The concept of distributed dipoles in molecular self-assembly on solid substrates was tested for the example of thiolate self-assembled monolayers (SAMs) on Au(111) containing dipolar 2,5'-bipyrimidine units. These were attached to a thiol anchoring group either directly or via a phenylene methylene spacer, with the spacer decoupling the dipolar moiety from the substrate and promoting layer formation. As expected, the SAMs containing the spacer groups exhibited a higher quality, including a higher packing density and nearly upright molecular orientation. The electrostatic effects of the dipolar bipyrimidine moieties were tested through C is and N is photoemission spectra, where electrostatic core-level shifts impact the shapes of the spectra. Additionally, changing the orientation of the dipoles allows a variation of the work function over a range of similar to 1.35 eV. The experiments were complemented by density-functional theory calculations. The work function tuning range was reasonably high, but smaller than expected considering that for SAMs with a single embedded pyrimidine group per molecule work function changes already amounted to similar to 1.0 eV. This behavior is rooted in an asymmetry of the studied SAMs: For dipoles pointing away from the substrate, the expected doubling of the work function change between monopyrimidine and bipyrimidine SAMs essentially occurs. Conversely, for the downward-oriented pyrimidine dipoles, the second polar ring has hardly any effect. Consistent observations were made for the core-level shifts. We discuss several factors, which are potentially responsible for this asymmetry, like disorder, depolarization, or Fermi-level pinning. Of these, the most likely explanation is the adsorption of airborne contaminants interacting with the nitrogen atoms in the immediate vicinity of the outer surface. These are present only in films with downward oriented dipoles. In spite of these complications, some of the introduced distributed dipole SAMs serve as important model systems for understanding electrostatic effects at interfaces. They are also of interest for controlling carrier-injection barriers in organic (opto) electronic devices.

A two-step reaction sequence for the highly stereodivergent construction of 1,3-diamines with three continuous stereocenters is reported. This novel method enables the controlled synthesis of any given diastereomer of the 1,3-diamine scaffold from a simple set of starting materials in a highly modular manner. The disclosed approach is based on the reaction of an enamide with an in situ generated N-acylimine followed by a subsequent trapping of the generated intermediate with a suitable nucleophile. By careful choice of starting materials, reagents, and reaction conditions, each stereocenter can be constructed in a highly selective fashion.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Azobenzene compounds are known as versatile examples for photoswitchable systems because of their isomeric cis- and trans-configurations. The switching between these isomers can be reversibly controlled by light excitation. In this study we characterize two members of this class by joining the azobenzene moiety with each two paramagnetic nitroxide spin labels. Two different linkers were chosen to tune the molecular properties. The combined approach using optical and EPR spectroscopy proved the reversibility of photoexcitation and high fatigue resistance. Furthermore, depending on the nature of the linker, PELDOR distance measurements monitored clearly the photo-induced structural changes of the azobenzene unit. Thus, a powerful concept is presented resulting from the combination of these two complementary spectroscopic techniques.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

As a material with relatively small band gap and low lying valence orbitals, perfluoroanthracene (PFA) is of interest for the modification of electrode surfaces, for example, as charge injection layers for n-type organic semiconductors. To covalently attach PFA in the form of self-assembled monolayers (SAMs), we developed a synthesis of derivatives with a sulfur termination, linked to the 2-position of the PFA moieties by an -NH- group and a short alkane chain with two and three methylene groups, respectively. Spectroscopic characterization of the SAMs reveals that the molecules adopt an almost upright orientation on the gold surface, with the packing density mostly determined by the steric demands of the PFA units. The number of the methylene groups in the -NH- alkyl linker has only a minor impact on the SAM structure because of the nonsymmetric attachment of the PFA units, which permits the compensation of the orientational constraints imposed by the bending potential. The investigated SAMs alter the work function of gold by +(0.59-0.64) eV, suggesting comparably strong depolarization effects, affecting the extent of the work function modification.

