Interplanar Separation Research Articles

Dioxidobis(2-oxo-1,2-dihydropyridin-3-olato)molybdenum(VI)

In the title compound, [Mo(C5H4NO2)2O2], the MoVI atom exhibits a distorted octa­hedral coordination geometry formed by two terminal oxo ligands and two monoanionic O,O-bidentate pyridinone ligands. The two terminal oxo ligands lie in a cis arrangement, the ketonic O atoms of the pyridinone ligands are coordinated trans to the oxo ligands and the deprotonated hydroxyl O atoms are located trans to each other. The crystal structure contains inter­molecular N—H⋯O hydrogen bonds, C—H⋯O contacts and face-to-face π–π stacking inter­actions with an inter­planar separation of 3.25 (1) Å.

2-(2-Hydroxyethyl)phthalazin-1(2H)-one

In the mol­ecule of the title compound, C10H10N2O2, the rings are nearly coplanar, making a dihedral angle of 2.35 (5)°. In the crystal structure, inter­molecular C—H⋯O, C—H⋯N and O—H⋯O hydrogen bonds link the mol­ecules, generating R 4 4(22) and R 4 4(24) ring motifs to form a three-dimensional network. A weak π–π inter­action between the pyridazinone and benzene rings further stabilizes the crystal structure, with a centroid–centroid distance of 3.709 (3) Å and an inter­planar separation of 3.312 Å.

1,3-Bis(chloromethyl)-2-methyl-5-nitrobenzene

The title compound, C9H9Cl2NO2, is a natural product isolated from the endophytic fungus No. B77 of the mangrove tree from the South China Sea coast. In the crystal structure, the mol­ecules lie on twofold axes and form offset stacks through face-to-face π–π inter­actions. Adjacent mol­ecules in each stack are related by a centre of inversion and have an inter­planar separation of 3.53 (1) Å, with a centroid–centroid distance of 3.76 (1) Å. Between stacks, there are C—H⋯O inter­actions to the nitro groups and Cl⋯Cl contacts of 3.462 (1) Å.

1-Benzylimidazolium hexafluorophosphate–1-benzylimidazole (1/1)

In the title compound, C10H11N2 +·PF6 −·C10H10N2, the H atom involved in protonation is disordered equally between the cation and the neutral mol­ecule. The dihedral angle between the phenyl and imidazole rings is 82.6 (2)°. In the crystal structure, there are head-to-tail π–π stacking inter­actions between imidazole rings; the inter­planar separation is 3.295 (1) Å and the centroid–centroid separation is 3.448 (3) Å. In the centrosymmetric anion, two F atoms are disordered over two positions; the refined site-occupancy factors are 0.855 (11) and 0.145 (11).

Doxofyllinium tetrachloridoantimonate(III) monohydrate

The title compound, (C11H14N4O4)[SbCl4]·H2O, comprises a protonated doxofyllinium cation [7-(1,3-dioxolan-2-ylmeth­yl)-1,3-dimethyl-2,6-dioxo-3,7-dihydro-1H-purin-9-ium], an [SbCl4]− anion and a water mol­ecule linked by N—H⋯O and O—H⋯Cl hydrogen bonds: the [SbCl4]− anions form centrosymmetric dimers via weak Sb⋯Cl inter­actions [Sb⋯Cl = 3.1159 (9) Å]. The geometrical arrangement in the crystal structure is characterized by slipped π–π stacking of the parallel purine ring systems, with an inter­planar separation of 3.32 Å.

Bis[2-(2-aminoethyl)-1H-benzimidazole-κ2N2,N3]zinc(II) bis(perchlorate)

In the title compound, [Zn(C9H11N3)2](ClO4)2, the ZnII atom resides on a crystallographic twofold axis and is coordinated by two benzimidazole N [Zn⋯N = 1.993 (4) Å] and two amine N atoms [Zn⋯N = 2.036 (4) Å] in a distorted tetra­hedral geometry. The crystal packing is dominated by N—H⋯O inter­actions involving the perchlorate anions and π–π stacking inter­actions with an inter­planar separation of 3.42 Å. A weak C—H⋯O inter­action is also present.

3,5-Dibromo-2-hydroxybenzoic acid

The title compound, C7H4Br2O3, has an intra­molecular O—H⋯O=C hydrogen bond and aggregates to form hydrogen-bonded dimers via O—H⋯O inter­actions. The formation of zigzag one-dimensional mol­ecular tapes via C—H⋯Br inter­actions and π–π stacking inter­actions (inter­planar separation = 3.42 Å) completes the crystal structure.

