Novel CdCl2 and HgCl2 complexes with 3-monosubstituted and 3,3-disubstituted 1-furoylthioureas: IR and Raman spectra

Two series of coordination complexes of CdCl(2) and HgCl(2) with 3-monosubstituted and 3,3-disubstituted 1-furoylthioureas were prepared and characterized. These complexes were obtained with a medium to high yield from ethanolic solutions of both ligand and salt. The formed complex results from the salt-ligand interaction with participation of both the salt anion and cation. Information on the coordination chemistry of these complexes was derived from thermal stability data, and IR, Raman and (13)C CPMAS NMR spectra. On coordination the electronic structure of these ligands changes as a whole, affecting practically all their vibrational pattern, however, within that complex pattern some vibrations provide valuable information on the nature of the studied complexes. These thiourea derivatives behave as neutral ligands, which coordinate the metal ion through the sulfur atom of the thiocarbonyl group. This fact is supported by the observed frequency shift, to lower values, in the nu(CS) vibration on the coordination and the appearance of a low frequency Raman line which was assigned to the metal-sulfur stretching, nu(M-S), in the formed complex. The frequency of the nu(CO) vibration always increases on complex formation, which discards the participation of the carbonyl group in the coordination process. The complexation takes place preserving the free ligand conformation, established from intra-molecular interactions, particularly in 3-monosubstituted ligands. Such features of the studied ligands and their complexes are also supported by (13)C CPMAS NMR spectra. This spectroscopic information correlates with the reported behavior of the ligands in ion selective electrodes.     

FT-IR and FT-Raman study of hydrogen bonding in p-alkylcalix[8]arenes

The FTIR and FT Raman spectra of p-alkylcalix[8]arenes (alkyl = tert-butyl, isononyl) were recorded. Analysis of IR spectra showed that the cyclic cooperative intramolecular hydrogen bond is realized in calix[8]arene. It was found that the strength of the cyclic cooperative intramolecular hydrogen bond in the series of alkyl derivatives of calix[8]arenes depends very little on the replacement of the p-tert-butyl groups by the more bulky isononyl group. From our data follows that the orientation of aromatic fragments in calixarene molecules depends on the type of alkyl substituent.An analysis of the changes in the IR spectra with heating and dissolution shows that the conformation of the “pleated-loop” is retained in p-tert-butylcalix[8]arene. It turned out that the intramolecular hydrogen bond is a “probe” of the conformation of calixarene molecules and IR spectroscopy is a unique method that allows one to follow the slightest nuances of changes in the H-bound system of these supermolecules.     

Study of the interactions of sodium thiocyanate, potassium thiocyanate and ammonium thiocyanate in water+N,N-dimethylformamide mixtures by Raman spectroscopy

Raman spectra of water+N,N-dimethylformamide (DMF) mixtures and their solutions with NaNCS, KNCS and NH(4)NCS were obtained. The bands of nu(CO) stretching, delta(OCN) bending, r(CH(3)) rocking and nu(N-CH)(3)) stretching of the DMF molecule with and without salts were studied. The dependence of the vibration frequencies and Raman intensities of the bands on the composition of the mixed solvent was discussed. The change of the band frequencies as a result of the presence of the salts and the solvation of the cations by the solvent molecules was examined. The stronger cation solvation by the aprotic solvent molecules instead of the water molecules in DMF concentrated solutions was discussed. The nu(CN) and nu(CS) vibrations of the SCN(-) ions were observed as a function of the cation present and the solvent composition. The presence of the SCN(-) ions as "free", contact ion pairs, or solvent separated pairs, was discussed.     

Conformational isomerism of chlorophenylthioureas and intramolecular N---H … Cl hydrogen bonds: IR spectra of N---H stretching vibrations

The vN---H regions of the IR spectra of thioureas with chlorophenyl (ClPh) groups and those with halophenyl groups were measured in dilute CCl₄ solution. The observed vN---H bands were classified into eight groups according to the wavenumbers and the two substituent groups. The suggested conformational states and the formation of intramolecular N---H … Cl hydrogen bonds in these compounds were discussed in comparison with those of the urea analogs. It was found that these thiourea derivatives are more stable in the cis form than the urea analogs and that thioureas with o-ClPh groups form fewer intramolecular N---H … Cl hydrogen bonds than do the urea analogs.     

