Low frequency vibrational spectra of zirconocene and hafnocene sulfide [Cp2M(μ-S)]2 (MZr4+, Hf4+)

Metallocene sulfides [Cp₂M(μ-S)]₂ (I, M  Zr⁴⁺; II, M  Hf⁴⁺ and Cp = cyclopentadienyl) have been synthesized. I and II show charge transfer absorption in the visible region. FT-Raman, Raman and IR spectra of these compounds are reported for the first time. The MS stretching bands have been assigned with the help of a pre-resonance effect. The approximate normal coordinate analysis of the coordination skeleton (D_2h symmetry) aids the detailed assignment in the low frequency spectral region. Force constants of MCp and MS stretching imply that the bond order of HfL is higher than that of ZrL.     

Vibrational spectra and structure of methoxysilanes and products of their hydrolysis

Equilibrium geometries and force fields for the series of molecules (MeO)_nSiMe_4−n(I), (OH)_nSiMe_4−n(II), and (MeO)_nSi(OH)_4−n(III) with n = 1–4 are obtained at the DFT/B3LYP level of theory with 6-31G^* and aug-cc-pVDZ basis sets in order to predict the structural parameters and vibrational spectra of these molecules, the larger part of which was not characterized experimentally. The performance of these theoretical methods was assessed on the existing spectral data for series I. The B3LYP/aug-cc-pVDZ method, firstly applied to this class of molecules, demonstrates a fair agreement with experimental vibrational frequencies even without empirical scaling. For molecules of series II and III vibrational spectra are predicted in order to supply spectral data for monitoring the sol–gel processes at the hydrolysis stage. The hyperconjugative strengthening of SiO bonds with the number of oxygen atoms coordinated to silicon leads to the growth of their frequencies, but the larger increase of νSiO (due to kinematic factors) occurs at the SiOMe/SiOH substitution. The predicted distinctive feature of series II and III is the appearance of bands with high IR intensity in the 1000–900 cm⁻¹ spectral region that increase their frequencies with n. In series III it is accompanied with the steady increase of the ν_sSiO₄ frequency in the 700–600 cm⁻¹ range.     

Inter-hydrogen bond dynamical coupling effects in polarized IR spectra of N-methylacetamide single crystals

This article presents the investigation results of polarized IR spectra of the hydrogen bond in N-methylacetamide (NMA) crystals measured in the frequency range of the proton and deuteron stretching vibration bands, ν_N–H and ν_N–D. A similar study was also performed for crystals of the deuterium isotopomers of the compound, D₇-NMA (CD₃CONDCD₃) and D₆-NMA (CD₃CONHCD₃). On the basis of the analysis of the linear dichroic and temperature effects, the two-branch structure of the ν_N–H bands in the spectra was ascribed to centrosymmetric hydrogen bond pairs in the lattice. Each hydrogen bond in such a dimeric system belonged to another chain of the associated molecules. The exciton interactions involving the dimer hydrogen bonds were considered to be responsible for the band shape generation. For the deuterium-bonded crystals the exciton interactions were found to be weaker since the ν_N–D bands were less split. Within an individual hydrogen or deuterium bond chain the in-chain exciton couplings involving hydrogen bonds were estimated as considerably weaker than the inter-chain ones. The exciton dilution retains the two-branch fine structure pattern of the “residual” ν_N–H and ν_N–D bands. This means that the inter-chain couplings involving hydrogen bonds do not change, when the in-chain couplings vanish. These results are the evidence of the influence of non-conventional co-operative interactions occurring in the hydrogen bond systems on the spectra. These co-operative interactions are responsible for the non-random distribution of the hydrogen isotope atoms in the hydrogen bridge lattices, namely for the grouping of identical hydrogen isotope atoms in the dimers. The proposed interpretation of the IR spectra of the hydrogen bond in N-methylacetamide (NMA) crystals casts light on the spectra generation mechanisms and gives a new meaning to the traditional nomenclature applied for describing the ν_N–H band structure pattern in IR spectra of amides.     