4,4′-Bis(benzimidazol-1-yl)biphenyl

The mol­ecule of the title compound, C26H18N4, resides on a crystallographic inversion centre with a dihedral angle of 44.94 (5)° between the benzimidazole ring system and the benzene ring. The primary hydrogen bond is C—H⋯N and inversion-related pairs of these generate a chain of rings along the c-axis direction; π⋯π stacking involving the benzimidazole groups with inter­planar separations of ca 3.4 Å complete the inter­actions.

(Acetylacetonato)aqua(2,2′,2′′-terpyridine)chromium(III) bis(perchlorate) dihydrate hexamethylphosphoramide solvate

The title compound, [Cr(C5H8O2)(C15H11N3)(H2O)](ClO4)2·2H2O·C6H18N3OP, adopts a distorted octa­hedral configuration about the CrIII atom, mainly due to the rigidity of the terpyridyl ligand. The N—Cr—N bite angles are significantly distorted from 90° at 78.3 (1) and 78.6 (1)°. The Cr—N bond distances vary between 1.998 (1) and 2.068 (1) A. The crystal packing is controlled by hydrogen bonding and π-stacking, with an interplanar separation of 3.263 (2) A.

Temperature-dependent multilayer relaxation of clean and hydrogen-dosed Nb(100)

Low-energy-electron-diffraction intensity measurements and multiple scattering analysis are used to determine the multilayer surface relaxation of clean and hydrogen-dosed Nb(100) as a function of temperature. Accurate characterization of residual surface impurity concentration (oxygen) based on Auger electron spectroscopy is used to obtain a meaningful extrapolation of the first-layer relaxation to the clean surface value: ${d}_{12}=1.481\ifmmode\pm\else\textpm\fi{}.05\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$ corresponding to ${\ensuremath{\Delta}}_{12}=\ensuremath{-}10\ifmmode\pm\else\textpm\fi{}3%$, a 10% relaxation relative to the bulk value ${d}_{0}=1.645\phantom{\rule{0.3em}{0ex}}\mathrm{\AA{}}$. This experimental result for ${d}_{12}$ can be used to judge the accuracy of recent ab initio calculations for Nb(100). Temperature-dependent changes in surface relaxation resulting from hydrogen dosing of Nb(100) manifest an expansion of the near-surface lattice resulting from subsurface hydrogen atoms. The hydrogen-induced expansion of near-surface interplanar separation is determined to be $3\ifmmode\pm\else\textpm\fi{}1%$ at $T=125\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, $4\ifmmode\pm\else\textpm\fi{}1%$ at $T=300\phantom{\rule{0.3em}{0ex}}\mathrm{K}$, and $\ensuremath{-}1\ifmmode\pm\else\textpm\fi{}1%$ at $T=400\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. The measured hydrogen-induced surface lattice expansion is consistent with the bulk lattice constant change $(\ensuremath{\Delta}\ensuremath{\sim}4.5%)$ that occurs when Nb is hydrated to form $\ensuremath{\beta}\mathrm{Nb}\mathrm{H}$. The observed relaxation of the hydrogen-dosed near-surface interplanar separation to the clean surface value for $T>400\phantom{\rule{0.3em}{0ex}}\mathrm{K}$ is consistent with the subsurface ``hydrogen valve'' model that has been used to account for unusual hydrogen uptake kinetics associated with Nb(100).

One‐Dimensional, Cofacial Porphyrin Polymers Formed by Self‐Assembly of meso‐Tetrakis(ERE Donor) Zinc(II) Porphyrins