Rhenium-to-benzoylpyridine and rhenium-to-bipyridine MLCT excited states of fac-[Re(Cl)(4-benzoylpyridine)(2)(CO)(3)] and fac-[Re(4-benzoylpyridine)(CO)(3)(bpy)](+): a time-resolved spectroscopic and spectroelectrochemical study

The lowest allowed electronic transition of fac-[Re(Cl)(CO)(3)(bopy)(2)] (bopy = 4-benzoylpyridine) has a Re --> bopy MLCT character, as revealed by UV-vis and stationary resonance Raman spectroscopy. Accordingly, the lowest-lying, long-lived, excited state is Re --> bopy (3)MLCT. Electronic depopulation of the Re(CO)(3) unit and population of a bopy pi orbital upon excitation are evident by the upward shift of nu(CO) vibrations and a downward shift of the ketone nu(C=O) vibration, respectively, seen in picosecond time-resolved IR spectra. Moreover, reduction of a single bopy ligand in the (3)MLCT excited state is indicated by time-resolved visible and resonance Raman (TR(3)) spectra that show features typical of bopy(*)(-). In contrast, the lowest allowed electronic transition and lowest-lying excited state of a new complex fac-[Re(bopy)(CO)(3)(bpy)](+) (bpy = 2,2'-bipyridine) have been identified as Re --> bpy MLCT with no involvement of the bopy ligand, despite the fact that the first reduction of this complex is bopy-localized, as was proven spectroelectrochemically. This is a rare case in which the localizations of the lowest MLCT excitation and the first reduction are different. (3)MLCT excited states of both fac-[Re(Cl)(CO)(3)(bopy)(2)] and fac-[Re(bopy)(CO)(3)(bpy)](+) are initially formed vibrationally hot. Their relaxation is manifested by picosecond dynamic shifts of nu(C(triple bond)O) IR bands. The X-ray structure of fac-[Re(bopy)(CO)(3)(bpy)]PF(6).CH(3)CN has been determined.     

IR spectroscopy of hydrogen-bonded 2-fluoropyridine-methanol clusters

The electronic and infrared spectra of 2-fluoropyridine-methanol clusters were observed in a supersonic free jet. The structure of hydrogen-bonded clusters of 2-fluoropyridine with methanol was studied on the basis of the molecular orbital calculations. The IR spectra of 2-fluoropyridine-(CH3OH)n(n = 1-3) clusters were observed with a fluorescence-detected infrared depletion (FDIR) technique in the OH and CH stretching vibrational regions. The structures of the clusters are similar to those observed for 2-fluoropyridine-(H2O)n (n = 1-3) clusters. The existence of weak hydrogen bond interaction through aromatic hydrogen was observed in the IR spectra. The theoretical calculation also supports the result. The vibrational frequencies of CH bonds in CH3 group are affected by hydrogen bond formation although these bonds do not directly relate to the hydrogen bond interaction. The B3LYP/6-311 ++G(d,p) calculations reproduce well the vibrational frequency of the hydrogen-bonded OH stretching vibrations. However, the calculated frequency of CH stretching vibration could not reproduce the IR spectra because of anharmonic interaction with closely lying overtone or combination bands for nu3 and nu9 vibrations. The vibrational shift of nu2 vibration is reproduced well with molecular orbital calculations. The calculation also shows that the frequency shift of nu2 vibration is closely related to the CH bond length at the trans position against the OH bond in hydrogen-bonded methanol.     

Formation and characterization of carbon monoxide adducts of iron "twin coronet" porphyrins. Extremely low CO affinity and a strong negative polar effect on bound CO

The carbon monoxide (CO) adducts of iron "twin coronet" porphyrins (TCPs) are characterized by UV-vis, resonance Raman (RR), IR, and 13C NMR spectroscopies. A superstructured porphyrin, designated as TCP, was used as a common framework for the four different types of iron complexes. TCP bears two binaphthalene bridges on each side and creates two hydrophobic pockets surrounded by the bulky aromatic rings. In the CO-binding cavities, the hydroxyl groups are oriented toward the center above the heme. The iron complexes investigated are as follows: TCP (which is without a covalently linked axial ligand), TCP-PY (which has a linked pyridine ligand), and TCP-TB and TCP-TG (both of which have a linked thiolate ligand). These complexes were synthesized as ferric forms and identified by the various spectroscopic methods. The UV-vis spectra of TCP-CO and TCP-PY-CO exhibit lambda(max) at 432, 546 and 428, 541 nm, respectively. On the other hand, the CO adducts of TCP-TB and TCP-TG show typical hyperporphyrin spectra for a thiolate-ligated iron(II) porphyrin-CO complex. In the RR spectra, the nu(Fe-CO) bands were observed at 506, 489 cm(-1) (TCP), 465 cm(-1) (TCP-PY), 458, 437 cm(-1) (TCP-TG) and 429 cm(-1) (TCP-TB). Compared with the reported nu(Fe-CO) frequencies of hemoproteins and their model systems, these observed values are unusually low. Further, abnormally high nu(C-O) bands are observed at 1990 cm(-1) (TCP-CO) and 2008 cm(-1) (TCP-PY-CO) in IR spectra. The lower nu(Fe-CO) and the higher nu(C-O) frequencies can be ascribed to the strong negative polar effect caused by the vicinal hydroxyl groups in the cavity. This prediction is further supported by the observation of significant 13C shieldings exhibited by TCP-CO (delta = 202.6 ppm) and TCP-PY-CO (delta = 202.3 ppm), in comparison to hemoproteins and other heme models. The CO affinity of TCP-PY (P1/2CO = 0.017 Torr at 25 C) is unusually lower than other heme models. The unique behavior of these CO adducts is discussed in context of the TCP structures.     

