Search

There is much interest in interfaces between insulating oxides, such as SrTiO3 (STO) and LaAlO3 (LAO), where a two dimensional electron gas can form due to the so-called polar discontinuity. These interfaces are mostly fabricated by Pulsed Laser Deposition (PLD). We have investigated such interfaces by reactive RF sputtering in a high-pressure oxygen atmosphere. The films are smooth and crystalline. Transmission Electron Microscopy indicates that the interfaces are sharp and continuous while Electron Energy Loss Spectroscopy data indicate some slight intermixing. However, we find these interfaces to be non-conducting. It appears that the sputtered interface is not electronically reconstructed in the way reported for films grown by PLD, notwithstanding the good structural quality and composition of the films

Neutral macrocyclic alkali‐cation receptors have been covalently linked to one or more molecules of the membrane solvent 2‐nitrophenyl n‐octyl ether (NPOE). These compounds are all highly lipophilic and soluble in NPOE. The flux of alkali‐perchlorate salts through supported liquid membranes (SLMs) has been optimized by variation of the carrier content in the membrane and the temperature. With all carriers, the optimum flux is reached at carrier contents of about 20% (w/w) in NPOE. Above this carrier content the flux decreases because of an increase in the viscosity of the membrane solutions. Relatively low activation energies for transport indicate that the transport is diffusion‐limited. The excellent compatibility between the carriers and the membrane solvent leads to very stable membranes (NPOE/Accurel®). The mechanism of alkali perchlorate transport has been investigated by variation of the source‐phase salt activity and the carrier concentration. Indications about ion pair formation and 2/1 carrier/cation complexation have been obtained from variation of the carrier concentration and transport selectivity measurements.

A general method has been developed for the preparation of bis(syn‐proximally) functionalized calix[4]arenes (6, 8–10). Starting from p‐tert‐butylcalix[4]arene 1a and calix[4]arene 1b syn‐proximally dialkylated calix[4]arenes 2a and 2b, 4, and 5, respectively, were obtained by treatment with 4.2 equiv of NaH and 2.2 equiv of alkylating reagent in DMF. The syn‐proximal substitution pattern was unequivocally proven by an X‐ray structural determination of 2b. Furthermore the influence of different bases on the functionalization of the free hydroxyl groups of 2b with chloroacetone was studied. Cs2CO3 as the base gave the bis(syn‐proximally) functionalized calix[4]‐arene 6 in the highest yield (82%). Cation complexation studies, with the picrate extraction method, showed that subtle changes in regioselective functionalization influences the selectivity for Na4 considerably.

Two different routes are described for the synthesis of the 2,2,2‐trifluoro‐l‐[2‐(dialkyl‐amino)phenyl]ethanones 2 and 9 and their hydrates 3 and 10, respectively, via trifluoroacetylation of the N,N‐dialkylanilines 1 and via a Barbier reaction of 2‐fluorobenzaldehyde. These compounds were thermally converted into a mixture of cis‐ and trans‐pyrrolo‐ and pyrido[1,2‐a] [3,1]benzoxazines, (11: cis; 12: trans). The structure of these compounds was proven by X‐ray analysis (11a) and 1H NOE difference spectroscopy. Cyclization of (R)‐9b (R1 = CH3) gave predominantly one enantiomer (12f, 70%) and in addition two diastereomers of 17a and two of 18a (total yield ≈ 17%), while cyclization of (S)‐9c (R1 = CH2OCH3) gave a mixture of 12g (18%), two diastereomers of 17b (36%) and two diastereomers of 18b (18%). The benzaldehyde 19a (R3 = H), acetophenone 19d (R3 = CH3), trifluoroacetophenones 19b,c (R3 = CF3) and benzophenone 19e (R3 = C6H5) reacted with Lawesson's reagent to yield exclusively the trans‐pyrrolo[1,2‐a] [3,1]benzothiazines 21a‐e in yields of 33‐77%. Reaction of 19f (R1 = CH3, R3 = H), 19g (R1 = CH3, R3 = CF3) and 19h (R1 = CH3, R3 = CH3) with Lawesson's reagent resulted in the formation of mixtures of isomers 21‐24.

