far-IR Spectra Research Articles

Synthesis, spectral characterization, electrochemical and anti-microbial activities of new binuclear Schiff base metal complexes derived from 3,3’ diaminobenzedine

A novel oxime ligand has been synthesized by refluxing 3,3’-diaminobenzedine and phthalaldehyde monoxime. Copper (II), cobalt (II), nickel (II) and manganese (II) binuclear complexes of this ligand have been prepared and characterized by using elemental analysis, molar conductance studies, IR, UV, NMR, EPR and magnetic studies. The molar conductance measurements correspond to a non-electrolytic nature for all complexes which can be formulated as [M 2 (L)X 4 ] (Where M = Cu(II), Ni(II), Co(II) and Mn(II); X = Cl − ). The UV-visible spectra of all the complexes are well characterized by broad weak d - d band and a high intensity charge-transfer transition. Thermal studies supported the chemical formation of these complexes showed that they decomposed in three or four stages depending on the type of ligand. The far-IR spectrum confirms the presence of coordinate chloride ion in all the complexes as evidenced by one intense far IR bands around 310-330 cm −1 . In electrochemical studies the resulting cyclic voltammogram consists of single quasi-reversible one electron transfer. The ligand and complexes have been screened for their antimicrobial activity against two Gram-positive bacteria, two Gram-negative bacteria and fungi. The binuclear metal complexes were found to possess potent antimicrobial, antifungal activity better than ligand alone.

Elusive O═P≡N, a Rare Example of Phosphorus σ2λ5-Coordination

Two linear isomers, OPN and ONP, were formed in an Ar matrix at 16 K by ArF laser (λ = 193 nm) photolysis of phosphoryl triazide, OP(N(3))(3), and comprehensively characterized by their mid- and far-IR spectra as well as (14/15)N isotopic data. Two intermediates, (N(3))(2)P(O)N and N(3)P(O)N(4), have been isolated in an Ar matrix and spectroscopically characterized. Photolysis of these intermediates using near-UV/vis light (λ > 320 nm) was shown to yield exclusively ONP, which under ArF laser irradiation selectively photo-isomerized to OPN. The photochemical and molecular properties of OPN and ONP are discussed on the basis of experimental and ab initio calculated results.

Terpenes in the gas phase: The Far-IR spectrum of perillaldehyde

The far infrared spectrum of S-(-)-perillaldehyde, a monoterpene containing an aldehyde functional group, has been recorded in the gas phase using FTIR spectroscopy. The vibration signature of the three most populated rotamers has been observed and identified in the 30–650cm−1 range. The vibration assignment was based on the scaled B3LYP/cc-pVDZ harmonic force field of Partal Ureña et al., 2008 [10]. Anharmonic contributions calculated at the HF/6–31+G⁎ level were found negligible.

Modelling galaxy and AGN evolution in the infrared: black hole accretion versus star formation activity

We present a new backward evolution model for galaxies and active galactic nuclei (AGNs) in the infrared (IR). What is new in this model is the separate study of the evolutionary properties of different IR populations (i.e. spiral galaxies, starburst galaxies, low-luminosity AGNs, ‘unobscured’ type 1 AGNs and ‘obscured’ type 2 AGNs) defined through a detailed analysis of the spectral energy distributions (SEDs) of large samples of IR-selected sources. The evolutionary parameters have been constrained by means of all the available observables from surveys in the mid- and far-IR (source counts, redshift and luminosity distributions, luminosity functions). By decomposing the SEDs representative of the three AGN classes into three distinct components (a stellar component emitting most of its power in the optical/near-IR, an AGN component due to the hot dust heated by the central black hole peaking in the mid-IR, and a starburst component dominating the far-IR spectrum), we have disentangled the AGN contribution to the monochromatic and total IR luminosity emitted by different populations considered in our model from that due to star formation activity. We have then obtained an estimate of the total IR luminosity density [and star formation density (SFD) produced by IR galaxies] and the first ever estimate of the black hole mass accretion density (BHAR) from the IR. The derived evolution of the BHAR is in agreement with estimates from X-rays, though the BHAR values we derive from the IR are slightly higher than the X-ray ones. Finally, we have simulated source counts, redshift distributions, and SFD and BHAR that we expect to obtain with the future cosmological surveys in the mid-/far-IR that will be performed with the JWST-MIRI and SPICA-SAFARI. Outputs of the model are available online.1