Synthesis and characterization of tungsten carbonyl complexes containing N-methyl substituted urea and thiourea ligands

Six new mixed-ligand tungsten carbonyl complexes containing N-methyl substituted urea and thiourea of the type W(CO)₄[RCH₂N-(C=X)NH₂] where X?=?O or S and R?=?morpholine, piperidine and diphenylamine are reported. These have been prepared by refluxing hexacarbonyl tungsten(0) with corresponding ligands in THF to produce cis-disubstituted products, [(L-L)W(CO)₄] where L-L?=?a chelating bidentate ligand, morpholinomethyl urea (MMU), morpholinomethyl thiourea (MMTU), piperidinomethyl urea (PMU), piperidinomethyl thiourea (PMTU), diphenylaminomethyl urea (DAMU) and diphenylaminomethyl thiourea (DAMTU). The compounds have been characterized by elemental analysis, IR, electronic and ¹³C NMR spectra, magnetic moments and conductivity measurements. The IR spectra suggests that in all the complexes, the ligands are bidentate chelating, coordinating the metal through carbonyl oxygen or thiocarbonyl sulphur and the ring nitrogen or tert-nitrogen of diphenylamine. The CO force constants and CO–CO interaction constants for these derivatives have also been calculated using Cotton–Kraihanzel secular equations, which indicate poor π-bonding ability of the ligands. ¹³C NMR and electronic spectra reveal loss of cis-carbonyl ligands to produce cis-disubstituted tetracarbonyl derivatives. Molecular modeling studies have been carried out using Hyperchem release 7.52 which suggest a distorted octahedral geometry for these complexes.     

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.     

Ligand-to-diimine/metal-to-diimine charge-transfer excited states of [Re(NCS)(CO)3(alpha-diimine)] (alpha-diimine = 2,2'-bipyridine, di-iPr-N,N-1,4-diazabutadiene). A spectroscopic and computational study

Two new complexes fac-[Re(NCS)(CO)3(N,N)] (N,N = 2,2'-bipyridine (bpy), di-iPr-N,N-1,4-diazabutadiene (iPr-DAB)) were synthesized and their molecular structures determined by X-ray diffraction. UV-vis absorption, resonance Raman, emission, and picosecond time-resolved IR spectra were measured experimentally and calculated with TD-DFT. A good agreement between experimental and calculated ground- and excited-state spectra is obtained, but only if the solvent (MeCN) is included into calculations and excited state structures are fully optimized at the TD-DFT level. The lowest excited states of the bpy and iPr-DAB complexes are assigned by TD-DFT as 3aA' by comparison of calculated and experimental IR spectra. Excited-state lifetimes of 23 ns and ca. 625 ps were determined for the bpy and DAB complex, respectively, in a fluid solution at room temperature. Biexponential emission decay (1.3, 2.7 micros) observed for [Re(NCS)(CO)3(bpy)] in a 77 K glass indicates the presence of two unequilibrated emissive states. Low-lying electronic transitions and excited states of both complexes have a mixed NCS --> N,N ligand-to-ligand and Re --> N,N metal-to-ligand charge-transfer character (LLCT/MLCT). It originates in mixing between Re d(pi) and NCS pi characters in high-lying occupied MOs. Experimentally, the LLCT/MLCT mixing in the lowest excited state is manifested by shifting the nu(CO) and nu(NC) IR bands to higher and lower wavenumbers, respectively, upon excitation. Resonant enhancement of both nu(CO) and nu(NC) Raman bands indicates that the same LLCT/MLCT character mixing occurs in the lowest allowed electronic transition.     