Study of substituent effects on rotational isomers and monomer–dimer equilibria of the 3-carboxy group in 4-substituted (R)-2-(3,4-methylenedioxyphenyl)-6-isopropyloxy-2H-chromen-3-carboxylic acids in dilute CCl4 and CHCl3 solutions by FTIR spectroscopy

FTIR spectra of the title carboxylic acids (I–III) with 4-substituents (H, CH₃ or C₆H₅) and their related compounds IV–VI with 4-(substituted phenyl) groups were measured in dilute CCl₄ and CHCl₃ solutions. The concentration dependence of FTIR spectra of I–IV was also measured in these solutions. These spectra were subjected to curve analysis in order to quantitatively identify the rotational isomers of 3-carboxy group attributable to steric hindrance of the 4-substituents. For I, II and III–VI, two, four and five ν(CO) bands were observed for their carboxy groups, respectively, indicative of monomer–dimer equilibrium and two and three kinds of rotational isomers for II and III–VI, respectively. Compounds III–VI were found to form intra-molecular hydrogen bonds between the trans-type of the 3-carboxy group and the π-electrons in the 4-benzene ring. We have worked out a method to estimate the association constant (K) of complicated monomer–dimer equilibria such as II–VI. The K values of I–IV decrease remarkably in the order of H (I), C₆H₅ (III), CH₃ (II) and C₆H₄-p-OCH₃ (IV) in CCl₄ and I, II, III and IV in CHCl₃; these orders are discussed.     

Influence of the chain and layer structure of Fe(III) and In(III) aqua-pentachloro-complexes on the bending vibrations of water molecules

Studies of IR and Raman spectra of monohydrates M^I₂[M^IIICl₅(H₂O)] (where M^I=K⁺, Rb⁺, Cs⁺ and M^III=Fe³⁺, In³⁺) at 1400-1900 cm⁻¹ have been carried out. The medium intensity band, detected in the region 1580-1595 cm⁻¹ was assigned to bending vibrations of water molecules (δHOH). The shift of the δHOH band towards low wavenumbers (1580-1595 cm⁻¹) is a main sign of the water molecule interactions in the chain hydrates. Additionally in the IR and Raman spectra of these salts, the appearance of the low intensity band between 1750 and 1810 cm⁻¹ (ν_x(H₂O)) was observed. In the presented paper we also discuss the influence of M^I and M^III cations on the position and splitting of these bands.     

Hydrogen bonds formed by methyl groups of acetonitrile: Infrared and calorimetric study

Solutions of acetonitrile (I) in tetrachloromethane and deuteratred solvents (S) (benzene, acctonitrile, acetone and dimethylsulphoxide) have been studied by IR absorption spectra. The observed solvent effect on the IR spectrum of I was explained in terms of the existence of complexes with hydrogen bonding of the type NCCH₃…solvent (S). The strength of the hydrogen bonding was characterized by enthalpies of specific interactions of I with solvents ΔH^I/S_int(sp). The values ΔH^I/S_int(sp) were determined both by IR spectroscopy and calorimetry and were found to be within the range 0.3–1.5 kcal mol⁻¹.     

Assignments of the vibrational spectra of 2,5-dimethyl-2,4-hexadiene, 4-methyl-1,3-pentadiene and (E)-2-methyl-1,3-pentadiene. Effect of the terminal and lateral methyl groups

The complete assignment of the vibrational spectra of 2,5-dimethyl-2,4-hexadiene, 4-methyl-1,3-pentadiene and (E)-2-methyl-1,3-pentadiene was obtained from a comparative analysis of their i.r. and Raman spectra (solid, liquid and gas) in the range 3200-50 cm⁻¹. It is shown that particular vibrational motions strongly interact to give rise to very characteristic modes depending on the site of methyl substitution. The comparison of our results with those of analogous shorter and larger polyenes and polyenals allows us to discuss the various local coupled motions characteristic of unsubstituted (CHCH CH)CH and methyl substituted (CHC(CH₃)CH), ((CH₃)₂CCH) or (CH₃CHCH) fragments in polyenic chains.     

The effects of isotopic substitution (H2OD2O) in the Raman spectra of strontium formate dihydrate single crystals

Polarized Raman spectra measured in the temperature range between 10–293K are reported for SFDH, SFDD single crystals and isotopically samples of Sr(HCOO)₂.2(H,D)₂O.AtT=293 K the uncoupled OD(H) stretching motions are observed in the range ν=2200–2600(3000–3500) cm⁻¹ Plausible assignments to the distinct crystallographically non equivalent H₂O(D₂O) molecular group are given. The investigation has been conducted to elucidate this situation as well as that the structural role of lattice water molecules in molecular crystals.     

