Kurt Schenk

Bio: Kurt Schenk is an academic researcher from University of Lausanne. The author has contributed to research in topics: Crystal structure & Phase transition. The author has an hindex of 27, co-authored 92 publications receiving 1922 citations. Previous affiliations of Kurt Schenk include École Polytechnique Fédérale de Lausanne & École Polytechnique.

Luminescent Properties of Lanthanide Nitrato Complexes with Substituted Bis(benzimidazolyl)pyridines.

Abstract: The protonated form of the ligand 2,6-bis(1‘-methylbenzimidazol-2‘-yl)pyridine crystallizes as its perchlorate salt (HL1)ClO4 (1) in the orthorhombic system Pbca, with a = 13.976(3) A, b = 14.423(3) A, c = 19.529(4) A, Z = 8. The proton is located on one benzimidazole N-atom, and the two N-methyl substituents lie on the same side of the pyridine N-atom (cisoid conformation). New 1:1 nitrato complexes of composition [Eu(NO3)3(Li)](solv‘)y have been isolated with L4 (4), L6 (5), L7 (6), and L8 (7), and their structural and photophysical properties are compared with those of the previously reported complexes [Eu(NO3)3(L1)(MeOH)] (2) and [Eu(NO3)3(L3)] (3). The crystal and molecular structure of [Eu(NO3)3(L7)(MeCN)]·2.5MeCN at 180 K (6a, triclinic, P1, a = 12.137(2) A, b = 14.988(3) A, c = 16.926(3) A, α = 114.52(3)°, β = 98.28(3)°, γ = 103.99(3)°, Z = 2) shows a decacoordinated EuIII ion to six O-atoms from the nitrates, three N-atoms from L7, and one N-atom from a coordinated MeCN. The metal-centered lumin...

Hydrazone Derivatives, an Efficient Class of Crystalline Materials for Nonlinear Optics

Abstract: We report on the synthesis and optical characterization of hydrazone derivatives developed for second-order nonlinear optics. Electric-field-induced second harmonic generation (EFISH) as well as semiempirical quantum-chemical computations have been carried out to investigate and explain the nonlinear optical properties of these molecules. We obtained values of up to 220 x 10(-40) m(4)/V for the molecular hyperpolarizability beta at lambda = 1907 nm. The investigation of a series of 39 hydrazone derivatives with the second harmonic generation powder test according to Kurtz and Ferry revealed that an extraordinarily large fraction of these hydrazones show efficient second-order nonlinear activity. Among them, 4-(dimethylamino)-benzaldehyde-4-nitrophenylhydrazone (DANPH) and 4-(1-azacycloheptyl)-benzaldehyde-4-nitrophenylhydrazone (ACNPH) were selected for more detailed investigations. Their crystalline structures are presented, and the role played by hydrogen bonds in their molecular packing is emphasized. Finally, preliminary linear and nonlinear optical data of DANPH crystals are reported. [References: 42]

Stability and Size-Discriminating Effects in Mononuclear Lanthanide Triple-Helical Building Blocks with Tridentate Aromatic Ligands.

Abstract: The planar aromatic tridentate ligand 2,6-bis(1-methylbenzimidazol-2-yl)pyridine (L(1)) reacts with Ln(III) (Ln = La-Lu) in acetonitrile to give the successive complexes [Ln(L(1))(n)()](3+) (n = 1-3). Stability constants determined by spectrophotometry and potentiometric competitive titrations with Ag(I) show that the 1:1 and the 1:2 complexes display the usual thermodynamic behavior associated with electrostatic effects while the 1:3 complexes exhibit an unusual selectivity for the midrange Ln(III) ions (Delta log K(3)(Gd-Lu) approximately 4). A detailed investigation of the solution structure of [Ln(L(1))(3)](3+) (Ln = La-Dy) reveals that the closely packed triple-helical structure found in the crystal structure of [Eu(L(1))(3)](3+) is retained in acetonitrile for the complete series. A sharp control of the coordination cavity results from the interstrand pi-stacking interactions which appear to be optimum for Gd(III). For Yb(III), for instance, a 1:2 complex only could be isolated, which crystallizes as a hydroxo-bridged dimer [Yb(OH)(L(1))(2)](2)(ClO(4))(4)(HClO(4))(0.5)(CH(3)CN)(7.32)(L(1))(0.5) (triclinic, Po, a = 13.250(2) A, b = 16.329(2) A, c = 27.653(3) A, alpha = 99.941(9) degrees, beta = 93.394(9) degrees, gamma = 108.114(9) degrees, Z = 2). The binding of bulky substituents to the nitrogen atoms of the benzimidazole side arms in L(4) (i) severely affects the wrapping process, (ii) leads to less stable triple-helical building blocks, and (iii) removes the size-discriminating effect. The last can however be restored if a strong electron-donor group is connected to the central pyridine ring in L(8). Stability and solution structure data for [Ag(2)(L(i)())(2)](2+) (i = 1, 4, 8) are also reported and discussed.

Taking advantage of luminescent lanthanide ions

Abstract: Lanthanide ions possess fascinating optical properties and their discovery, first industrial uses and present high technological applications are largely governed by their interaction with light. Lighting devices (economical luminescent lamps, light emitting diodes), television and computer displays, optical fibres, optical amplifiers, lasers, as well as responsive luminescent stains for biomedical analysis, medical diagnosis, and cell imaging rely heavily on lanthanide ions. This critical review has been tailored for a broad audience of chemists, biochemists and materials scientists; the basics of lanthanide photophysics are highlighted together with the synthetic strategies used to insert these ions into mono- and polymetallic molecular edifices. Recent advances in NIR-emitting materials, including liquid crystals, and in the control of luminescent properties in polymetallic assemblies are also presented. (210 references.)