The vibrational spectrum of the stable free radical 1,1,3,3-tetramethylisoindolin-2-yloxyl

Solid and solution IR and Raman spectra of a stable nitroxide radical, 1,1,3,3-tetramethylisoindolin-2-yloxyl (TMIO), are reported and compared to ab initio density functional theory calculations of the vibrational frequencies to obtain unequivocal band assignments, in particular of the NO stretching frequency, nu(NO). The band position was found to be at 1431 cm(-1) for the solid, which is well outside the previously published range of 1310-1380 cm(-1) for nitroxide radicals. This apparently anomalous peak position was confirmed by undertaking isotopic substitution studies through the preparation and recording of vibrational spectra of tetrakis(trideuteriomethyl)isoindolin-2-yloxyl ([2H12]-TMIO) and [2H12,15N]-TMIO analogues. Solution spectra of TMIO in methanol and CCl4 are assessed for possible solvent-dependent spin density distribution effects in the NO bond.     

A short hydrogen bond investigation by polarized Raman spectra of Co2+ and Zn2+ salts of pyromellitic acid

Cobalt and zinc salts of 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid), [C(6)H(2)(COO)(4)H(4)], have been synthesized and investigate by polarized Raman spectroscopy. These compounds present short intramolecular hydrogen bonds (SHB) between adjacent carboxyl groups. Raman spectra indicate the presence of this interaction in both salts. Three specific vibrational of SHB modes have been investigated: O-H-O symmetric [nu(sym)(OHO)] and asymmetric [nu(asym)(OHO)] stretching modes and O-H stretching mode [nu(O-H)], which they were observed around 300, 850 and 2500 cm(-1), respectively. In crystallographic point of view, the cobalt salt presents a symmetric SHB while the zinc salt presents an asymmetric SHB. In cobalt salt all three vibrational modes of O-H-O groups in polarized Raman spectra occur in A(g) orientation although in zinc salts two of them are observed in A(g) orientation and one in B(g). Spectra analysis indicate that nu(sym)(OHO) mode is observed as A(g) to cobalt salt and B(g) to zinc salt. This mode occurs in a crowded spectral region and its identification was made by deconvolution techniques. Comparing spectra of the two salts, it is observed a small difference in relative intensity and wavenumber shift of nu(sym)(OHO) (deviance of 43 cm(-1)) and nu(OH) (deviance of 21 cm(-1)) modes due probably to differences in O...O distance between salts and in orientation of pyromellitate anion in unit cell. The nu(asym)(OHO) mode does not present significant wavenumber shift due difference in SHB. The nu(OH) band presents a great potential for hydrogen bond studies due to the fact that in its vibrational region (around 2500 cm(-1)) it is not observed other vibrational modes of these compounds.     

2-Benzyl-2-methyl-2H-benzimidazole 1,3-dioxide derivatives: Spectroscopic and theoretical study

The spectroscopic behavior of 2-benzyl-2-methyl-2H-benzimidazole 1,3-dioxide derivatives in solution was studied in terms of electronic and nuclear magnetic resonance ((1)H and (13)C NMR) techniques. The experimental spectra were compared to the theoretical ones, obtained at DFT level, proving that the compounds adopt in solution a bird-like conformational distribution. Also, theoretically this conformational distribution resulted the most stable in gas phase. Infrared spectroscopy was used to study solid state behavior identifying experimentally the N-O stretching near to 1380, 1365 and 1225 cm(-1) and the vibrational benzimidazole skeleton near to 1610 and 1590 cm(-1). The vibrational spectrum was satisfactorily described by DFT calculations funding the N-O stretching as a coupled vibration near to 1470, 1350 and 1285 cm(-1). The fragmentation that takes place in mass spectrometry was assigned for all of the new derivatives.     

Inversion vibration of PH3+(X2A2") studied by zero kinetic energy photoelectron spectroscopy

