Mössbauer effect study of the magnetic structure in δ-FeOOH

Two samples of-FeOOH with different particle sizes have been studied in an external field of 4 T and as a function of temperature. They were found to have a ferrimagnetic structure due to an unequal occupancy of antiferromagnetically coupled octahedral ferric ions. The large surface contribution, which is characterized by a canted spin structure and by highly deformed Fe³⁺ co-ordinations, strongly influences the magnetic properties observed with Mössbauer spectroscopy.     

High glass transition temperature chromophore functionalised poly(phenylquinoxalines) for nonlinear optics

New chromophore functionalised second-order nonlinear optical (NLO) poly(phenylquinoxalines) were prepared by reaction of a bis(1,2-dicarbonyl)chromophore monomer and a tetraamine at room temperature. The heterocyclic polymers have high glass transition temperatures (>195 °C) and can therefore be excellent polymeric materials with high poling stabilities of the NLO effect.     

Efficient,Reversible Redox‐Switching of Molecular First Hyperpolarizabilities in Ruthenium(II) Complexes Possessing Large Quadratic Optical Nonlinearities

Low‐energy metal‐to‐ligand charge‐transfer (MLCT) excitations are associated with the very large molecular nonlinear optical (NLO) coefficients, β, of the complexes [Ru^II(NH₃)₅(N‐R‐4,4′‐bipyridinium)]³⁺ (R=methyl, phenyl, or 4‐acetylphenyl). Chemical oxidation to the Ru^III forms causes bleaching of the MLCT absorptions and marked attenuation of the NLO responses. Both effects are completely reversed upon re‐reduction, and the extent of the β switching is about 10‐ to 20‐fold.     

Tetraalkynyl calix[4]arenes with advanced NLO properties

Rigid, highly conjugated tetraalkynyl-calix[4]arenes synthesised via Sonogashira coupling give rise to improved second-order hyperpolarizability values as determined by hyper-Rayleigh scattering--a technique that in addition to X-ray crystallography also allows for the conformational analysis of the calixarene structures in solution.     

Mössbauer study of Co-substituted magnetite

Some aspects of a comprehensive Mössbauer spectroscopic study at variable temperatures and in applied magnetic fields of the spinel system Co _x Fe_3?x O₄ with 0≤x≤0.6 are presented. Emphasis is given to the dipolar contributionB _dip to the magnetic hyperfine field at the octahedral sites. Its dependence on the temperature and on the Co concentration is determined and discussed.     

Donor‐Embedded Polybinaphthalenes for Nonlinear Optical Applications: Influence of the Incorporation of a Double Bond

Summary: In this paper two new donor‐embedded polybinaphthalenes prepared by the Heck reaction are presented. By introducing a double bond in the polymer backbone, the supramolecular structure was altered in comparison with polymers without the double bond. Comparison between the CD/UV‐Vis spectra of polymers, with and without the double bond (previously synthesized in our laboratory) proved this change in a supramolecular structure. The double bonds also allow crosslinking upon heat treatment. NLO experiments demonstrated a more stable nonlinearity over time depending on the degree of crosslinking.

     

Organometallic complexes for nonlinear optics: Part 21. Syntheses and quadratic hyperpolarizabilities of alkynyl complexes containing optically active 1,2-bis(methylphenylphosphino)benzene ligands

The preparation of the chloro complex trans-[FeCl₂{(R,R)-diph}₂] (1) and the alkynyl complexes trans-[M(4-CCC₆H₄R)Cl{(R,R)-diph}₂] [M=Fe, R=NO₂ (2); M=Ru, R=H (4), NO₂ (5), (E)-CH=CH-4-C₆H₄NO₂ (6); M=Os, R=NO₂ (7)], incorporating the optically active diphosphine 1,2-bis(methylphenylphosphino)benzene (diph), are described. Oxidation potentials, as determined by cyclic voltammetry, increase as 2<7<5. Molecular quadratic nonlinearities by hyper-Rayleigh scattering at 1064 nm increase upon introduction of an acceptor group (4<5), chain-lengthening of bridging group (5<6), and proceeding from 3d to 4d and 5d metal (2≤5≤7). Two-level-corrected nonlinearities reproduce the first two trends, but metal variation follows the sequence 2<7<5. The experimental and two-level-corrected nonlinearities for 6 (2795×10⁻³⁰ and 406×10⁻³⁰ esu, respectively), are amongst the largest observed thus far for organometallic complexes. Crystals of complexes 2 and 7 exhibit second-harmonic generation (assessed using the Kurtz powder technique), with an efficiency for the former of twice that of urea.