Cluster bonding and energetics of the borane anions,BnHn2− (n = 5–12): A comparative study using bond length—bond enthal

Cluster bond enthalpies, E_L(BB), and orders, n?(BB), for the structurally characterised closo anions, B_nH_n^2? (n = 6 and 8–12), have been estimated using the logarithmic length—enthalpy and enthalpy—order relationships E_L(BB) (kJ mol^?1) = 1.766 × 10¹¹ [L(BB)]^?4.0 and E_L(BB) (kJ mol^?1) = 318.8[n?(BB)]^0.697, respectively. In a parallel study, the molecular-orbital bond index CNDO-based calculation method has been used to give BB and BH bond indices, I(BB) and I(BH), from which bond index based bond enthalpies, E_I, have been calculated using the relationships E_I(BB) = 297.9 I(BB) and E_I(BH) = 374.8I(BH) (enthalpies in kJ mol^?1; lengths in pm). From these, total skeletal bond enthalpies Σ E(BB), and total bond enthalpies, Σ E(BB) + Σ E(BH), have been calculated. Although calculated values of E_L and Σ E_L generally exceed those of E_I and Σ E_I by some 8% and calculated values of I generally exceed those of n? by a greater amount, the trends in these parameters for the series of B_nH_n^2? anions are very similar, showing the greater efficiency with which the n + 1 skeletal electron pairs are used as n increases. However, the two approaches differ in that, whereas the Σ E_I values suggest that the anions are all of comparable stability, the ΣE_L values clearly show B₆H₆^2?, B₁₀H₁₀^2? and B₁₂H₁₂^2? to be more stable than B₈H₈^2?, B₉H₉^2? and B₁₁H₁₁^2?. The interatomic distances in B₇H₇^2? and in the unknown B₅ H₅^2? are estimated and used to assess their relative stabilities. The E_L values suggest that B₇ H₇^2? is of comparable stability to B₈H₈^2? etc., but show B₅H₅^2? as relatively unstable. The E_I values suggest that both of these anions should be relatively stable members of the series of closo anions.     

Zur reaktion von metall-koordiniertem kohlenmonoxid mit yliden : VII. Trimethylphosphoranylidenmethyl(trimethylsiloxy)carben-komplexe von chrom,molybdän und wolfram: aufbau einer metallvinyl-einheit durch c(carbanion)c(carben)-π-wechselwirkung und photochemische e/z-isomerisierung

The treatment of the hexacarbonylmetal compounds M(CO)₆ (M = Cr. Mo, W) with two equivalents Me₃PCH₂ yields the phosphonium acylmetalphosphorus ylides Me₄P[(CO)₅MC(O)CHPMe₃] 1a–1c. Their reaction with Me₃SiOSO₂CF₃ leads via O-silylation to formation of the neutral “siloxy(ylidecarbene) complexes” (CO)₅MC(OSiMe₃)CHPMe₃2a–2c, which are protonated by HX (X = Cl, CF₃SO₃) to give the thermolabile carbene complexes [(CO)₅MC(OSiMe₃)H₂CPMe₃]X, 3a, 3b. ¹H, ¹³C NMR and IR data suggest, that delocalization of the ylidic charge to the carbene carbon generates a metal-coordinated vinyl group in the case of 2a–2c. In addition this fact is proved by the X-ray analysis of 2c, for which a C(ylide)C(carbene) bond distance of 133 pm is found. 2a–2c are obtained as pure E-isomers but can be converted to the Z-isomers 2a′–2c′ upon photolysis.     

Self assembly of three new copper coordination polymers based on N-[(3-pyridine)-sulfonyl]aspartate: Synthesis and structure

Three new copper coordination polymers [Cu(L) · 6H₂O] _n (I), [Cu₂(L)₂] _n (II), and [Cu(HL)₂] _n (III), where H₂L is N-[(3-pyridine)-sulfonyl]aspartate, have been synthesized and characterized by singlecrystal X-ray diffraction (CIF files CCDC nos. 1435871 (I), 1435872 (II), 1435873 III), elemental analysis and IR spectra. Moreover, the variable-temperature magnetic susceptibility had been studied for complex I. A structural comparison of these polymers suggests that different reaction temperatures play important role in the construction of resulting architectures for I–III.     

Concerning the silicon-germanium bond: mass spectral fragmentations of isomeric SiGe compounds R3EE′R3 (E  Si,E′  Ge,R  Ph,Me,(η5-C5H4)Fe (C5H5), (η5-C5H5)Fe(CO)2 and (η5-C9H7) Fe(CO)2)

