Crystal structure of a novel dimesogen

The title compound, 4-(cholestroxycarbonyl)pentyloxy-4'-heptyloxycarbonylbiphenyl (C₅₃H₇₈O₅), is a novel dimesogen comprising two mesogenic units dissimilar in nature. It crystallizes in the orthorhombic space group P2₁2₁2₁ with cell parameters a = 6.241(3), b = 17.943(5), c = 43.13(5), Z = 4. The structure was solved using SHELXS (Sheldrick, 1997) and refined using SHELXL (Sheldrick, 1997). The final residual was R = 0.0803 for 1769 reflections with I < 2 σ(I). In the crystal phase the molecule is linear and the terminal groups show stretching with higher bond distances. The packing of the molecules shows imbrication, herringbone and stacking along the a, b, and c axes, respectively. The structure also exhibits an intermolecular hydrogen bond of the type CH…O. The space group suggests the possibility of a chiral mesophase.     

Structure and energy of the positively ionized water clusters

Geometry optimization of small (H₂O)_n⁺ clusters (n ≤ 4) at the UHF/4–31 + + G^** level indicates that the cations consist of two fragments: the OH radical and the H_2n−1 O⁺_n−1 ion. The latter can be considered as a thermodynamically stable combination of a distorted H₃O⁺ ion and (n−2) H₂O molecules. The H bond between the fragments becomes weaker with increasing cluster size. Extrapolation of the adiabatic ionization potentials calculated for the (H₂O)_n oligomers (n ≤ 4) at the MP2 level to an infinite cluster size provides the value of approximately 8.7 eV, which can be presumably necessary for the ionization of liquid water in a vacuum. © 1997 John Wiley & Sons, Inc.     

A toyocamycin analogue with the sugar moiety in a syn conformation

The title compound [systematic name: 4‐amino‐5‐cyano‐1‐(β‐d ‐ribofuranosyl)‐7H‐pyrrolo[2,3‐d]pyrimidine hemihydrate], C₁₂H₁₃N₅O₄·0.5H₂O, is a regioisomer of toyocamycin with the ribofuranosyl residue attached to the pyrimidine moiety of the heterocycle. This analogue exhibits a syn glycosylic bond conformation with a χ torsion angle of 57.51 (17)°. The ribofuranose moiety shows an envelope C2′‐endo (²E) sugar conformation (S‐type), with P = 161.6 (2)° and τ_m = 41.3 (1)°. The conformation at the exocyclic C4′—C5′ bond is +sc (gauche, gauche), with a γ torsion angle of 54.4 (2)°. The crystal packing is stabilized by intermolecular O—H...O, N—H...N and O—H...N hydrogen bonds; water molecules, located on crystallographic twofold axes, participate in interactions. An intramolecular O—H...N hydrogen bond stabilizes the syn conformation of the nucleoside.     

Electron correlation effects on the shape of the Kohn–Sham molecular orbital

Even systems in which strong electron correlation effects are present, such as the large near-degeneracy correlation in a dissociating electron pair bond exemplified by stretched H₂, are represented in the Kohn–Sham (KS) model of non-interacting electrons by a determinantal wavefunction built from the KS molecular orbitals. As a contribution to the discussion on the status and meaning of the KS orbitals we investigate, for the prototype system of H₂ at large bond distance, and also for a one-dimensional molecular model, how the electron correlation effects show up in the shape of the KS σ _g orbital. KS orbitals φ^HL and φ^FCI obtained from the correlated Heitler-London and full configuration interaction wavefunctions are compared to the orbital φ^LCAO, the traditional linear combination of atomic orbitals (LCAO) form of the (approximate) Hartree-Fock orbital. Electron correlation manifests itself in an essentially non-LCAO structure of the KS orbitals φ^HL and φ^FCI around the bond midpoint, which shows up particularly clearly in the Laplacian of the KS orbital. There are corresponding features in the kinetic energy density t _s of the KS system (a well around the bond midpoint) and in the one-electron KS potential v _s (a peak). The KS features are lacking in the Hartree-Fock orbital, in a minimal LCAO approximation as well as in the exact one. Received: 11 December 1996 / Accepted: 10 January 1997     

