Vibrational structure of electronic transitions in conjugated molecules

A general approach is presented for calculating the vibronic structure (Frank-Condon factors) of electronic transitions in conjugated molecules. Application to the lowest allowed ΠΠ^* transition of ethylene, 1,3-cyclohexadiene, 1,3,5-hexatriene, and β-ionone are given.     

Vibrational center-ligand couplings in transition metal complexes

The mode-tracking principle [J. Chem. Phys. 2003, 118, 1634] for the direct quantum chemical calculation of preselected, characteristic molecular vibrations makes vibrational analyses of very large molecules feasible. This is demonstrated here for the [(Ph(3)PAu)(6)C](2+) complex, in which 18 phenyl groups in the ligand sphere are explicitly taken into account. We are aiming at the motion of the endohedral carbon atom, which is in an extraordinary bonding situation because it is surrounded by an octahedral core of gold atoms in this cluster. Secondary effects of the full ligand sphere on the vibrations of the [Au(6)C] core embedded in [(R(3)PAu)(6)C](2+) clusters are investigated. For this purpose, local vibrations of the octahedral core are generated, and their long-range couplings with the phosphine ligand sphere become visible in the mode-tracking iterations. The exact normal modes of these characteristic vibrations of the cluster are then obtained after convergence of the mode-tracking refinement. This protocol allows us to assess the coupling of the outer ligand sphere with the inner core of the cluster in terms of changes of the vibrational frequencies and of the collective motions of the atomic nuclei. The vibrational frequencies of the octahedral [Au(6)C] core split due to symmetry breaking in the C(1)-symmetric [(Ph(3)PAu)(6)C](2+) cluster. Our study demonstrates how effects of the periphery of a large molecule on local vibrations can be quantified. Furthermore, we predict the first set of characteristic vibrational frequencies obtained with first-principles methods for this gold cluster, whose vibrational spectra have not yet been recorded experimentally.     

Vibrational spectroscopic studies of 4,4′-bipyridyl metal(II) tetracyanonickelate complexes and their clathrates

The infrared spectra of M(4,4-bipyridyl)Ni(CN)₄ complexes (M=Ni or Cd) and their dioxane, benzene, toluene, aniline andN,N-dimethylaniline clathrates are reported. Additional information regarding the structure of the host lattice is obtained from the Raman spectra of the M=Cd complex. It is shown that the structure of the host lattice consists of infinite polymeric layers of {M-Ni(CN)₄} analogous to those of Hofmann type clathrates that have tetragonal symmetry. Bidentate 4,4-bipyridyl molecules form bridges between the metal atoms {M} in the adjacent {M-Ni(CN)₄} layers. It is found that the 4,4-bipyridyl molecules are centrosymmetric in this structure.Presented at the Fourth International Symposium on Inclusion Phenomena and the Third International Symposium on Cyclodextrins, Lancaster, U.K., 20–25 July 1986     

Generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their synthetic applications

Organomagnesium compounds, represented by the Grignard reagents, are one of the most classical yet versatile carbanion species which have widely been utilized in synthetic chemistry. These reagents are typically prepared via oxidative addition of organic halides to magnesium metals, via halogen–magnesium exchange between halo(hetero)arenes and organomagnesium reagents or via deprotonative magnesiation of prefunctionalized (hetero)arenes. On the other hand, recent studies have demonstrated that the organo-alkaline earth metal complexes including those based on heavier alkaline earth metals such as calcium, strontium and barium could be generated from readily available non-polar unsaturated molecules such as alkenes, alkynes, 1,3-enynes and arenes through unique metallation processes. Nonetheless, the resulting organo-alkaline earth metal complexes could be further functionalized with a variety of electrophiles in various reaction modes. In particular, organocalcium, strontium and barium species have shown unprecedented reactivity in the downstream functionalization, which could not be observed in the reactivity of organomagnesium complexes. This perspective will focus on the newly emerging protocols for the generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their applications in chemical synthesis and catalysis.

In this perspective, we highlight the recent development of metallation protocols of non-polar unsaturated molecules for the generation of organo-alkaline earth metal compounds and their applications in chemical synthesis and catalysis.     

