Search

Twenty seven N-(methoxysalicylidene)-haloaniline (halo = F, Cl or Br) compounds were synthesized. The crystal structures of all 27 compounds have been determined at low temperature and are reported herein, along with a variable-temperature neutron diffraction study on two of the compounds. New polymorphs were identified for two of the compounds along with a temperature-induced phase transition for one of the other compounds. Visual observations on the thermochromism of the 27 compounds are also reported. The interplanar angle between the two aromatic rings and the intermolecular interactions in the structures are examined and linked to the visual observations on the thermochromism.

The synthesis and structures of two polymorphs, A and B, of Co(NCS)2(abpt)2 and Ni(NCS)2(abpt)2 are reported. The polymorph structures of A with CoII or NiII were found to be isostructural, as were the corresponding pair of polymorph B structures with the different metals., The synthesis and structures of bis­[4-amino-3,5-bis­(pyridin-2-yl)-1,2,4-triazole-κ2 N 2,N 3]bis­(thio­cyanato-κN)cobalt(II), [Co(NCS)2(C12H10N6)2] or Co(NCS)2(abpt)2, and bis­[4-amino-3,5-bis­(pyridin-2-yl)-1,2,4-triazole-κ2 N 2,N 3]bis­(thio­cyan­ato-κN)nickel(II), [Ni(NCS)2(C12H10N6)2] or Ni(NCS)2(abpt)2, are reported. In both cases, two polymorphs, A and B, were identified and structurally characterized. For both polymorphs, the structures obtained with the different metals, i.e. CoII or NiII, were found to be isostructural. All of the structures contained an intra­molecular N—H⋯N hydrogen bond, C—H⋯N inter­actions and π–π stacking inter­actions. No structural evidence was observed for a thermal spin crossover for either of the Co(NCS)2(abpt)2 polymorphs between 300 (2) and 120 (2) K.

Reaction of complex (ArN)Mo(H)(Cl)(PMe3)3 (1) with BPh3 and silane H3SiPh affords a new silyl complex (ArN)Mo(SiH2Ph)(Cl)(PMe3)2 (3) that catalyses facile H–H/Si–H exchange. EXSY experiments suggest that this exchange does not involve the classical pathways such as oxidative addition of hydrogen or silane to the complex or σ-bond metathesis. It is suggested that the exchange may occur in an FLP cage comprised by the complex and the silane.

The iron(ii) salt [Fe(bpp)2](isonicNO)2·HisonicNO·5H2O (1) (bpp = 2,6-bis(pyrazol-3-yl)pyridine; isonicNO = isonicotinate N-oxide anion) undergoes a partial spin crossover (SCO) with symmetry breaking at T1 = 167 K to a mixed-spin phase (50% high-spin (HS), 50% low-spin (LS)) that is metastable below T2 = 116 K. Annealing the compound at lower temperatures results in a 100% LS phase that differs from the initial HS phase in the formation of a hydrogen bond (HB) between two water molecules (O4W and O5W) of crystallisation. Neutron crystallography experiments have also evidenced a proton displacement inside a short strong hydrogen bond (SSHB) between two isonicNO anions. Both phenomena can also be detected in the mixed-spin phase. 1 undergoes a light-induced excited-state spin trapping (LIESST) of the 100% HS phase, with breaking of the O4W⋯O5W HB and the onset of proton static disorder in the SSHB, indicating the presence of a light-induced activation energy barrier for proton motion. This excited state shows a stepped relaxation at T1(LIESST) = 68 K and T2(LIESST) = 76 K. Photocrystallography measurements after the first relaxation step reveal a single Fe site with an intermediate geometry, resulting from the random distribution of the HS and LS sites throughout the lattice., A proton migration across a short strong hydrogen bond can be triggered by spin crossover of a remote Fe2+ cation, with the onset of a photoinduced activation energy barrier for proton motion at low temperatures.

The crystal structure of the radical ferromagnet 1a at 2 K reveals a contraction in the unit cell c constant which, at the molecular level, translates into a decrease in slippage of the radical π-stacks and an increase in ferromagnetic exchange interactions along the stacking axis. The results of BS-DFT calculations using long-range corrected functionals are consistent with an overall ferromagnetic topology.