A study of Sn addition on bonding arrangement of Se-Te alloys using far infrared transmission spectroscopy

Far infrared transmission spectra of Se92Te8−xSnx (x = 0, 1, 2, 3, 4, 5) glassy alloys are obtained in the spectral range 50–600 cm−1 at room temperature. The results are interpreted in terms of the vibrations of the isolated molecular units in such a way so as to preserve fourfold and twofold coordination for Sn and chalcogen atoms (Se,Te), respectively. With the addition of Sn, Far-IR spectra shift toward high frequency side and some new bands start appearing. Sn atoms appear to substitute for the selenium atoms in the outrigger sites due to large bond formation probability. Theoretical calculations of bond energy, relative probability of bond formation, force constant, and wave number were also made to justify the result.

DFT calculation analysis of terahertz time-domain spectra of polyalanines

Density functional theory (DFT) calculation was applied to simulate the far infrared (far-IR) spectra in the 700–0 cm−1 region of α-helical l-alanine oligomer models with the number of peptide bonds (n) of 24–8. The simulation for the model with n = 24 is in reasonable agreement with the dichroic IR spectra in the 700–60 cm−1 region already reported [K. Itoh and T. Shimanouchi, Biopolymers 9 (1970) 383], indicating the high reliability of the calculation. Terahertz (THz) time-domain spectroscopy was used to measure the far-IR spectra in the 160 – ca. 5 cm−1 region for poly-l-alanine in powder and film states. On treatment of the α-helical poly-l-alanine film with formic acid for 5 min a parallel band at 127 cm−1 and perpendicular bands at 116 and 82 cm−1 shift to 116, 109 and 73 cm−1, respectively, with concomitant intensity diminution, and on further treatment for 1 h the bands disappear and the far-IR spectrum in the region of 160 – ca. 5 cm−1 becomes almost transparent. On the other hand, the film treated with formic acid for 1 h still gives rise to the amides I and II bands due the α-helical structure with appreciable intensity. The calculated frequencies and intensities of bands corresponding to the observed bands at 127, 116 and 82 cm−1 decrease with decreasing the number of peptides bonds from 24 to 8, suggesting that the observed frequency lowering and intensity diminution are due to the decrease in the average number of the l-alanine residues forming the α-helix. After the treatment for 1 h the average number becomes too small to give the far-IR bands, resulting in the almost transparent spectral feature. The simulation also predicted the appearance of the accordion-like modes of the α-helical rod at 23 (n = 24), 26.5 (n = 20), 32 (n = 16), 39 (n = 12) and 48.5 cm−1 (n = 8) and the bending modes at 14 (n = 24), 19 (n = 20) and 27 cm−1 (n = 16). The observation of these modes, which should be called as “collective modes” in the strict sense of the word, will give information about static as well as dynamical structures of the α-helical sequences in polypeptides and proteins.

EMISSION FROM HOT DUST IN THE INFRARED SPECTRA OF GAMMA-RAY BRIGHT BLAZARS

A possible source of $\gamma$-ray photons observed from the jets of blazars is inverse Compton scattering by relativistic electrons of infrared seed photons from a hot, dusty torus in the nucleus. We use observations from the Spitzer Space Telescope to search for signatures of such dust in the infrared spectra of four $\gamma$-ray bright blazars, the quasars 4C 21.35, CTA102, and PKS 1510$-$089, and the BL Lacertae object ON231. The spectral energy distribution (SED) of 4C 21.35 contains a prominent infrared excess indicative of dust emission. After subtracting a non-thermal component with a power-law spectrum, we fit a dust model to the residual SED. The model consists of a blackbody with temperature $\sim1200$ K, plus a much weaker optically thin component at $\sim660$ K. The total luminosity of the thermal dust emission is $7.9\pm0.2 \times 10^{45}$ erg s$^{-1}$. If the dust lies in an equatorial torus, the density of IR photons from the torus is sufficient to explain the $\gamma$-ray flux from 4C 21.35 as long as the scattering occurs within a few parsecs of the central engine. We also report a tentative detection of dust in the quasar CTA102, in which the luminosity of the infrared excess is $7 \pm 2 \times 10^{45}$ erg s$^{-1}$. However, in CTA102 the far-IR spectra are too noisy to detect the $10 \mu$m silicate feature. Upper limits to the luminosity from thermal emission from dust in PKS 1510-089, and ON231, are, $2.3\times10^{45}$, and $6.6\times10^{43}$ erg s$^{-1}$, respectively. These upper limits do not rule out the possibility of inverse Compton up-scattering of IR photons to $\gamma$-ray energies in these two sources. The estimated covering factor of the hot dust in 4C 21.35, 22%, is similar to that of non-blazar quasars; however, 4C 21.35 is deficient in cooler dust.