Neutral d8 metal bis-dithiolene complexes: Synthesis,electronic properties and applications

Transition metal bis-dithiolene complexes show a large variety of physical properties such as conductivity, magnetism, optics, which render them attractive for new generations of devices. This review scans neutral d⁸ metal bis-dithiolene complexes as a function of their chemical structure, and the properties that make them top-quality products for applications in the opto-electronic domain.     

Synthesis and properties of hyperbranched polyester polyacrylic acids and their metal complexes

New polydentate ligands based on the hyperbranched third generation polyesters containing terminal acrylic acid fragments were synthesized. The ionization and complexation parameters of new compounds in solution were estimated by spectrophotometry and pH-metric titration followed by experimental data processing using mathematical simulation by the CPESSP program. The procedure for the synthesis was proposed. The polynuclear cobalt(II), nickel(II), and copper(II) complexes with polyester polycarboxylates were synthesized.     

Electrochemical synthesis of metal and semimetal nanotube-nanowire heterojunctions and their electronic transport properties

Metal and semimetal nanotube-nanowire heterojunction arrays have been achieved by sequential electrochemical-deposition inside the nanochannels of anodic aluminium oxide template with a layer of Au thin enough to leave the pores open.     

Vibrational spectroscopy and analysis of pseudo-tetrahedral complexes with metal imido bonds

A number of assignments have been previously posited for the metal-nitrogen stretch (nu(M-NR)), the N-R stretch (nu(MN-R)), and possible ligand deformation modes associated with terminally bound imides. Here we examine mononuclear iron(III) and cobalt(III) imido complexes of the monoanionic tridentate ligand [PhBP3] ([PhBP3] = [PhB(CH2PPh2)3]-) to clarify the vibrational features for these trivalent metal imides. We report the structures of [PhBP3]FeNtBu and [PhBP3]CoNtBu. Pseudo-tetrahedral metal imides of these types exhibit short bond lengths (ca. 1.65 A) and nearly linear angles about the M-N-C linkages, indicative of multiple bond character. Furthermore, these compounds give rise to intense, low-energy visible absorptions. Both the position and the intensity of the optical bands in the [PhBP3]MNR complexes depend on whether the substituent is an alkyl or aryl group. Excitation into the low-energy bands of [PhBP3]FeNtBu gives rise to two Raman features at 1104 and 1233 cm(-1), both of which are sensitive to 15N and 2H labeling. The isotope labeling suggests the 1104 cm(-1) mode has the greatest Fe-N stretching character, while the 1233 cm(-1) mode is affected to a lesser extent by (15)N substitution. The spectra of the deuterium-labeled imides further support this assertion. The data demonstrate that the observed peaks are not simple diatomic stretching modes but are extensively coupled to the vibrations of the ancillary organic group. Therefore, describing these complexes as simple diatomic or even triatomic oscillators is an oversimplification. Analogous studies of the corresponding cobalt(III) complex lead to a similar set of isotopically sensitive resonances at 1103 and 1238 cm(-1), corroborating the assignments made in the iron imides. Very minimal changes in the vibrational frequencies are observed upon replacement of cobalt(III) for iron(III), suggesting similar force constants for the two compounds. This is consistent with the previously proposed electronic structure model in which the added electron resides in a relatively nonbonding orbital. Replacement of the tBu group with a phenyl ring leads to a significantly more complicated resonance Raman spectrum, presumably due to coupling with the vibrations of the phenyl ring. Polarization studies demonstrate that the observed modes have A(1) symmetry. In this case, a clearer resonance enhancement of the signals is observed, supporting a charge transfer designation for the electronic transitions. A series of isotope-labeling experiments has been carried out, and the modes with the greatest metal-nitrogen stretching character have been assigned to peaks at approximately 960 and approximately 1300 cm(-1) in both the iron and cobalt [PhBP3]MNPh complexes. These results are consistent with a multiple M-N bond for these metal imides.     

