Synthesis and mesomorphism of diacetylene-bridged triphenylene discotic liquid crystal dimers

Connecting two discotic mesogens via a spacer not only stabilizes the columnar mesophase but also leads to the formation of glass columnar phase, and therefore improves the physical properties of discotic liquid crystals as organic semiconductor. Here, we report the synthesis of eight diacetylene-bridged triphenylene discotic liquid crystal dimers, [C18H6(OCnH2n+1)4(OMe)O2C-C8H16-C≡≡ C-]2, 3(n), (n = 4-8), [C18H6(OC6H13)5O2C-C8H16-C≡≡ C-]2, 6 and [C18H6(OC6H13)5O-(CH2)m-C≡≡ C-]2, 8(m), (m = 1, 3) by Eglinto...     

The hapticity of octafluorocyclooctatetraene in its first-row mononuclear transition metal carbonyl complexes: effect of perfluorination

The iron tricarbonyl complex of octafluorocyclooctatetraene was synthesized by Hughes and co-workers and shown by X-ray crystallography to have a trihapto–monohapto structure (η^3,1-C₈F₈)Fe(CO)₃ in contrast to the tetrahapto structure (η⁴-C₈H₈)Fe(CO)₃ formed by the non-fluorinated cyclooctatetraene. This difference has stimulated a comprehensive density functional theoretical study of the octafluorocyclooctatetraene metal carbonyl complexes (C₈F₈)M(CO) _n (n = 4, 3, 2, 1 for M = Ti, V, Cr, Mn, and Fe; n = 3, 2, 1 for M = Co, Ni) for comparison with their hydrogen analogues (C₈H₈)M(CO) _n . In most such systems, the substitution of fluorine for hydrogen leads to relatively small changes in the preferred structures. However, for the iron carbonyl derivatives (C₈X₈)Fe(CO)₃ (X = H, F), the difference observed experimentally has been confirmed by theory with (η^3,1-C₈F₈)Fe(CO)₃ and (η⁴-C₈H₈)Fe(CO)₃ being the lowest energy structures by 4 and 14 kcal/mol, respectively. The ligand exchange reactions C₈H₈ + (C₈F₈)M(CO) _n  → C₈F₈ + (C₈H₈)M(CO) _n are predicted to be exothermic for almost all of the systems considered, with the (η^3,1-C₈X₈)Fe(CO)₃ system being the main exception. This suggests that the C₈F₈ ligand generally bonds more weakly to transition metals than the C₈H₈ ligand in accord with the electron-withdrawing effect of the ligand fluorine atoms.     

Systematic study of (Na n )2 dimer transient state in Na n +Na n collisions (n=8, 9, 19, and 20)

From distance dependent tight-binding molecular dynamics simulations, we systematically study the Na _n +Na _n collision dynamics around the first two closed shells (n=8 and 20). We investigate the stability of sodium cluster dimers (Na _n )₂, for many events with random relative orientation at finite temperature, various impact parameters and incident energies. We find that (Na₈)₂, (Na₉)₂, (Na₁₉)₂ and (Na₂₀)₂ can exist during about 3000 fs in central collisions while they can exist up to about ten thousands fs in peripheral collisions with larger impact parameters in fusion mechanism at c.o.m energy per atomE _cm/n=0.025 eV. We observe that the lower the incident energy, the longer the lifetime of the cluster dimers in both central and peripheral collisions. There is no apparent difference in the dynamical stability of (Na₈)₂ and (Na₉)₂, (Na₁₉)₂ and (Na₂₀)₂ although (Na₈)₂ and (Na₂₀)₂ are respectively slightly colder than (Na₉)₂ and (Na₁₉)₂ for the same incident energy per atom and the same impact parameter.     