We report the first rotationally resolved spectroscopic studies on PH3+(X2A2") using zero kinetic energy photoelectron spectroscopy and coherent VUV radiation. The spectra about 8000 cm(-1) above the ground vibrational state of PH3+(X2A2") have been recorded. We observed the vibrational energy level splittings of PH3+(X2A2") due to the tunneling effect in the inversion (symmetric bending) vibration (nu2+). The energy splitting for the first inversion vibrational state (0+/0-) is 5.8 cm(-1). The inversion vibrational energy levels, rotational constants, and adiabatic ionization energies (IEs) for nu2+ = 0-16 have been determined. The bond angles between the neighboring P-H bonds and the P-H bond lengths are also obtained using the experimentally determined rotational constants. With the increasing of the inversion vibrational excitations (nu2+), the bond lengths (P-H) increase a little and the bond angles (H-P-H) decrease a lot. The inversion vibrational energy levels have also been calculated by using one dimensional potential model and the results are in good agreement with the experimental data for the first several vibrational levels. In addition to inversion vibration, we also observed firstly the other two vibrational modes: the symmetric P-H stretching vibration (nu1+) and the degenerate bending vibration (nu4+). The fundamental frequencies for nu1+ and nu4+ are 2461.6 (+/-2) and 1043.9 (+/-2) cm(-1), respectively. The first IE for PH3 was determined as 79670.9 (+/-1) cm(-1).     

Measurement and revised analysis of the torsional combination band of the nonpolar N2O dimer at 2249 cm(-1)

The high-resolution infrared spectrum of the weakly-bound dimer (N(2)O)(2) is studied using a rapid-scan tunable-diode laser spectrometer to probe a pulsed supersonic jet expansion. An observed band with c-type rotational structure is assigned as a combination of the intramolecular N(2)O nu(1) stretching vibration and the intermolecular out-of-plane dimer torsional vibration, with a vibrational origin at 2249.360 cm(-1). The resulting torsional frequency for the nonpolar N(2)O dimer is about 21.5 cm(-1). The present rotational analysis is completely different from that reported previously for the same band [Hecker et al., Phys. Chem. Chem. Phys., 2003, 5, 2333], which gave a band origin some 1.53 cm(-1) lower.     

Controlled radical polymerization of styrene in the presence of nitronyl nitroxides

Bulk radical polymerization of styrene in the presence of nitronyl nitroxides (2-(4-substituted phenyl)-4,4,5,5-tetramethyl-4,5-dihydroimidazolyl-1-oxyl 3-oxide) was studied. All nitronyl nitroxides, like other nitroxyl radicals such as 2,2,6,6-tetramethylpiperidine 1-oxyl radical (TEMPO), act as reversible radical scavengers. The efficiency of controlling the polymerization is affected by the substituent at the 4′-position. The efficiency increases with electron donating strength of 4′-substituents, at least at the beginning of the reaction. However, the thermal stability of nitronyl nitroxides decreases in the same order. Thus, TEMPO is more suitable than nitronyl nitroxides for controlled/“living” radical polymerization of styrene.     

Coordination complexes of 2-(4-quinolyl)nitronyl nitroxide with M(hfac)(2) [M = Mn(II), Co(II), and Cu(II)]: syntheses, crystal structures, and magnetic characterization

Three new complexes of the formula M(2)L(2) derived from 2-(4-quinolyl)nitronyl nitroxide (4-QNNN) and M(hfac)(2) [M = Mn(II), Co(II), and Cu(II)], (4-QNNN)(2).[Mn(hfac)(2)](2) (1), (4-QNNN)(2).[Co(hfac)(2)](2).2H(2)O (2), and (4-QNNN)(2).Cu(hfac)(2).Cu'(hfac)(2) (3), were synthesized and characterized structurally as well as magnetically. Complexes 1 and 2 are four-spin complexes with quadrangle geometry, in which both the nitrogen atoms of quinoline rings and oxygen atoms of nitronyl nitroxides are involved in the formation of coordination bonds. For complex 3, however, the nitrogen atoms of quinoline rings are coordinated with Cu(II) ion to afford a three-spin complex, which is further linked to another molecule of Cu(hfac)(2) (referred to as Cu'(hfac)(2)) to form a 1D alternating chain. The magnetic behaviors of the three complexes were investigated. For complex 1, as the nitronyl nitroxides and Mn(II) ions are strongly antiferromagnetically coupled, consequently its temperature dependence of magnetic susceptibility was fitted to the model of spin-dimer with S = 2, yielding the intradimer magnetic exchange constant of J = -0.82 cm(-1). For complex 2, the temperature dependence of the magnetic susceptibility in the T > 50 K region was simulated with the model of two-spin unit with S(1) = 3/2 and S(2) = 1/2, leading to J = -321.9 cm(-1) for the magnetic interaction due to Co(II).O coordination bonding, D = -16.3 cm(-1) (the zero-field splitting parameter), g = 2.26, and zJ = -3.8 cm(-1) for the magnetic interactions between Co(II) ions and nitronyl nitroxides through quinoline rings and those between nitronyl nitroxides due to the short O.O short contacts. The temperature dependence of magnetic susceptibility of 3 was approximately fitted to a model described previously affording J(1) = -6.52 cm(-1) and J(2) = 3.64 cm(-1) for the magnetic interaction between nitronyl nitroxides and Cu(II) ions through the quinoline unit via spin polarization mechanism and the weak O.Cu coordination bonding, respectively.     