Starting from (S)-β-phenylalanine, easily accessible by lipase-catalyzed kinetic resolution, a chiral triamine was assembled by a reductive amination and finally cyclized to form the title compound 10. In the crystals of the guanidinium benzoate salt the six membered rings of 10 adopt conformations close to an envelope with the phenyl substituents in pseudo-axial positions. The unprotonated guanidine 10 catalyzes Diels–Alder reactions of anthrones and maleimides (25–30% ee). It also promotes as a strong Brønsted base the retro-aldol reaction of some cycloadducts with kinetic resolution of the enantiomers. In three cases, the retro-aldol products (48–83% ee) could be recrystallized to high enantiopurity (≥95% ee). The absolute configuration of several compounds is supported by anomalous X-ray diffraction and by chemical correlation.

Doramapimod (BIRB 796) is a potent inhibitor of p38α nitrogen-activated protein kinase. By using biophysical methods, a clear correlation between kinase binding and the torsion angle θ of doramapimod analogues was found, highlighting the importance of inhibitor conformation for protein binding.

The reaction of SiCl4 with Na[SitBu3] in thf at −78 °C yielded tBu3Si-SiCl3 along with tBu3SiCl, tBu3Si-SitBu3, and tBu3SiH. After HPLC separation we isolated crystalline tBu3Si-SiCl3 from the eluate (retention time: τ = 39 min). During the work-up process further derivatives of tBu3Si-SiCl3 namely tBu3Si-Si(OH)3 (triclinic space group P-1), tBu3Si-Si(OMe)(OH)2 (monoclinic space group P21/c), and tBu3Si-Si(OMe)2(OH) (monoclinic space group P21/c) crystallize from the eluate. By the reaction of tBu3Si-SiCl3 with K in benzene we obtained the tetrasilatetrahedrane (tBu3Si)4Si4 (tetrasupersilyl-tetrahedro-tetrasilane) along with tBu3Si-SitBu3 and tBu3SiH. In contrast to the reaction in benzene treatment of tBu3Si-SiCl3 with K in thf yielded K[SitBu3]. We further investigated the cleavage of Si−Si bond by treatment of tBu3Si-SiCl3 with [nBu4N]Cl. Thereby tBu3SiCl and [nBu4N]2[Si6Cl14] were formed.

A series of three homologous arene[2,3-d]-oxazole-2-thiols (benzoxazole-2-thiol (BOxSH), naphthaleneoxazole-2-thiol (NOxSH), and anthraceneoxazole-2-thiol (AOxSH)) were deposited onto Au(111) to obtain surfaces suitable as injection layers for organic electronics. The guiding idea was that the increasingly extended conjugated system would lower the band gap of the films while the introduction of the annulated heteroaromatic ring would provide the opportunity for pseudosymmetric attachment of the sulfur anchor, what should lower the conformational freedom of the system. In fact, the annulation of the oxazole ring lowers the optical band gaps of the parent compounds to 3.1-4.0 eV, depending on the number of benzene rings. To characterize the respective monolayers, a variety of spectroscopic techniques such as ellipsometry, infrared reflection-absorption spectroscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure spectroscopy have been utilized. The monolayers of BOxS exhibit a lower film quality than those of NOxS and AOxS, with enhanced molecular density and more upright molecular orientation with increasing molecular length. Infrared spectroscopy suggests that the nitrogen atoms of the oxazole rings are located more closely to the Au(111) surface than the oxygen atoms, although no hints for an electronic interaction between the N atoms and the gold surface could be found. This preferred orientation could be tentatively traced to packing effects, solving a conundrum of the literature.

A new procedure developed for the synthesis and crystallization of various zinc(II) fumarate hydrate coordination polymers is described. In the first step, anhydrous Zn(II) fumarate, [Zn(C4H2O4)] (1), is synthesized from Zn(II) acetate and fumaric acid in methanol. Subsequently, this product is used as a starting material for growing small crystals of bis-aqua Zn(II) fumarate, [Zn(H2O)(2)(C4H2O4)] (2), triaqua Zn(II) fumarate monohydrate, [Zn(H2O)(3)(C4H2O4)]H2O (3), tetraaqua Zn(II) fumarate, [Zn(H2O)(4)(C4H2O4)] (4), and tetraaqua Zn(II) fumarate monohydrate, [Zn(H2O)(4)(C4H2O4)]H2O (5). All structures were determined or redetermined by X-ray structure analyses. The hitherto unknown compound 3 exhibits a zig-zag chain structure with five-coordinate Zn(II) ions.