Reactions of the four-membered cyclic nitrones 1 with acetyl chloride differ strongly from those of other (cyclic) nitrones. In the presence of water, the nitrones 1 yield the 2-[(acetyloxy)-amino]-N,N-diethylalkanamides 4. The structure of 4b was confirmed by X-ray analysis. In the absence of water, the N,N-diethyl-4-methylene-2-azetidinecarboxamides 5 or the N,N-diethyl-2,3-dihydro-2-azetecarboxamides 6 were obtained. X-ray analysis elucidated the structure of 5a. Under acidic conditions, compounds 5a yielded the 2-oxa-5-azabicyclo[2.1.1]hexan-3-one derivative 13. Acid hydrolysis of 6a gave the α-chloroketone derivative 18 and the 2-oxopropanamide derivative 19.

Crystals of 5,17‐bis(acetamido)‐25,26,27,28‐tetrapropoxycalix[4]arene · ethyl‐acetate (1: 1), C44H54N2O6 · C4H8O2 are triclinic, space group P‐1, a = 13.319(4), b = 15.519(4), c = 22.386(6) Å, α = 104.73(3), β = 99.02(3), γ = 95.30(3)°, T = 100(5) K, Z = 4. The asymmetric unit contains two calix[4]arene molecules and two ethyl acetate molecules. The two calix[4]arene molecules have different pinched cone conformations. The phenyl rings show small but consistent boat‐like deformations. The final R factor is 7.9%.

High-quality crystalline $KY(WO_4)_2:Yb^{3+}$ layers codoped with large concentrations of optically inert Gd3+ and Lu3+ ions were grown by liquid phase epitaxy. Continuous-wave laser operation in a planar waveguide configuration was observed at 1025 nm. For 23% output coupling, a maximum output power of 195 mW was obtained; a slope efficiency of 82.3% was derived, which to the best of our knowledge is the highest value yet reported for a planar waveguide laser to date. For 1.7% output coupling, a laser threshold as low as 18 mW of absorbed pump power was achieved, which is largely due to the enhanced refractive index contrast of ~$7.5\times 10^{-3}$ between the active layer and the undoped $KY(WO_4)_2$ substrate attained by the co-doping, leading to well-confined pump and laser modes

1:1 adducts of N,N′-bis(benzophenone)-1,2-diiminoethane (bz2en) with copper(I) chloride, bromide and iodide, [Cu(bz2en)2][CuX2] (X = Cl, Br, and I), have been synthesized and the structures of the solid bromide and iodide adducts were determined by X-ray crystallography from single-crystal data. The solid-state structure reveals ionic complexes containing a cation of copper(I) ion coordinated to four nitrogen atoms of two bz2en molecules (distorted tetrahedron) and a linear dibromocuprate(I) and a di-μ-iodo-diiododicuprate(I) anion for the bromo and iodo adducts, respectively. The bromo adduct structure contains CHBr intermolecular hydrogen bonds. The complexes are very stable towards atmospheric oxygen in the solid state. The spectral properties of the above complexes are also discussed.

Understanding the nature of the ground state and its low-lying excitations in the copper oxide superconductors is a prerequisite for determining the origin of high-temperature superconductivity. A superconducting order parameter (that is, the energy gap) with a predominantly dx2-y2 symmetry is well-established. However, various deviations from a pure d-wave pair state, such as the possibility of Cooper pairing with broken time-reversal symmetry or an admixed dx2-y2+s pair state, have been theoretically predicted and actively sought in numerous experimental studies. Here, we present an angle-resolved phase-sensitive technique for accurately determining the in-plane pairing symmetry, and demonstrate this technique in optimally doped YBa2Cu3O7-δ. We find that the gap along the b-axis (Cu–O chain) direction is at least 20% larger than that along the a-axis direction, and that any imaginary idxy, is or ip component must be smaller than a few per cent of the dx2-y2 component of the gap.

The atomic surface structure of single terminated SrTiO3(0 0 1) (1 × 1) is investigated employing surface X-ray diffraction. In order to obtain these surfaces a special treatment is needed consisting of chemical etching and annealing. Since this is done in an aqueous and subsequently oxygen environment, after which the crystals are kept at ambient conditions, the surface is studied in air. Crystal truncation rods are measured and several models that are proposed in literature in recent years are tested against the experimental data. These models include surface rumpling, low temperature-like distortions, strontium adatom and lateral displacement distortions for both TiO2 and SrO-terminated surfaces. None of these models represents the data very accurately. A much better fit to the experimental results is obtained by using a model in which a TiO2-terminated crystal is covered by an oxygen layer.

