Solid-State Properties of Hexaazatriphenylenehexacarbonitrile HAT(CN)6.− Radical Anions in Crystalline Salts Containing Cryptand(M+) and Crystal Violet Cations

Crystalline {Cryptand[2.2.2](Na⁺)}{HAT(CN)₆^.−}⋅0.5C₆H₄Cl₂ ( 1 ), {Cryptand[2.2.2](K⁺)}{HAT(CN)₆^.−} ( 2 ), (CV⁺){HAT(CN)₆^.−} ( 3 ), and (CV⁺){HAT(CN)₆^.−}⋅2C₆H₄Cl₂ ( 4 ) salts (where CV⁺ is the crystal violet cation) containing hexaazatriphenylenehexacarbonitrile radical anions have been obtained. The solid-state molecular structure as well as the optical and magnetic properties of HAT(CN)₆^.− are studied. The formation of HAT(CN)₆^.− in 1 – 4 leads to the appearance of new bands in the visible range, at 694 and 740 nm. The HAT(CN)₆^.− radical anions have spin state S=1/2 and are packed in one-dimensional stacks containing the {HAT(CN)₆^.−}₂ dimers alternated with weaker interacting pairs of HAT(CN)₆^.− in 1 and nearly isolated {HAT(CN)₆^.−}₂ dimers in 2 . The {HAT(CN)₆^.−}₂ dimers are diamagnetic in 1 but they effectively mediate one-dimensional antiferromagnetic coupling of spins within the stacks with moderate exchange interaction of J/k_B = −80 K. The behaviour of salt 2 is described by a singlet–triplet model for the {HAT(CN)₆^.−}₂ dimers with an energy gap of 434(±7) K. Magnetic behaviour of both salts agree well with the data of extended Hückel calculations. Salts 3 and 4 contain isolated stacks of alternated HAT(CN)₆^.− and CV⁺ ions, and in this case, nearly paramagnetic behaviour is observed with Weiss temperatures of −1 and −7 K, respectively. Narrow Lorentzian EPR signals with g = 2.0033–2.0039 were found for the HAT(CN)₆^.− radical anions in 1 and 4 but in solution g-factor shifts to 1.9964. The electronic structure of HAT(CN)₆^.− is analysed based on X-ray diffraction data for 2 , showing a Jahn–Teller distortion of the radical anion that reduces the symmetry from D_3h to C_s and splits the initially degenerated LUMOs.     

Coumarins and esters ofFerula microcarpa

Summary 1. In addition to known compounds, a new terpenoid coumarin has been isolated fromFerula microcarpa — fecarpin, which is the stereoisomer of kamolol in relation to the orientation of the hydroxy group.2. Microferin and microferinin — esters of a new guaiane alcohol microferol with p-hydroxybenzoic and vanillic acids, respectively — have been isolated.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 566–570, September–October, 1978.     

Probing the ground state properties of iron-based superconducting pnictides and related systems by muon-spin spectroscopy

In this short review, we attempt to give a comprehensive discussion of studies performed to date by muon-spin spectroscopy (more precisely the relaxation and rotation technique, also know as μSR) on the recently discovered layered iron-based superconductors. On one side, μSR has been used to characterize the magnetic state of different families of layered iron-based systems. Similarly the subtle interplay of the magnetic state and the structural transition present in some families has been investigated. We will also discuss the information provided by this technique on the interaction between the magnetic state and the superconducting phase. Finally the μSR technique has been used to investigate the magnetic penetration depth of the superconducting ground state. The study of its absolute value, temperature and magnetic field dependence provides crucial tests for investigating possible unconventional superconducting states in such systems.     

Relaxation of the shallow acceptor center in germanium

Polarized negative muons were used to study relaxation mechanisms of shallow acceptors in germanium. In p-type germanium at low temperatures relaxation of the muon spin was observed, indicating that the muonic atom (gallium-like acceptor center) formed via capture of the negative muon by a host atom is in the paramagnetic state and its magnetic moment is relaxing. The relaxation rate of the muon spin was found to depend on temperature and on concentration of gallium impurity. We conclude that to the relaxation of the magnetic moment of the Ga acceptor in Ge there contribute both scattering of phonons and quadrupole interaction between the acceptors. We estimate, for the first time, the hyperfine interaction constant for the gallium acceptor in germanium as 0.11 MHz.     