Theoretical study of the stability of X N n (n=−1, 0, +1, +2; X=Ag,Cu;N≤25) clusters as a function of size using a non-local density functional formalism

The spherical jellium model and self-consistent Weighted Density Approximation (WDA) to density functional theory have been used to study the stability of X _N ⁿ (n=?1, 0, +1, +2; X=Ag, Cu;N≤25) clusters. The calculated magic numbers coincide with the observed ones. The first (IP1) and second (IP2) ionization potentials of Ag _N and Cu _N as a function of size show the typical oscillations induced by the electronic shell-filling effect. IP1 of Cu _N is about 0.5 eV higher than IP1 of Ag _N in the range studied (N≤25). For both Cu _N and Ag _N , IP1 appears to converge well towards the respective experimental values of the work function. The use of WDA allows us to obtain bound negative clusters of small size or with a nearly empty external shell, which is not possible using the Local Density Approximation (LDA) [1, 2]. However the electron affinity of X _N clusters obtained as the difference of energies of the neutral and the negatively charged clusters, becomes negative forN=2, 3 and 8 (very close to zero forN=8), revealing that WDA needs further refinements.     

Characterization of the new series of quasi one-dimensional compounds(MX4)nY (M =Nb,Ta; X =S,Se; Y =Br,I)

A detailed investigation on the new series of compounds(MX₄)_nY (M =Nb, Ta; X =S, Se; Y =Br, I)is given through structural information and resistivity measurements. All these compounds are built with the same framework which is composed ofMX₄chains and halogen atoms between these chains. It is found that the resistivity behavior is closely related to the metal-metal sequence along theMX₄chain.     

Excitonic interactions in covalently-linked porphyrin dimers

We have studied the absorption spectra, emission spectra, and fluorescence excitation polarization spectra of a series of free base and diprotonated etioporphyrin-I dimers covalently linked through (CH₂)_n bridges, n = 0–8. The absorption spectra of the n = 0 and n = 1 dimer show red shifts, which are largest (≈15 mm) for the Soret band of the n = 0 dimer. The Soret bands of the diprotonated dimers n = 0–3 show splitting (≈500–1000 cm^?1) which can be interpreted by an exciton model assuming a reasonable geometry. The fluorescence spectra and quantum yields are similar to that of the monomer, except for the same red shift seen in absorption; however, the n = 0 diprotonated dimer shows an anomalo vibronic structure. The fluorescence excitation polarization spectra for the n = 0 and the n = 1 dimers differ substantially from the monomer; dimers n ? 3 have fluorescence excitation polarization spectra that suggest that some of the excitation stays localized in one moiety while the r hops to the dimer partner.     

Synthesis and characterization of tri-block fluorinated-n-alkanes

A series of triblock semifluorinated n-alkanes of general formula F(CF₂)_n(CH₂)_m(CF₂)_nF (n = 6, 8 and m = 4, 6, 8) have been synthesized and characterized. The synthesis of triblock compounds was performed in two different ways according to the length of the hydrogenated moiety. Coupling of two molecules of β-(perfluoro-n-alkyl)ethyl iodides leads to the triblock materials F(CF₂)₆(CH₂)₄(CF₂)₆F and F(CF₂)₈(CH₂)₄(CF₂)₈F. The synthesis of compounds with larger hydrogenated part is accomplished in two steps by the addition of perfluoro-n-alkyl iodide F(CF₂)_nI to 1,5-hexadiene and 1,7-octadiene, respectively to give the diiodo-adducts which are subsequently deiodinated to the final triblock products F(CF₂)₆(CH₂)₆(CF₂)₆F, F(CF₂)₆(CH₂)₈(CF₂)₆F, F(CF₂)₈(CH₂)₆(CF₂)₈F and F(CF₂)₈(CH₂)₈(CF₂)₈F. The obtained triblock semifluorinated n-alkanes are characterized by low surface free energies with good lubricant properties usable as additives in ski-wax formulations.     