Films of BaTiO3ranging from 20 nm to 300 nm in thickness were grown with pulsed laser deposition on Nb:SrTiO3. The quality of the layers was investigated using atomic force microscopy, X-ray reflectivity and X-ray diffraction. Both the micrographs and the X-ray reflectivity spectra indicate a smooth surface of the layers. The X-ray diffraction profiles measured using synchrotron radiation show features characteristic for highly crystalline thin films. The application of an external electric field parallel to thecaxis changes anhklreflection of BaTiO3to anhk\bar{l} reflection. Due to the anomalous dispersion, the intensities of these two reflections are not equal and the atomic displacements can be determined from the intensity differences. The electric field-induced intensity changes can be as large as a few percent, which makes data collection from a 100 nm film using CuKα radiation from an X-ray tube feasible. The ΔI/Ivalues of a number of reflections from the 20 and 50 nm films were measured using synchrotron radiation. The observed ΔI/Ivalues were in good agreement with the intensity changes expected for polarization switching in the bulk.

Highly stable films of tetranitrotetrapropoxycalix[4]arene (9) with second-order nonlinear optical (NLO) properties and a noncentrosymmetric structure were obtained by a novel crystallization process at 130-140 degrees C in a de electric field. The packing of 9 in these films was elucidated by a combination of X-ray diffraction, angle-dependent second- harmonic generation, and scanning force microscopy (SFM). The experimental results agree well with solid-state molecular dynamics calculations for these films. No crystalline phase was observed for nitrocalix[4]arene derivatives with longer or branched alkyl chains; this explains the limited NLO stability of films of these calixarenes. Scanning force microscopy o­n the aligned films of 9 showed two distinct surface lattice structures: a rectangular lattice (a = 9.3, b = 11.7 Angstrom) and a pseudohexagonal lattice (d approximate to 11.4 Angstrom). The combination of these data with the interlayer distance of 8.9 Angstrom (X-ray diffraction) allowed the packing of molecules of 9 in these structures to be fully elucidated at the molecular level.

Combination of calix[4]arenes functionalized at the upper rim at the 5- and 17-positions with amino and formyl groups, respectively, gives a new series of "head-to-head" linked double calix[4]arenes in nearly quantitative yield. The X-ray structure of a modified double calix[4]arene is reported. The novel, highly preorganized receptor molecules complex silver(I) ions (K(ass) = 9.5 x 10(5) M(-)(1) in CDCl(3)); the selectivity of complexation was studied by supported liquid membrane transport experiments and chemically modified field effect transistor measurements.

We have investigated the properties of interfaces between LaAlO3 films grown on SrTiO3 substrates singly terminated by TiO2. We used RF sputtering in a high-pressure oxygen atmosphere. The films are smooth, with flat surfaces. Transmission electron microscopy shows sharp and continuous interfaces with some slight intermixing. The elemental ratio of La to Al, measured by the energy dispersive X-ray technique, is found to be 1.07. Importantly, we find these interfaces to be non-conducting, indicating that the sputtered interface is not electronically reconstructed in the way reported for films grown by pulsed laser deposition because of the different interplays among stoichiometry, mixing, and oxygen vacancies.

A new method for the selective functionalization of resorcinarene cavitands is described starting from tetrakis(bromomethyl)cavitands.

Nineteen novel alkyl substituted porphyrins have been synthesized and their thermal phase behaviour has been investigated in detail. Twelve compounds showed a reversible phase transition below the isotropization temperature. From time resolved microwave conductivity (TRMC) measurements and powder X-ray diffractometry it was concluded that the molecular packing does not change significantly at the lower phase transition temperature and that the porphyrin cores occupy isolated positions. Single X-ray diffraction measurements showed that the porphyrins are arranged in a layered structure and that the space between the layers is occupied by the alkyl substituents of the pyrrole units. The phase transitions at the lower temperature were therefore identified as changes in the crystal ordering of the porphyrins.