Uncoupled peptide bond vibrations in alpha-helical and polyproline II conformations of polyalanine peptides

We examined the 204-nm UV resonance Raman (UVR) spectra of the polyproline II (PPII) and alpha-helical states of a 21-residue mainly alanine peptide (AP) in different H2O/D2O mixtures. Our hypothesis is that if the amide backbone vibrations are coupled, then partial deuteration of the amide N will perturb the amide frequencies and Raman cross sections since the coupling will be interrupted; the spectra of the partially deuterated derivatives will not simply be the sum of the fully protonated and deuterated peptides. We find that the UVR spectra of the AmIII and AmII' bands of both the PPII conformation and the alpha-helical conformation (and also the PPII AmI, AmI', and AmII bands) can be exactly modeled as the linear sum of the fully N-H protonated and N-D deuterated peptides. Negligible coupling occurs for these vibrations between adjacent peptide bonds. Thus, we conclude that these peptide bond Raman bands can be considered as being independently Raman scattered by the individual peptide bonds. This dramatically simplifies the use of these vibrational bands in IR and Raman studies of peptide and protein structure. In contrast, the AmI and AmI' bands of the alpha-helical conformation cannot be well modeled as a linear sum of the fully N-H protonated and N-D deuterated derivatives. These bands show evidence of coupling between adjacent peptide bond vibrations. Care must be taken in utilizing the AmI and AmI' bands for monitoring alpha-helical conformations since these bands are likely to change as the alpha-helical length changes and the backbone conformation is perturbed.     

The rotational and vibrational spectra of 1,3-dithiole- 2-one

Microwave spectra of 1,3-dithiole-2-one show that the molecule has a planar equilibrium conformation. IR and Raman spectra are analysed to give the normal modes of vibration.     

Synthesis and different substituent effects on spectral and electrochemical properties of porphyrin nicotinic acid binary compounds

The porphyrin nicotinic acid binary compounds with different substituents in porphine rings (5-(4-nicotinicoxyldecyloxy)phenyl-10,15,20-triphenylporhyrin 2a, 5-(4-nicotinicoxyldecyloxy)phenyl-10,15,20-tri(4-chlorophenyl)porphyrin 2b and 5-(4-nicotinicoxyldecyloxy)phenyl-10,15,20-tri(4-methoxyphenyl)porphyrin 2c) were synthesized. All of them have been characterized, assigned and analyzed by UV–vis, IR, MS and ¹H NMR spectra. Their electrochemical and spectroscopic properties were studied by using cyclic voltammetry, fluorescence spectra and Resonance Raman spectra. Different substituents have a little influence on electrochemical behavior and fluorescence spectra. In the Resonance Raman spectra, the substituent has little influence on the skeleton vibration of porphyrin and has much influence on the vibration of phenyl.     

Vibrational behavior of the phosphates ions in dittmarite-type compounds M'M'PO4.H2O (M'=K+, NH4+; M'=Mn2+, Co2+, Ni2+)

The IR and Raman spectra of the isostructural M'M'PO4.H2O compounds (M'=K+, NH4+; M'=Mn2+, Co2+, Ni2+) are reported and discussed with respect to the normal vibrations of the PO(4)3- ions. The vibrational behavior of PO4(3-) is in agreement with its low site symmetry Cs in the lattices-the symmetric nu1 and nu2 modes are activated in the IR spectra and the degeneration of the asymmetric nu3 and nu4 modes is lifted. A relatively large unit-cell group splitting is observed for nu1 in both the IR and Raman spectra and for nu3 in Raman spectra. It has been established that the mean wavenumbers of the P-O stretches (nuPO) are not affected by the M2+ ions present, but they are lower for the NH4-series than for the K-one (predominant influence of both the smaller repulsion potential and the hydrogen bonds in the NH4-lattices over the influence of the M+-O interactions). The extent of the energetic distortion of the PO(4)3- ions has been estimated based on the spectroscopic data for the site group splitting of the asymmetric modes (Deltanu3 and Deltanu4), the separation between the highest and the lowest wavenumbered P-O stretches (Deltanumax) and the intensity of nu1 in the IR spectra. The data provide an evidence that the PO4(3-) ions in KM'PO4.H2O are more distorted regarding the P-O bond lengths than those in NH4M'PO4.H2O, but their angular distortion is the same in both series. The trends for the energetic distortion of the phosphate ions found from the spectroscopic data correspond to the data for their geometric distortion deduced from the values of the distortion indices DI(PO) and DI(OPO).     