Simple tests for density functional methods

The performance of the currently used generalized gradient approximation density functionals is analyzed using several simple, yet critical requirements. We analyze the effects of the self-interaction error, the inclusion of the exact exchange, and the parameter settings used in the popular three-parameter hybrid density functionals. The results show that the elimination of the self-interaction error from the current density functionals lead to very poor results for H₂. The inclusion of the exact exchange does not significantly influence the self-interaction corrected results. The variation of the A, B, and C parameters of a hybrid DFT method influences the H(SINGLE BOND)H equilibrium bond length through a very simple linear equation, and it is possible to reproduce the experimental H(SINGLE BOND)H distance with appropriate selection of these parameters, although an infinite number of solutions exists. Similar results were obtained for the total energy and the electron density along the internuclear axis. The analysis of the exact KS potential at the bond critical point of the dissociating H₂ molecule shows that, for this property, the second order Moller–Plesset perturbation theory yields a better potential than the density functionals studied in this article. © 1997 John Wiley & Sons, Inc. J Comput Chem 18 : 1534–1545, 1997     

Diphenylalanine in tetrahydrofuran: a highly potent candidate for the development of novel nanomaterials

The peptide di‐l ‐phenylalanine (FF) has emerged as a highly potent candidate for the development of novel nanomaterials. The unprotected peptide was dissolved in 1,1,1,3,3,3‐hexafluoropropan‐2‐ol (HFIP) mixed with tetrahydrofuran (THF) and single crystals of the THF monosolvate, C₁₈H₂₀N₂O₃·C₄H₈O, were grown by slow evaporation in a `vial‐in‐closed‐bottle' system. THF is a molecule that can only act as a hydrogen‐bond acceptor. Thus, the hydrogen‐bond patterns observed in the crystal structures at 100 and 299 K are different compared to that of crystals grown from water and methanol [Mason et al. (2014). ACS Nano. 8 , 1243–1253].     

Synthesis and crystal structure of 2‐isocyano‐4‐methylphenyl diphenylacetate: a rare case of an easily accessible odourless isocyanide

Acidic hydrogen containing 2‐isocyano‐4‐methylphenyl diphenylacetate, C₂₂H₁₇NO₂, (I), was synthesized by the base‐promoted reaction between 5‐methylbenzoxazole and diphenylacetyl chloride. Achiral (I) crystallizes in the chiral P2₁2₁2₁ space group. The C[triple‐bond]N bond length is 1.164 (2) Å and the angle between the OCO and 2‐isocyano‐4‐methylphenyl planes is 69.10 (16)°. Molecules are linked via C=O...H_phenyl and bifurcated N[triple‐bond]C...H_phenyl/N[triple‐bond]C...H_methine hydrogen bonds, forming one‐dimensional arrays.     

A novel chelatofore functionalized spiropyran of the 2‐oxaindane series

A novel chelatofore functionalized spiropyran of the 2‐oxaindane series, namely 8‐formyl‐7‐hydroxy‐3′,3′‐dimethylspiro[2H‐chromene‐2,1′(3′H)‐2‐benzofuran], C₁₉H₁₆O₄, is reported. In the crystalline state, dimers are formed as a result of the π–π stacking of aromatic groups of the 2H‐chromene part of the molecule and C—H...O interactions. The C_spiro—O bond length in the pyran ring is 1.4558 (10) Å, which is longer than or equal to the bond length in thermo‐ and photochromic 2‐oxaindane spiropyrans synthesized previously, except for the 7,8‐benzo/6‐NO₂ derivative, in which this bond length is 1.465 (2) Å.     

Ⅱ conjugation in the butadiene

The π electronic delocalization in trans-C4H6 and cis-C4H6 has been investigated in the frame of ab initio valence bond theory with 6-31G basis set. The result shows that the Csp2-Csp2 single bond length (1.506 A) is only about 0.024 A shorter than the Csp3-Csp3 bond, thus the central bond length shortening would be mainly due to π conjugation. The theoretical resonance energies of the trans-C4H6 and cis-C4H6 are 8.48 and 7.44 kcal/mol, respectively.     

Effect of Ethylene Glycol on the Molecular Organization of H2O in Comparison with Methanol and Glycerol: A Calorimetric Study