Conformation and conformation-dependent properties of chain molecules

This paper is dedicated to the memory of Professor N.A. Platé for his outstanding contributions to polymer science and his extraordinary leadership in the world scientific community. The long-lasting personal and professional relationship with Nikolai came to the end rather untimely, but his enthusiasm for science and people will always be remembered. The rotational isomeric state treatment has been extended to elucidate conformation and conformation-dependent properties of chain molecules occurring under the condition for which some special care is required. Examples include the odd-even effect of n-alkane chains, dipole moment of polymethylmathacrylate (PMMA), enhancement of optical rotation of vinyl polymers, screw-sense reversal of polyaspartates, and the anisotropy of a flexible spacer involved in the main-chain liquid crystal. Major conclusions are as follows: (1) The distinct odd-even effect is a peculiar character of the methylene sequence -(CH₂) _n -attributable to its bond angle (tetrahedral) and rotational preference (trans). In the other chains including carbonate linkages or oxyethylene units, the correlation along the chain unnecessarily accompany the odd-even phenomenon. (2) When the meso dyad of the PMMA chain takes the trans-trans conformation, the two adjacent ester groups are situated at a separation of only ca. 0.27 nm. The strong dipole-dipole interaction between the two polar ester groups may be alleviated by taking a staggered arrangement. The importance of such neighbor-dependent correlation in treating dielectric properties has been pointed out. (3) The amplification of conformational asymmetry has been discussed for two seemingly dissimilar examples: i.e., flexible vinyl polymers having asymmetric side chains and tightly hydrogen-bonded α-helical polypeptides. The conformation of the side chain has been elucidated for each of the enantiomeric forms of the backbone. The small free-energy difference between the two forms may cooperatively trigger a drastic effect in these polymeric systems. (4) A long oxyethylene spacer carrying mesogenic units on both terminals can be rather easily accommodated in the nematic LC phase. The nematic conformation of the spacer was found to play a crucially important role in determining the orientational order and the packing entropy of the nematic state.     

Some electronic properties of TMPD,CA and TCNQ molecules and their mono- and diions

Semiempirical RHF and UHF PPP calculations have been performed on three molecules involved in charge transfer systems. The same set of parameters has been used for the three ionic states of each molecule. Particular attention has been given to the choice of both number and type of configurations taken into account in the Cl treatment following the RHF SCF calculation; it is shown that they have a great influence on the results. Calculations carried out for several experimental molecular geometries showed that their influence is not always negligible. Experimental data have been collected in a critical way. The unique set of parameters gives satisfactory results for the optical spectra of the neutral molecules and monoions but gives a poor agreement for diions. Spin densities appeared to be very sensitive to both the methods of calculations and the variation of parameters.     

Perfluoroalkyl-substituted triazapentadienes and their metal complexes

Triazapentadienides, C(3)F(7)-C(=NR)-N=C(NHR)-C(3)F(7), result from the reaction of primary amines RNH(2) with the fluorinated imine C(3)F(7)-CF=N-C(4)F(9). The aniline derivative (R = Ph) is a weak monoprotic acid in dmso. Its conjugate base exhibits an extensive coordination chemistry. It acts as a bidentate ligand toward the molecular fragments Pd(C(3)H(5)), Rh(c-C(8)H(12)), Ir(c-C(8)H(12)), and Rh(CO)(2). The chelates [C(3)F(7)-C(NPh)-N-C(NPh)-C(3)F(7)](2)M, M = Mg, Mn, Fe, Co, Ni, Cu, Zn, and Pd, were prepared. In the crystallographically characterized Co complex, the metal is 3d(7), S = (3)/(2) and tetrahedrally coordinated. Spin densities at carbon in the C(6)H(5) and C(3)F(7) groups were estimated from the (1)H and (19)F contact shifts. Spin delocalization onto phenyl sp(2) carbons is approximately 10 times greater than onto the fluorinated sp(3) carbons.     