POLYCYCLIC AROMATIC HYDROCARBON FAR-INFRARED SPECTROSCOPY

The far-IR characteristics of astrophysically relevant polycyclic aromatic hydrocarbons (PAHs) averaging in size around 100 carbon atoms have been studied using the theoretical spectra in the NASA Ames PAH IR Spectroscopic Database. These spectra were calculated using density functional theory. Selections of PAH species are made, grouped together by common characteristics or trends, such as size, shape, charge, and composition, and their far-IR spectra compared. The out-of-plane modes involving the entire molecule are explored in detail, astronomical relevance is assessed, and an observing strategy is discussed. It is shown that PAHs produce richer far-IR spectra with increasing size. PAHs also produce richer far-IR spectra with increasing number of irregularities. However, series of irregular-shaped PAHs with the same compact core have common "Jumping-Jack" modes that "pile up" at specific frequencies in their average spectrum. For the PAHs studied here, around 100 carbon atoms in size, this band falls near 50 μm. PAH charge and nitrogen inclusion affect band intensities but have little effect on far-IR band positions. Detailed analysis of the two-dimensional, out-of-plane bending "drumhead" modes in the coronene and pyrene "families" and the one-dimensional, out-of-plane bending "bar" modes in the acene "family" show that these molecular vibrations can be treated as classical vibrating sheets and bars of graphene, respectively. The analysis also shows that the peak position of these modes is very sensitive to the area of the emitting PAH and does not depend on the particular geometry. Thus, these longest wavelength PAH bands could provide a unique handle on the size of the largest species in the interstellar PAH family. However, these bands are weak. Observing highly excited regions showing the mid-IR bands in which the emission from classical dust peaks at short wavelengths offers the best chance of detecting PAH emission in the far-IR. For these regions sensitivity is not an issue, spectral contrast is maximized and the PAH population is only comprised of highly stable, compact symmetric PAHs, such as the members of the pyrene and coronene "families" discussed in detail here.

The NASA Ames PAH IR Spectroscopic Database and the far-IR

Polycyclic Aromatic Hydrocarbons (PAHs) are widespread across the Universe and influence many stages of the Galactic lifecycle. The presence of PAHs has been well established and the rich mid-IR spectrum is now commonly used as a probe into (inter)stellar envi- ronments. The NASA Ames IR Spectroscopic Database has been key to test and refine the PAH hypothesis. This database is a large coherent set (>600 spectra) of laboratory measured and DFT computed infrared spectra of PAHs from C10H8 to C130H28 and has been made available on the web at (http://www.astrochem.org/pahdb). With a new spectral window opening up; the far-IR, the study of far-IR spectra and the quest for identifying a unique member of the interstel- lar family has begun. To guide this research, the far-IR (>20 µm) spectra of different sets of PAHs are investigated using the NASA Ames IR Spectroscopic Database. These sets explore the influence of size, shape, charge and composition on the far-IR spectrum. The far-IR is also the domain of the so-called modes and other molecular vibrations involving low order bending vibrations of the car- bon skeleton as a whole. As with drums, these are molecule and shape specific and promise to be a key diagnostic for specific PAHs. Here, the sensitivity of these modes to size and shape is assessed by comparing the frequencies of the lowest drumhead modes of a family of circular shaped (the coronene family) and rhombus shaped (the pyrene family) molecules. From this study, some consequences for an observing strategy are drawn.