Excess partial molar enthalpies of ethylene glycol, H ^E _EG, in binary ethylene glycol–H₂O, and those of 1-propanol, H ^E _IP, in ternary 1-propanol–ethylene glycol (or methanol)–H₂O were determined at 25°C. From these data, the solute–solute interaction functions, H ^E _EG–EG = N(H ^E _EG/n _EG) and H ^E _1P–1P = N(H ^E _1P/n _1P), were calculated by graphical differentiation without resorting to curve fitting. Using these, together with the partial molar volume data, the effect of ethylene glycol on the molecular organization of H₂O was investigated in comparison with methanol and glycerol. We found that there are three concentration regions, in each of which the mixing scheme is qualitatively different from the other regions. Mixing scheme III operative in the solute-rich region is such that the solute molecules are in a similar situation as in the pure state, most likely in clusters of its own kind. Mixing scheme II, in the intermediate region, consists of two kinds of clusters each rich in solute and in H₂O, respectively. Thus, the bond percolation nature of the hydrogen bond network of liquid H₂O is lost. Mixing scheme I is a progressive modification of liquid H₂O by the solute, but the basic characteristics of liquid H₂O are still retained. In particular, the bond percolation of the hydrogen bond network is still intact. Similar to glycerol, ethylene glycol participates in the hydrogen bond network of H₂O via-OH groups, and reduces the global average of the hydrogen bond probability and the fluctuations inherent in liquid H₂O. In contrast to glycerol, there is also a sign of a weak hydrophobic effect caused by ethylene glycol. However, how these hydrophobic and hydrophilic effects of ethylene glycol work together in modifying the molecular organization of H₂O in mixing scheme I is yet to be elucidated.     

Infrared and X-ray studies of hydrogen intercalation in different tungsten trioxides and tungsten trioxide hydrates

Hydrogen intercalation via spillover reaction in various tungsten trioxides leads to the formation of blue hydrogen bronzes. These reversible reactions induce changes in the W-O bond system while maintaining the W-O skeleton. The effect of the intercalation process on the host crystalline structure has been studied with respect to the ν(O-W-O) stretching vibration changes and lattice parameter variations by means of infrared and X-ray diffraction measurements. Among the main results, the intercalation process is shown to be strongly influenced by the structural type of the host compound as well as its amorphous versus crystalline nature. For instance, for the ReO₃ type oxides (monoclinic and cubic WO₃) and hexagonal WO₃, ν(O-W-O) shifts to higher frequency are assigned to a shortening effect of W-O bonds. A W-O bond system arrangement is also measured for the crystallized and amorphous hydrates WO₃ · H₂O, but no detectable changes could be found in the pyrochlore WO₃ and in the hydrate WO₃·1/3 H₂O. Received: 5 March 1997 / Accepted: 21 May 1997     

Analysis of bonding properties in molecular ground and excited states by a Cohen-type bond order

We propose a Cohen-type bond order analysis in terms of orthogonalized atomic basis functions which can be used to analyze NDO wave functions of large organic and metal–organic molecules. It is shown that for small molecules the results gained with this method are in excellent agreement with the same analysis based on ab initio STO -3G wavefunctions. For large planar aromatic systems these all-valence electron bond orders are found to be a consistent generalization of the π-bond order. A simple relation between these bond orders and the corresponding covalent bond energies is established. The method can be easily extended to study excited state multiconfiguration wave functions. We present calculations for C₂H₂, C₂H₄, C₂H₆, and Mn₂(CO)₁₀. The results indicate that the method can be used to discuss the photochemistry of organic and metal–organic compounds.     

An unusual partial occupancy of labile chloride and aqua ligands in cocrystallized isomers of a nickel(II) complex bearing a tripodal N4‐donor ligand

A novel Ni²⁺ complex with the N₄‐donor tripodal ligand bis[(1‐methyl‐1H‐imidazol‐2‐yl)methyl][2‐(pyridin‐2‐yl)ethyl]amine (L), namely, aqua{bis[(1‐methyl‐1H‐imidazol‐2‐yl‐κN³)methyl][2‐(pyridin‐2‐yl‐κN)ethyl]amine‐κN}chloridonickel(II) perchlorate, [NiCl(C₁₇H₂₂N₆)(H₂O)]ClO₄ or [NiCl(H₂O)(L)Cl]ClO₄ ( 1 ), was synthesized and characterized by spectroscopic and spectrometric methods. The crystal structure of 1 reveals an interesting and unusual cocrystallization of isomeric complexes, which are crystallographically disordered with partial occupancy of the labile cis aqua and chloride ligands. The Ni²⁺ centre exhibits a distorted octahedral environment, with similar bond lengths for the two Ni—N(imidazole) bonds. The bond length increases for Ni—N(pyridine) and Ni—N(amine), which is in agreement with literature examples. The bond lengths of the disordered labile sites are also in the expected range and the Ni—Cl and Ni—O bond lengths are comparable with similar compounds. The electronic, redox and solution stability behaviour of 1 were also evaluated, and the data obtained suggest the maintenance of structural integrity, with no sign of demetalation or decomposition under the studied conditions.     