Vibrational states of chlorophyll and related compound molecules. Metal complexes of octaethylchlorin

Fine-structure fluorescence spectra and i.r. spectra of the model compound chlorophyll-Zn-octaethylchlorin (Zn OEC), and its three deuterated derivatives at meso-positions and Zn OEC-¹⁵N₄ have been obtained. Polarization measurements for individual zero-phonon lines show that in the vibronic spectra of the above compounds the totally symmetric vibrations are mainly active. A joint analysis of the experimental data and calculation results of normal vibrations has served as a basis for the interpretation of the spectra obtained as well as resonance Raman spectra. It is pointed out that the vibrations of ethyl substituents largely form a vibrational structure of the vibronic Zn OEC spectrum. An assignment of some lines in a fine-structure spectrum of chlorophyll a is discussed.     

Vibrational and electronic properties of single-walled and double-walled boron nitride nanotubes

We calculated IR, nonresonance Raman spectra and vertical electronic transitions of the zigzag single-walled and double-walled boron nitride nanotubes ((0,n)-SWBNNTs and (0,n)@(0,2n)-DWBNNTs). In the low frequency range below 600 cm⁻¹, the calculated Raman spectra of the nanotubes showed that RBMs (radial breathing modes) are strongly diameter-dependent, and in addition the RBMs of the DWBNNTs are blue-shifted reference to their corresponding one in the Raman spectra of the isolated (0,n)-SWBNNTs. In the high frequency range above ∼1200 cm⁻¹, two proximate Raman features with symmetries of the A_1g (∼1355 ± 10 cm⁻¹) and E_2g (∼1330 ± 25 cm⁻¹) first increase in frequency then approach a constant value of ∼1365 and ∼1356 cm⁻¹, respectively, with increasing tubes’ diameter, which is in excellent agreement with experimental observations. The calculated IR spectra exhibited IR features in the range of 1200–1550 cm⁻¹ and in mid-frequency region are consistent with experiments. The calculated dipole allowed singlet–singlet and triplet–triplet electronic transitions suggesting a charge transfer process between the outer- and inner-shells of the DWBNNTs as well as, upon irradiation, the possibility of a system that can undergo internal conversion (IC) and intersystem crossing (ISC) processes, besides the photochemical and other photophysical processes.     

四苯骈卟啉及其金属配合物的合成

卟啉类化合物作为电子给体在光合作用模拟研究中占据着重要位置 ,在卟啉环上引入供电子基团以增大共轭体系 ,常有利于卟啉环的给电子作用 ,过去常用的卟啉化合物为四苯基卟啉及其衍生物 ,但由于空阻作用 ,四个亚甲基上的苯基不能很好与卟啉环共平面而降低了共轭效应 ,为了寻求一种更有利于卟啉环共轭大Π键形成的结构 ,我们合成了比四苯基卟啉共平面效果更好的卟啉化合物———四苯骈卟啉 (Ｈ2 ＴＢＰ)及其与Ｎｉ2 + 、Ｃｏ2 + 、Ｚｎ2 + 的金属配合物以及研究它的给电子作用效果。四苯骈卟啉配合物早在 1 92 8年就为人们所认识[1] ,但其研…     

Data base for electronic spectra of metal complexes

An information system for electronic spectra of transition elements called ESTE—DBS (DBS for data base system) has been described and discussed. This relational system is divided in two main parts, one containing data extracted from experimental spectra, the second created by simulation on the basis of the ligand field theory and some empirical parameters.     

Electrochemical properties of metal complexes of dithio-acid derivatives and their application in extraction polarography

Metal complexes with dithiocarbamic (dtc), xanthic (xan) and dithiophosphoric (dtp) acids give rise to one or more polarographic waves in dimethylformamide and in mixtures of extracting solvents and ethanol. The electrons are found to be transferred stepwise in the case of unfilled d-shell metal complexes. The shift of half-wave potential depends on the ligand, increasing in the order dtp < xan < dtc. In solvents with low solvation power the electrode processes are more reversible. The linear dependence of the limiting current on the chelate concentration has been used for determining the metal in the organic phase without re-extraction. Pb(II), Bi(III) and As(III) have been separated with dtp as extractant, and the concentrations of Co(II), Ni(II) and Zn(II) complexes (simultaneously extracted) have been determined polarographically.