Three {[(isoxazol-3-yl)imino]­meth­yl}phenols were synthesized and structurally characterized. All three structures contain an intra­molecular O—H⋯N hydrogen bond and none were found to be strongly thermochromic., The synthesis and structures of three isoxazole-containing Schiff bases are reported, namely, (E)-2-{[(isoxazol-3-yl)imino]­meth­yl}phenol, C10H8N2O2, (E)-2-{[(5-methyl­isoxazol-3-yl)imino]­meth­yl}phenol, C11H10N2O2, and (E)-2,4-di-tert-butyl-6-{[(isoxazol-3-yl)imino]­meth­yl}phenol, C18H24N2O2. All three structures contain an intra­molecular O—H⋯N hydrogen bond, alongside weaker inter­molecular C—H⋯N and C—H⋯O contacts. The C—O(H) and imine C=N bond lengths were consistent with structures existing in the enol rather than the keto form. Despite having dihedral angles

Three di-tert-butyl-substituted N-salicylideneaniline derivatives were synthesized, structurally characterized and their chromic properties investigated. Polymorphism was found to affect the photochromic behaviour of the first com­pound, while the second two com­pounds were found to display a temperature-induced phase transition. All of the structures contained an intra­molecular O—H⋯N hydrogen bond., The synthesis, single-crystal structures and chromic behaviour of three related Schiff bases, namely, (E)-2,4-di-tert-butyl-6-{[(4-fluoro­phen­yl)imino]­meth­yl}phenol, C21H26FNO, 1, (E)-2,4-di-tert-butyl-6-{[(4-chloro­phen­yl)imino]­meth­yl}phenol, C21H26ClNO, 2, and (E)-6-{[(4-bromo­phen­yl)imino]­meth­yl}-2,4-di-tert-butyl­phenol, C21H26BrNO, 3, are reported. Two polymorphs of 1 were obtained, which were found to have different photochromic properties. Schiff bases 2 and 3 were found to be isostructural and underwent a phase transition upon cooling which was attributed to the dynamic disorder in one of the tert-butyl groups resolving at low temperature. All of the structures were found to exist in the enol rather than the keto form based on the C—O(H) and imine C=N bond lengths, and contained an intra­molecular O—H⋯N hydrogen bond alongside weaker inter­molecular C—H⋯O contacts.

The spin-crossover behaviour of [Fe(abpt)2(NCS)2] (abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) polymorphs B and D have been studied using single crystal X-ray diffraction to monitor changes in structural features. High pressure single crystal measurements on polymorph B showed that it underwent a monoclinic P21/n (Z’ = 0.5) to triclinic P-1 (Z’ = 2 x 0.5) phase transition between 11.5-13.5 kbar. At which point, it also starts to undergo a thermally inaccessible spin crossover. In polymorph D which also crystallises in the mononclinic space group P21/n (Z’ = 2 x 0.5) one of the unique Fe centres undergoes a thermal spin transition. It also displays light-induced excited spin-state trapping (LIESST), and a structure has been obtained at 30 K through continuous irradiation with a 670 nm 5 mW CW laser. In addition high pressure single crystal measurements on polymorph D showed a stepped pressure induced spin transition. At ~9.6 kbar one of the unique Fe centres had undergone a spin transition and by ~15 kbar both of the unique Fe centres are shown to be essentially low spin, a situation that is thermally inaccessible. Crystallographic data were collected for both polymorphs using variable temperature or high pressure single crystal X-ray diffraction to allow changes in cell parameters, bond lengths and distortion parameters to be monitored for the spin crossover or phase transitions.

Quaternary 4-(2-naphthyl)pyridinium salts with various N-substituents were synthesized. The structure of these salts was determined by X-ray crystallography. The self-assembly of the salts with cavitand molecules – β- and γ-cyclodextrins and cucurbit[7,8]urils – in aqueous solutions was studied by electronic spectroscopy and 1H NMR spectroscopy, including spectrophotometric, fluorescence, and 1H NMR titrations. The formation of inclusion complexes of different stoichiometry and stability, was observed, depending on the structure of N-substituent in the quaternary salt and the cavitand nature and cavity size. The complex formation with cucurbiturils results in considerable changes in the absorption and fluorescence spectra of naphthylpyridine derivatives. Motion of the guest molecules in the cavitand cavities was detected. The X-ray diffraction study was carried out for two polymorphs of 2 : 1 complexes formed by betaine type naphthylpyridine and cucurbit[8]uril, in which the cavitand was located either above the naphthalene residues of a dimeric pair of guest molecules or above the centers of their conjugated moieties.

The spin crossover salt [Fe(bpp) 2 ](isonicNO) 2 ·2.4H 2 O ( 1 ·2.4H 2 O) (bpp = 2,6‐bis(pyrazol‐3‐yl)pyridine; isonicNO = isonicotinate N‐oxide anion) exhibits a very abrupt spin crossover at T 1 /2 = 274.4 K. This triggers a supramolecular linkage (H‐bond) isomerization that responds reversibly towards light irradiation or temperature change. Isotopic effects in the thermomagnetic behaviour reveal the importance of hydrogen bonds in defining the magnetic state. Further, the title compound can be reversibly dehydrated to afford 1 , a material that also exhibits spin crossover coupled to H‐bond isomerization, leading to strong kinetic effects in the thermomagnetic properties.