Crystal structures are reported for four (2,2'-bipyridyl)(ferrocenyl)boronium derivatives, namely (2,2'-bipyridyl)(ethenyl)(ferrocenyl)boronium hexafluoridophosphate, [Fe(C5H5)(C17H15BN2)]PF6, (Ib), (2,2'-bipyridyl)(tert-butylamino)(ferrocenyl)boronium bromide, [Fe(C5H5)(C19H22BN3)]Br, (IIa), (2,2'-bipyridyl)(ferrocenyl)(4-methoxyphenylamino)boronium hexafluoridophosphate acetonitrile hemisolvate, [Fe(C5H5)(C22H20BN3O)]PF6·0.5CH3CN, (IIIb), and 1,1'-bis[(2,2'-bipyridyl)(cyanomethyl)boronium]ferrocene bis(hexafluoridophosphate), [Fe(C17H14BN3)2](PF6)2, (IVb). The asymmetric unit of (IIIb) contains two independent cations with very similar conformations. The B atom has a distorted tetrahedral coordination in all four structures. The cyclopentadienyl rings of (Ib), (IIa) and (IIIb) are approximately eclipsed, while a bisecting conformation is found for (IVb). The N-H groups of (IIa) and (IIIb) are shielded by the ferrocenyl and tert-butyl or phenyl groups and are therefore not involved in hydrogen bonding. The B-N(amine) bond lengths are shortened by delocalization of π-electrons. In the cations with an amine substituent at boron, the B-N(bipyridyl) bonds are 0.035 (3) Å longer than in the cations with a methylene C atom bonded to boron. A similar lengthening of the B-N(bipyridyl) bonds is found in a survey of related cations with an oxy group attached to the B atom.

The six-component pentagon P1 with its five dynamic vertices was conceived on the basis of three different orthogonal metal complex units in a 1-fold completive self-sorting of four linear ligands and two metal ions without using directional bonding.

Crystal structures are reported for three fluoro-or chloro-substituted 1'-deoxy-1'-phenyl-beta-D-ribofuranoses, namely 1'-deoxy-1'-(2,4,5-trifluorophenyl)-beta-D-ribofuranose, C11H11F3O4, (I), 1'-deoxy-1'-(2,4,6-trifluorophenyl)-beta-d-ribofuranose, C11H11F3O4, (II), and 1'-(4-chlorophenyl)-1'-deoxy-beta-D-ribofuranose, C11H13ClO4, (III). The five-membered furanose ring of the three compounds has a conformation between a C2'-endo, C3'-exo twist and a C2'-endo envelope. The ribofuranose groups of (I) and (III) are connected by intermolecular O-H center dot center dot center dot O hydrogen bonds to six symmetry-related molecules to form double layers, while the ribofuranose group of (II) is connected by O-H center dot center dot center dot O hydrogen bonds to four symmetry-related molecules to form single layers. The O center dot center dot center dot O contact distance of the O-H center dot center dot center dot O hydrogen bonds ranges from 2.7172 (15) to 2.8895 (19) A. Neighbouring double layers of (I) are connected by a very weak intermolecular C-F center dot center dot center dot pi contact. The layers of (II) are connected by one C-H center dot center dot center dot O and two C-H center dot center dot center dot F contacts, while the double layers of (III) are connected by a C-H center dot center dot center dot Cl contact. The conformations of the molecules are compared with those of seven related molecules. The orientation of the benzene ring is coplanar with the H-C1' bond or bisecting the H-C1'-C2' angle, or intermediate between these positions. The orientation of the benzene ring is independent of the substitution pattern of the ring and depends mainly on crystal-packing effects.

A versatile synthetic procedure is described to prepare the benzimidazole-fused 1,2,4-thiadiazoles 2a-c via a methanesulfonyl chloride initiated multistep cyclization involving the intramolecular reaction of an in-situ generated carbodiimide with a thiourea unit. The structure of the intricate heterocycle 2a was confirmed by single-crystal X-ray analysis and its mechanism of formation supported by DFT computations.