Mechanochemical synthesis in copper(ii) halide/pyridine systems: single crystal X-ray diffraction and IR spectroscopic studies

Whereas complexes of divalent metal halides (X = Cl, Br, I) with/from pyridine commonly crystallise as trans-[M(py)(4)X(2)]·2py, M on a site of 222 symmetry in space group Ccca, true for CuCl(2) and CuBr(2) in particular, the copper(II) iodide adduct is of the form [Cu(py)(4)I]I·2py, Cu on a site of mm2 symmetry in space group Cmcm, and five-coordinate (square-pyramidal), the same cationic species also being found in 2[Cu(py)(4)I](I(3))·[(py)(2)Cu(μ-I)(2)Cu(py)(2)] (structurally defined). Bromide or N-thiocyanate may be substituted for the unbound iodide ion in the solvated salt, resulting in complexes which crystallize in space group Ccca, but with both anions and the metal atom disordered. In [Cu(py)(4)(I(3))(2)], a pair of long Cu···I contacts approach a square-planar Cu(py)(4) array. Assignments of the ν(CuN) and ν(CuX) (X = Br, I, SCN) bands in the far-IR spectra are made, the latter with the aid of analogous assignments for [Cu(py)(2)X(2)] (X = Cl, Br), which show a dependence of ν(CuX) on the Cu-X bond length that is very similar to that determined previously for copper(i) halide complexes. The structure of the adventitious complex [(trans-)(H(2)O)(py)(4)CuClCu(py)(4)](I(3))(3)·H(2)O is also recorded, with six- and five-coordinate copper atoms; rational synthesis provides [{Cu(py)(4)}(2)(μ-Cl)](I(3))(3)·H(2)O with one water molecule less. In [{Cu(py)(4)Cl}((∞|∞))](I(3))·3py, square pyramidal [Cu(py)(4)Cl](+) cations, assisted by Cl···Cu interactions, stack to give rise to infinite polymeric strings. Several of these compounds were prepared mechanochemically, illustrating the applicability of this method to syntheses involving redox reactions as well as to complex syntheses involving up to five components. The totality of results demonstrates that the [Cu(II)(py)(4)] entity can be stabilized in an unexpectedly diverse range of mononuclear and multinuclear complexes through the presence of lattice pyridine molecules, the bulky triiodide ion, or a combination of both.

Dicarboxylate assisted synthesis of the monoclinic heterometallic tetrathiocyanato bridged copper(II) and mercury(II) coordination polymer {Cu[Hg(SCN) 4]} n: Synthesis, structural, vibration, luminescence, EPR studies and DFT calculations

The synthesis of the monoclinic polymorph of {Cu[Hg(SCN) 4]} n is reported. The compound, as determined by X-ray diffraction of a twinned crystal, consists of mercury and copper atoms linked by μ 1,3-SCN bridges. The crystal packing shows a highly porous infinite 3D structure. Diagnostic resonances for the SCN – ligand and metal–ligand bonds in the IR, far-IR and Raman spectra are assigned and discussed. The electronic band structure along with density of states (DOS) calculated by the DFT method indicates that the compound is an indirect band gap semiconductor. The DFT calculations show that the observed luminescence of the compound arises mainly from an excited LLCT state with small MLCT contributions (from the copper to unoccupied π ⁎ orbital of the thiocyanate groups). The X-band EPR spectrum of the powdered sample at room temperature reveals an axial signal with anisotropic g factors consistent with the unpaired electron of Cu(II) ion in the d x 2 − y 2 orbital.

Structural and spectroscopic characterization of silver(I) tribenzylphosphane complexes including chloro and bromo derivatives with unusual stoichiometries and an iodo complex with a Ag 13I 13 cluster core