A novel poly­morph of (E)-4-bromo-2-[(phenyl­imino)­meth­yl]phenol is reported, with a dihedral angle between the planes of the two aromatic rings of 45.6 (1)°, significantly different to that of the previously published poly­morph. The structure contains an intra­molecular O—H⋯N hydrogen bond forming an S(6) ring., A new poly­morph of (E)-4-bromo-2-[(phenyl­imino)­meth­yl]phenol, C13H10BrNO, is reported, together with a low-temperature structure determination of the previously published poly­morph. Both poly­morphs were found to have an intra­molecular O—H⋯N hydrogen bond between the phenol OH group and the imine N atom, forming an S(6) ring. The crystals were observed to have different colours at room temperature, with the previously published poly­morph being more orange and the new poly­morph more yellow. The planarity of the mol­ecule in the two poly­morphs was found to be significantly different, with dihedral angles (Φ) between the two aromatic rings for the previously published ‘orange’ poly­morph of Φ = 1.8 (2)° at 120 K, while the new ‘yellow’ poly­morph had Φ = 45.6 (1)° at 150 K. It was also observed that both poly­morphs displayed some degree of thermochromism and upon cooling the ‘orange’ poly­morph became more yellow, while the ‘yellow’ poly­morph became paler upon cooling.

The physicochemical properties of highly stable supramolecular donor–acceptor (D–A) complexes of a bis(18-crown-6)azobenzene (weak π-donor) with a series of bis(ammonioalkyl) derivatives of viologen-like molecules (π-acceptors) in acetonitrile were studied using cyclic voltammetry, UV–vis absorption spectroscopy, 1H NMR spectroscopy, and density functional theory (DFT) calculations. The crystalline structures of the bis(crown)azobenzene and its complex with a bis(ammoniopropyl) derivative of 2,7-diazapyrene were determined by X-ray diffraction analysis. In solution, all of the supramolecular D–A complexes studied have a pseudocyclic structure owing to ditopic coordination of the ammonium groups of the acceptor to the crown ether moieties of the donor. These complexes show somewhat lower stability as compared with the previously studied complexes of the related derivative of stilbene (strong π-donor), which is explained by the relatively weak intermolecular charge-transfer (CT) interactions. Time-dependent DFT calculations predict that the low-energy CT transition in the D–A complex of the bis(crown)azobenzene with a bis(ammoniopropyl) derivative of 4,4′-bipyridine lies between the local ππ* and nπ* transitions of the azobenzene. The absorption band associated with the CT transition is indiscernible in the spectrum since it is overlapped with broad and more intense ππ* and nπ* bands. It was found that the E → Z photoisomerization quantum yield of the bis(crown)azobenzene decreases by almost an order of magnitude upon the complexation with the 4,4′-bipyridine derivative. This effect was tentatively attributed to the intermolecular electron transfer that occurs in the 1ππ* excited state of the azobenzene and competes with the 1ππ* → 1nπ* internal conversion.

Alternative (‘repeat’) determinations of organic crystal structures deposited in the Cambridge Structural Database are analysed to characterise the nature and magnitude of the differences between structure solutions obtained by diffraction methods. Of the 3132 structure pairs considered, over 20% exhibited local structural differences exceeding 0.25 Å. In most cases (about 83%), structural optimisation using density functional theory (DFT) resolved the differences. Many of the cases where distinct and chemically significant structural differences remained after optimisation involved differently positioned hydroxyl groups, with obvious implications for the correct description of hydrogen bonding. 1H and 13C chemical shifts from solid-state NMR experiments are proposed as an independent methodology in cases where DFT optimisation fails to resolve discrepancies., DFT optimisation often resolves conflicting crystal structure determinations, with NMR shifts helping in cases where optimisation diverges to different structures.

Two new coordination polymers [Cu(btzx)2(MeOH)2](NO3)2 (1) and [Cu(btrcy)2(H2O)2](ClO4)2·btrcy (2) have been synthesized by reacting two bis-triazole/tetrazole-ligands namely m-xylylene-bis(tetrazole) (btzx) and bis(1,2,4-triazole)-trans-cyclohexane (btrcy) with Cu(NO3)2 and Cu(ClO4)2 respectively in a 1:3 metal/ligand ratio. These compounds are shown to form X-ray quality single-crystals under different conditions, and the crystal structures have been determined by single-crystal X-ray diffraction (SXRD). The SXRD data analysis revealed that 1 and 2 are 1D looped chain and 2D-square grid coordination polymers, respectively. More interestingly, the 2D-square grid architecture in 2 acts as an excellent host for the large guest ligand molecule btrcy, which is encapsulated within the voids of the 2D coordination polymer., info:eu-repo/semantics/published