A series of fluoroalkyl-substituted enyne-allenes have been synthesized by a new route with the aim of elucidating the possibility of a fluoro-ene reaction via an intermediate fulvenyl diradical generated in the thermal C-2-C-6 (Schmittel) cyclization reaction. As a result of the strong C-F bond, fluorine atom transfer was not observed. Instead, 1H-cyclobuta-[a]indenes were formed in good yields despite the high strain energy. DFT calculations at the B3LYP level of theory indicated that although the fluoro-ene reaction is the most exothermic reaction available, cyclobutene formation is kinetically favored over the [1,5]-fluorine shift by 5-15 kcalmol(-1) in various model compounds.

Crystal structures are reported for three fluoro- or chloro-substituted 1′-deoxy-1′-phenyl-β-D-ribofuranoses, namely 1′-deoxy-1′-(2,4,5-trifluorophenyl)-β-D-ribofuranose, C 11 H 11 F 3 O 4 , (I), 1′-deoxy-1′-(2,4,6-trifluorophenyl)-β-D-ribofuranose, C 11 H 11 F 3 O 4 , (II), and 1′-(4-chlorophenyl)-1′-deoxy-β-D-ribofuranose, C 11 H 13 ClO 4 , (III). The five-membered furanose ring of the three compounds has a conformation between a C2′- endo ,C3′- exo twist and a C2′- endo envelope. The ribofuranose groups of (I) and (III) are connected by intermolecular O—H...O hydrogen bonds to six symmetry-related molecules to form double layers, while the ribofuranose group of (II) is connected by O—H...O hydrogen bonds to four symmetry-related molecules to form single layers. The O...O contact distance of the O—H...O hydrogen bonds ranges from 2.7172 (15) to 2.8895 (19) Å. Neighbouring double layers of (I) are connected by a very weak intermolecular C—F...π contact. The layers of (II) are connected by one C—H...O and two C—H...F contacts, while the double layers of (III) are connected by a C—H...Cl contact. The conformations of the molecules are compared with those of seven related molecules. The orientation of the benzene ring is coplanar with the H—C1′ bond or bisecting the H—C1′—C2′ angle, or intermediate between these positions. The orientation of the benzene ring is independent of the substitution pattern of the ring and depends mainly on crystal-packing effects.

A five-component supramolecular nanorotor with reversibly acting brakes has been prepared from a four-component nanorotor by adding the photo- and heat-responsive 2,2'-diazastilbene as a signal transducer. The rotational speed was reversibly switched between 86 and 38 kHz.

Crystals of hexa- tert -butyldisilane, C 24 H 54 Si 2 , undergo a reversible phase transition at 179 (2) K. The space group changes from Ibca (high temperature) to Pbca (low temperature), but the lattice constants a , b and c do not change significantly during the phase transition. The crystallographic twofold axis of the molecule in the high-temperature phase is replaced by a noncrystallographic twofold axis in the low-temperature phase. The angle between the two axes is 2.36 (4)°. The centre of the molecule undergoes a translation of 0.123 (1) Å during the phase transition, but the conformation angles of the molecule remain unchanged. Between the two tri- tert -butylsilyl subunits there are six short repulsive intramolecular C—H...H—C contacts, with H...H distances between 2.02 and 2.04 Å, resulting in a significant lengthening of the Si—Si and Si—C bonds. The Si—Si bond length is 2.6863 (5) Å and the Si—C bond lengths are between 1.9860 (14) and 1.9933 (14) Å. Torsion angles about the Si—Si and Si—C bonds deviate by approximately 15° from the values expected for staggered conformations due to intramolecular steric H...H repulsions. A new polymorph is reported for the crystal structure of 1,1,2,2-tetra- tert -butyl-1,2-diphenyldisilane, C 28 H 46 Si 2 . It has two independent molecules with rather similar conformations. The Si—Si bond lengths are 2.4869 (8) and 2.4944 (8) Å. The C—Si—Si—C torsion angles deviate by between −3.4 (1) and −18.5 (1)° from the values expected for a staggered conformation. These deviations result from steric interactions. Four Si—C( t -Bu) bonds are almost staggered, while the other four Si—C( t -Bu) bonds are intermediate between a staggered and an eclipsed conformation. The latter Si—C( t -Bu) bonds are about 0.019 (2) Å longer than the staggered Si—C( t -Bu) bonds.