The reaction of tribenzylphosphane (PBn 3) with silver(I) halides, AgX (X = Cl, Br and I), afforded the cluster compound, [Ag 13I 13(PBn 3) 6 ] ( 1), a low-yielding ionic salt, [Ag(PBn 3) 2] 8[AgCl 3]Cl 6·6H 2O ( 2), and a non-stoichiometric compound, Ag ∼11.5Br ∼11.5(PBn 3) 16·∼5.5H 2O ( 3). As well, reactions with the appropriate Ag salt and PBn 3 in a 1:2 M ratio yielded [Ag(PBn 3) 2]PF 6 ( 4), [Ag(PBn 3) 2]BF 4 ( 5) and [Ag(PBn 3) 2Cl]·0.33CHCl 3 ( 6) while [Ag(PBn 3) 2I] ( 7) was obtained when the ratio was 4:1. The iodo-cluster 1 has an onion-like structure with an iodide ion at its center surrounded trigonal-prismatically by an inner core of six silver ions. These silver ions are tetrahedrally coordinated to the innermost iodide ion and by six iodides that bridge to an outer layer of six silver ions which themselves are tetrahedrally coordinated by six bridging iodides and capped by the six PBn 3 ligands. The top of the onion features a silver ion with three iodo ligands arranged in a near-planar trigonal arrangement around it. Single crystal X-ray crystallography shows the complexes 2 and 3 to contain columns of discrete [Ag(PBn 3) 2] + cations with a linear P–Ag–P coordination, as also observed in the simple salts, 4 and 5, where the anion is [PF 6] − and [BF 4] −. The phenyl groups of PBn 3 swing back over the silver to generate a sixfold phenyl embrace. However, in 3, although the PBn 3 sites are fully occupied, about a quarter of the sixfold phenyl embraces are devoid of the object of their attention, the encapsulated silver ion. For 2, the [AgCl 3] 2− anions are trigonal-planar, three-coordinated. For 3, the AgBr 3 2 - appear as motifs in an approximately 25% silver-deficient Ag 4 Br 6 2 - cluster. The crystal structures of the three-coordinate halides, 6 and 7, show that the geometry around the silver is close to a T-shape, with the chloride and iodide ions bound. The far-IR and 31P CP MAS NMR spectra of a selection of the new complexes confirm aspects of their symmetry as deduced from the crystallographic studies.

One-dimensional ladder like and two-dimensional polymorphs of heterometallic thiocyanate bridged copper(II) and mercury(II) coordination polymer: Syntheses, structural, vibration, luminescence and EPR studies

The 1D triclinic {CuHg(en)(μ-NCS–N,S)4}n (1) and 2D monoclinic {CuHg(en)(μ-NCS–N,S)3(SCN)}n (2) (en=ethylenediamine) heterometallic coordination polymers, as the two polymorphs of the {CuHg(en)(NCS)4}n, were synthesized at room temperature by the reaction of mercuric thiocyanate, potassium thiocyanate, copper(II) malonate and ethylenediamine using different reagent ratios. XRD on single crystals shows that the compound 1 consists of 1D ladder like zigzag ribbons extended along the b axis, whereas compound 2 shows a 2D wavy polymeric structure running parallel to the ab plane. In the crystal packing of the both polymorphs, the polymeric structures are further interlinked to each other via weak interactions and hydrogen bonding to afford a 3D network. Diagnostic ligand and metal–ligand bands in the IR, far-IR and Raman spectra are assigned for the studied compounds. While compound 1 shows no significant emission upon excitation at any wavelength in the UV–Vis region, compound 2 exhibits intense emission at around 410nm. Moreover, the room temperature X-band EPR spectrum of a powdered sample of 1, shows a signal of rhombic symmetry with g1=2.2637, g2=2.0765 and g3=2.0483. In contrast to this, 2 reveals an axial signal with g⊥=2.0742; however, the g|| is unresolved.

ChemInform Abstract: Torsional Vibrations and Barriers to Internal Rotation for Ethanol and 2,2,2-Trifluoroethanol.

