The ‘triplet-excited region’ in linear polyenes: Real or artifactual?

The geometries for the planar T₁ states of linear polyenes C_nH_n+2 (n=8, 10, 12, 14, 16, 18, 20, and 22) were optimized by ab initio SCI calculations. It was found that the bond alternation which existed in the S₀ state disappears only in the central region of the polyene chain. This is quite similar to the ‘triplet-excited region’ which was observed in PPP SDCI calculations for decapentaene (n=10), tetradecaheptaene (n=14), octadecanonaene (n=18), and docosaundecaene (n=22) (M. Kuki, Y. Koyama, N. Nagae, J. Phys. Chem. 95 (1991) 7171). However, CASSCF calculations performed for octatetraene (n=8) gave considerably different geometries from the SCI geometries. The reason for this is discussed and we conclude that the appearance of the ‘triplet-excited region’ in SCI and SDCI calculations is artifactual.     

Tris-chelate complexes with chiral ligands: In search of diastereoisomeric selectivity with remote stereogenic centres

The chiral ligands, 4,4′-bis{(1S,2R,4S)-(−)-bornyloxy}-2,2′-bipyridine, (1S,2R,4S)-1, and 4,4′-bis{(1R,2S,4R)-(+)-bornyloxy}-2,2′-bipyridine, (1R,2S,4R)-1, have been prepared and characterized by spectroscopic techniques and, for (1S,2R,4S)-1, by single crystal X-ray diffraction. Despite the use of enantiomerically pure ligands, the formation of the complexes [Fe((1S,2R,4S)-1)₃]²⁺, [Ru((1S,2R,4S)-1)₃]²⁺, [Ru((1S,2R,4S)-1)(bpy)₂]²⁺ and [Ru((1R,2S,4R)-1)(bpy)₂]²⁺ proceeds without preference for either the Δ or Λ-diastereoisomers.     

Structural and spectroscopic effects of vibronic coupling in the C2F radical

The lowest three (1²A^′,2²A^′,1²A^′′) potential energy surfaces of the C₂F radical have been studied at the ab initio level, using Multi Reference Configuration Interaction techniques. For linear geometries, the three surfaces correlate with a ²Π and a ²Σ⁺ state, which are very close in energy. Only the X²A^′ ground state was found to be bent, with R_CC=1.271 Å; R_CF=1.276 Å; CCF=165°, and a barrier to linearity of 275 cm⁻¹. The spin–rovibronic energy levels up to J=7/2 have been calculated using a recently developed method [Carter et al., Mol. Phys. 98 (2000) 1967]. Almost all of the resulting levels arise from a strong mixture of two out of three electronic states and their assignment is intrinsically ambiguous. A partial characterization, based on the shape of the vibronic wavefunctions, has been made.     

Investigation on lanthanide binuclear complexes of 1,5-bis-(1′-phenyl-3′-methyl-5′-pyrazolone-4′)-1,5-pentanedione and 2,2′-bipyridine

The coordination of 1,5-bis-(1′-phenyl-3′-methyl-5′-pyrazolone-4′)-1,5-pentanedione (BPMPPD) and 2,2′-bipyridine (bipy) with lanthanide ions in water-alcohol solution has been studied. Binuclear complexes of the types : Ln₂(BPMPPD)₃(bipy)₂·nH₂O (n = 2 for Y, n = 4 for Eu, Gd, Dy, Ho, Er, Tm and Yb); Ln₂(BPMPPD)₃bipy·nH₂O (n = 10 for La, n = 3 for Pr, Nd, Sm and Tb) were formed. The compounds were characterized by elemental analysis, molar conductance, IR, UV, ¹H NMR spectroscopy, thermogravimetric analysis and fluorescence spectra.     

Synthesis, crystal structure and third-order non-linear optical property of heterobimetallic cluster compound [MoOICu3S3(2,2′-bipy)2]

Nest-shaped cluster [MoOICu₃S₃(2,2′-bipy)₂] (1) was synthesized by the treatment of (NH₄)₂MoS₄, CuI, (n-Bu)₄NI, and 2,2′-bipyridine (2,2′-bipy) through a solid-state reaction. It crystallizes in monoclinic space group P2₁/n, a=9.591(2) Å, b=14.820(3) Å, c=17.951(4) Å, β=91.98(2)°, V=2549.9(10) ų, and Z=4. The nest-shaped cluster was obtained for the first time with a neutral skeleton containing 2,2′-bipy ligand. The non-linear optical (NLO) property of [MoOICu₃S₃(2,2′-bipy)₂] in DMF solution was measured by using a Z-scan technique with 15 ns and 532 nm laser pulses. The cluster has large third-order NLO absorption and the third-order NLO refraction, its ₂ and n₂ values were calculated as 6.2×10⁻¹⁰ and −3.8×10⁻¹⁷ m² W⁻¹ in a 3.7×10⁻⁴ M DMF solution.     