Crystal structure of L-leucinium tetrafluoroantimonate(III)

The crystal structure of L-leucinium tetrafluoroantimonate(III) of the composition (C₆H₁₄NO₂)SbF₄ (orthorhombic symmetry: a = 6.1459(6) Å, b = 14.994(1) Å, c = 24.789(2) Å, Z = 8, P 2₁2₁2₁ space group) synthesized for the first time is determined. The (C₆H₁₄NO₂)SbF₄ structure represents a new structure type of tetrafluoroantimonate(III). It is formed by (C₆H₁₄NO₂)+ cations and chain complex [Sb₂F₈]_n ²ⁿ anions composed of Sb₂F₈ dimers linked into chains by bridging F atoms. The Sb₂F₈ dimers consist of SbF₃ and SbF₅ groups bound by bridging fluoride atoms of the SbF₅ group. Chains in the structure are linked by N-H…F, N-H…O, and O-H…F hydrogen bonds into a three-dimensional framework.     

Critical temperatures,pressures, and densities for the mixtures CO2–C3H8, CO2–nC4H10, C2H6–C3H8, and C3H8–nC4H10

A simple method is developed to estimate mixture critical temperatures (T_c), pressures (P_c), and densities (ρ_c) as a function of overall composition (X) from near critical region experimental coexistence data. This three-step method is applied to four mixtures, CO₂–C₃H₈, CO₂–nC₄H₁₀, C₂H₆–C₃H₈, and C₃H₈–nC₄H₁₀. Isothermal liquid–vapor coexistence data, which includes temperature, vapor pressure, coexisting densities (ρ^ℓ and ρ^v), and coexisting compositions for the more volatile component (x₁^v and x₁^ℓ) are used. In the first step, the difference of the saturated liquid and vapor densities (ρ^ℓ−ρ^v) is fitted to an empirical function in ((P_c−P)/P_c) to obtain P_c. Then P/P_c and ((ρ^ℓ+ρ^v)/2ρ_c) are simultaneously fitted to functions of a polynomial in (X₁−(x₁^v+x₁^ℓ)/2) yielding estimates of ρ_c and X₁. Finally, the discrete estimated critical data points are fitted with an equation to provide a continuous representation of the critical lines. The method is successfully tested for the mixtures, CO₂–C₃H₈ and CO₂–nC₄H₁₀, for which there is a reasonable amount of isothermal data. The procedure is then applied to the mixtures, C₂H₆–C₃H₈ and C₃H₈–nC₄H₁₀, for which there are sparse data. For all four mixtures, the critical temperature line, T_c vs. X₁, matches literature values within ±0.5%. The critical pressure line, P_c vs. X₁, and critical density line, ρ_c vs. X₁, match literature values, in general, within ±2%.     

Hydrothermal Synthesis and Spectroscopic and Magnetic Behavior of the Mn7(HOXO3)4(XO4)2(X=As, P) Compounds. Crystal Structure of Mn7(HOAsO3)4(AsO4)2

The Mn₇(HOXO₃)₄(XO₄)₂ (X=As, P) compounds have been synthesized by using hydrothermal conditions. The arsenate phase was obtained under autogeneous pressure at 170°C. However, more drastic conditions at both pressure and temperature were necessary in the attainment of the phosphate compound. The crystal structure of Mn₇(HOAsO₃)₄(AsO₄)₂ was solved using single-crystal data. The unit-cell parameters are a=6.810(3) Å, b=8.239(2) Å, c=10.011(4) Å, α=104.31(2)°, β=108.94(3)°, γ=101.25(2)°. Triclinic, P-1 with Z=1. The isostructural Mn₇(HOPO₃)₄(PO₄)₂ phase was characterized from X-ray powder diffraction techniques. The crystal structure of both compounds consists of zig-zag chains constructed by dimeric edge-sharing Mn₂O₁₀ octahedra linked through the MnO₅ trigonal bipyramids. The three-dimensional framework is completed by the connection between isolated MnO₆ entities to the dimers octahedra and trigonal bipyramids. The existence of hydrogenarsenate and hydrogenphosphate anions has been confirmed by IR and Raman spectroscopies. Magnetic measurements indicate the existence of antiferromagnetic interactions in both compounds, which are slightly stronger in the arsenate phase.     