The ethylene dimerization performance of a range of bis(imido)tungsten pre-catalysts, after activation with aluminum co-catalysts, has been assessed. The best performing system achieved an activity of 409,410 (mol C2H4)(mol W)–1h–1 [79.6 wt% 1-butene] with a 1-butene selectivity of 82.4 wt% [290,770 (mol C2H4)(mol W)–1h–1 activity]. In addition to selected previously reported variants, the symmetrical bis(imido)tungsten(VI) complexes [WCl2(NPh)2(tmeda)] (3) and [WCl2(NR)2(dme)] [R = 2,4,6-trifluorophenyl, 7; 2,4,6-triphenylphenyl, 8; 2,4,6-tris(trifluoromethyl)phenyl, 9], were prepared. A series of unsymmetrical bis(imido)tungsten(VI) complexes [WCl2(NDipp)(NR)(dme)] (R = iPr, 11; tBu, 12; 2,4,6-trimethylphenyl, 13; 2,4,6-trichlorophenyl, 14; 2,4,6-trifluorophenyl, 15; 2,6-dinitrophenyl, 16; 2,4,6-triphenylphenyl, 17) were also synthesized using an improved version of a previous preparative route that eases purification. The molecular structures of complexes 5-13 and 15-17 were determined by X-ray crystallographic analysis. Catalysis employing complexes 1-17 unveils a complicated relationship between steric and electronic factors that affects activity and catalyst lifetime, however selectivity is dominated by electronic considerations. Higher reaction temperatures were shown to favor 1-butene selectivity and higher activity, whilst replacement of EtAlCl2 with MeAlCl2 as co-initiator was found to be detrimental. Tungsten(IV) species were demonstrated to be unlikely as the active species during catalysis. Studies of catalysis runs undertaken to varying productivities found that during the nascent phase of reaction a notably lower activity is observed, whilst the selectivity favors C8+ formation during this period, most likely due to activation processes still occurring. The rate of formation of 1-butene was shown to increase with productivity, as a result of the greater solubility of ethylene in the 1-butene generated compared to the chlorobenzene solvent. The formation of C6 by-products was shown to be independent of 1-butene concentrations, consistent with a mechanism whereby 1-butene is only incorporated into secondary products when it reacts prior to dissociation from the tungsten center.

The coordination properties of the 2-aryl-1,3,2-dioxaphospholane 2,6-(CF3)2C6H3P(OCH2)2 1 (L) have been investigated, by reaction with elemental selenium in solution to form the phosphorus(V) oxidation product 2,6-(CF3)2C6H3P(Se)(OCH2)2 2, and with metal-containing precursors to form three new complexes trans-[PdCl(μ-Cl)(L)]2 3, cis-[PdMe2L2] 4 and [AuCl(L)] 5. All of the metal complexes have been characterised by single-crystal X-ray structure determination.

The complex formation of thiamonomethine cyanine dyes bearing two N-ammoniohexyl or two N-ethyl substituents with cucurbit[5,7]urils (CB[5,7]) in aqueous solutions was studied by electronic and 1H NMR spectroscopy, including spectrophotometric, fluorescence, and 1H NMR titration methods. It was found that CB[5] forms external complexes with the dyes, while CB[7] forms internal (inclusion) complexes of 1:1 and 1(dye):2(CB[5,7]) composition. The complexation with CB[5,7] changes the absorption spectra of cyanine dyes and induces a considerable fluorescence enhancement. The stability constants of the complexes were determined (logK1:1 varies in the range from 3.53 to more than 6, and logK1:2 varies in the range from 3.5 to 4.32). The dye with ammoniohexyl substituents forms more stable complexes owing to hydrogen bond formation between the NH3+ groups and the carbonyl groups of the CB[5,7] portals. The structure of supramolecular complexes was confirmed by quantum chemical calculations.

The spin crossover behaviour of [Fe(abpt)2(NCSe)2] (abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole) polymorph A has been examined using single crystal X-ray diffraction and variable temperature UV-Vis transmission spectroscopy. The crystal structure of A is reported at sixteen temperatures between 30 and 375 K, all of which are in the monoclinic space group P21/n with Z’ = 0.5. Changes in the crystallographic cell parameters, bond lengths, distortion parameters and intra and intermolecular interactions between 375 K and 30 K are discussed. Continuous irradiation with a 670 nm, 5 mW CW laser at 30 K enabled a light induced excited spin state trapping (LIESST) metastable high spin structure, HS*, to be obtained.