A series of meso-tetrakis-(ERE donor) zinc(II) porphyrins nZn (ERE donor = 4-R-3,5-bis[(E)-methyl]phenyl; 1Zn: E = NMe2, R = Br; 2Zn: E = NMe2, R = H; 3Zn: E = OMe, R = Br; 4Zn: E = OMe, R = H) have been synthesized in excellent yields. As a result of the combination of a Lewis acidic site and eight Lewis basic sites within one molecule, monomeric molecules of nZn self-assemble to form one-dimensional porphyrin polymers [nZn](infinity) in the solid state, as confirmed for 1Zn and 3Zn by X-ray crystallography. The coordination environment around the zinc(II) ions in these polymers is octahedral. They are ligated by four equatorial nitrogen atoms of the porphyrin and two apical E atoms (E = N, O) provided by the EBrE donor groups of adjacent nZn molecules. Complexes 2Zn and 4Zn did not form single crystals, but solid-state UV/Vis analysis points to the formation of similar structures. Solution UV/Vis and 1H NMR spectroscopy indicated that interactions between 1Zn and 2Zn monomers in the polymers are stronger than between 3Zn and 4Zn monomers. Interestingly, they also revealed that the presence of a neighboring bromine atom in the EBrE donor groups has a considerable influence on the coordination properties of the benzylic N or O atoms. The zinc(II) ions of the porphyrins most likely adopt only hexacoordination in the solid state, owing to the unique predisposition of Lewis acidic and basic sites in the nZn molecules. Several parameters of the aggregates, for example, the interplanar separation between porphyrins and the zinc-zinc distances, change as a function of the coordinating E groups. The high degree of modularity in their synthesis makes these zinc(II) porphyrins an interesting new entry in noncovalent multiporphyrin assemblies.

2,5-Bis(2-naphthylmethylsulfanyl)-1-thia-3,4-diazacyclopenta-2,5-diene

The title molecule, C24H18N2S3, consists of three essentially planar fragments viz. two methylnaphthalene groups and a five-membered thiadiazole ring. The dihedral angles between the two methylnaphthalene groups and the central 1-thia-3,4-diazacyclopenta-2,5-diene group are 78.9 (1) and 68.8 (1)°. In the crystal structure, - stacking interactions exist between pairs of symmetry-related naphthalene fragments with an interplanar separation of 3.35 A. All bond lengths and angles are comparable with previous reports except that both C-S bond lengths are slightly longer than normal. In addition, the C-S-C and S-C-C bond angles appear to be smaller than normal and this could be due to the steric hindrance of the methylnaphthalene fragments.

Bis(2,9-dimethyl-1,10-phenanthroline)copper(I) tetraphenylborate dichloromethane solvate

In the title compound, [Cu(C14H12N2)2]C24H20B·CH2Cl2, CuI is chelated by two 2,9-dimethyl-1,10-phenanthroline (2,9-Me2phen) ligands, in a distorted tetrahedral coordination geometry. The average Cu—N bond length is 2.032 Å, and the interligand dihedral angle is 77.60 (6)°. The complexes form π–π stacking interactions between 2,9-Me2phen ligands, with a perpendicular interplanar separation of 3.652 (5) Å.

Suitanes

Suitanes

The contact behavior of elastic/plastic non-Gaussian rough surfaces

A three-dimensional contact analysis was conducted to investigate the contact behavior of elastic--perfectly plastic solids with non-Gaussian rough surfaces. The effect of skewness, kurtosis and hardness on contact statistics and the effect of skewness and kurtosis on subsurface stress are studied. Non-Gaussian rough surfaces are generated by the computer with skewness, Sk, of −0.3, 0.0 and 0.3, and kurtosis, K, of 2.0, 3.0 and 4.0. Contact pressures and subsurface stresses are obtained by contact analysis of a semi-infinite solid based on the use of influence functions and patch solutions. Variation of fractional elastic/plastic contact area, maximum contact pressure and interplanar separation as a function of applied load were studied at different values of skewness and kurtosis. Contact pressure profiles, von Mises stresses, tensile and shear stress contours as a function of friction coefficient were also calculated for surfaces with different skewness and kurtosis. In this study, it is observed that surfaces with Sk = 0.3 and K = 4 in the six surfaces considered have a minimum contact area and maximum interplanar separation, which may provide low friction and stiction. The critical material hardness is defined as the hardness at which severe level of plastic asperity deformation corresponding to the Greenwood and Williamson’s cut-off A plastic/A real = 0.02 occurs for a given surface and load condition. The critical material hardness of surfaces with Sk = 0.3 and K = 4 is higher than that of other surfaces considered.

