Frustration of H-Bonding and Frustrated Packings in a Hexamorphic Crystal System with Reversible Crystal-Crystal Transitions.

The study of transitions between polymorphic phases is a less investigated chapter of the widely studied book of polymorphism. In this paper, we discuss the phase behavior of a new compound that has been rationally designed to show frustration of H-bonds for the strong amide N-H donor, which cannot be involved in H-bonding nor in van der Waals interactions. The compound (ImB) is a showcase of almost all possible cases of transitions between polymorphs [monotropic/enantiotropic, fast/slow, diffusive/displacive, and single-crystal-to-single-crystal (SCSC)] and of relation between polymorphs with different Z'. Six crystal phases (I, II, III, IV, V, and VI) were identified for it with five crystal-crystal transitions. Two transitions are reversible/SCSC/fast. Of the three monotropic transitions, all non-SCSC, one is slow, and the others are fast. Of the two enantiotropic SCSC transitions, one does not exhibit undercooling, while the other shows strong undercooling. Phase III, with Z' = 6, is stable at room temperature between phase II (Z' = 1), stable at high temperature, and phase IV (Z' = 2), stable at low temperature. All six polymorphs are based on the same O-H···O═C H-bonding synthon, which produces infinite chains in five polymorphs and ring tetramers in one. The sequence of reversible SCSC transitions IV ⇆ III ⇆ II involves a remarkable ping pong of the symmetry rules by which H-bonded chains are built. Based on all of this, a possible roadmap for prediction of SCSC transitions in crystals is shortly outlined.

Asymmetrical Diketopyrrolopyrrole Derivatives with Improved Solubility and Balanced Charge Transport Properties.

The diketopyrrolopyrrole (DPP) unit represents one of the building blocks more widely employed in the field of organic electronics; in most of the reported DPP-based small molecules, this unit represents the electron acceptor core symmetrically coupled to donor moieties, and the solubility is guaranteed by functionalizing lactamic nitrogens with long and branched alkyl tails. In this paper, we explored the possibility of modulating the solubility by realizing asymmetric DPP derivatives, where the molecular structure is extended in just one direction. Four novel derivatives have been prepared, characterized by a common dithyenil-DPP fragment and functionalized on one side by a thiophene unit linked to different auxiliary electron acceptor groups. As compared to previously reported symmetric analogs, the novel dyes showed an increased solubility in chloroform and proved to be soluble in THF as well. The novel dyes underwent a thorough optical and electrochemical characterization. Electronic properties were studied at the DFT levels. All the dyes were used as active layers in organic field effect transistors, showing balanced charge transport properties.

Novel Thienyl DPP derivatives Functionalized with Terminal Electron-Acceptor Groups: Synthesis, Optical Properties and OFET Performance.

Three novel diketopyrrolopyrrole (DPP) based small molecules have been synthesized and characterized in terms of their chemical-physical, electrochemical and electrical properties. All the molecules consist of a central DPP electron acceptor core symmetrically functionalized with donor bi-thienyl moieties and flanked in the terminal positions by three different auxiliary electron-acceptor groups. This kind of molecular structure, characterized by an alternation of electron acceptor and donor groups, was purposely designed to provide a significant absorption at the longer wavelengths of the visible spectrum: when analysed as thin films, in fact, the dyes absorb well over 800 nm and exhibit a narrow optical bandgap down to 1.28 eV. A detailed DFT analysis provides useful information on the electronic structure of the dyes and on the features of the main optical transitions. Organic field-effect transistors (OFETs) have been fabricated by depositing the DPP dyes as active layers from solution: the different end-functionalization of the dyes had an effect on the charge-transport properties with two of the dyes acting as n-type semiconductors (electron mobility up to 4.4 ⋅ 10-2  cm2 /V ⋅ s) and the third one as a p-type semiconductor (hole mobility up to 2.3 ⋅ 10-3  cm2 /V ⋅ s). Interestingly, well-balanced ambipolar transistors were achieved by blending the most performant n-type and p-type dyes with hole and electron mobility in the order of 10-3  cm2 /V ⋅ s.

High-Energy-Density Materials: An Amphoteric N-Rich Bis(triazole) and Salts of Its Cationic and Anionic Species.