Anionic derivatives of pentafluoro-λ-sulfanyl (fluorosulfonyl) acetic acid esters

New ester salts [R₃NH]⁺[F₅SC(SO₂F)C(O)OR′]⁻ where RH, CH₃CH₂ and R′CH₃,(CH₃)₂CH have been prepared from corresponding esters and amines. The sodiumsalt Na[F₅SC(SO₂F)C(O)OCH(CH₃)₂] was used to prepare the following -substitutedderivatives: SF₅CX(SO₂F)C(O)OCH(CH₃)₂, XBr, Cl. The crystal structure of[(C₂H₅)₃NH]⁺[F₅SC(SO₂F)C(O)OCH₃]⁻ was determined and is monoclinic: P2₁/n;a=8.758(2) Å, b=9.645(2) Å and c=19.167(4) Å; β=97.92(3)°; V=1603.6 ų; Z=4.     

La-NMR-spektroskopie an allyllanthan(III)-komplexen

¹³⁹La-NMR chemical shifts were measured for several anionic complexes of formulae Li(C₄H₈O₂)_3/2 [La(ν³-C₃H₅)₄], [Li(C₄H₈O₂)₂][Cp′_nLa(ν³-C₃]H₅)_4−n] (Cp′ = Cp(ν⁵-C₅H₅); n = 1, 2 and Cp′ = Cp * (ν⁵-C₅Me₅); N = 1) and Li[R_nLa(ν³-C₃H₄)₄−n] (R = N(SiMe₃)₂; n = 1, 2 and R = CCsIMe₃; n = 4), as well as for neutral compounds for formulae La(ν³-C₃H₅)₃L_n (L = (C₄H₈O₂)_1.5, (HMPT)₂, TMED), Cp′_nLa(ν³-C₃H₅)_3−n (Cp′= Cp(ν⁵-Cp₅H₅), Cp *(ν⁵-C₅Me₅); n = 1, 2) and La(ν³-C₃H₂)₂X(THF)₂ X = Cl, Br, I). Typical ranges of the ¹³⁹La-NMR chemical shifts were found for the different types of complex independent of number and kind of organyl groups directly bonded to lanthanum.

Zusammenfassung

¹³⁹La-NMR-Spektroskopie wurde an einer Reihe anionischer Allyllanthanat(III)-Komplexe der Zusammensetzung ]- [La)ν³-C₃H₅)₄, [Li(C₄H₈)₂][Cp′_nLa(ν³-C₃H₅)_4−n(Cp′ = Cp(ν⁵-C₅H₅); n = 1, 2 und Cp′ = Cp * (ν⁵-C₅Me₅); N = 1) und Li[R_nLa(ν³-C₃H₅)_4−n (R = B(SiMe₃)₂; n = 1, 2 und R = CCSiMe₃; n = 4 sowie neutraler Allyllanthan(III)-Komplexe der Zusammensetzung La(ν³-C₃H₅)₃L_n (L_n = (C₄H₈O₂)_1.5, (HMPT)₂, TMED), Cp′_n, La(ν³-C₃H₅)_3−n (Cp′ = Cp(ν⁵-C₅H₅), Cp * (ν⁵- Cp₅Me₅); n = 1, 2) und La(ν³-Cp₃H₅)₂X(THF)₂ (X = Cl, Br, I) durchgefürt. In Abhängikeit von der Anzahl und der Art der am Lanthan gebundenen Gruppen wurden für die verschieden Komplextypen charakteristische Resonanzbereiche ermittelt.     

Asymmetric deuteration and deuteriooligomerization of 1-pentene

1-Pentene has been polymerized in the presence of deuterium using as catalyst precursors [Al(CH₃)-O]n and (−)-ethylenebis(4,5,6,7-tetrahydro)-(R)-1-indenylzirconium derivatives ((−)-(R)-EBTHI-ZrX₂, X = CH₃ (I); X = (R)-1′,1″-bi-2-naphtholate (II)). The investigation of 1,2-dideuteriopentane and of the deuteriooligomers thus obtained shows that the (Re) enantioface of the olefin is predominantly involved in the deuteration but its (Si) enantioface in the dimerization and oligomerization. These results, which show the participation of the growing chain in the enantioface discrimination in the stereospecific polymerization of 1-pentene are discussed on the basis of a simple stereochemical model for the transition state of the olefin insertion step.     