The overall dynamics of partially phosphorylated and thiophosphorylated p-tert-butylcalix[6]arenes has been studied by NMR spectroscopy. When p-tert-butylcalix[6]arene is monosubstituted with a phosphate or thiophosphate group, the calix[6]arene skeleton is remarkably rigidified. The 1,3- and 1,4-(thio)phosphorylated p-tert-butylcalix[6]arenes are more flexible. 2D NMR spectroscopy showed that these calix[6]arenes adopt syn conformations. A combination of 1H and 31P NMR spectroscopy revealed that the calix[6]arene (thio)phosphates are involved in at least three dynamic processes, viz., macrocyclic ring interconversion, hydrogen bond array reversal, and pinched conformer interconversion. The activation barrier (ΔGm⧧) for macrocyclic ring interconversion depends on the type and number of substituents and ranges from 67 to 86 kJ·mol-1. The activation barrier (ΔGh⧧) for hydrogen bond array reversal depends on the number of hydroxyl groups and ranges from 31 to 45 kJ·mol-1. For the pinched conformer interconversion an activation barrier (ΔGp⧧) ranging from 44 to 55 kJ·mol-1 was found. Pinched conformations have been frequently observed in the solid state, for example, for mono- and 1,4-bis(thiophosphorylated) p-tert-butylcalix[6]arene. These studies, however, show for the first time that these conformations also exist in solution and that differently pinched conformers may rapidly interconvert.

The correlation between the vicinal properties of SrTiO3 (001) substrates and the twinning in YBa2Cu3O7–x thin films grown by pulsed-laser deposition is studied using x-ray diffraction with reciprocal space mapping. The vicinal properties, i.e., angle and in-plane orientation, play a significant role in the anisotropic strain starting at the interface between substrate surface and film, and affect the twin behavior of YBa2Cu3O7–x. On substrates having an [110] in-plane orientation of the step edges, a completely preferred twin pair is observed if the vicinal angle is increased to 0.60°. Whereas on substrates having their step edges oriented along one of the crystallographic axis, the films exhibit a detwinning as the vicinal angle increases. For α = 1.10° a maximum detwinned, i.e., monocrystalline film is obtained. At this angle, the diffusion length of YBa2Cu3O7–x during the growth matches the terrace length of SrTiO3. Up to this specific angle, the films are grown perpendicular to the optical instead of the crystallographic surface.

We have studied the polar surface of singly terminated DyScO3 (110) crystals by reflective high-energy electron diffraction, surface x-ray diffraction and angle-resolved mass spectroscopy of recoiled ions. These techniques show that the surfaces are (1 × 1) reconstructed, which points to the absence of ordered cation vacancies at the surface. The best surfaces were obtained after a selective chemical wet etch. We suggest that for ScO2 terminated surfaces, adsorbates, or oxygen vacancies are most likely to occur in order to overcome the polarity difference between stoichiometric bulk crystal and vacuum.

The formation of a stable calix[4]arene monohemiketal is described. X-ray crystallographic data provide conclusive evidence for the presence of a stabilizing hydrogen bond.

Complexes of 18-crown-6 with alkali-metal cations (Na+, K+, and Rb+), urea, and the uncomplexed crown ether were studied in vacuo with the molecular dynamics method. Conformational data from these calculations (simulation times in the range from 6-15 ns) was compared with information from the Cambridge Structural Database. Despite the differences in condition between the simulations and the solid state, a number of interesting similarities are observed.

In DMF or acetonitrile with NaH as a base at room temperature the tetraalkylation of calix[4]arenes 1a and 1b proceeds via the syn-1,2-disubstituted products to the tetraalkylated calix[4]arenes in the cone conformation. With KH as a base the tetraalkylated calix[4]arenes are predominantly formed in the partial cone conformation, and the reaction proceeds via both the syn-1,3-di and the syn-1,2-disubstituted products. Also the solvent influences the pathway via which tetraalkylation takes place. The syn-1,2-disubstituted calix[4]arenes 4-6 can be isolated in 15-55 % from the NaH/DMF or MeCN reactions when only 2.2 equiv of the electrophile are used.

A series of new metallo-macrocycles with a furan, pyridine, terphenyl, and xylene moiety has been synthesized.