Abstract The far-IR (370-50 cm −1 ) spectra of gaseous ethanol, CH 3 CH 2 OH, and the O- d compound have been recorded at a resolution of 0.10 cm −1 . Similar far-IR spectra have been collected for 2,2,2-trifluoroethanol, CF 3 CH 2 OH, and the O- d , C- d 2 and - d 3 isotopic species. In addition, the Raman (4000-50 cm −1 ) and the mid-IR (5000-400 cm −1 ) spectra have been collected for CF 3 CH 2 OH and the isotopic compounds in the vapor phase. A detailed examination of the torsional modes has been carried out and potential functions for the hindered internal rotation of the OH and OD groups and the CH 3 and CF 3 rotors are calculated. For ethanol, the fundamental OH torsion for the trans conformer is observed at 202.6 cm −1 whereas for the gauche conformation, the 1 −1 ← 0 + transition is found at 243.1 cm −1 and the 1 + ← 0 − transition is 195.8 cm −1 . An asymmetric potential function utilizing these transitions gives values of 403 cm −1 (1.15 kcal mol −1 ) for the trans/gauche barrier and 399 cm −1 (1.14 kcal mol −1 ) for the gauche/gauche barrier with the trans conformer more stable by 42 cm −1 (120 cal mol −1 ) than the gauche conformer. Potential functions for the hydroxy torsions are also calculated for the ethanol O- d compound and the four 2,2,2-trifluoroethanol isotopic molecules. The CH 3 torsional transitions of trans ethanol give a V 3 barrier of 1185 ± 16 cm −1 (3.39±0.05 kcal mol −1 ) and the corresponding barrier for the gauche conformer is 1251±2 cm −1 (3.58±0.01 kcal mol −1 ). Similarly, a series of CF 3 torsional transitions was observed for the trans and gauche conformations of the CF 3 CH 2 OH molecule as well as for some of the isotopic species. In addition to the examination of the far-IR spectra, a series of sum and difference bands associated with the OH and OD stretching fundamentals is found in the mid-IR spectra for the 2,2,2-trifluoroethanol compounds and a possible explanation for these modes is given.

Optical properties of amorphous Sb2Se3:Sn films

The measurements and analysis of optical transmission and far-infrared (IR) reflectivity spectra of thermally evaporated Sb2Se3:Sn films are reported. The refractive index and film thickness have been determined from the upper and lower envelopes of the transmission spectra (Swanepoel's standard envelope method), measured at normal incidence, in the spectral range from 800 to 2500 nm. Values of the refractive index fit well to Cauchy's dispersion relation. The optical gap decreases with an increase in the Sn content, while a maximum in the tailing parameter and Urbach's energy occurs with only a small amount (∼1 at %) of this additive. Characteristic vibrational bands for SbSe3 structural units are revealed in the far-IR spectrum with no additional ones arising from the Sn additive. The Kramers–Kronig analysis has been used to calculate the dielectric constants and hence the longitudinal optic and transverse optic splitting for various compositions. The inclusion of Sn as a charged entity along with the Coulomb interactions which serve to polarize the glass medium is found to be responsible for these results.

FTIR imaging and ATR-FT-Far-IR synchrotron spectroscopy of pig ear skin

FTIR imaging was performed on pig ear skin samples cryo-sectioned perpendicular to the skin surface. The OH-stretch region revealed the distribution of water; the amide II band gave the protein distribution; the C═O stretch and C–H stretch regions showed the variation in lipids. Water and proteins were similarly distributed. Triglycerides were predominantly found in the deeper skin layers whereas free fatty acids and ceramides were more dominant in the upper layers. ATR-FT-Far-IR spectroscopy with synchrotron radiation was used on full thickness pig ear skin biopsies. The Far-IR spectra showed bands in the region from 100–150 cm–1due to hydrogen bonded proteins and a band around 180 cm–1arising from “free” water.

FTIR imaging and ATR-FT-Far-IR synchrotron spectroscopy of pig ear skin

FTIR imaging was performed on pig ear skin samples cryo-sectioned perpendicular to the skin surface. The OH-stretch region revealed the distribution of water; the amide II band gave the protein distribution; the C=O stretch and C-H stretch regions showed the variation in lipids. Water and proteins were similarly distributed. Triglycerides were predominantly found in the deeper skin layers whereas fatty acids and ceramides were more dominant in the upper layers. ATR-FT-Far-IR spectroscopy with synchrotron radiation was used on full thickness pig ear skin biopsies. The Far-IR spectra showed hands in the region from 100-150 cm(-1) due to hydrogen bonded proteins and a band around 180 cm(-1) arising from free water.