The synthesis and characterization of the N-rich bis(triazole) compound 1H,4'H-[3,3'-bis(1,2,4-triazole)]-4',5,5'-triamine (C4H7N9) with a N content of 69.6% by weight is reported. The compound exhibits a rich acid-base behavior because it can accept up to two protons, forming a monocation and a dication, and can lose one proton, forming an anion. Measurement of the acid constants has shown that there exist well-defined pH intervals in which each of the four species is predominant in solution, opening the way to their isolation and characterization by single-crystal X-ray analysis as salts with different counterions. Some energetic salts of the monocation or dication containing oxidizing inorganic counterions (dinitramide, perchlorate, and nitrate) were also prepared and characterized in the solid state for their sensitivity. In particular, the neutral compound shows a very remarkable thermal stability in air, with Td = 347 °C, and is insensitive to impact and friction. Salts of the dication with energetic counterions, in particular perchlorate and nitrate, show increased sensitivities and reduced thermal stability. The salt of the monocation with dinitramide as the counterion outperforms other dinitramide salts reported in the literature because of its higher thermal stability (Td = 230 °C in air) and friction insensitiveness.

Solid State Separation and Isolation of Tautomers of Fused-Ring Triazolotriazoles.

Fine control of the tautomeric forms of [1,2,4]triazolo[3,2-c][1,2,4]triazole derivatives in acidic conditions has been achieved by acting on the electronic character of the substituent at position 7 of the heterobicycle and on the counterion. Strong electron releasing or electron withdrawing substituents lead almost exclusively to a single tautomeric form, the 1H-3H or the 2H-3H, respectively. In the case of the phenol substituent, both tautomeric forms are present in comparable amount in solution; the two tautomers can also be selectively precipitated in different crystalline salts using suitable counterions.

Structural, electronic and vibrational properties of N,N'-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDI-FCN2) crystal.

We present a theoretical and experimental investigation of the crystalline structure of N,N'-1H,1H-perfluorobutyl dicyanoperylenecarboxydiimide (PDI-FCN2) that has been deduced combining experimental XRD data, obtained from powders, with global-optimization algorithms which allow to identify Bravais lattice, primitive cell parameters, and space group of the crystal. The XRD spectrum calculated for the proposed crystalline structure very well reproduces the measured XRD data. Our results suggest the triclinic lattice structure of spatial groups P1 and P1, respectively, for the crystalline PDI-FCN2-1,7 and PDI-FCN2-1,6 isomers. In both cases, the primitive cell contains a single molecule. On the proposed crystalline structures, KS-DFT cell energy calculations, including van der Waals interactions, have been performed to assign the minimum energy geometrical structure and orientation of the molecule inside the corresponding primitive cell. These calculations evidence the molecular packing that characterizes the strong anisotropy of the PDI-FCN2 crystal. Electronic band-structures calculated for both isomers within the Kohn-Sham density-functional theory indicate that the crystalline P1 structure is an indirect gap semiconductor, while the P1 structure is a direct gap semiconductor. The electronic band structure calculations on the optimized crystal geometries highlight strong anisotropy in the dispersion curves E(k), which roots at the molecular packing in the crystal. Finally, the vibrational spectrum of both crystalline isomers has been calculated in the harmonic approximation and the dominant vibrational frequencies have been associated to collective motions of selected atoms in the molecules.

4,5-Di-amino-3-[(E,E)-4-(4,5-di-amino-4H-1,2,4-triazol-3-yl)buta-1,3-dien-yl]-4H-1,2,4-triazol-1-ium chloride.

The title compound, C8H13N10 (+)·Cl(-), is the monochlorhydrate salt of an aromatic bis-(di-amino-triazole). The cation is centrosymmetric, lying about an inversion centre (Ci symmetry) because the acidic H atom is disordered over two centrosymmetrically related ring N atoms, with equal multiplicity. It is noteworthy that protonation occurs at an N atom of the ring, instead of at the C-NH2 or N-NH2 amino groups. The chloride anions are also in special positions, as they lie on binary axes, and so the crystallographically independent unit contains half of a formula unit. The N atom of the C-NH2 group is sp (2)-hybridized and the amino group is coplanar with the triazole ring [dihedral angle = 5 (3)°], while the N atom of the N-NH2 amino group is pyramidal. The C=C bonds are in E conformations and the cation is flat because the conformation of the carbon chain is fully extended. The chloride anions are hexa-coordinated, in a distorted trigonal-prismatic geometry, and they are involved, as acceptors, in six hydrogen bonds. Chains of hydrogen-bonded cations, running along c and a + c, are generated by c-glide and C 2 rotation, respectively. This combination of N-H⋯Cl and N-H⋯N hydrogen bonds leads to the formation of a three-dimensional network.

N,N'-Di-hydroxy-benzene-1,2:4,5-tetra-carboximide dihydrate.