Peisleyite an unusual mixed anion mineral--a vibrational spectroscopic study

The mineral peisleyite has been studied using a combination of electron microscopy and vibrational spectroscopy. Scanning electron microscope (SEM) photomicrographs reveal that the peisleyite morphology consists of an array of small needle-like crystals of around 1 microm in length with a thickness of less than 0.1 microm. Raman spectroscopy in the hydroxyl stretching region shows an intense band at 3506 cm(-1) assigned to the symmetric stretching mode of the OH units. Four bands are observed at 3564, 3404, 3250 and 3135 cm(-1) in the infrared spectrum. These wavenumbers enable an estimation of the hydrogen bond distances 3.052(5), 2.801(0), 2.705(6) and 2.683(6)A. Two intense Raman bands are observed at 1023 and 989 cm(-1) and are assigned to the SO(4) and PO(4) symmetric stretching modes. Other bands are observed at 1356, 1252, 1235, 1152, 1128, 1098 and 1067 cm(-1). The bands at 1067 cm(-1) is attributed to AlOH deformation vibrations. Bands in the low wavenumber region are assigned to the nu(4) and nu(2) out of plane bending modes of the SO(4) and PO(4) units. Raman spectroscopy is a useful tool in determining the vibrational spectroscopy of mixed hydrated multianion minerals such as peisleyite. Information on such a mineral would be difficult to obtain by other means.     

Vibrational dynamics of acetate in D2O studied by infrared pump-probe spectroscopy

Solute-solvent interactions between acetate and D(2)O were investigated by vibrational spectroscopic methods. The vibrational dynamics of the COO asymmetric stretching mode in D(2)O was observed by time-resolved infrared (IR) pump-probe spectroscopy. The pump-probe signal contained both decay and oscillatory components. The time dependence of the decay component could be explained by a double exponential function with time constants of 200 fs and 2.6 ps, which are the same for both the COO asymmetric and symmetric stretching modes. The Fourier spectrum of the oscillatory component contained a band around 80 cm(-1), which suggests that the COO asymmetric stretching mode couples to a low-frequency vibrational mode with a wavenumber of 80 cm(-1). Based on quantum chemistry calculations, we propose that a bridged complex comprising an acetate ion and one D(2)O molecule, in which the two oxygen atoms in the acetate anion form hydrogen bonds with the two deuterium atoms in D(2)O, is the most stable structure. The 80 cm(-1) low-frequency mode was assigned to the asymmetric stretching vibration of the hydrogen bond in the bridged complex.     

The ultraviolet spectrum of the CoCl2 radical, studied at vibrational and rotational resolution

The laser excitation spectrum of the 327 nm band system of CoCl2, formed in a free-jet expansion, has been recorded at a rotational temperature of approximately 10 K. The spectrum is congested and suffers extensive perturbations. A progression in the excited state symmetric stretching vibration has been identified. The decrease in the symmetric stretching vibrational wave number on excitation is considerable [nu1 '=195.7(12), nu1 (")=358.1(17) cm(-1)]. Despite widespread perturbations in the rotational structure of these vibronic bands, they can be confidently assigned to a parallel Omega=72-72 transition, consistent with an inverted 4Deltag ground electronic state. The rotational constant for Co35Cl2 in the ground state is determined to be 0.056 65(11) cm(-1), which corresponds to a value for the zero-point averaged Co-Cl bond length r0 of 2.062 8(40) A. The perturbations are found to be strongly isotopomer dependent.     