Velocity map imaging of the photolysis of n-C4H9Br in UV region

Using velocity map ion imaging technique, the photodissociation of n-C₄H₉Br in the wavelength range 231–267 nm was studied. The results and our ab initio calculations indicated that the absorption of n-C₄H₉Br in the investigated region originated from the excitations to the lowest three repulsive states, as assigned as 1A″, 2A′ and 3A′ in C_s symmetry. Dissociations occurred on the PES surfaces of the three states, terminating in C₄H₉+Br (²P_3/2) or C₄H₉ + Br^* (²P_1/2) as two channels, and being impacted by an avoided crossing between the PES surfaces of the 2A′ and 3A′ states. The transition dipole to the 1A″ state was perpendicular to the symmetry plane, so perpendicular to the C–Br bond. The transitions to the 3A′ state was polarized parallel to the symmetry plane, and also parallel to the C–Br bond. While the transition dipole to the 2A′ state was in the symmetry plane, but formed an angle of about 53.1° with the C–Br bond. We have also determined the avoided crossing probabilities, which affected the relative fractions of the individual pathways, for the photolysis of n-C₄H₉Br near 234 nm and 267 nm.     

On the vibrational spectra and conformational stability of 1,1-dimethylhydrazine from temperature dependent FT-IR spectra of krypton solutions and ab initio calculations

Variable temperature (−105 to −150 °C) studies of the infrared spectra (3500–400 cm⁻¹) of 1,1-dimethylhydrazine, (CH₃)₂NNH₂, in liquid krypton have been carried out. No convincing spectral evidence could be found for the trans conformer which is expected to be at least 600 cm⁻¹ less stable than the gauche form. The structural parameters, dipole moments, conformational stability, vibrational frequencies, and infrared and Raman intensities have been predicted from MP2/6-31G(d) ab initio calculations. The predicted infrared and Raman spectra are compared to the experimental ones. The adjusted r₀ parameters from MP2/6-311+G(d,p) calculations are compared to those reported from an electron diffraction study. The energy differences between the gauche and trans conformers have been obtained from MP2 ab initio calculations as well as from density functional theory by the B3LYP method calculations from a variety of basis sets. All of these calculations indicate an energy difference of 650–900 cm⁻¹ with the B3LYP calculations predicted the larger values. The potential function governing the conformational interchange has been predicting from both types of calculations and comparisons have been made. The barrier to internal rotation by the independent rotor model of the inner methyl group is predicted to have a value of 1812 cm⁻¹ and that of the outer one of 1662 cm⁻¹ from ab initio MP2/6-31G(d) calculations. These values agree well with the experimentally determined values of 1852±16 and 1558±12 cm⁻¹, respectively, from a fit of the torsional transitions with the coupled rotor model. For the coupled rotor model the predicted V′₃₃ (sin 3τ₀ sin 3τ₁ term) value which ranged from 190 to 232 cm⁻¹ is in reasonable agreement with the experimental value of 268±3 cm⁻¹ but the predicted V₃₃ (cos 3τ₀ cos 3τ₁ term) value of −73 to −139 cm⁻¹ is 25% smaller and of the opposite sign of the experimental value of 333±22 cm⁻¹. These theoretical and spectroscopy results are compared to similar quantities of some corresponding molecules.     

A comparative electron correlation treatment in H(2)S-benzene dimer with DFT and wavefunction-based ab initio methods

The S₀ (X¹A′), T₁ (a³A″), S₁ (A¹A″), T₂ (b³A′), and S₂ (B¹A′) states of the (trans-)HONO molecule were studied by using the CASSCF and CASPT2 methods. The CASPT2(//CASPT2) adiabatic and vertical excitation energy values are in good agreement with available experimental data. The CASPT2//CASSCF potential energy curves (PECs) calculations indicate that: (i) all the five states correlate with the products of OH (X²Π) + NO (X²Π); (ii) along each of the T₁, S₁, and T₂ PECs there is a minimum followed by a transition state (barrier); and (iii) the repulsive S₂ PEC crosses the T₂, S₁, and T₁ PECs. The geometries and relative energies for the stationary points along these PECs were calculated at the CASPT2(//CASPT2) level, and the calculations predict that the barrier height value for S₁ is negligibly small (0.0018 eV).     