In the title compound, C10H4N2O6·2H2O, the organic mol-ecule has crystallographically imposed inversion symmetry. The atoms of the three fused rings of the mol-ecule are coplanar within 0.0246 (8) Å, while the two hy-droxy O atoms are displaced from the mean plane of the mol-ecule by 0.127 (1) Å. In the crystal, infinite near-planar layers of close-packed mol-ecules are formed by hydrogen bonding between water O-H donor groups and carbonyl O-atom acceptors, and by weak inter-actions between C-H donor groups and water O-atom acceptors. The layers are parallel to the {102} family of planes. The stacked planes are held together by hydrogen bonding between N-OH donor groups and water O-atom acceptors.

2-(4-Methyl-phen-yl)-6-nitro-1,3-benzoxazole.

The title compound, C14H10N2O3, is a π-conjugated mol-ecule containing a benzoxazole aromatic fused heterobicycle. The benzoxazole ring system is planar within 0.01 Å. The mol-ecule assumes an approximately flat conformation, the benzoxazole ring system forming dihedral angles of 6.52 (12) and 7.4 (3)° with the benzene ring and the nitro group, respectively. In the crystal, mol-ecules are connected by very weak C-H⋯O hydrogen inter-actions, forming chains running parallel to the a or c axes. The methyl H atoms are disordered over two sets of sites of equal occupancy rotated by 60°.

3,3'-({4-[(4,5-Di-cyano-1H-imidazol-2-yl)diazen-yl]phen-yl}imino)-dipropionic acid.

The title compound, C17H15N7O4, is a push-pull non-linear optical chromophore containing a di-alkyl-amino donor group and the di-cyano-imidazolyl acceptor separated by a π-conjugated path. The benzene and imidazole rings are not coplanar, making a dihedral angle of 10.0 (2)°. In the crystal, mol-ecules are linked by an extended set of hydrogen bonds and several motifs are recognized. Pairs of mol-ecules are held together by hydrogen bonding between carb-oxy O-H donor groups and diazenyl N-atom acceptors, forming R 2 (2)(24) ring patterns across inversion centres. Four-mol-ecule R 4 (4)(28) ring motifs are formed, again across inversion centres, through hydrogen bonding involving carb-oxy O-H donor groups and diazenyl and imidazole N-atom acceptors. Four-mol-ecule R 4 (4)(42) patterns are formed among mol-ecules related by translation and involve carb-oxy O-H and imidazole N-H donor groups with carbonyl O-atom and imidazole N-atom acceptors.

{4-Bromo-2-[(2-{(ethyl-sulfan-yl)[(2-oxido-benzyl-idene-κO)amino-κN]methyl-idene}hydrazinyl-idene-κN (1))meth-yl]phenolato-κO}(ethanol-κO)dioxido-uranium(VI).

In the title complex, [U(C17H14BrN3O2S)O2(C2H5OH)], the U(VI) cation has a distorted penta-gonal-bipyramidal environment with the penta-gonal plane defined by two N and two O atoms of the tetra-dentate Schiff base ligand and the O atom of the ethanol mol-ecule. Two oxide O atoms occupy the axial positions. The azomethine C=N group and the Br atom are disordered over two positions in a 0.8356 (18):0.1644 (18) ratio. The ethyl-thiolyl group is disordered over three conformations in a 0.8356 (18):0.085 (6):0.079 (6) ratio, and the ethanol ligand is also disordered over three orientations in a 0.470 (16):0.277 (19):0.253 (18) ratio. In the crystal, mol-ecules form centrosymmetric dimers through hydrogen bonding between ethanol O-H donors and phenolate O-atom acceptors. Weak C-H⋯O inter-actions consolidate the crystal packing.

(3S,3aS,6R,6aR)-2-Oxohexa-hydro-furo[3,2-b]furan-3,6-diyl dibenzoate.

The title compound, C20H16O7, contains a cis-fused γ-lactone tetra-hydro-furan ring system functionalized with two benzo-yloxy groups. Both rings adopt an envelope conformation. The mol-ecule assumes an elongated shape and exibits non-crystallographic C 2 symmetry. The benzo-yloxy groups are almost planar [maximum deviations of 0.0491 (15) and 0.0336 (17) Šfor the O atoms] and their mean planes are inclined to one another by 16.51 (4)°. The crystal packing features weak C-H⋯O inter-actions. The aryl groups of adjacent mol-ecules are parallel shifted with face-to-face contacts and a shortest inter-molecular C⋯C distance of 3.482 (4) Å.

3ß,6ß-Diacet-oxy-5,9α-dihy-droxy-5α-cholest-7-en-11-one acetic acid 0.04-solvate.