Synthesis and characterization of partially fluorinated ethers

A series of partially fluorinated ethers PFE-m,n with general formula F(CF₂)_mCH₂CH₂O(CH₂)_nH (m = 4, 6, 8 and n = 2, 3, 5, 8, 14, 18, 21) has been synthesized and characterized. The present work aimed to investigate the synthesis of PFE-m,n and evaluate some of their fundamental physico-chemical properties such as: specific gravity, refractive index, viscosity, solid-solid transitions, solubility and amphiphile surface activity in a variety of solvents. Further, a comparison between PFE-m,n and the well known semifluorinated n-alkanes F(CF₂)_m-(CH₂)nH (FHm, n) with the same value of the m/n ratio have been reported.     

Evaluation of the ONIOM(B3PW91:HF) hybrid method for modeling butyltin chlorides

The ONIOM(B3PW91:HF) hybrid method has been evaluated for the purposes of modeling butyltin chlorides, X_nSnCl_4-n (X = n-butyl, sec-butyl, isobutyl, tert-butyl; n = 1, 2, 3). Three different partitioning schemes of a molecule within ONIOM(B3PW91:HF) were taken into account. For each of these partitioning schemes, conformational analyses of the X_nSnCl_4-n molecules were performed and then several molecular properties of the resulting rotamers were calculated. The values of molecular properties obtained by ONIOM(B3PW91:HF) were compared in a statistical manner with the reference values calculated by B3PW91. A careful choice of partitioning scheme for X_nSnCl_4-n allowed ONIOM(B3PW91:HF) to achieve a significant saving in computational cost, together with a relatively small decrease in the accuracy of the X_nSnCl_4-n molecular properties routinely obtained from conformational analysis (structural parameters, etc.). Unfortunately, the hybrid method turned out to be ineffective in reproducing the ¹H, ¹³C and ¹¹⁹Sn NMR chemical shifts in X_nSnCl_4-n accurately.      

Optically active cyclic poly(ether sulfone)s based on chiral 1,1′-bi-2-naphthol

Optically active cyclic poly(ether sulfone)s are prepared from 4-fluorophenyl sulfone and (R)- or (S)-1,1′-bi-2-naphthol. The measurement of MALDI-TOF MS shows that the product is composed of a series of cyclic and linear oligomers where the repeating unit number (n) is from 2 to 12, from which the cyclic dimers (n=2), and cyclic trimer (n=3) have been separated from their homologous compounds by TLC successfully. Specific optical rotation [α]_D²⁵ is −583.0 for (R)-cyclic dimer, +588.0 for (S)-cyclic dimer, +22.7 for (R)-cyclic trimer, and −20.3 for (S)-cyclic trimer. Their properties are also determined by other methods, such as ¹H NMR and CD etc.     

Synthesis and characterization of a new class of polyfluorinated alkanes: tetrakis(perfluoroalkyl)alkane

The synthesis and physico-chemical characterization of 1,1,2,2-tetrakis(perfluoroalkyl-methylene)ethane {[F(CF₂)_nCH₂]₂CH}₂ (n=6, TK6; n=8, TK8) are reported. The synthesis consists of four steps: (1) addition of allyl alcohol to a perfluoroalkyl iodide, F(CF₂)_nI (n=6,8) to give the corresponding iodo-adduct; (2) dehalogenation of the adduct by treatment with zinc in aqueous acetic acid, yielding 3-perfluoro-n-alkyl-1-propene; (3) addition of 3-perfluoro-n-alkyl-l-propene to perfluoroalkyl iodide, F(CF₂)_nI (n=6,8) to give 1,3-perfluoro-n-alkyl-2-iodo-propane; (4) coupling of 1,3-perfluoro-n-alkyl-2-iodo-propane by zinc in acetic anhydride giving the final products. TK6 and TK8 are characterized by very low surface tension values and exhibit very good properties as potential ski-waxes.     

The response of metal clusters toq- andL-dependent external fields

We have calculated the static polarizability and mean excitation energy of metal clusters submitted toq-andL-dependent external fields ofj _L (qr)Y _L0(Ω) type. Use has been made of an Extended Random-Phase Approximation which includes exchange and correlation effects within a local model, and of the spherical jellium model to describe the neutralizing positive background.     