Fourfold clusters of rovibrational energies in H2Te studied with an ab initio potential energy function

We report here an ab initio investigation of the cluster effect (i.e., the formation of four-member groups of nearly degenerate rotation-vibration energy levels at higher J and K_a values) in the H₂Te molecule. The potential energy function has been calculated ab initio at a total of 334 molecular geometries by means of the CCSD (T) method where the (1s-4f) core electrons of the Te atom were described by an effective core potential. The values of the potential energy function obtained cover the region up to around 10 000 cm⁻¹ above the equilibrium energy. On the basis of the ab initio potential, the rotation-vibration energy spectra of H₂ ¹³⁰Te and its deuterated isotopomers have been calculated with the MORBID (Morse oscillator rigid bender internal dynamics) Hamiltonian and computer program. In particular, we have calculated the rotational energy manifolds for J40 in the vibrational ground state, the ν₂ state, the “first triad” (the ν₁/ν₃/2 ν₂ interacting vibrational states), and the “second triad” (the (ν₁ + ν₂)/(ν₂ + ν₃)/3 ν₂ states) of H₂¹³⁰Te. We have also investigated the cluster formation in the vibrational ground state of H₂ ¹³⁰Te by first fitting the rotational data available from experiment with a modified Watson-type effective Hamiltonian and then using the optimized ground state constants to extrapolate the rotational structure to higher J values. Both the ab initio calculation and the prediction with the effective Hamiltonian show that the cluster formation in H₂Te is very similar to that in H₂Se and H₂S, which we have studied previously. However, contrary to semiclassical predictions, we do not determine any significant displacement of the clusters towards lower J values relative to H₂Se. Hence the experimental observation of the cluster states in H₂Te will be at least as difficult as in H₂Se.     

Alkali exchange reactions: Product-state analysis by laser-induced fluorescence

Internal-energy distribution measurements of reaction products using laser-induced fluorescence (LIF) are reported on two alkali---alkali dimer exchange reactions, Li + Na₂ and Na + K₂. The observation of non-statistical internal-state distribution of the MM′ products implies incomplete randomization of energy; the degree of significant rotational excitation is remarkable.     

Dynamical couplings of the predissociative n = 3 triplet gerade complex of H2

We have performed ab initio configuration interaction calculations for the states involved in the n = 3 triplet gerade complex of H₂. The corresponding radial and rotational couplings needed in collisional studies have been evaluated analytically. Their physical origin, dynamical implications and comparison with previous data are discussed in some detail.     

3-exo,3′-exo-(1R,1′R)-Bithiocamphor — a versatile source for functionally different 3,3′-bibornane derivatives, II. 1 An access to 3-exo,3′-exo-(1r,1′r)-bicamphor and related compounds

3-exo,3′-exo-(1R,1′R)-bicamphor (12) is obtained from 3-exo,3′-exo-(1R,1′R)-bithtiocamphor (3) by condensation with hydrazine hydrate followed by hydrolysis of the resulting dihydropyridazine 11. Deprotonation of 12 with NaH and subsequent treatment with potassium hexacyanoferrate (III) furnishes the 2,2′-dioxo-3,3′-bibornanylidene 13, whilst reduction of 12 with L1AlH₄ affords the 3,3′-biisoborneol 16. Further related transformations to various 2,2′-difunctional 3,3′-bibornane derivatives are described, which are could be of interest as chiral ligands     

Exchange reactions of distibines

Distibines of the type R₂SbSbR′₂ with R = CH₃, R′ = C₂H₅ (1), R = CH₃, R′= n-C₃H₇ (2), R = CH₃, R′= C₆H₅ (3), R = C₂H₅, R′= C₆H₅ (4), R = n-C₃H₇, R′ = C₆H₅ (5), and R = CH₃, R′ = 2,4,6-(CH₃)₂C₆H₂ (6) are formed in equilibria by exchange reactions of the respective distibines of the type R₄Sb₂ and R′₄Sb₂.     

