentrations of sodium nitrite. The predominant species present are suggested to be Hg(NO 2) 2 and Hg(NO 2) 4 2−. The conclusions are supported by spectrophotometric and conductivity measurements. The solid state Raman spectra of Hg(NO 2) 2 and K 3[Hg(NO 2) 4]NO 3 are reported. The nitrite groups are found to be coordinated to mercury and spectra of the latter compound at room temperature and 77K suggest that restricted rotation of the bidentate nitrite groups may occur at room temperature.

Solid-state vibrational spectroscopy. Part I. The vibrational spectra of some halide complexes

The vibrational spectra of (NEt4)2CdCl4, NEt4NbCl6, and NEt4AlCl4 are reported and assignments suggested for the vibrational spectra of the anions. The solid-state Raman spectrum of arsenic tribromide is discussed with particular reference to recent crystallographic studies.

The Raman spectra of metal halide complexes containing 1,4-dioxan

The solid-state Raman spectra of several 1:1 and 1:2 adducts of 1,4-dioxan with manganese(II), iron(II), nickel(II), zinc(II) and mercury(II) halides and the species FeCl 3, C 4H 8O 2 and 3CuCl 2, 2C 4H 8O 2 have been recorded using laser excitation. The absence of infrared-Raman coincidences can be interpreted in terms of the presence of bridging centrosymmetric 1,4-dioxan molecules in the “chair” conformation. The low frequency Raman spectra are also discussed and in several instances give further information on the structures of the complexes.

Vibrational spectra of halopentacarbonylmanganese(I) derivatives

The solid-state infrared (i.r.) and laser Raman spectra of the halopentacarbonylmanganese(I) derivatives, Mn(CO)5X (X = Cl, Br,and I), have been recorded in the C—O stretching and the low frequency (700–33 cm−1) regions. The i.r. overtone and combination spectra recorded in the regions 2800–2250 and 1350–700 cm−1 have been used to help in the assignment of some of the low frequency fundamentals. The solid-state i.r. and laser Raman spectra of the dimeric halotetracarbonylmanganese(I) derivatives, [Mn(CO)4X]2 (X = Br and I), have been recorded in the C—O stretching and the low frequency regions for comparative purposes and shown to be consistent with the expected D2h symmetry of the molecules.