Łukasz Dobrzycki

Quadrannulene: A Nonclassical Fullerene Fragment

The presence of nonhexagonal rings in an otherwise graphitic lattice induces curvature. Pentagons are common—twelve pentagons surrounded by hexagons make up C60. Larger rings are present in Stone–Wales defects, and the polyhedral formula of Euler mandates their existence in carbon nanotube Y-junctions. Except for a single, partially saturated example, four-membered rings in graphitic structures are, however, unknown. The smallest examples of these graphitic structures are the [n]circulenes, wherein a central n-sided polygon is surrounded by n-fused benzenoid rings. [7]Circulene, first prepared by Yamamoto, Nakazaki, and coworkers in 1983, is saddle shaped. [6]Circulene, or coronene, is the trivial, planar case, and it was first synthesized by Scholl andMeyer in 1932 but also occurs naturally. [5]Circulene, or corannulene, comprises 1/3 of the C60 skeleton and has been intensely studied, and it was first prepared by Lawton and Barth in 1971. Whereas a few pioneering attempts have been reported, [4]circulene has never been synthesized before. We report herein the preparation and characterization of a stable [4]circulene. By analogy with Lawton s naming of corannulene (Latin: cor, heart; annula, ring), we suggest the trivial name quadrannulene (Latin: quadra, square; annula, ring) for the [4]circulene parent. Hence, we name this derivative 1,8,9,16-tetrakis(trimethylsilyl)tetra-cata-tetrabenzoquadrannulene, abbreviated TMS4-TBQ. The IUPAC name and atom numbering are given in the Supporting Information. Our unoptimized five-step synthesis (Scheme1) provides TMS4-TBQ in very low yield. Hopf and co-workers recently summarized two synthetic strategies to the quadrannulene core: making the four-membered ring from [2,2]-paracyclo-

Complete Series of Alkali-Metal M(BH3NH2BH2NH2BH3) Hydrogen-Storage Salts Accessed via Metathesis in Organic Solvents

We report a new efficient way of synthesizing high-purity hydrogen-rich M(BH3NH2BH2NH2BH3) salts (M = Li, Na, K, Rb, Cs). The solvent-mediated metathetic synthesis applied here uses precursors containing bulky organic cations and weakly coordinating anions. The applicability of this method permits the entire series of alkali-metal M(BH3NH2BH2NH2BH3) salts (M = Li, Na, K, Rb, Cs) to be obtained, thus enabling their comparative analysis in terms of crystal structures and hydrogen-storage properties. A novel polymorphic form of Verkades base (C18H39N4PH)(BH3NH2BH2NH2BH3) precursor was also characterized structurally. For all compounds, we present a comprehensive structural, spectroscopic, and thermogravimetric characterization (PXRD, NMR, FTIR, Raman, and TGA/DSC/MS).

Nickel macrocycles with complex hydrides—new avenues for hydrogen storage research

As part of an investigation into Ni(macrocycle) complexes as a new class of complex hydride hydrogen store catalysts, two isomers of the unusually stable nickel borohydride, Ni(cyclam)(BH4)2 (cyclam = 1,4,8,11-tetraazacyclotetradecane), have been isolated and characterised by means of single crystal X-ray diffraction, infrared spectroscopy, thermogravimetry and calorimetry. trans-Ni(cyclam)(BH4)2 crystallizes monoclinic (P21/c, a = 7.1397(5) A, b = 12.8109(7) A, c = 8.7041(5) A, β = 109.948(6)°, V = 748.36(8) A3, Z = 2); cis-Ni(cyclam)(BH4)2 crystallizes orthorhombic (Pnma, a = 14.4512(7) A, b = 9.4625(6) A, c = 11.7824(7) A, V = 1611.18(16) A3, Z = 4, with static disorder). The compounds were found to be considerably more thermally stable than the unchelated relative, Ni(BH4)2, with the onset of decomposition for the trans isomer at 170 °C, thus nearly 200 °C higher than the decomposition temperature of Ni(BH4)2. This spectacular stabilisation holds promise for related macrocycle complexes of late transition metals to be used as hydrogenation catalysts on an equal footing with their unligated early transition metal counterparts.