2′‐Deoxyimmunosine: a thiazolo[4,5‐d]pyrimidine nucleoside adopting the syn conformation

The title compound [systematic name: 5‐amino‐3‐(2‐deoxy‐β‐d ‐erythro‐pentofuranosyl)thiazolo[4,5‐d]pyrimidine‐2,7‐(3H,6H)‐dione], C₁₀H₁₂N₄O₅S, exhibits a syn glycosylic bond conformation, with a torsion angle χ of 61.0 (3)°. The furanose moiety adopts the N‐type sugar pucker (³T₄), with P = 33.0 (5)° and τ_m = 15.1 (1)°. The conformation at the exocyclic C4′—C5′ bond is +ap (trans), with the torsion angle γ = 176.71 (14)°. The extended structure is a three‐dimensional hydrogen‐bond network involving O—H...O and N—H...O hydrogen bonds.     

Cooperativity between the Halogen Bond and the Hydrogen Bond in H3N⋅⋅⋅XY⋅⋅⋅HF Complexes (X,Y=F,Cl, Br)

Ab initio calculations are used to provide information on H₃N???XY???HF triads (X, Y=F, Cl, Br) each having a halogen bond and a hydrogen bond. The investigated triads include H₃N???Br₂‐HF, H₃N???Cl₂???HF, H₃N???BrCI???HF, H₃N???BrF???HF, and H₃N???ClF???HF. To understand the properties of the systems better, the corresponding dyads are also investigated. Molecular geometries, binding energies, and infrared spectra of monomers, dyads, and triads are studied at the MP2 level of theory with the 6‐311++G(d,p) basis set. Because the primary aim of this study is to examine cooperative effects, particular attention is given to parameters such as cooperative energies, many‐body interaction energies, and cooperativity factors. The cooperative energy ranges from ?1.45 to ?4.64 kcal mol^?1, the three‐body interaction energy from ?2.17 to ?6.71 kcal mol^?1, and the cooperativity factor from 1.27 to 4.35. These results indicate significant cooperativity between the halogen and hydrogen bonds in these complexes. This cooperativity is much greater than that between hydrogen bonds. The effect of a halogen bond on a hydrogen bond is more pronounced than that of a hydrogen bond on a halogen bond.     

Theoretical study on Pd dimer and trimer interaction with the hydrogen molecule

The H₂ interaction with the Pd dimer and trimer were studied using multiconfigurational self-consistent field (MC-SCF) calculations with the relativistic effective core potential (RECP); the correlation energy correction was included in the extended multireference configuration interaction (MRCI), variational and perturbative to second order. Here, we considered the Pd₂ first six states: ³Σ⁺_u, ¹Σ⁺_g, ³Π_g, ³Δ_xy, ¹Σ⁺_u, and ³Σ⁺_g. For them, the four geometrical approaches included were the side-on H₂ toward Pd₂, for the hydrogen molecule in and out the Pd dimer plane; the perpendicular end-on H₂ toward Pd₂; and the perpendicular end-on Pd₂ to H₂. The Pd₂ ground state is ³Σ⁺_u, which only captures H₂ in the C_2v end-on approach, softly relaxing the H(SINGLE BOND)H bond. The closed-shell ¹Σ⁺_g captures the H₂ molecule in all the approaches considered: The side-on approach of this state presents deep wells and relaxes the H(SINGLE BOND)H bond, and the end-on approach captures H₂ with a relatively longer H(SINGLE BOND)H distance and also a deep well. The ³Π_g state was the only one which did not capture H₂. For the triangular Pd₃ clusters, H₂ was approached in the C_2v symmetry in and out of the Pd₃ plane. In the triangular case, H₂ was absorbed in both spin states, with deep wells and relaxing the H(SINGLE BOND)H distance. The linear Pd₃ singlet and triplet states capture outside of the Pd₃ and break the H(SINGLE BOND)H bond. © 1997 John Wiley & Sons, Inc.     

Hydrosilylation Induced by N→Si Intramolecular Coordination: Spontaneous Transformation of Organosilanes into 1‐Aza‐Silole‐Type Molecules in the Absence of a Catalyst