Ab initio prediction of MnOH2/MnOH2 electron transfer reactivity at electron correlation level

An ab initio calculation of electron transfer reactivity of Mn²⁺OH₂/Mn³⁺OH₂ redox system, in gas and in solution, has been made in this paper. The detailed geometry optimization and the scanning of the potential energy surfaces have been carried out at UMP2 (full)/6-311+G^* level. The relevant energy quantities (such as the activation energy and the binding energy) are calculated at different levels of theory (HF, MP2, MP3, MP4 and QCISD and corresponding spin-projection PUHF, PMP2 and PMP3) with the same basis set (6-311+G^*). Both all-electrons and valence electrons have been correlated in energy calculations. The electronic transmission coefficient is calculated using the ab initio potential energy surface slopes and the coupling matrix element determined from the two-state model and the Slater-type d-electron wave functions. The pair distribution function is obtained using both a classical sphere approximation scheme and a novel scheme. The relevant kinetic parameters are obtained at different ab initio levels in terms of the new model. The contact-distance dependence of these parameters and the applicability of the presented models are also discussed.     

Evaluation of the immobilized artificial membrane phosphatidylcholine: Drug discovery column for high-performance liquid chromatographic screening of drug–membrane interactions

Chromatographic retention factors (k′) of a series of eight β-adrenoceptor antagonist compounds (β-adrenolytic drugs) were determined employing an immobilized artificial membrane column (IAM.PC.DD). The influence of mobile phase pH, ionic strength, and organic modifier composition was studied in order to examine column performance. After the IAM.PC.DD columns were exposed to approximately 7000 column volumes of a 0.01 M PBS mobile phase, five out of six columns tested showed significant peak broadening and decreased k′ values indicative of premature column failure. The data suggested that the immobilized phospholipids stationary phase was removed by the 0.01 M PBS mobile phase. The β-adrenolytic drug's log k′_IAM values obtained with an IAM.PC.DD column were compared to an ^esterIAM.PC.MG column for predicting drug membrane interactions. For the linear regression analysis between log k′_IAM and the logarithm of the n-octanol–water partition coefficients (r_IAM.PC.DD=0.8710 vs. r_IAM.PC.MG=0.9538), the C₁₈ HPLC retention factors (r_IAM.PC.DD=0.8408 vs. r_IAM.PC.MG=0.9380), the liposome partition coefficients (r_IAM.PC.DD=0.8887 vs. r_IAM.PC.MG=0.9187), and various pharmacokinetic parameters, significantly better correlations were obtained with the ^esterIAM.PC.MG column than the IAM.PC.DD column.     

四丁基碘化铵催化甲基丙烯酸甲酯的可逆-休眠自由基溶液聚合

以四丁基碘化铵(BNI) 为有机催化剂, 碘单质(I₂) 与偶氮二异庚腈(ABVN) 原位生成的碘代异庚腈为引发剂, 进行甲基丙烯酸甲酯(MMA) 的溶液聚合. 以甲苯为溶剂, MMA:I₂:ABVN的摩尔比为200:1:1.7, 考察了催化剂用量对聚合的影响. 结果表明, 加入催化剂可以缩短诱导期, 当I₂:BNI摩尔比为1:1时聚合反应的诱导期最短(1.7 h); 当BNI:I₂摩尔比为0.25:1~2:1之间时, 聚合物实测分子量与理论值十分接近, 分子量分布较窄, 分子量分布指数(M_w/M_n) 多在1.2以下. 考察了在N,N'-二甲基甲酰胺(DMF)、 四氢呋喃(THF)、 苯甲醚、 苯和甲苯5种溶剂中的聚合反应, 发现在苯和甲苯中聚合可控性最佳, M_w/M_n多在1.2以下; 苯甲醚和THF中聚合速率较快, 聚合物分子量分布较苯中的略宽. 以DMF为溶剂时所得聚合物分子量分布很宽, 聚合可控性差. 核磁共振分析聚合物为碘封端结构, 碘原子封端的聚合物链所占比为91.6%.     

Conformational and structural analysis of N-N′-bis(4-methoxybenzylidene)ethylenediamine

The Schiff base compound, N-N′-bis(4-methoxybenzylidene)ethylenediamine (C₁₈H₂₀N₂O₂) has been synthesized and its crystal structure has been investigated by X-ray analysis and PM3 method. The compound crystallizes in monoclinic space group P2₁/n with a=10.190(1), b=7.954(1), c=10.636(1) Å, β=111.68(1)°, V=801.1(1) ų, Z=2 and D_cal=1.229 Mgm⁻³. The title structure was solved by direct methods and refined to R=0.056 for 2414 reflections [I>3.0σ(I)] by full-matrix anisotropic least-squares methods. The energy profile of the compound was calculated by PM3 method as a function of θ[N1′–C9′–C9–N1]. The most stable molecular structure of the title compound is the anti conformation, which is different in energy by 5.0 and 1.0 kcal mol⁻¹ from the eclipsed conformation I and gauche conformations, (III and V), respectively.