Binding of alkanediammonium ions +H3N(CH2)nNH3+, n = 2–6, to (E)-bis(18-crown-6)stilbene initiates the [2 + 2] photocycloaddition reaction leading mainly to the rctt isomer of 1,2,3,4-tetrakis(benzo-18-crown-6)cyclobutane. The high efficiency and stereoselectivity of this photoreaction in dilute solution are due to the formation of bis-pseudosandwich complexes consisting of two stilbene molecules and two alkanediammonium ions. With a decrease in the length of the polymethylene spacers in the 2:2 complex, the quantum yield of supramolecular [2 + 2] photocycloaddition increases from 0.02 to 0.27, while the quantum yield of the competing E–Z photoisomerization decreases from 0.12 to 0.06. Spectrophotometric observations and density functional theory calculations revealed that (Z)-bis(18-crown-6)stilbene, unlike the E isomer, is able to form pseudocyclic 1:1 complexes with +H3N(CH2)nNH3+, n = 2–6, owing to the proximity of two crown ether moieties. The peculiar spectral properties of these complexes are associated with large torsion angles around the ethylene–benzocrown single bonds. X-ray diffraction analysis showed that co-crystallization of (E)-bis(18-crown-6)stilbene with 1,6-hexanediammonium diperchlorate affords a linear polymer in which the alternating stilbene molecules and diammonium ions are connected by hydrogen bonds.

A novel compound 2-chloro-3,6-bis-(quinolin-8-yloxymethyl)-quinoline 3 bearing a tri-quinoline moiety has been synthesized from 2-chloro-3,6-dimethyl quinoline 1 and 8-hydroxy quinoline 2 using dry acetone and K 2 CO 3 as a base. 3 has been characterized by using FT-IR, FT-Raman, UV–Vis, 1 H NMR, 13 C NMR spectra and single crystal X-ray diffraction methods. We have also made a combined experimental and theoretical study on the molecular structure, vibrational spectra, NMR, FT-IR, FT-Raman and UV–Vis spectra of 2-chloro-3,6-bis-(quinolin-8-yloxymethyl)-quinoline. The theoretical studies of the title compound have been evaluated by using density functional theory calculations using B3LYP/6-31+G(d,p) and M06-2X/6-31+G(d,p) level of theories. The calculated theoretical values were found to be in good agreement with the experimental findings. The single crystal structure 3 crystallized in the orthorhombic space group Pna 2 1 . The compound 3 exhibits higher cytotoxicity in human cervical cancer cell lines (HeLa) than human breast cancer cell lines (MCF7).

The niobium and tantalum imido complexes [CpMCl2(NDipp)], [MCl3(NR)(dme)] (R = tBu, Ph, 2,6‐iPr2C6H3 (Dipp), and Mes), and [TaCl3(NDipp)(tmeda)] were tested in combination with EtAlCl2 for the dimerization of ethylene. The niobium systems afforded dimers or polymers, depending on the nature of the imido ligand, with overall productivities in the range 720 to 13,720 (mol C2H4)(mol Nb)‐1. The nature of the polyethylene produced (LDPE or HDPE) depended on the imido ligand and the niobium concentration at which catalysis was run. In contrast, the tantalum/dme systems all mediated ethylene dimerization with productivities of up to 4,503 (mol C2H4)(mol Ta)–1, with overall selectivities to butenes of between 73 ‐ 81 wt%; selectivity within the dimer fraction to 1‐butene was in the range 72 to 100%. The productivity of [TaCl3(NDipp)(tmeda)] was six times higher than that of its dme‐bearing counterpart, but at the cost of selectivity to 1‐butene. For the tantalum imido‐mediated ethylene dimerization the composition of the product slate formed is indicative of a metallacyclic mechanism being operative.

Invited for the cover of this issue are Yann Garcia from Université catholique de Louvain, Belgium, and collaborators from partner universities and research centers. The cover image shows the square grid shape of an unprecedented Cu(II) coordination polymer with an “ancient temple architecture”.

The acylation of unsymmetrical N-benzylbispidinols in aromatic solvents without an external base led to the formation of supramolecular gels, which possess different thicknesses and degrees of stability depending on the substituents in para-positions of the benzylic group as well as on the nature of the acylating agent and of the solvent used. Structural features of the native gels as well as of their dried forms were studied by complementary techniques including Fourier-transform infrared (FTIR) and attenuated total reflection (ATR) spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and small-angle X-ray scattering and diffraction (SAXS). Structures of the key crystalline compounds were established by X-ray diffraction. An analysis of the obtained data allowed speculation on the crucial structural and condition factors that governed the gel formation. The most important factors were as follows: (i) absence of base, either external or internal, (ii) presence of HCl, (iii) presence of carbonyl and hydroxyl groups to allow hydrogen bonding, and (iv) presence of two (hetero)aromatic rings at both sides of the molecule. The hydrogen bonding involving amide carbonyl, hydroxyl at position 9, and, very probably, ammonium N-H+ and Cl&minus, anion appears to be responsible for the formation of infinite molecular chains required for the first step of gel formation. Subsequent lateral cooperation of molecular chains into fibers occurred, presumably, due to the aromatic &pi, &minus, &pi, stacking interactions. Supercritical carbon dioxide drying of the organogels gave rise to aerogels with morphologies different from that of air-dried samples.

