Completely spirocyclopropanated macrocyclic oligodiacetylenes and their permethylated analogues: preparation and properties

The acyclic dehydrotrimer (12) and -hexamer (28) of 1,1-diethynyl-2,2,3,3-tetramethylcyclopropane were prepared from 1-chloro-1-(trimethylsilylethynyl)-2,2,3,3-tetramethylcyclopropane (4) in six and nine steps, respectively, in 36 and 8 % overall yield, respectively, using Cadiot-Chodkiewicz or Hay coupling procedures as key steps. Mono-tert-butyldimethylsilyl (TBDMS) protection of the acyclic dehydrotrimer (20) and -hexamer (23) of 1,1-diethynylcyclopropane followed by Hay coupling and protiodesilylation furnished the acyclic dehydrohexamer (23) and -dodecamer (29) in 35 and 56 % overall yield, respectively. Subsequent cyclizing oxidative dimerization of 12 or cyclization of 28 using a modified Glaser protocol produced the first completely permethylspirocyclopropanated macrocyclic oligodiacetylene, compound 30 in 49 and 21 % yield, respectively. The cyclic dehydrohexa- (31) and dehydrododecamer (32) have been prepared from 23 and 29 in 49 and 7 % yield by applying the same protocol. The macrocycle 32 is particularly interesting in that it contains 60 carbon atoms in the inner ring, and indeed a decomposition mode consecutively cleaving off ethylene units from it as well as from 31 and tetramethylethylene from the permethylated exp-[6]rotane 30 has been proved by differential scanning calorimetry with evolved gas analysis. The thermal decomposition of these "exploding" [6]rotanes 31 and 30 set on at 100 and 135 degrees C, respectively, and release energies of 478 and 285 kcal. mol(-1), respectively, significantly more than the energy release of the explosive hexogen with 143 kcal mol(-1).     

Synthesis and structure of a heptanuclear nickel(II) complex uniquely exhibiting four distinct binding modes,two of which are novel,for a hydroxamate ligand

The reaction of 2-(dimethylamino)phenylhydroxamic acid (2-dmAphaH) with NiSO(4).6H2O gives the complex [Ni7(2-dmAphaH-1)2(2-dmApha)8(H2O)2]SO(4).15H2O uniquely exhibiting four distinct hydroxamate binding modes, two of which are novel, and showing both antiferromagnetic and ferromagnetic interactions in contrast to [Cu5(2-dmAphaH-1)4(HSO4)2(MeOH)2].2MeOH, a strongly antiferromagnetic metallacrown formed with CuSO(4).5H2O.     

Determination of hyperfine tensor components from nuclear frequencies at canonical orientations of the g-tensor

The analytical procedure for the determination of all components of the symmetric hyperfine tensor of the I=1/2 nucleus in the g-tensor coordinate system is described, assuming that nuclear frequencies corresponding to the principal directions of the g-tensor and exact values of the external magnetic field (or nuclear Zeeman frequencies) are experimentally available.     

Electron irradiation effects in doped high temperature superconductors YBa2Cu3? x M x O y (M = Fe, Ni; x=0; x =0:01)

The influence of irradiation by electrons with an energy of 8 MeV, at dose intervals between 10¹³ and 2×10¹⁸el/cm², on the properties of impurity doped, high-temperature superconductor YBa₂Cu_3−x M _x O _y (M = Fe, Ni; x=0; x=0:01) ceramics has been studied. It has been established that, as the irradiation dose is increased, the onset temperature of the transition to the superconducting state (T _c ^on ), and the intergranular weak link coupling temperature between granules (T _m ^J ), exhibit an oscillation around their initial values of approximately about 1–1.5 K. This oscillation indicates that the process of radiation defect formation in HTSC occurs in multiple stages. It was also found that the critical current (J _c )decreases with an increase of the irradiation dose, and exhibits a local minimum at a dose of 8×10¹⁶el/cm²coinciding with minima for T _c ^on and T _m ^J at this dose. It was found that the introduction of Fe atoms to the ceramic decreases T _m ^J , while introducing Ni atoms decreases both T _c ^on and T _m ^J ; it is suggested that this is a result of Ni substitution of Cu both in Cu2 plane sites and Cu1 chain sites. The introduction of Ni causes a large change in the intergranular critical current density, J _c . A critical irradiation dose is obtained (2×10¹⁸)after which all HTSC parameters strongly decrease, i. e. the superconductivity of HTSC is destroyed.      

Free field representation for massive integrable models

A new approach to massive integrable models is considered. It allows one to find symmetry algebras which define the spaces of local operators and to get general integral representations for form-factors in theSU(2) Thirring and Sine-Gordon models.     

Femtosecond spectroscopy of optical excitations in single-walled carbon nanotubes: evidence for exciton-exciton annihilation

Frequency-resolved femtosecond transient absorption spectra and kinetics measured by optical excitation of the second and first electronic transitions of the (8,3) single-walled carbon nanotube species reveal a unique mutual response between these transitions. Based on the analysis of the spectra, kinetics, and their distinct amplitude dependence on the pump intensity observed at these transitions, we conclude that these observations originate from both the excitonic origin of the spectrum and nonlinear exciton annihilation.     

LiInSe2 nanosecond optical parametric oscillator

Optical parametric oscillation using the new lithium selenoindate nonlinear crystal is reported for what is to our knowledge the first time. A 17 mm long, type II phase-matched sample is pumped by a 10 ns Nd:YAG laser. The minimum pump energy threshold is 3 mJ for a signal-resonant configuration. The signal and idler waves are tunable between 1.47 and 1.57 microm, and 3.3 and 3.78 microm, with a total output energy of 170 microJ corresponding to a 2.4% energy conversion at 8 mJ pump, only limited by the AR coatings damage. With optimized crystal quality and coatings, lithium selenoindate should show superior performance as compared with AgGaS(e)2 crystals, owing to its 4x larger thermal conductivity.