On polymorphism and planarity of benzidine dihydrochloride

We present the correct structure of the known polymorph of benzidine dihydrochloride and also the second structure of a new polymorph of this compound, analyse weak interactions in these systems and pinpoint that most similar systems could be wrongly determined to be planar when the weakest reflections are not recorded during data collection and not taken into account during refinement.

New alkoxycarbonyl derivatives of dibenzotetraaza[14]annulene. Crystal and molecular structure of [5,14-dihydro-7,16-diisopropoxycarbonyl-8,15-dimethyl-6,17-diphenyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecinato(2-)-κ4N]nickel(II)

Abstract The reaction of Ni(II) complex of 5,14-dihydro-6,17-dimethyl-8,15-diphenyldibenzo[b,i][1,4,8,11]tetraazacyclotetradecine with oxalyl chloride and appropriate alcohols and phenols afforded new meso alkoxy- and aryloxycarbonyl derivatives. The demetallation of Ni(II) complexes equipped with isopropoxycarbonyl-benzyloxycarbonyl-, 4-acetylphenoxycarbonyl- and biphenyloxycarbonyl- meso substituents by means of gaseous HCl gave corresponding free bases. Single crystal X-ray analysis of acetone solvate of isopropoxycarbonyl derivative disclosed the structure with saddle-shaped molecules arranged in stacking columns with molecules of acetone locked in the cavities and interacting with the host’s molecules via CH⋯⋯O hydrogen bonds. The new products have been characterised by elemental analysis, 1H, 13C NMR, IR, ESI and MALDI MS spectra.

On two alizarin polymorphs

For centuries alizarin has been used as natural pigment, yet, now it is also used in histochemistry and dermatology, and as a dye for semiconductor solar cells. Here, the crystal structure of the previously known form of alizarin is determined accurately and its new polymorph is discovered. The two polymorphs crystallize into the same monoclinic crystal system. The previously known form is centrosymmetric (P21/c space group) whereas the new one is not (space group Pc). Both crystals are twinned, disordered, and have the molecules packed into the crystal lattices in a comparable way. However the powder patterns of both forms are visibly different. In addition the analysis of the fingerprints of H⋯O intermolecular interactions based on Hirshfeld surfaces also indicates differences in the packing. Yet, these similarities between two forms of alizarin make their vibrational spectra hardly distinguishable.

Towards Clathrates: Frozen States of Hydration of tert-Butylamine†

The dilution of tert-butylamine (tBA) with water and subsequent cooling leads to a large series of different crystalline hydrates by an in situ IR laser melting-zone procedure. The crystal structures were determined for tBA⋅n H2 O, with n=0, 1/4, 1, 7 1/4, 7 3/4, 9 3/4, 11, and 17. For the two lower hydrates (n= 1/4, 1), one- and two-dimensional hydrogen-bonded networks are formed, respectively. The higher hydrates (n>1) exhibit a clathrate-like three-dimensional water framework with the tBA molecules as part of, or sitting inside, the cages. In all cases, tBA is hydrogen-bonded to the H2 O framework. In the intermediate range (1<n<7 1/4), crystallization is hindered, and no crystalline phases could be observed. The crystal structures that are achieved from the dilution of tBA with water are considered to be frozen stages of hydration, describing the genesis of such clathrate-like structures, finally ending at ice as an example of an infinitely diluted hydrate.