The acylation of unsymmetrical N-benzylbispidinols in aromatic solvents without an external base led to the formation of supramolecular gels, which possess different thicknesses and degrees of stability depending on the substituents in para-positions of the benzylic group as well as on the nature of the acylating agent and of the solvent used. Structural features of the native gels as well as of their dried forms were studied by complementary techniques including Fourier-transform infrared (FTIR) and attenuated total reflection (ATR) spectroscopy, atomic force microscopy (AFM), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and small-angle X-ray scattering and diffraction (SAXS). Structures of the key crystalline compounds were established by X-ray diffraction. An analysis of the obtained data allowed speculation on the crucial structural and condition factors that governed the gel formation. The most important factors were as follows: (i) absence of base, either external or internal; (ii) presence of HCl; (iii) presence of carbonyl and hydroxyl groups to allow hydrogen bonding; and (iv) presence of two (hetero)aromatic rings at both sides of the molecule. The hydrogen bonding involving amide carbonyl, hydroxyl at position 9, and, very probably, ammonium N-H+ and Cl− anion appears to be responsible for the formation of infinite molecular chains required for the first step of gel formation. Subsequent lateral cooperation of molecular chains into fibers occurred, presumably, due to the aromatic π−π-stacking interactions. Supercritical carbon dioxide drying of the organogels gave rise to aerogels with morphologies different from that of air-dried samples.

Liquid crystal n-(alkyloxybenzilidene)-n'-toluidines R−O−C6H4−CH = N−C6H4−CH3 (R = C9H20 1 and C10H21 2) have been investigated by single crystal X-ray structural analysis. The investigation of 2 h...

A series of cross-conjugated dienones was synthesized to study the dependence of physicochemical characteristics on the nature of substituents in the aromatic groups of symmetric cyclopentanone dibenzylidene derivatives. The structure of compounds was established by electronic, IR, and NMR spectroscopy and X-ray diffraction study. All the compounds obtained possess the E,E-geometry. In the crystalline state, the arrangement of the dienone molecules is unfavorable for the intermolecular [2+2] photocycloaddition to take place. The low-temperature phases transition for unsubstituted diphenyl derivative of cyclopentanone was detected using variable-temperature X-ray diffraction and differential scanning calorimetry. Oxidation and reduction potentials of the dienones were measured by cyclic voltammetry. Their dependence on the nature and placement of substituents in the benzene rings was demonstrated. A linear correlation (R = 0.9343) between the difference of electrochemical oxidation and reduction potentials and the energy of the long-wavelength absorption maximum was found, that allows us to recommend the use of the data obtained in the correlation analysis of other compounds of this class.

Polymorphism in racemic pharmaceutical compounds is relatively unexplored. However, this phenomenon may provide an additional tool to crystal engineering, opening the doors to rational design of chiral resolution, chiral enrichment, and chiral purification of pharmaceutical compounds. In this work we report two racemic polymorphs occurring for the nitrate salt of the antidepressant drug fluoxetine (FLX): a racemate (P21/n, Z = 4, Z′ = 1) and a kryptoracemate (Pca21, Z = 4, Z′ = 2). The relative stability of these polymorphs was established through a combination of techniques, namely, differential scanning calorimetric (DSC), thermogravimetric analysis (TGA), hot stage microscopy (HSM), and solubility measurements. Though the two polymorphs share some structural features, the N+–H···O– hydrogen bonds have created dissimilar racemic motifs in their packing, resulting in different enantiomer orientations. The racemate is more stable over the temperature ranges we studied and is monotropically related to kryp...

New 4-pyridine-derived styryl dyes having an ammonioalkyl N-substituent in the pyridine moiety and various substituents in the benzene moiety were synthesized. The formation of pseudodimeric complexes of ammonioalkyl styryl dye derivatives with 18-crown-6-containing styryl dyes of the 4-pyridine, 4-quinoline, and 2-benzothiazole series was studied by 1H NMR in MeCN-d3. It was found that the stability of supramolecular complexes is mainly determined by the monotopic interaction of the ammonioalkyl group with the crown ether moiety via hydrogen bonding. The components of pseudodimeric complexes undergo stereospecific cross-[2+2] photocycloaddition reaction to give unsymmetrical rctt isomers of cyclobutane derivatives owing to the syn-head-to-tail arrangement of components in the initial complex. The efficiency of photoreaction is affected by the N-substituent length, the nature of the substituent in the benzene ring of the ammonioalkyl component, and the nature of the heterocyclic residue of the crown-containing component. The structures of dyes, pseudodimeric complexes, and the cyclobutane derivative were studied by X-ray diffraction.