Structural and spectroscopic studies of some adducts of silver(i) halides with thiourea and N-ethyl substituted thioureas

Syntheses, single crystal X-ray structural and spectroscopic characterizations are described for a variety of adducts of silver halides with thiourea ('tu'), N-ethylthiourea ('ettu' = EtNH.CS.NH(2)) and N,N'-diethylthiourea ('detu' = EtNH.CS.EtNH). This study greatly extends our knowledge of the complex chemistry of silver(i) halides with tu. The unexpected diversity of composition of such complexes was initially revealed by the powerful mechanochemical/IR method and the structures of several of the new complexes were determined by X-ray crystallographic studies of samples subsequently prepared from aqueous solution. Structural characterizations provide extensive geometrical data for (mononuclear 1 : 3) [XAg(xtu)(3)] arrays (xtu = ettu, detu; X = Cl, Br, I), assisting vibrational spectroscopic assignments. With the parent tu ligand, binuclear ionic forms are obtained: [tu(2)Ag(mu-tu)(2)Agtu(2)]X(2), the chloride as the dihydrate and the bromide as a di(thiourea) dihydrate adduct. With tu 1 : 2 complexes are defined for X = Cl, Br, as isomorphous one-dimensional polymers; AgCl:tu (1 : 1) is a two-dimensional net with six-membered Ag(3)S(3) rings and terminal chloride. Intermediate stoichiometries are defined in AgBr:tu (2 : 3), a one-dimensional polymer of Ag(2)S(2) rhombs linked at the silver atoms, while [Cl(2)Ag(3)(tu)(4)](NO(3)).H(2)O is also a one-dimensional polymer in which chloride and thiourea sulfur atoms link six-membered Ag(3)S(3) rings. Diagnostic bands in the IR and far-IR spectra of all of the synthesized complexes are assigned and interpreted in relation to the structures.

IR Spectroscopy of Two Polymorphs of Copper(I) Thiocyanate and of Complexes ofCopper(I) Thiocyanate with Thiourea and Ethylenethiourea

Syntheses and infrared spectroscopic studies are reported for two different polymorphs of copper( I) thiocyanate and for adducts of copper(I) thiocyanate with thiourea (‘tu’) and ethylenethiourea (‘etu’ = imidazolidine-2-thione; (CH2NH)2CS)). These include the previously reported complex CuSCN/etu (1 : 2), which has a trigonal monomeric structure, and CuSCN/etu (1 : 1), which has a three-dimensional polymeric structure. A mechanochemical/infrared study of the CuSCN: tu (1 : 2) system showed that no 1 : 2 complex exists in this case, the product being a mixture of a 1 : 3 complex and a novel 1 : 0.5 complex. The latter complex was prepared both mechanochemically and from solution, and characterized by infrared and solid-state 65Cu broadline NMR spectroscopy. Diagnostic ligand and metal-ligand bands in the IR and far-IR spectra are assigned for both polymorphs of CuSCN and for all of the complexes studied and are discussed in relation to the structures of the complexes

Vibrational interactions in dimethylgold(III) halides and carboxylates

The far-infrared and Raman spectra of binuclear molecules [Me 2AuX] 2 (X = Cl, Br, I) and [Me 2Au(OOCR)] 2 (R = Me, CF 3, Bu t, Ph) in the 600–70 cm −1 region are reported. The experimentally measured vibrational frequencies of [Me 2AuX] 2 are in a good agreement with density functional theory predictions. The Au…Au vibrational interactions predicted to be in the 270–60 cm −1 region of [Me 2AuX] 2 far-IR and Raman spectra have been observed. The Raman-active Au…Au vibrations of the [Me 2Au(OOCR)] 2 molecules were found to be in the same region as those of [Me 2AuX] 2. The Au–X stretching modes were observed between 100 and 250 cm −1 in accordance with the DFT predictions. Their frequencies in the IR spectra of [Me 2AuX] 2 increase in the sequence I < Br < Cl while the AuC 2 stretching frequencies decrease in the same order. This fact might be an evidence of the decreasing covalent character of the gold-halogen bridges. The Au–O stretching bands of dimethylgold(III) carboxylates have been observed in the 500–250 cm −1 region, and Au–C stretching frequencies of both [Me 2AuX] 2 and [Me 2Au(OOCR)] 2 compounds have been found between 600 and 500 cm −1.