Kinetics of the reaction between nitroxide and thiyl radicals: nitroxides as antioxidants in the presence of thiols

Cyclic nitroxides effectively protect cells, tissues, isolated organs, and laboratory animals from radical-induced damage. The present study focuses on the kinetics and mechanisms of the reactions of piperidine and pyrrolidine nitroxides with thiyl radicals, which are involved in free radical "repair" equilibria, but being strong oxidants can also produce cell damage. Thiyl radicals derived from glutathione, cysteine, and penicillamine were generated in water by pulse radiolysis, and the rate constants of their reactions with 2,2,6,6-tetramethylpiperidine-1-oxyl (TPO), 4-OH-TPO, and 3-carbamoyl-proxyl were determined to be (5-7) x 10 (8) M (-1) s (-1) at pH 5-7, independent of the structure of the nitroxide and the thiyl radical. It is suggested that the reaction of nitroxide (>NO (*)) with thiyl radical (RS (*)) yields an unstable adduct (>NOSR). The deprotonated form of this adduct decomposes via heterolysis of the N-O bond, yielding the respective amine (>NH) and sulfinic acid (RS(O)OH). The protonated form of the adduct decomposes via homolysis of the N-O bond, forming the aminium radical (>NH (*+)) and sulfinyl radical (RSO (*)), which by subsequent reactions involving thiol and nitroxide produce the respective amine and sulfonic acid (RS(O) 2OH). Nitroxides that are oxidized to the respective oxoammonium cations (>N (+)O) are recovered in the presence of NADH but not in the presence of thiols. This suggests that the reaction of >N (+)O with thiols yields the respective amine. Two alternative mechanisms are suggested, where >N (+)O reacts with thiolate (RS (-)) directly generating the adduct >NOSR or indirectly forming >NO (*) and RS (*), which subsequently together yield the adduct >NOSR. Under physiological conditions the adduct is mainly deprotonated, and therefore nitroxides can detoxify thiyl radicals. The proposed mechanism can account for the protective effect of nitroxides against reactive oxygen- and nitrogen-derived species in the presence of thiols.     

Ferro- and antiferromagnetic interactions in polymeric and molecular complexes of Cu(hfac)2 with 1-oxoazin-2-yl-substituted nitronyl nitroxides

Solid heterospin compounds based on Cu(hfac)₂ complexes with a new group of nitronyl nitroxides bearing different azine-N-oxide substituents at position 2 of the 2-imidazoline ring (Lⁿ) were studied. The major factor responsible for the change in the magnetic characteristics of the [Cu(hfac)₂L¹] complex with triazine nitronyl nitroxide with temperature was shown to be the specific pairwise packing of heterospin molecules with the dominant antiferromagnetic exchange between the radical fragments of adjacent molecules. For complexes of Cu(hfac)₂ with 1-oxoazin-2-yl-substituted nitronyl nitroxides L² and L⁴, 7-membered metallocycles were obtained, although they form rarely. It was shown that polymer chains formed in the solid complex with spin-labeled pyrazine-N-oxide [(Cu(hfac)₂)₃(L³)₂] due to the cross-linking of {(Cu(hfac)₂)₂(L³)₂} binuclear fragments via the bridging [Cu(hfac)₂].     

Vibrational normal modes of diazo-dimedone: a comparative study by Fourier infrared/Raman spectroscopies and conformational analysis by MM/QM

The 2-diazo-5,5-dimethyl-cyclohexane-1,3-dione (3) was synthesized and the FT-IR/Raman spectra were measured with the purpose of obtain a full assignment of the vibrational modes. Singular aspects concerning the -CNN oscillator are discussed in view of two strong bands observed in the region of 2300-2100 cm(-1) in both, Infrared and Raman spectra. The density functional theory (DFT) was used to obtain the geometrical structure and for assisting in the vibrational assignment joint to the traditional normal coordinate analysis (NCA). The observed wavenumbers at 2145 (IR), 2144(R) are assigned as the coupled nu(NN)+nu(CN) vibrational mode with higher participation of the NN stretching. A 2188 cm(-1) (IR) and at 2186 cm(-1) (R) can be assigned as a overtone of one of nu(CC) normal mode or to a combination band of the fundamentals delta(CCH) found at 1169 cm(-1) and the delta (CCN) found at 1017 cm(-1) enhanced by Fermi resonance.     

1D silver(I) complex of nitronyl nitroxide with strong spin-spin interaction through silver(I) ion

A 1D silver(I) complex of nitronyl nitroxide was prepared and its structure was determined by X-ray diffraction analysis; magnetic studies indicate that the spin-spin interaction of nitronyl nitroxides through silver(I) ions along the chain are fairly strong (J/kb = -84 K).     