Hydrogen bonding from a urea group to hydrogen bond acceptor anions can adopt either R_2^1 (6) or R_2^2 (8) motifs depending on the proximity of hydrogen bond acceptor atoms. However, for the sterically bulky and weaker hydrogen bond acceptor triflate anion, hydrogen bond acceptor polymorphism is observed

New styryl dyes of the 2-benzoselenazole series which contain iodide, triiodide, and tosylate anions were synthesized. Crystals of these compounds were grown in different crystal forms – solvent free and hydroquinone, benzene or ethyl acetate solvated ones. X-ray structural studies of the crystals shows that those containing tosylate and triiodide anions form the centrosymmetrically related stacking motif, typical for styryl dye cations and favorable for [2 + 2] photocycloaddition (PCA) reactions. This reaction takes place in crystals with tosylate anions as a single crystal-to-single crystal process. On the contrary, in the triiodide dye crystals, the PCA reaction is lacking, probably due to a weak directional interaction of the selenium atoms with the anions. The iodide dye crystals demonstrate non-typical packing for styryl dyes and manifest as a two-dimensional close packing motif of the cations which is unfavorable for cycloaddition.

The syntheses of novel Group 5 and Group 6 hydrosilylamido complexes of the type R(ArN[double bond, length as m-dash])M{N((t)Bu)SiMe2-H}X (M = Ta, R = Cp; M = Mo, R = ArN; X = Cl, H, OBn, Me) are described. The various substituents in the X position seem to play the key role in determining the extent of β-agostic interaction with the Si-H bond. The Mo agostic hydrido complex (ArN[double bond, length as m-dash])2Mo{η(3)-N((t)Bu)SiMe2-H}H is a pre-catalyst for the hydrosilylation of carbonyls. The stoichiometric reaction between benzaldehyde and (ArN[double bond, length as m-dash])2Mo{η(3)-N((t)Bu)SiMe2-H}H gives the benzoxy complex (ArN[double bond, length as m-dash])2Mo{N((t)Bu)SiMe2-H}(OBn), which showed a similar catalytic reactivity compared to the parent hydride. Mechanistic studies suggest that a non-hydride mechanism is operative.

The study addresses the spectral and photochemical properties of N-(3-ammoniopropyl)-4-styrylpyridinium diperchlorate and its substituted analogs containing either electron-donating (OMe, SMe, NMe2) or electron-withdrawing (NO2, Cl) groups on the benzene ring. These styryl dyes in MeCN form pseudodimeric complexes with uncharged 18-crown-6-containing 4-styrylpyridine due to hydrogen bonding between the ammonium group and the crown ether oxygen atoms. The stability constants of the complexes were determined by spectrophotometric and 1H NMR titration methods. Owing to complexation, the dyes containing OMe or SMe groups and the dye with unsubstituted benzene ring undergo a stereospecific [2 + 2]-cross-photocycloaddition to the crown-containing styrylpyridine to give unsymmetrical cyclobutane derivatives as single rctt isomers. The structure of cyclobutanes was confirmed by X-ray diffraction analysis. The most probable conformations of the pseudodimeric complexes in MeCN were determined by density functional theory calculations. The cross-photocycloaddition quantum yields, measured upon selective excitation of the styryl dye, and other relevant data suggested that the barrier for this photoreaction increases with an increase in the reorganization energy of the singlet excited state of the dye.

In combination with EtAlCl2, complexes {[WCl3(μ-Cl)(N-2,6-iPr2C6H3)]2}, [WCl4(NR)(thf)] (R = Et, iPr, cHx, Ph, 2,6-iPr2C6H3, 4-F-C6H4, and 2,4,6-F3-C6H2), and [WCl2(NR′)(PMe3)3] (R′ = Ph, 2,6-iPr2C6H3) were all productive ethylene dimerization pre-catalysts, giving turnover numbers (TONs) in the range of 400–144 000 (mol C2H4)(mol W)−1 and moderate selectivities toward 1-butene (>66%) depending on the nature of the imido substituent. The formation of C6 side-products resulted from the incorporation of 1-butene rather than direct trimerization, something that is independent of butene concentration. Stoichiometric reactions between the tungsten mono(imido) complexes and alkylaluminum reagents are described, which are consistent with the reduction of the tungsten centre playing an important part in the initiation process. Testing discrete WV and WIV mono(imido) complexes for olefin dimerization revealed the former to be significantly more active, which offers insight into the mode of action of the commercially relevant tungsten mono(imido)-selective dimerization initiators described herein.