The title compound, C31H48O7·0.04CH3COOH, is a polyoxy-genated steroid obtained by selective chemical oxidation of 7-de-hydro-cholesteryl acetate. The asymmetric unit comprises three mol-ecules of the steroid (Z' = 3) and a mol-ecule of acetic acid which has occupancy factor 0.131 (5). The geometric parameters of the independent mol-ecules do not reveal significant differences. In one mol-ecule, the terminal isopropyl group is disordered over two sets of sites with occupancy ratio 0.869 (5):0.131 (5). The three mol-ecules reveal different hydrogen-bonding patterns. Each of them is involved in an intra-molecular S(6) hydrogen-bonding motif, involving hy-droxy groups as donor and acceptor. In the crystal, two independent mol-ecules form dimers through hydrogen bonding between an OH donor and an acetate carbonyl acceptor, giving rise to R 2 (2)(16) ring patterns. A single hydrogen bond between the OH group and a ketone carbonyl group is observed between two symmetry-independent mol-ecules.

(3R,3aR,6R,6aR)-Hexa-hydro-furo[3,2-b]furan-3,6-diyl dibenzoate.

The title compound, C20H18O6, prepared from d-mannitol by a two-step procedure, is a functionalized fused bis-tetra-hydro-furan. In the central fragment, consisting of two fused tetra-hydro-furan rings, one O atom and its two adjacent C atoms, a methyl-ene and a bridgehead C atom, are disordered over two sets of sites with an occupancy ratio of 0.735 (9):0.265 (9). In the major component, the ring containing the disordered O atom is a half-chair conformation with twisted methylene and benzoate-substituted C atoms, whereas the other ring has a half-chair or T-form conformation. In the minor component, the ring with the disordered O atom has an envelope conformation, with the O atom as the flap, and the other ring has a half-chair conformation, with the O atom and the other bridgehead CH atom being twisted. The two aromatic rings are inclined to one another by 20.00 (12)°. In the crystal, adjacent molecules are linked via C-H⋯π interactions, forming chains propagating along [010].

3ß,6α-Diacet-oxy-5,9α-dihy-droxy-5α-cholest-7-en-11-one.

The title compound, C31H48O7, a polyoxygenated steroid, was obtained by chemical oxidation of 7-de-hydro-cholesteryl acetate. The mol-ecular geometry features trans A/B and C/D junctions at the steroid core with the acetyl groups in the equatorial position and a fully extended conformation for the alkyl side chain. A chair conformation is observed for rings A and C while ring B adopts a half-chair conformation. The five-membered ring D has an envelope conformation, with the C atom bearing the methyl group at the flap. The terminal isopropyl group and one acetyl group are disordered over two sets of sites with 0.774 (8):0.226 (8) and 0.843 (7):0.157 (7) ratios, respectively. An intra-molecular S(6) O-H⋯O hydrogen-bonding motif involving a hy-droxy donor and acceptor is observed. In the crystal, chains of mol-ecules running along the b axis are formed via O-H⋯O hydrogen bonds between hy-droxy donors and carbonyl acceptors of the ordered acetyl group, giving rise to a C(14) motif. The chains are wrapped around the 21 screw axes.

New Hg(II) coordination polymers based on a thioimidazole ligand with good performance to detoxify Hg(II) and reversibly capture iodine.

In the current paper, we have successfully synthesized three new mercury coordination polymers with fascinating structures and properties via a flexible sulfur donor ligand, namely, {[Hg(µ2-Cl)(µ2-Ls)]}n[BF4]n(1), {[Hg(µ2-Cl)(µ2-Ls)]}n[ClO4]n(2), and [Hg(SCN)2(µ2-Ls)]n(3) [Ls = 1,1-bis(3-methyl-4-imidazoline-2-thione)methane]. These complexes have been characterized by means of different techniques such as single crystal X-ray crystallography, FT-IR, elemental analysis (CHNS), UV-Vis, PXRD, BET, and TGA. Suitable single crystals of all complexes were obtained using the branch tube method with a very high yield and good stability due to the high affinity of mercury to bind to the thione groups. The cationic moieties of polymers 1 and 2 were isostructural, with a HgCl2S2 coordination core structure. The voids of the quasi-hexagonal packing of the columnar chains were occupied by unbonded tetrahedral BF4- ions in 1 and perchlorate anions in polymer 2. Polymer 3 has a less distorted tetrahedral geometry than 1 and 2, with a HgS4 core structure. By considering the thiophilicity of mercury, a thioamide-based Ls ligand was used to detoxify Hg(II) into insoluble polymers 1-3. The results of an MTT assay for (HepG2) liver cells confirmed the excellent cytoprotective effect of this ligand against mercury. Based on IC50 calculations, their toxicity was in order of polymer 1 > polymer 2 > polymer 3. These polymers were also considered as adsorbents for the reversible removal of iodine from solution and the kinetics of the process has been studied in detail. Interestingly, all of them showed an excellent stability and high capacity, in order of 763.53 mg g-1, 877.10 mg g-1, and 905.31 mg g-1 for polymers 1-3, respectively.