Infrared spectra and ab initio calculations for the F- -(CH4)n (n = 1-8) anion clusters

Infrared spectra of mass-selected F- -(CH4)n (n = 1-8) clusters are recorded in the CH stretching region (2500-3100 cm-1). Spectra for the n = 1-3 clusters are interpreted with the aid of ab initio calculations at the MP2/6-311++G(2df 2p) level, which suggest that the CH4 ligands bind to F- by equivalent, linear hydrogen bonds. Anharmonic frequencies for CH4 and F--CH4 are determined using the vibrational self-consistent field method with second-order perturbation theory correction. The n = 1 complex is predicted to have a C3v structure with a single CH group hydrogen bonded to F-. Its spectrum exhibits a parallel band associated with a stretching vibration of the hydrogen-bonded CH group that is red-shifted by 380 cm-1 from the nu1 band of free CH4 and a perpendicular band associated with the asymmetric stretching motion of the nonbonded CH groups, slightly red-shifted from the nu3 band of free CH4. As n increases, additional vibrational bands appear as a result of Fermi resonances between the hydrogen-bonded CH stretching vibrational mode and the 2nu4 overtone and nu2+nu4 combination levels of the methane solvent molecules. For clusters with n < or = 8, it appears that the CH4 molecules are accommodated in the first solvation shell, each being attached to the F- anion by equivalent hydrogen bonds.     

Assignment of rovibrational transitions of propyne in the region of 2934-2952 cm(-1) measured by two-color IR-vacuum ultraviolet laser photoion-photoelectron methods

The infrared (IR) spectrum of propyne in the region of 2934-2952 cm(-1) has been recorded by the IR-vacuum ultraviolet (VUV)-photoion method. The spectrum is shown to consist of two near-resonant, but noncoupled vibrational bands: the nu2 symmetric methyl C-H stretching vibrational band and a combination vibrational band nucs. The previously unobserved Q line of the nucs band is observed. The rotational transition lines of the nu2=1 band produces IR-VUV-pulsed field ionization-photoelectron (IR-VUV-PFI-PE) signal at the C3H4+ (nu2+=1) photoionization threshold. The rotational transition lines associated with the nucs band do not produce IR-VUV-PFI-PE signal. Rotational transition lines of both vibrational bands are assigned and simulated; and ab initio calculations further confirm the assignment.     

Infrared and infrared emission spectroscopy of the zinc carbonate mineral smithsonite

Infrared emission and infrared spectroscopy has been used to study a series of selected natural smithsonites from different origins. An intense broad infrared band at 1440cm(-1) is assigned to the nu(3) CO(3)(2-) antisymmetric stretching vibration. An additional band is resolved at 1335cm(-1). An intense sharp Raman band at 1092cm(-1) is assigned to the CO(3)(2-) symmetric stretching vibration. Infrared emission spectra show a broad antisymmetric band at 1442cm(-1) shifting to lower wavenumbers with thermal treatment. A band observed at 870cm(-1) with a band of lesser intensity at 842cm(-1) shifts to higher wavenumbers upon thermal treatment and is observed at 865cm(-1) at 400 degrees C and is assigned to the CO(3)(2-)nu(2) mode. No nu(2) bending modes are observed in the Raman spectra for smithsonite. The band at 746cm(-1) shifts to 743cm(-1) at 400 degrees C and is attributed to the CO(3)(2-)nu(4) in phase bending modes. Two infrared bands at 744 and around 729cm(-1) are assigned to the nu(4) in phase bending mode. Multiple bands may be attributed to the structural distortion ZnO(6) octahedron. This structural distortion is brought about by the substitution of Zn by some other cation. A number of bands at 2499, 2597, 2858, 2954 and 2991cm(-1) in both the IE and infrared spectra are attributed to combination bands.     

Anharmonic vibrational frequencies and vibrationally averaged structures and nuclear magnetic resonance parameters of FHF-