Crystals of 5,17-bis(acetamido)-25,26,27,28-tetrapropoxycalix[4]arene · ethyl-acetate (1: 1), C44H54N2O6 · C4H8O2 are triclinic, space group P-1, a = 13.319(4), b = 15.519(4), c = 22.386(6) A, α = 104.73(3), β = 99.02(3), γ = 95.30(3)°, T = 100(5) K, Z = 4. The asymmetric unit contains two calix[4]arene molecules and two ethyl acetate molecules. The two calix[4]arene molecules have different pinched cone conformations. The phenyl rings show small but consistent boat-like deformations. The final R factor is 7.9%.

A general method has been devoloped for the preparation of tetra-O-alkylated calix[4]arenes in the 1,3-alternate conformation (3a,c-e) starting from p-tert-butylcalix[4]arenes 1a,b using Cs 2 CO 3 in DMF. The 1,3-alternate conformation was unequivocally proved by an X-ray structure determination of 3a. The scope of the reaction was investigated starting from a series of diametrically di-O-alkylated calix[4]arenes 4a-e having different substituents R 2 (t-Bu,CHO,NO 2 ,Br,CN) at the para positions of the phenolic rings

Preparations of the Högberg compounds (Ia–e) with functionalized box-like cavities, designed for complexation of soft cations like silver and copper(II), are described. The structure of1a was determined by X-ray analysis.

Metalloclefts and metallomacrocycles possessing a Lewis acidic uranyl cation were synthesized from the corresponding aldehydes. The complexation of these compounds with neutral molecules was assessed by 1 H NMR spectroscopy, X-ray structure determination, polarography, and molecular modeling. 1 H NMR titration experiments and the crystal structure indicate that the neutral guests coordinate with their Lewis basic site at the uranyl, and that π-π stacking of the aromatic rings of host and guest stabilizes the complexes

Macrocyclic heterotrinucleating ligands that have one compartment for complexation of alkaline or alkaline earth cations and two compartments for transition-metal cations have been synthesized

Calix[41 arenes, in which two opposite p-positions are linked by an aliphatic chain, and their derivatives show transport or complexation properties strongly dependent on the length of this chain. Bicyclo-calix[4]arenes, a special case of 1,3-bridged calix[41 arenes, and annelated calix[41 arenes, a special case of 1 ,&bridged calix [4] arenes, are also described. Although the preferred conformation of calix[4]arenes is the coneconformation due to its stabilization by a cyclic array of hydrogen bonds between the phenolic hydroxyl goups, these molecules are flexible, with a cone to cone inversion rate of about 150 8-1 for a calix[glarene at 47OC (ref. 1). The cone (or any other) conformation may be fixed by derivatisation of the phenolic oxygens. Another possibility is, to connect two p-positions of opposite (1) or adjacent (3) phenolic units by a suitable bridge. Although partial cone or alternate conformations still are possible in these compounds, the complete ring inversion is entirely prevented by the bridge. Compounds of type 1 with (CH2 In -bridges are available by reaction of suitable diphenols with bisbromomethylated phenols in dioxane in the presence of Tic14 (ref. 2).

The initial heteroepitaxial growth of YBa2Cu3O7-delta films on SrTiO3(001) substrates during pulsed laser deposition shows a growth-mode transition and a change of growth unit. The growth starts with two blocks, each two-thirds the size of the complete unit cell. The first of these blocks grows in a step-flow fashion, whereas the second grows in the layer-by-layer mode. Subsequent deposition occurs layer-by-layer of complete unit cells. These results suggest that the surface diffusion in the heteroepitaxial case is strongly influenced by the competition with formation energies, which is important for the fabrication of heteroepitaxial devices on the unit cell scale.

The atomic interface structure between SrTiO3 and LaAlO3 was studied at elevated temperatures employing in situ surface x-ray diffraction. The results at 473 K indicate that the lattice distorts significantly in two ways. First, the interatomic distances between the cations across the interface become as large as 4.03(2) A. Second, the TiO6 octahedra at the interface contract their principal axis along the surface normal considerably and the Ti displaces off center. These distortions can be ascribed to the charge inbalance introduced by the change in atomic species across the interface and to a Jahn-Teller effect. The latter distortion suggests the presence of extra electrons at the interface, which is important for understanding the electronic properties of this system.

