Controlling pattern formation in nanoparticle assemblies via directed solvent dewetting

We have achieved highly localized control of pattern formation in two-dimensional nanoparticle assemblies by direct modification of solvent dewetting dynamics. A striking dependence of nanoparticle organization on the size of atomic force microscope-generated surface heterogeneities is observed and reproduced in numerical simulations. Nanoscale features induce a rupture of the solvent-nanoparticle film, causing the local flow of solvent to carry nanoparticles into confinement. Microscale heterogeneities instead slow the evaporation of the solvent, producing a remarkably abrupt interface between different nanoparticle patterns.     

Recognition of ionic guests by ionic beta-cyclodextrin derivatives

Inclusion compounds of cationic, anionic, and neutral p-substituted derivatives of tert-butylbenzene complexed in beta-cyclodextrin and its ionic 6-mono and 6-hepta derivatives were systematically investigated by isothermal titration calorimetry (ITC). All inclusion compounds showed 1:1 stoichiometry with binding constants ranging from 10 to 3 x 10(6) M(-1). The binding free energies could be subdivided into apolar and electrostatic contributions. The electrostatic interactions could be quantitatively described by Coulomb's law by taking into account the degree of protonation of hosts and guests, the orientations of the guests within the hosts, and ion shielding as described by the Debye-Hückel-Onsager theory. The orientations of the guests within the cyclodextrin cavities were determined by ROESY NMR spectroscopy.     

Two New Compounds in the Group of Zinc Phenoxides and Zinc Phenylamides

The synthesis and characterization of ethyl{2‐[(phenylamino)methyl]phenoxy}zinc ( 1 ) and ethyl{2‐[(propan‐2‐ylideneamino)methyl]phenylamido}zinc ( 2 ) are reported. The phenoxide 1 was prepared starting from 2‐(phenylaminomethyl)phenol and diethylzinc and the phenylamide 2 was obtained from 2,2‐dimethyl‐1,2,3,4‐tetrahydroquinazoline and diethylzinc. The compounds were characterized by NMR spectroscopy (¹H, ¹³C{¹H}), IR spectroscopy, elemental analysis, TGA measurements, and X‐ray structure analysis. In the solid state both compounds form dimers where ( 1 )₂ · 4thf shows a planar Zn₂O₂ and ( 2 )₂ a planar Zn₂N₂ unit. Noteworthy, the aminal ring of 2,2‐dimethyl‐1,2,3,4‐tetrahydroquinazoline was opened by its reaction with diethylzinc to give an ylidene moiety at the benzylic nitrogen atom.     

Investigations to calibrate reference standards for the thickness of coatings

Investigations on the traceability of coating thickness measurements to the national standard of length were carried out by topographical and lateral methods. The topographical method used an interference-optical microscope and a modified scanning force microscope to measure the coating thickness as the height of a step on partially coated samples. For the lateral method, a scanning electron microscope was equipped with additional components to measure the coating thickness on cross sections as the distance of material boundary lines. Standards with a coating thickness of about h = 10 nm to 50 μm may be calibrated. The achievable uncertainty depended strongly on the specimen preparation and the specimens themselves. Received: 14 January 1999 / Revised: 22 March 1999 / Accepted: 23 March 1999     

A phase polymorphism N?SAd?I in liquid-crystalline polymethacrylates with 4′-trifluoromethoxyazobenzene mesogenic side groups

The mesophase behaviour of liquid-crystalline polymethacrylates with 4′-trifluoromethoxyazobenzene mesogens and alkylene spacers $ \left( {\rlap{--} ({\rm CH}_{\rm 2} \rlap{--} )_n ,n = 2 - 6} \right) $ in the side chains was investigated and compared with that of the corresponding non-fluorinated polymers. The fluorinated polymers with spacer lengths n = 5 and 6 are the first side-group liquid-crystalline polymethacrylates showing a nematic phase below a smectic A phase.     

Nb2Se2I6: Eine neue Strukturvariante bei Niobchalkogenidhalogeniden mit Kettenstruktur

Nb₂Se₂I₆: A New Structural Variation of Niobium Chalcogenide Halides with Chain Structure Single crystals of Nb₂Se₂I₆, exhibiting a metallic lustre, (monoclinic, C2/c; a = 7.110(1), b = 13.899(3), c = 13.688(3) Å, β = 99.58(3)°; Z = 8) have been obtained by heating mixture of the elements (molar ratio Nb : Se : I = 3 : 1 : 7) in evacuated sealed fused silica tubes at 1073 K for two weeks. After rapid quenching, the tube was reheated to 773 K and then cooled at a rate of 2 K h^–1. Crystals of the title compound formed at the colder part of the tube besides higher niobium iodides. Nb₂Se₂I₆ can also be obtained by slow cooling of a stoichiometric mixture of the elements from 1073 K as a minor product besides triclinic NbSe₂I₂ [1]. The crystal structure is built up with one-dimensional infinite chains [Nb₂Se₂I₄I_4/2]. The main structural features are a short Nb–Nb distance (2.903(1) Å) and a short Se–Se distance (2.318(2) Å) which is expected for +4 and –1 oxidation states, respectively. Homeotypic phases with Nb₂Y₂X₆ chains (Y = Se, Te; X = Br, I) are known [2] except for the combination Y = Se, X = I. They show a primitive rod packing of the Nb₂Y₂X₆ chains in contrast to the title compound which shows a centered rod packing.     

Molekulare gemischtvalente Platin-Iod-Amin-Komplexe: Das dreikernige Pt3I8(NHEt2)2 mit kantenverknüpften planaren und oktaedrischen Baugruppen

Mixed Valence Molecular Platinum Iodide Amin Complexes: The Trinuclear Pt₃I₈(NHEt₂)₂ with Edgeshared Planar and Octahedral Building Groups PtI₂ · NHEt₂ was prepared by reaction of K₂PtCl₄ with KI and NEt₂H in aqueous solution. The crystal structure of the monoclinic compound (a = 20.558(4) Å; b = 7.254(1) Å; c = 13.790(3) Å; β = 100.47(3)°; space group C2/c) consists of binuclear molecules of [{Pt(NH(Et)₂)I}₂(μ-I)₂]. On oxidation of this Pt(II) compound by I₂ in CH₂Cl₂ mixtures of the trinuclear mixed-valence compound Pt₃I₈(NHEt₂)₂ and of the binuclear Pt^IV complex [{Pt(NHEt₂)I₃}₂(μ-I)₂] were obtained. The monoclinic crystal structure of Pt₃I₈(NHEt₂)₂ (a = 20.278(4) Å; b = 10.627(2) Å, c = 14.232(3) Å; β = 115.66(3)° space group C2/c) is built up by trimeric units of two planar Pt^III₃(NHEt₂) groups sharing edges with a central Pt^IVI₆-octhedron.