Isomeric pairs of silicon-germanium compounds containing a SiGe bond (Me₃SiGePh₃ (I) and Ph₃SiGeMe₃ (II); FpSiMe₂GeMe₃ (III) and FpGeMe₂SiMe₃ (IV) (Fp = (η⁵-C₅H₅)Fe(CO)₂); IFpSiMe₂GeMe₃ (V) and IFpGeMe₂SiMe₃ (VI) (IFp = (η⁵-C₉H₇)Fe(CO)₂); IFpSiMe₂GePh₃ (VII) and IFpGeMe₂SiPh₃ (VIII) and the complex FcSiMe₂GeMe₂Fc (IX) (Fc = ferrocenyl) have been synthesized and examined by mass spectrometry.The R₃SiGeR′₃ compounds I and II exhibit considerable exchange of R groups to produce [R_3-nR′_nSi]⁺ and [R′_3-nR_nGe]⁺ ion in progressively lesser amounts as n = 1 → 2 → 3. For the metal-substituted complexes containing the grouping FeSiGe fragmentation occurs predominantly via SiGe bond cleavage with formation of ions containing the silylene ligand [FeSiR₂]⁺. Complexes with the FeGeSi backbone undergo preferential scission of the FeGe bond, illustrating the general bond strength trend FeSi > SiGe. Upon direct cleavage of the SiGe bond in R₃SiGeR₃ compounds, the percentage of the charge carried by [R₃Si]⁺ ions significantly exceeds that carried by [R₃Ge]⁺ ions, reflecting the greater electronegativity of Ge polarizing the SiGe bond.     

DFT predictions of vibrational spectra of titanium tetramethoxide oligomers and the structure of titanium tetraalkoxides in liquid and solid phases

Plausible structures of the titanium tetramethoxide trimer were optimized at the B3LYP/6-31+G^* level. From the four types of structures of the Ti₃O₁₂ cage found earlier for the Ti(OH)₄ trimer only two isomers were found as energy minima on the Ti₃(OMe)₁₂ potential energy surface. One isomer (I), belonging to the C_i point group, is built from three interconnected titanium oxide tetrahedra with a linear arrangement of titanium atoms. This structure have a titanium oxide skeleton similar to that of Ti₃(OH)₁₂. The other isomer (II), of C₂ symmetry, is built by edge sharing TiO₆ groups. Theoretical IR spectra of these isomers are compared with reported experimental IR spectra of solid titanium tetramethoxide and newly obtained Raman spectra of commercial powders. It was shown that the number and position of observed bands in the CO stretching region of the IR spectra of the so-called modification A of solid titanium tetramethoxide are in a good agreement with the predicted vibrational spectrum of trimer I. The equilibrium structure and IR and Raman spectra were also obtained for the Ti₄(OMe)₁₆ tetramer. The comparison of the predicted vibrational spectrum with the experimental IR spectra of modification B as well as of the Raman spectrum of solid titanium tetramethoxide allows us to confirm the tetrameric structure of this modification and to propose the similar structure for commercial samples.     

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.     

A Salt-Like Compound Containing the Cation [Tris(1,10-Phenanthroline)manganese(II)](2+) and the Anion 3,3-Commo-Bis[η5-1,2-Dicarba-(3)-Cobalt(III)-closo-Dodecaborate](1–), [MnII(1,10-C12H8N2)3]2+{CoIII[η5-(3)-1,2-B9C2H11]2}– 2: Synthesis and Study

In this paper, the results of a comparative study of a salt-like paramagnetic Mn(II) (d ⁵) complex [Mn^II(1,10-C₁₂H₈N₂)₃]²⁺[Co^III(B₉C₂H₁₁)₂]^– ₂ (I) against [Mn^II(1,10-C₁₂H₈N₂)₂(NCS)₂]⁰ (II) and [Mn^II(1,10-C₁₂H₈N₂)₃]²⁺[B₉C₂H₁₂]^– ₂ (III) are presented. Complexes I and III were synthesized by precipitating the Mn(II) cations with the corresponding anions in the stoichiometric ratio at a pH of ～ 4.5 and were studied by X-ray diffraction analysis on single crystals; by IR, Raman, and EPR spectroscopy; and using magnetochemical methods. The structures and crystal-chemical parameters of I at 190 and 293 K are identical. The crystals are mono-clinic; space group P2₁/n. Two crystallographic types of the [Co(B₉C₂H₁₁)₂]^– anion in structure I have different conformational combinations (cisoid and transoid) of the –C₂– groups in each pair of the B₉C₂H^2– ₁₁ cluster ligands. The short contacts C–H^δ+···^δ–H–B between different-type hydrogen atoms show themselves in the IR spectra. The apparent magnetic moments of the Mn(II) atom in I, II, and III at 293 K correspond to μ = 5.86 μ_B and do not depend on its ligand or anion environment. The temperature dependences μ = f(T) pass through a maximum at about 20 K, which suggests the occurrence of ferromagnetic exchange interactions in complexes I and III, which both contain cluster carborane derivatives with three-dimensional aromaticity.     