Sputter deposition of oxide materials in a high-pressure oxygen atmosphere is a well-known technique to produce thin films of perovskite oxides in particular. Also interfaces can be fabricated, which we demonstrated recently by growing LaAlO3 on SrTiO3 substrates and showing that the interface showed the same high degree of epitaxy and atomic order as is made by pulsed laser deposition. However, the high pressure sputtering of oxides is not trivial and number of parameters are needed to be optimized for epitaxial growth. Here we elaborate on the earlier work to show that only a relatively small parameter window exists with respect to oxygen pressure, growth temperature, radiofrequency power supply and target to substrate distance. In particular the sensitivity to oxygen pressure makes it more difficult to vary the oxygen stoichiometry at the interface, yielding it insulating rather than conducting.

The large anisotropies observed in the in-plane transport properties of untwinned single crystals of YBa2Cu3O6.95 reside in the orthorhombic nature of its band structure which includes CuO chains as well as CuO2 planes. An infinite band model with distinct effective mass in a and b-direction is used to study the a.c. conductivity of a d-wave BCS superconductor. A subdominant s-wave admixture is also included in the gap because both symmetries belong to the same irreducible representation in an orthorhombic system. Parameters are fit to experimental data.

Superconducting thin films have been prepared on Si-substrates, using pulsed laser deposition from a target composed of a mixture of Mg and MgB2 powders. The films were deposited at room temperature and post-annealed at 600 degrees C. The zero resistance transition temperatures were 12 K, with an onset transition temperature of 27 K. Special care has been taken to avoid oxidation of Mg in the laser plasma and deposited film, by optimizing the background pressure of Ar gas in the deposition chamber. For this the optical emission in the visible range from the plasma has been used as indicator. Preventing Mg from oxidation was found to be essential to obtain superconducting films.

C 13 H 22 N 2 O 2 cristallise dans P2 1 /c avec a=6.228, b=20.315, c=11.104A, β=103.87°, Z=4; affinement jusqu'a R=0.059. Desordre pour l'un des atomes C du cyclohexene et dans l'un des groupes ethyl. Connection des molecules grâce a des liaisons hydrogene O-H..O.

The design and synthesis of neutral macrocyclic receptors that complex cations in apolar solvents with a high degree selectivity are based on the ability to organize nucleophilic binding sites (Lewis bases) in a complementary array. Although macrocycles with quaternary ammonium salts are known to complex anions, selectivity is not simply introduced. Macrocyclic and acyclic ligands that contain Lewis acidic binding sites such as boron, silicon, tin, and mercury bind anions, but these structures lack the possibility of subtle structural variation that is the basis for the selectivity in cation complexation. In this communication we report a novel class of neutral receptors for anions that contain an immobilized Lewis acidic binding site (UO{sub 2}){sup 2+} and in which there are ample opportunities to introduce specific secondary binding sites. This concept leads to high thermodynamic stabilities combined with high selectivities. Neutral anion receptors are very important for application in sensors and membrane transport experiments. This unique combination of a Lewis acidic uranyl center and the presence of amide NH groups which can form a favorable H-bond with a coordinated anion guest, in a preorganized receptor, can lead to highly specific anion recognition. 20 refs., 2 figs., 1 tab.

Lucidene (1), a bis(benzopyranyl) sesquiterpene was isolated from the rootbark of Uvaria lucida ssp. lucida, and its structure was determined by spectroscopic methods and single-crystal X-ray crystallography. It is optically inactive and crystallizes in enantiomeric pairs. High-resolution 1H NMR (400 and 600 MHz) spectroscopy allowed the assignment of all protons and indicated the existence of relatively slowly interconverting conformations. The three known dihydrochalcones, uvaretin, diuvaretin, and chamuvaretin, as well as benzyl benzoate were isolated from the same plant as well.

Using 58 keV (0.214 Å) synchrotron radiation we have obtained virtually extinction-free data on Al2O3. Refinement of a multipole model against these data produced deformation densities of high quality, which compare well with theoretical maps.