Our attempts to synthesize the N→Si intramolecularly coordinated organosilanes Ph₂L¹SiH ( 1 a ), PhL¹SiH₂ ( 2 a ), Ph₂L²SiH ( 3 a ), and PhL²SiH₂ ( 4 a ) containing a CH?N imine group (in which L¹ is the C,N‐chelating ligand {2‐[CH?N(C₆H₃‐2,6‐iPr₂)]C₆H₄}^? and L² is {2‐[CH?N(tBu)]C₆H₄}^?) yielded 1‐[2,6‐bis(diisopropyl)phenyl]‐2,2‐diphenyl‐1‐aza‐silole ( 1 ), 1‐[2,6‐bis(diisopropyl)phenyl]‐2‐phenyl‐2‐hydrido‐1‐aza‐silole ( 2 ), 1‐tert‐butyl‐2,2‐diphenyl‐1‐aza‐silole ( 3 ), and 1‐tert‐butyl‐2‐phenyl‐2‐hydrido‐1‐aza‐silole ( 4 ), respectively. Isolated organosilicon amides 1 – 4 are an outcome of the spontaneous hydrosilylation of the CH?N imine moiety induced by N→Si intramolecular coordination. Compounds 1–4 were characterized by NMR spectroscopy and X‐ray diffraction analysis. The geometries of organosilanes 1 a – 4 a and their corresponding hydrosilylated products 1 – 4 were optimized and fully characterized at the B3LYP/6‐31++G(d,p) level of theory. The molecular structure determination of 1 – 3 suggested the presence of a Si?N double bond. Natural bond orbital (NBO) analysis, however, shows a very strong donor–acceptor interaction between the lone pair of the nitrogen atom and the formal empty p orbital on the silicon and therefore, the calculations show that the Si?N bond is highly polarized pointing to a predominantly zwitterionic Si⁺N^? bond in 1 – 4 . Since compounds 1 – 4 are hydrosilylated products of 1 a – 4 a , the free energies (ΔG₂₉₈), enthalpies (ΔH₂₉₈), and entropies (ΔH₂₉₈) were computed for the hydrosilylation reaction of 1 a – 4 a with both B3LYP and B3LYP‐D methods. On the basis of the very negative ΔG₂₉₈ values, the hydrosilylation reaction is highly exergonic and compounds 1 a – 4 a are spontaneously transformed into 1 – 4 in the absence of a catalyst.     

Molecular and crystal structure of the adduct of cyclohexylisonitrile and praseodymium tricyclopentadienide

The crystal structure of (C₅H₅)₃Pr·CNC₆H₁₁ was determined from single-crystal X-ray diffraction data. The monoclinic unit cell of dimensions a = 8.298(3), b = 21.66(1), c = 11.943(4) Å, and β = 104.98(3)° contains four molecules in general positions of space group P2₁/c. Each molecule is composed of three C₅H₅ rings in a nearly exact trigonal array, η⁵-bonded to the Pr atom at a distance of 2.53 Å to the centroid of each ring, plus a single CNC₆H₁₁ adduct attached to the Pr atom along the trigonal axis at 2.65 Å. The presence of a CN triple bond in the isonitrile moiety and the nearly linear CN---C configuration add credence to the previous proposal that there is a pure donor bond from the isonitrile carbon to the metal atom.     

DFT study on the intermolecular interactions between Aun (n = 2–4) and thymine

Density functional B3LYP method with 6-31++G** basis set is applied to optimize the geometries of the luteolin, water and luteolin–(H₂O)_n complexes. The vibrational frequencies are also studied at the same level to analyze these complexes. We obtained four steady luteolin–H₂O, nine steady luteolin–(H₂O)₂ and ten steady luteolin–(H₂O)₃, respectively. Theories of atoms in molecules (AIM) and natural bond orbital (NBO) are used to investigate the hydrogen bonds involved in all the systems. The interaction energies of all the complexes corrected by basis set superposition error, are within −13.7 to −82.5 kJ/mol. The strong hydrogen bonding mainly contribute to the interaction energies, Natural bond orbital analysis is performed to reveal the origin of the interaction. All calculations also indicate that there are strong hydrogen bonding interactions in luteolin–(H₂O)_n complexes. The OH stretching modes of complexes are red-shifted relative to those of the monomer.     

A CASSCF and CCI study of the formation of the Ni2(C2H4) complex

Complete active space SCF and contracted CI calculations have been performed on the potential surface of the Ni₂-C₂H₄ complex in the singlet state. The ethene geometry and position relative to Ni₂ was optimized while the Ni-Ni distance was kept fixed at 2.5 Å.Four possible symmetric geometric arrangements were considered, yielding only an end on -bonded structure as bound. This is a consequence of the charge buildup between the nickel atoms and charge depletion at the ends, coupled with electron mobility along the bond axis, in the nickel dimer.The energy minimum corresponds to a C₂H₄ moiety distorted 21% towards a C₂H₆ geometry, with a bond energy o 24.6 kcal/mol at the CCI level and 28.1 kcal/mol with cluster corrections included. The binding is described by a donation backdonation mechanism. These results are discussed in connection with earlier work on Ni(C₂H₄) and Ni₂(C₂H₄) and in connection with experimental work.