The anharmonic vibrational frequencies of FHF(-) were computed by the vibrational self-consistent-field, configuration-interaction, and second-order perturbation methods with a multiresolution composite potential energy surface generated by the electronic coupled-cluster method with various basis sets. Anharmonic vibrational averaging was performed for the bond length and nuclear magnetic resonance indirect spin-spin coupling constants, where the latter computed by the equation-of-motion coupled-cluster method. The calculations placed the vibrational frequencies at 580 (nu(1)), 1292 (nu(2)), 1313 (nu(3)), 1837 (nu(1) + nu(3)), and 1864 cm(-1) (nu(1) + nu(2)), the zero-point H-F bond length (r(0)) at 1.1539 A, the zero-point one-bond spin-spin coupling constant [(1)J(0)(HF)] at 124 Hz, and the bond dissociation energy (D(0)) at 43.3 kcal/mol. They agreed excellently with the corresponding experimental values: nu(1) = 583 cm(-1), nu(2) = 1286 cm(-1), nu(3) = 1331 cm(-1), nu(1) + nu(3) = 1849 cm(-1), nu(1) + nu(2) = 1858 cm(-1), r(0) = 1.1522 A, (1)J(0)(HF) = 124+/-3 Hz, and D(0) = 44.4+/-1.6 kcal/mol. The vibrationally averaged bond lengths matched closely the experimental values of five excited vibrational states, furnishing a highly dependable basis for correct band assignments. An adiabatic separation of high- (nu(3)) and low-frequency (nu(1)) stretching modes was examined and found to explain semiquantitatively the appearance of a nu(1) progression on nu(3). Our calculations predicted a value of 186 Hz for experimentally inaccessible (2)J(0)(FF).     

Raman spectra of carotenoids in natural products

Resonance Raman spectra of naturally occurring carotenoids have been obtained from nautilus, periwinkle (Littorina littorea) and clam shells under 514.5 nm excitation and these spectra are compared with the resonance Raman spectra obtained in situ from tomatoes, carrots, red peppers and saffron. The tomatoes, carrots and red peppers gave rise to resonance Raman spectra exhibiting a nu1 band at ca. 1520 cm(-1), in keeping with its assignment to carotenoids with ca. nine conjugated carbon-carbon double bonds in their main chains, whereas the resonance Raman spectrum of saffron showed a nu1 band at 1537 cm(-1) which can be assigned to crocetin, having seven conjugated carbon-carbon double bonds. A correlation between nu1 wavenumber location and effective conjugated chain length has been used to interpret the data obtained from the shells, and the wavenumber position (1522 cm(-1)) of the nu1 band of the carotenoid in the orange clam shell suggests that it contains nine conjugated double bonds in the main chain. However, the black periwinkle and nautilus shells exhibit nu1 bands at 1504 and 1496 cm(-1), respectively. On the basis of the correlation between nu1 wavenumber location and effective conjugated chain length, this indicates that they contain carotenoids with longer conjugated chains, the former having ca. 11 double bonds and the latter ca. 13 or even more. Raman spectra of the nautilus, periwinkle and clam shells also exhibited a strong band at 1085 cm(-1) and a doublet with components at 701 and 705 cm(-1), which can be assigned to biogenic calcium carbonate in the aragonite crystallographic form.     

Raman and infrared spectroscopy of selected vanadates

Raman and infrared spectroscopy has been used to study the structure of selected vanadates including pascoite, huemulite, barnesite, hewettite, metahewettite, hummerite. Pascoite, rauvite and huemulite are examples of simple salts involving the decavanadates anion (V10O28)6-. Decavanadate consists of four distinct VO6 units which are reflected in Raman bands at the higher wavenumbers. The Raman spectra of these minerals are characterised by two intense bands at 991 and 965 cm(-1). Four pascoite Raman bands are observed at 991, 965, 958 and 905 cm(-1) and originate from four distinct VO6 sites. The other minerals namely barnesite, hewettite, metahewettite and hummerite have similar layered structures to the decavanadates but are based upon (V5O14)3- units. Barnesite is characterised by a single Raman band at 1010 cm(-1), whilst hummerite has Raman bands at 999 and 962 cm(-1). The absence of four distinct bands indicates the overlap of the vibrational modes from two of the VO6 sites. Metarossite is characterised by a strong band at 953 cm(-1). These bands are assigned to nu1 symmetric stretching modes of (V6O16)2- units and terminal VO3 units. In the infrared spectra of these minerals, bands are observed in the 837-860 cm(-1) and in the 803-833 cm(-1) region. In some of the Raman spectra bands are observed for pascoite, hummerite and metahewettite in similar positions. These bands are assigned to nu3 antisymmetric stretching of (V10O28)6- units or (V5O14)3- units. Because of the complexity of the spectra in the low wavenumber region assignment of bands is difficult. Bands are observed in the 404-458 cm(-1) region and are assigned to the nu2 bending modes of (V10O28)6- units or (V5O14)3- units. Raman bands are observed in the 530-620 cm(-1) region and are assigned to the nu4 bending modes of (V10O28)6- units or (V5O14)3- units. The Raman spectra of the vanadates in the low wavenumber region are complex with multiple overlapping bands which are probably due to VO subunits and MO bonds.