Thin films of tetranitrotetrapropoxycalix[4]arene (1) show an unusual phase behavior and the formation of a complex multidomain structure. An endothermic phase transition, which occurs between 130 and 140 °C in bulk, was studied using differential scanning calorimetry, optical microscopy, magic angle solid-state NMR, and X-ray crystallography. In annealed films of 1, two types of crystalline domains (I and II) can be distinguished with different optical, morphological, and friction properties. These domains were investigated at the molecular level by a combination of multimode scanning force microscopy (SFM), optical microscopy, and X-ray diffraction experiments. SFM force measurements as well as tapping mode phase images showed that different functional groups are exposed at the surface for the different domains. The friction forces observed in SFM depend on the type of domain, the applied load, and the orientation of the domain with respect to the scanning direction. The friction forces observed at normal forces below ca. 240 nN are lower for type I domains than for type II domains. For forces higher than 260 nN an inversion of the relative friction is observed. Moreover, type I domains exhibit a friction anisotropy that can be attributed to different orientations of the molecular crystal structure with respect to the scanning direction. Two lattices were observed by high-resolution SFM in type I domains, one of rectangular symmetry (x = 10.0 Å, y = 11.8 Å, α = 90°) and one of pseudohexagonal symmetry (d = 11.6 Å), which were in agreement with the parameters of the (010) and (011) facets of the X-ray single-crystal structure (a = 23.94 Å, b = 33.01 Å, c = 20.59 Å, and α, ß, γ = 90°). In conclusion, the molecular packing and friction properties of the multidomain structure of thin films of 1 could be elucidated by SFM and complementary methods.

A systematic investigation of the conceptofpre-organization of nonlinear optical (NLO) active chromophoric groups in calix[4]arene derivatives and the influence on the absolute second-order nonlinear optical coefficients is reported. Several calix[4]arenes were synthesized by modification of the electron-withdrawing groups at the upper rim of the aromatic and extension of the conjugated system of the pre-organized chromophoric groups. Electrical field induced second harmonic generation (EFISH) experiments showed high (0) values up to 1165·10-48 esu. Compared with the corresponding reference compounds, enhancements of the (0) values varying up to 2.5 times per chromophore were observed which proves the benefit of pre-organization of NLO-active units in a multi-chromophoric system. Another important advantage is that the increase in NLO activity observed for these systems is not accompanied with a shift of the absorption band to longer wavelengths exceeding 20 nm. This makes these calix[4]arene derivatives promising building blocks for the development of stable, NLO-active materials that are suitable for frequency doubling.

Three types of lower-lower rim linked biscalix[4]arenes that contain carboxylic ester (1) and/or amide functions (2 and 3) at their remaining phenolic oxygen atoms were synthesized. The homo- and heterodinuclear lanthanide ion complexes based on these ligands were used to study the energy transfer between different lanthanide ions. Photophysical studies comparing the luminescence properties of the homodinuclear Eu3+ complex and the heterodinuclear Eu3+-Nd3+ complex of 2 indicated that energy transfer is likely to occur from Eu3+ to Nd3+ with an efficiency of > 50%. The luminescence properties turned out to be strongly solvent dependent, which is attributed to structural changes leading to different positions of the lanthanide ions in the cavities provided by the biscalix[4]arene.

The solid-state structure of 1·NaClO4 has been determined by X-ray diffraction and shows the Na+ complexed in an approximate hexagonal bipyrimidal fashion. The six ether oxygens form the ground plane, the inner carbonyl group and one of the two outer carbonyl groups occupy the apical positions. The solution structure in methanol, as determined by NMR spectroscopy, has a time-averaged plane of symmetry through the inner phenyl ring. This plane of symmetry is the result of a fast interconversion of conformations in which either one of the outer carbonyl groups is coordinated to the Na+. The enthalpy of activation in methanol determined by T1p measurements is 5 ± 1 kcal mol–1. This process of fast exchange was supported by TRAVEL/CHARMm simulations which revealed a transition-state structure with the two outer carbonyl groups coordinated to the Na+ with a plane of symmetry through the inner phenyl ring. The calculated activation energy is 6.1 kcal mol–1, in very good agreement with the experimental value. A significant influence of the solvent on the structure of 1·Na+ could be ruled out by an MD simulation in methanol. The structure is very similar to the solid-state structure.

The structure of the title compound C17H18N4O3, has been determined. The crystal structure contains four independent molecules which differ in the conformation of the methoxymethyl side chains.