Synthesis,X-ray diffraction and vibrational study of silicates and germanates isostructural with kentrolite Pb2Mn2Si2O9

New germanates Pb₂M^III₂Ge₂O₉ (M^III = Fe, Mn, Sc, In) and silicates Pb₂M^IIM^IVSi₂O₉ (M^II = Mg, Ni, Co, Cu for M^IV = Sn; M^II = Co, Ni for M^IV = Ti) have been synthesized by solid state reaction. Their X-ray powder diagrams may be indexed in the orthorhombic system and show that these compounds are isostructural with kentrolite Pb₂Mn₂Si₂O₉. Doubts are expressed about the published structure of kentrolite and it is shown that some aspects of the structure should be re-examined.The I.R. and Raman spectra of these compounds are fairly complicated, and their discussion is restricted to the region of SiO or GeO stretching frequencies. These spectra show the existence of a pyro-silicate or -germanate group. The symmetric and antisymmetric frequencies of the SiOSi bridge have been identified with the help of ²⁸Si³⁰Si isotopic shifts. Their difference ν_as?ν_sym depends on the ionic radius of the cations, and points to a non-linear bridge of the pyrosilicate group.     

Syntheses and luminescence of three lanthanide complexes constructed by flexible carboxylate ligand

Three new complexes, namely {[Ln(L)₃(2,2′-Bipy)] _n · H₂O} (Ln = Pr (I), Sm (II), and Nd (III)) (HL = 3-(2-hydroxyphenyl)propanoic acid), have been synthesized and structurally characterized. The structural determinations indicated (CIF files CCDC nos. 1472729 (I), 1472730 (II), 1472734 (III)) that I–III have similar dinuclear structures, which can be further linked into 2D sheet via the hydrogen bond interactions. Furthermore, the luminescent properties of I–III show the strong emissive power and feature.     

Conformational studies of α-substituted carbonyl compounds—V. Evidence for hyperconjugative interactions in 2-iodosubstituted carbonyl systems. ω-iodo-p-substituted acetophenones

The infrared carbonyl stretching (ν_CO) frequencies as well as the carbon—iodine (ν_CI) Raman and infrared frequencies for some ω-iodo-p-substituted acetophenones are reported. Although in the title compounds the solvent effect on the carbonyl band does not indicate the existence of cis/gauche rotational isomerism, the comparison between the ν_CO frequencies in the fundamental transition with those in the 1st overtone (in CCl₄) indicates the presence of the cis/gauche rotational isomerism. On going from electron-donating to electron-attracting substituents in the ω-iodo-series, the progressive increase in the gauche carbonyl shifts (Δν_g) together with the progressive decrease in the ν_CI frequencies suggest the increasing contribution of the hyperconjugative interaction between π_CO and σ_CI orbitals. The u.v. spectra of the title compounds display the n → π*_CO band which is bathochromically shifted in relation to the corresponding acetophenones, indicating the π*_CO/σ*_CI hyperconjugative interaction in the excited state. [¹³C] NMR data for the methylene group of the ω-iodoacetophenones in comparison with those of ω-bromoacetophenones [1] as well as with those for the methyl group of the unsubstituted acetophenones corroborates the existence of the π_CO/σ_CI hyperconjugation in the fundamental state of the title compounds.     

The characteristic IR spectra of heterothiometallic cluster compounds

This article summarizes and presents the obtainable characteristic IR spectra of the existing heterothiometallic cluster compounds containing the [MXS₃]²⁻ (X=O, S; M=V, Mo, W, Re) moiety. The MS stretching vibration modes are classified into four categories including ν(MS_t), ν(Mμ₂-S), ν(Mμ₃-S) and ν(Mμ₄-S) according to the different conjunction ways between the transition metal and sulfur atoms. The structures of the heterothiometallic cluster compounds could be inferred from their characteristic IR spectra, the core structure's symmetry of the heterothiometallic clusters and the M/M′ ratio.     

Effects of dynamical couplings in hydrogen bond systems in the polarized IR spectra of 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde crystals

This paper presents the investigation results of the polarized IR spectra of 3-hydroxybenzaldehyde and 4-hydroxybenzaldehyde crystals measured at 293 and 77 K. Analysis of the results concerned the linear dichroic, H/D isotopic and temperature effects observed in the spectra of the hydrogen and deuterium bond at the frequency ranges of the ν_O–H and the ν_O–D bands, respectively. The main spectral properties of the crystals were interpreted in terms of the “strong-coupling” theory on the basis of the hydrogen bond dimer model. The spectra revealed that the strongest vibrational exciton coupling involved the closely-spaced hydrogen bonds, each belonging to a different chain of associated molecules. The reason for two different crystalline systems, are characterized by almost identical ν_O–H and ν_O–D band shapes, is explained. It was proved that a random distribution of the protons and deuterons took place in the lattices of the isotopically diluted crystals.