Two-Dimensional Simulations of CuPc−PCTDA Solar Cells: The Importance of Mobility and Molecular π Stacking

An existing two-dimensional microkinetical model for the photovoltaic effect of molecular-based solar cells has been extended to include electron-hole pair recombination between donor and acceptor sites. Simulations of the short circuit current for simple two-dimensional model heterojunction structures composed of copper phthalocyanine (CuPc) and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) are presented. The short circuit current was investigated as a function of the thickness of the photoactive layer for different choices of mobility for CuPc and PTCDA. The hole mobility of CuPc and/or the electron mobility of PTCDA limits the photovoltaic performance if chosen below a certain threshold determined by the net electron-hole generation rate at the CuPc-PTCDA interface. Also, the mobilities should be of the same order of magnitude. The effect of changing the interplanar separation alpha between the pi stacking molecules was investigated, and it was found that increasing alpha from 0.33 to 0.6 nm increases the short circuit current up to 5 orders of magnitude. This was rationalized in terms of the charge separation energetics of geminate electron-hole pairs and its dependence on alpha. As mobilities decrease with increasing alpha and thus opposes this effect, an optimum for alpha approximately 0.66 nm was found for the CuPc-PTCDA heterojunction model structures. The simulations are interpreted in a simple kinetic picture of an electron-hole pair generation step at the CuPc-PTCDA interface and subsequent transport in the CuPc and PTCDA domains. It is argued that an optimal device configuration involves an amorphous region at the CuPc-PTCDA interface and a gradual increase of the molecular order as the electrodes are approached in the respective CuPc and PTCDA transport regions.

Crystal structure and Raman spectra of rubidium hydrogen squarate

Rubidium hydrogen squarate (RbHC 4O 4, RbHSQ) crystallized in monoclinic space group P2 1/ c. This compound form a short asymmetric intermolecular hydrogen bond whose O–O distance is 2.482(4) Å. The hydrogen squarate anions are forming head-to-tail infinite chain hydrogen-bonding motifs. A long interplanar separation (4.15 Å) indicates that a weak π interaction occurs between hydrogen squarate anions in RbHSQ. The hydrogen bond and cation–anion interactions are the predominant driving forces in the crystal packing. The Raman spectrum of RbHSQ shows an average behaviour between squaric acid and squarate dianion, however, the vibrational modes at ca. 1800 cm −1 (CO stretching mode) and in the region 1500–1700 cm −1 (CO+CC stretching modes) are the most affected by the presence of strong hydrogen bonding interactions.

Supramolecular recognition: association of palladium molecular clefts with planar platinum complexes

The crystal structures of two new molecular recognition adducts formed between a dicationic, di-terpyridyl-Pd–Cl molecular cleft and two square planar platinum complexes are reported. In both structures, the planar platinum-containing guests are located within the molecular cleft formed by the two parallel disposed terpyridyl-Pd–Cl + units of the receptor. The crystal structure of the adduct formed between the molecular cleft and a neutral platinum complex has interplanar distances between the host and guest of 3.24 Å, a distance shorter than that usually ascribed to π-stacking interaction (∼3.45 Å). The short distance is likely the result of metal–metal interaction between the host and guest. The second adduct, that between the dicationic molecular receptor and an anionic platinum complex, also bears the guest within the molecular cleft. The interplanar distances between the cationic terpyridyl-Pd–Cl units of the host and the anionic guest (3.21 and 3.29 Å) are also shorter than typical π-stacking distances but no metal–metal interaction is present. Coulombic attraction between the host and guest is believed to be responsible for the short interplanar separation. These data are discussed in relation to analogous systems that associate through π–π and metal–metal interaction.

Di-μ-2-aminopyridinato-bis[(2,2′-bipyridine)platinum(II)] dinitrate tetrahydrate as a head-to-tail isomer

In the title compound, [Pt2(C10H8N2)2(C5H5N2)2](NO3)2·4H2O, two 2-amino­pyridinate ligands bridge two Pt atoms in a head-to-tail fashion, the Pt—Pt distance being 2.8724 (6) A. The dimers form a one-dimensional stack based on π–π stacking interactions between the bpy (2,2′-bi­pyridine) units, where the interplanar separations are estimated as 3.44 (2) and 3.45 (1) A. No metal–metal interaction exists between the dimers.

10,10-Bis(trimethylsilylethynyl)-9-methylenefluorene–tetracyano-para-quinodimethane (2/1)

The title compound {systematic name: 9-[bis­(tri­methylsilyl­ethynyl)­methyl­ene]­fluorene–tetra­cyano-para-quinodimeth­ane (2/1)}, 2 C24H26Si2·C12H4N4, consists of sandwich-like fluorene–TCNQ–fluorene units with inversion symmetry. The ring systems of the sandwich are parallel; the interplanar separation is 3.3–3.4 Å. The packing of the sandwich units is a herringbone pattern.