Hirshfeld atom refinement (HAR) is a novel X-ray structure refinement technique that employs aspherical atomic scattering factors obtained from stockholder partitioning of a theoretically determined tailor-made static electron density. HAR overcomes many of the known limitations of independent atom modelling (IAM), such as too short element–hydrogen distances, r(X—H), or too large atomic displacement parameters (ADPs). This study probes the accuracy and precision of anisotropic hydrogen and non-hydrogen ADPs and of r(X—H) values obtained from HAR. These quantities are compared and found to agree with those obtained from (i) accurate neutron diffraction data measured at the same temperatures as the X-ray data and (ii) multipole modelling (MM), an established alternative method for interpreting X-ray diffraction data with the help of aspherical atomic scattering factors. Results are presented for three chemically different systems: the aromatic hydrocarbon rubrene (orthorhombic 5,6,11,12-tetraphenyltetracene), a co-crystal of zwitterionic betaine, imidazolium cations and picrate anions (BIPa), and the salt potassium hydrogen oxalate (KHOx). The non-hydrogen HAR-ADPs are as accurate and precise as the MM-ADPs. Both show excellent agreement with the neutron-based values and are superior to IAM-ADPs. The anisotropic hydrogen HAR-ADPs show a somewhat larger deviation from neutron-based values than the hydrogen SHADE-ADPs used in MM. Element–hydrogen bond lengths from HAR are in excellent agreement with those obtained from neutron diffraction experiments, although they are somewhat less precise. The residual density contour maps after HAR show fewer features than those after MM. Calculating the static electron density with the def2-TZVP basis set instead of the simpler def2-SVP one does not improve the refinement results significantly. All HARs were performed within the recently introduced HARt option implemented in the Olex2 program. They are easily launched inside its graphical user interface following a conventional IAM.

A series of cross-conjugated compounds based on an (E)-4,4′-(hexa-3-en-1,5-diyne-3,4-diyl)bis(N,N-bis(4-methoxyphenyl)aniline) skeleton (1–6) have been synthesized. The linear optical absorption properties can be tuned by modification of the substituents at the 1 and 5 positions of the hexa-3-en-1,5-diynyl backbone (1: Si(CH(CH3)2)3, 2: C6H4C≡CSi(CH3)3, 3: C6H4COOCH3, 4: C6H4CF3, 5: C6H4C≡N, 6: C6H4C≡CC5H4N), although attempts to introduce electron-donating (C6H4CH3, C6H4OCH3, C6H4Si(CH3)3) substituents at these positions were hampered by the ensuing decreased stability of the compounds. Spectroelectrochemical investigations of selected examples, supported by DFT-based computational studies, have shown that one- and two-electron oxidation of the 1,2-bis(triarylamine)ethene fragment also results in electronic changes to the perpendicular π-system in the hexa-3-en-1,5-diynyl branch of the molecule. These properties suggest that (E)-hexa-3-en-1,5-diynyl-based compounds could have applications in molecular sensing and molecular electronics.

1-(3-Ammoniopropyl)-4-[(E)-2-(3,4-dichlorophenyl)vinyl]pyridinium diperchlorate was synthesized and its crystal structure was studied by X-ray diffraction. The photochemical properties of this compound and its complexation with a 18-crown-6-containing derivative of 4-styrylpyridine were studied by electronic spectroscopy. These compounds form a supramolecular complex (logK = 3.89 in MeCN at an ionic strength of 0.01 mol L–1), in which the styryl chromophores are arranged one above another due to stacking interactions. The complexation activates the cross [2+2] photocycloaddition of styrylpyridine derivatives. A procedure is proposed for the global analysis of spectrophotometric data, which takes into account the effect of the ionic strength of the solution on the observed equilibrium reaction.

X-ray structure determinations of three crystal forms of a 18-crown-6-containing styryl dye of the pyridine series in iodide form (1), containing various solvate molecules, namely water (1a), 2,6-dihydroxyoaphthalene (1b), 1,4-hydroquinone (1c), and analysis of crystal packings of these crystals, together with the previously investigated non-solvated form (crystal 1) and the solvates with benzene and water (crystal 1d) has been carried out. Crystal packing in 1a, 1b, 1c, and 1d involves a stacking leading to dimers of the dye cations, structurally preorganized for the [2+2]-photocycloaddition (PCA) reaction. On irradiation of with visible light, the PCA reaction with the centrosymmetric rctt isomer leads to the cyclobutane derivative formation. In the case of 1a and 1b the PCA proceeds with the retention of crystallinity, while with other solvates crystals are transformed into a glass. The glasses keep the form and the shine of the initial crystals, nevertheless. In the cases of the non-solvated crystal form (1), translation-related stacks form, with the geometry inconsistent with that of the preorganized dimer. These crystals are stable in visible light.