Slavikite—Revision of chemical composition and crystal structure

Abstract Given its abundant occurrence at Wieściszowice, SW Poland, we have carried out a revision of the chemical composition and crystal structure of the sulfate mineral slavikite. Slavikite crystallizes in the trigonal space group R3̅. The unit-cell parameters, determined using single-crystal X-ray diffraction (R1 = 0.0356) at 100 K, are a = 12.1347(6) Å, c = 34.706(3) Å, and V = 4425.9(5) Å3. The results of chemical analyses reported in the literature and made on material from Wieściszowice unequivocally show that Na is not an essential component of slavikite, at odds with the generally accepted Süsse formula and model of the crystal structure. Our chemical analyses and structure determination lead us to propose a new, more adequate, formula for slavikite: (H3O+)3Mg6Fe15(SO4)21(OH)18·98H2O. The crystal structure consists of infinite layers of Fe-hydroxy-sulfate linked with [Mg(H2O)6]2+ octahedra, forming a honeycomb-like structure. These layers are perpendicular to the Z axis and are built up from two types of SO-24 tetrahedra and two types of Fe octahedra (Fe1 with O and OH, and Fe2 with O, OH, and H2O ligands attached, respectively). Compared to previous studies, the main skeleton of the slavikite structure, i.e., the layers of Fe3+- hydroxy-sulfate, Mg[(H2O)6]2+ octahedra and disordered isolated sulfate ions, remains unchanged. However, on the basis of careful chemical analysis and single-crystal X-ray diffraction studies, we conclude that Na cations are absent from the structure of slavikite and their positions are occupied by disordered protonated water clusters balancing the excess of negative charge in the structure. These protonated water clusters are located at the inversion centers on the 3 axes of symmetry between two [Mg(H2O)6]2+ cations also lying on such axes (but not at the inversion centers). This structure also contains another disordered moiety-an isolated sulfate anion located at the inversion center of the 3 axis. This SO-24 anion is disordered in such a way that each oxygen atom partially occupies 5 positions resulting from 5 different orientations of the anion. This complex anion is linked by hydrogen bonds with the O atoms of ordered water molecules. In consequence, the disordered sulfate anion is surrounded by 12 ordered water molecules, thus forming a spherical water environment around the sulfate.

The role of steric hindrance in the intramolecular oxidative aromatic coupling of pyrrolo[3,2-b]pyrroles

The presence of steric hindrance triggers different reaction pathways in the intramolecular oxidative aromatic coupling of tetraaryl-pyrrolo[3,2-b]pyrroles and leads to the formation of a fluorene moiety and a new cationic π-system linked together by a spiro carbon atom. Computational studies elegantly rationalized these results. These previously unknown functional dyes emit red light with reasonable efficiency.

The Coumarin-Dimer Spring - The Struggle Between Charge Transfer and Steric Interactions

The synthesis of a weakly coupled, strongly polarized coumarin dimer has been achieved for the first time. The three-step strategy comprises the Skattebøl formylation followed by the Knoevenagel reaction and the formation of a tertiary amide by using a peptide-type procedure. The molecule consists of two different coumarin moieties: One is a classical donor-acceptor system and the second one possesses a weaker amide donor at the 7-position. The polarized coumarin dimer can form an electronically conjugated structure possessing an electric dipole larger than that of 7-(dimethylamino)coumarin-3-carboxylic acid. The limited flexibility of the inter-coumarin connection results in stable conformers of different electric dipole moments and complex photophysics. In the solid state, this compound has a strongly bent conformation with the two coumarin units forming an angle of around 74°. In solution, two conformers are in equilibrium. The existence of the molecule as two conformers in the ground state has been confirmed by optical studies, and further corroborated by molecular calculations. The fluorescence spectra possess a unique feature: A charge-transfer band (ca. 550 nm) is visible only in nonpolar or weakly polar solvents. Optical spectroscopy studies coupled with molecular calculations allowed us to rationalize this phenomenon: The large amplitude of intramolecular motions is responsible for the conformational isomerization as well as producing a conical intersection between the potential energy surfaces of the excited singlet state and the ground state, which opens an internal conversion channel that effectively competes with the fluorescence of the conformers.