Efficient High-Refractive-Index Azobenzene Dendrimers Based on a Hierarchical Supramolecular Approach.

Real-time manipulation of light in a diffractive optical element made with an azomaterial, through the light-induced reconfiguration of its surface based on mass transport, is an ambitious goal that may enable new applications and technologies. The speed and the control over photopatterning/reconfiguration of such devices are critically dependent on the photoresponsiveness of the material to the structuring light pattern and on the required extent of mass transport. In this regard, the higher the refractive index (RI) of the optical medium, the lower the total thickness and inscription time can be. In this work, we explore a flexible design of photopatternable azomaterials based on hierarchically ordered supramolecular interactions, used to construct dendrimer-like structures by mixing specially designed sulfur-rich, high-refractive-index photoactive and photopassive components in solution. We demonstrate that thioglycolic-type carboxylic acid groups can be selectively used as part of a supramolecular synthon based on hydrogen bonding or readily converted to carboxylate and participate in a Zn(II)-carboxylate interaction to modify the structure of the material and fine-tune the quality and efficiency of photoinduced mass transport. Compared with a conventional azopolymer, we demonstrate that it is possible to fabricate high-quality, thinner flat diffractive optical elements to reach the desired diffraction efficiency by increasing the RI of the material, achieved by maximizing the content of high molar refraction groups in the chemical structure of the monomers.

2-Cyano-5-({4-[N-methyl-N-(2-hy-droxy-eth-yl)amino] phen-yl}diazen-yl)pyridine.

In the title compound, C(15)H(15)N(5)O, the benzene and pyridine rings make a dihedral angle of 30.86 (7)°. In the crystal, chains of mol-ecules are wrapped around the screw axes into compressed helices, through hydrogen bonding between the hy-droxy and cyano groups. The chains are linked by weak C-H⋯N and C-H⋯O inter-actions. The π conjugated unit of the mol-ecule is almost perpendicular to the helix axis, and the formation of the helix is allowed by a gauche-type torsion angle in the hy-droxy-ethyl tail. In this way, consecutive chromophore units along the chain are placed in a strict anti-parallel arrangement, and this is energetically favoured because of the high dipole moment of the mol-ecule.

Crystal and mesophase structure of a bicyclohexyl cyano mesogen.

The phase behaviour of 4-[trans-4-(trans-4-propylcyclohexyl)cyclohexyl]benzonitrile, C22H31N, 1, has been examined. This compound has two different solid phases, denoted I and II, and exhibits thermotropic liquid-crystalline behaviour, with a remarkable interval of stability of the mesophase between the lower melting solid phase (75 °C) and the isotropization temperature (247 °C). The crystal and molecular structures of solid phase I have been determined at 173 K. The cyclohexyl rings both adopt the chair conformation and are equatorially substituted. The packing of 1 in the crystalline state is driven by the antiparallel arrangement of cyano dipoles with the formation of close contacts involving the strong cyano acceptor and weak aromatic C-H or aliphatic C-H donors. The crystal packing is discussed and compared with X-ray diffraction data in the liquid-crystalline state. The combination of thermal analysis, optical polarizing microscopy and X-ray diffraction analysis suggests that the mesophase is a partially ordered smectic phase. The lamellar structure of the mesophase is retained in crystalline solid phase II obtained by cooling the liquid-crystalline phase.

Isolation of a bis-iodurated tetra-THF as a trace product from the oxidation of squalene with RuO4 and its double ring expansion to a novel bis-THF-bis-THP compound.

A novel bis-iodurated polyether compound, based on an unprecedented tetra-THF backbone, has been isolated as a trace by-product of the oxidation of squalene with the catalytic system RuO2(cat.)/NaIO4. The double erythro configuration of the central portion of the molecule furnishes the first indirect support of the previously postulated pathway operating in the oxidative pentacyclization of the isoprenoid substrate. A bidirectional double oxidative bis-cyclization is invoked to explain the formation of this compound. The isolated substance was successfully subjected to a double rearrangement-ring expansion to give a novel bis-THF-bis-THP compound.