A theoretical study of the staggered and eclipsed forms of the dinuclear complex Mn Re(CO)10

Two possible conformers of the dinuclear complex Mn Re(CO)10, each of C(4v) symmetry, with eclipsed and staggered conformations, have been analyzed theoretically. Using both the B3LYP and BP86 density functionals we find that the staggered form is lower in energy. A determination of the B3LYP potential energy surface as a function of the Mn-Re distance is presented for both conformers. The computed bond lengths, bond angles, and rotational constant for the staggered conformation compare favorably with the results from microwave experiments. The harmonic frequencies for the staggered structure have been determined using several basis sets, with both analytical and finite difference methods. These unscaled vibrational frequencies, together with their intensities for both infrared and Raman activity, are used to assign the three most intense experimental IR and Raman bands, and in particular, the nu(CO) region. The lowest A(2) vibration was calculated to occur at 41 cm(-1) in the staggered conformer; this frequency becomes imaginary in the (saddle point) eclipsed form. Several fundamentals remain to be observed experimentally.     

Conformational analysis of 2-oxo(thio)-1,3,2-dioxaphosphorinanes with a P-H bond from vibrational spectroscopic data

The steric structure of four 2-hydro-2-oxo(thio)-1,3,2-dioxaphosphorinane (DOP) molecules has been studied by means of Raman and IR spectroscopy. A characteristic feature of these compounds is the presence of a hydrogen atom as a "light" exocyclic substituent whose vibration is not mixed with the vibrations of the molecular skeleton.A. E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Center, Russian Academy of Sciences, 420083 Kazan, Tatarstan, Russia. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 12, pp. 2725–2730, December, 1992.     

弱氢键作用对硫脲水溶液拉曼光谱影响的密度泛函理论计算

将拉曼光谱和密度泛函理论(DFT)计算结合能够把拉曼谱峰和分子结构及分子间氢键作用之间的变化联系起来, 反映分子周围的结构信息. 本文通过理论计算水分子和硫脲形成复合物的拉曼光谱, 并结合实验报道的拉曼光谱, 探究硫脲基频对分子局域结构的依赖性. 通过轨道分析, 发现水分子的氢键作用可以引起硫脲的前线轨道对易, 这将影响到硫脲的拉曼光谱性质. 最后计算也表明在中性水溶液中由于大的正Gibbs 自由能变, 硫脲不易发生异构转变.     

弱氢键作用对硫脲水溶液拉曼光谱影响的密度泛函理论计算

将拉曼光谱和密度泛函理论(DFT)计算结合能够把拉曼谱峰和分子结构及分子间氢键作用之间的变化联系起来,反映分子周围的结构信息.本文通过理论计算水分子和硫脲形成复合物的拉曼光谱,并结合实验报道的拉曼光谱,探究硫脲基频对分子局域结构的依赖性.通过轨道分析,发现水分子的氢键作用可以引起硫脲的前线轨道对易,这将影响到硫脲的拉曼光谱性质.最后计算也表明在中性水溶液中由于大的正Gibbs自由能变,硫脲不易发生异构转变.     

Infrared and polarized Raman spectra of (CH3)2NH2Al(SO4)2 x 6H2O

FTIR and single crystal Raman spectra of (CH3)2NH2Al(SO4)2 x 6H2O have been recorded at 300 and 90 K and analysed. The shifting of nu1 mode to higher wavenumber and its appearance in Bg species contributing to the alpha(xz) and alpha(yz) polarizability tensor components indicate the distortion of SO4 tetrahedra. The presence of nu1 and nu2 modes in the IR spectrum and the lifting of degeneracies of nu2, nu3, and nu4 modes are attributed to the lowering of the symmetry of the SO4(2-) ion. Coincidence of the IR and Raman bands for different modes suggest that DMA+ ion is orientationally disordered. One of the H atoms of the NH2 group of the DMA+ ion forms moderate hydrogen bonds with the SO4(2-) anion. Al(H2O)6(3+) ion is also distorted in the crystal. The shifting of the stretching modes to lower wavenumbers and the bending mode to higher wavenumber suggest that H2O molecules form strong hydrogen bonds with SO4(2-) anion. The intensity enhancement and the narrowing of nu1SO4, deltaC2N and Al(H2O)6(3+) modes at 90 K confirm the settling down of the protons in the hydrogen bonds formed with H2O molecules and NH2 groups. This may be one of the reasons for the phase transition observed in the crystal.