An Ab initio molecular orbital study of the systematics in the photoelectron spectra of halomethanes

Ab initio molecular orbital calculations on fluoro- and chloro-methanes, CH_4—nX_n, predict the correct trends in the photoelectron spectra except in the case of the C(2s) bands of fluoromethanes. Thus, the calculated energies corresponding to the lone pair, σ (CX) and C(1s) bands increase with increasing n as found experimentally; the C(2s) energy in chloromethanes decreases with increasing n, again, in agreement with experiment.     

Vibrational spectra and electronic structure of 1-germatranol, 1,1-quasi-germatrandiole,and 1,1,1-hypogermatrantriole (HO)4−n Ge(OCH2CH2) n NR3−n (R = H,Me; n = 1–3)

IR spectra of 1-germatranol, 1,1-quasi-germatrandiole, 1,1,1-hypogermatrantriole with a general formula (HO)_4?n Ge(OCH₂CH₂) _n NR_3?n (n = 1–3) are obtained. At the B3LYP/aug-cc-pVDZ density functional level the equilibrium structures and vibrational spectra of these compounds along with their hydrogen-bonded dimers are calculated. Based on the calculations the band assignment is performed in the IR spectra of 1-germatranol, 1,1-quasi-germatrandiole, and 1,1,1-hypogermatrantriole. The existence of dimers is manifested in the IR spectra as the absence of bands in the frequency ranges characteristic of the bending vibrations of Ge-OH groups and the presence of bands in the vibrational range of hydrogen-bonded germatranyl groups.     

Electronic properties of aluminum clusters compared with the jellium model

The experimental polarizabilities, ionization potentials and electron affinities of aluminum clusters are compared with jellium predictions. It is found that the clusters have radii and work functions which are close to the jellium model predictions for clusters with more than 13 atoms. The polarizabilities of Al _n correspond with the jellium only forn>40 and the shell structure features in the ionization potentials are anomalous up to 37. We conclude that nonjellium effects are important up ton=40.     

Synthesis and properties of multinuclear cobalt(iii) complexes containing dicarbollide(2−) and dicarbacanastide(4−) anions

A series of chain multinuclear cobaltacarboranes of the general formula [(C₂B₉H₁₁)₂Co _n (C₂B₈H₁₀) _n?1] ^n?, wheren = 4 to 7, were synthesized. These compounds, containing derivatives ofortho-carborane(12) as ligands and dicarbollide C₂B₉H₁ ^2? and bidentate dicarbacanastide C₂B₈H₁₁ ^4? ligands, were studied by IR, UV, and H and¹¹B NMR spectroscopy. The nonequivalence of the dicarbacanastide ligands that occupy different positions in the chain with respect to the terminal dicarbollide ligands was discovered.     

Stability and acidity contributions of heteropolymetalates: a theoretical study of the Keggin and Dawson ions

The Dawson-type anion [X⁽ⁿ⁾₂M₁₈O₆₂]^{2(8 − n)}−, is derived from the Keggin anion [X⁽ⁿ⁾M₁₂O₄₀]^{(8 −n)−} (X=Si, Ge, P, S) by fusing two trivalant shells, producing an oval shaped closed framework. The central oxoanions, contributing an overall charge to the clathratic cluster, retain tetrahedral coordination. Generally, the Dawson heteropolyoxometalates are more thermally stable and catalytically more active than the corresponding Keggin ions. In this work, the comparisons among the Keggin and Dawson ions are addressed in terms of relative stability, hardness and acidity. These predictions are based on the theoretical results obtained from the extended Hückel, EH calculations. This analysis of the Dawson structure presently represents the most significant modelling work on large oxyanions. Absolute comparisons between the EH and density functional are not available for Dawson structures. The correlations between these methods have been shown valid for the Keggin ions and are expected to be similar for the Dawson ions. The substitution chemistry of the central oxoanions is similar to that of the Keggin clusters in both the stability and acidity.