Highly transparent ceramics with disordered crystal structure

A highly transparent ceramic has been synthesized from Nd³⁺:Y₂O₃ to which 6 mol. % ZrO₂ and 25 mol. % Sc₂O₃ or Lu₂O₃ were added for disordering the crystal structure. Nanopowders with an average particle size of 10–15 nm served as an initial material. They were compacted by the method of uniaxial static pressing combined with ultrasonic action on nanoparticles. The compacting pressure was 200 MPa; the power of the ultrasonic generator was 1.5 kW. It has been shown that the replacement of Y by isovalent Sc and Lu ions and by heterovalent Zr ions reduces the content of pores and the sizes of crystallites. The transparency of the Nd³⁺:Y₂O₃ ceramic with these additives reaches a maximum of 82.2%, and the 40% intensity level spectral band corresponding to the ⁴F_3/2 → ⁴I_11/2 transition widens from 11.4 to 40 nm.     

Estimation of mechanical properties of a viscoelastic medium using a laser-induced microbubble interrogated by an acoustic radiation force

An approach to assess the mechanical properties of a viscoelastic medium using laser-induced microbubbles is presented. To measure mechanical properties of the medium, dynamics of a laser-induced cavitation microbubble in viscoelastic medium under acoustic radiation force was investigated. An objective lens with a 1.13 numerical aperture and an 8.0 mm working distance was designed to focus a 532 nm wavelength nanosecond pulsed laser beam and to create a microbubble at the desired location. A 3.5 MHz ultrasound transducer was used to generate acoustic radiation force to excite a laser-induced microbubble. Motion of the microbubble was tracked using a 25 MHz imaging transducer. Agreement between a theoretical model of bubble motion in a viscoelastic medium and experimental measurements was demonstrated. Young's modulii reconstructed using the laser-induced microbubble approach were compared with those measured using a direct uniaxial method over the range from 0.8 to 13 kPa. The results indicate good agreement between methods. Thus, the proposed approach can be used to assess the mechanical properties of a viscoelastic medium.     

Microscopic coexistence of superconductivity and magnetism in Ba(1-x)K(x)Fe2As2

It is widely believed that, in contrast to its electron-doped counterparts, the hole-doped compound Ba(1-x)K(x)Fe(2)As(2) exhibits a mesoscopic phase separation of magnetism and superconductivity in the underdoped region of the phase diagram. Here, we report a combined high-resolution x-ray powder diffraction and volume-sensitive muon spin rotation study of Ba(1-x)K(x)Fe(2)As(2) showing that this paradigm does not hold true in the underdoped region of the phase diagram (0≤x≤0.25). Instead we find a microscopic coexistence of the two forms of order. A competition of magnetism and superconductivity is evident from a significant reduction of the magnetic moment and a concomitant decrease of the magnetoelastically coupled orthorhombic lattice distortion below the superconducting phase transition.     

Crystal structure and magnetic properties of an ionic C60 complex with decamethylcobaltocene: (Cp*2Co)2C60(C6H4Cl2, C6H5CN)2. Singlet-triplet transitions in the C60(2-) anion

The C(60) complex with decamethylcobaltocene, (Cp(2)Co)(2)C(60)(C(6)H(4)Cl(2), C(6)H(5)CN)(2) (1) (C(6)H(4)Cl(2) = 1,2-dichlorobenzene; C(6)H(5)CN = benzonitrile), has been obtained as single crystals by the diffusion method. The IR and UV-vis-NIR spectra show the presence of the C(60)(2)(-) and the Cp(2)Co(+) ions, which form a three-dimensional framework with channels accommodating solvent molecules. EPR and SQUID measurements show that C(60)(2)(-) has a diamagnetic singlet (S = 0) state in the 2-140 K range. The appearance of a broad EPR signal and the increase in magnetic susceptibility of 1 above 140 K are assigned to a thermal population of a close lying triplet (S = 1) state. The singlet-triplet energy gap for C(60)(2)(-) in solid 1 is estimated to be 730+/-10 cm(-)(1).     

Structure and configuration of cauferinin

Summary From the roots ofFerula conocaula Korov. a terpenoid coumarin of the iresane series with three hydroxy groups has been isolated which has been called cauferinin.On the basis of the result of a study of its chemical and spectral characteristics and its conversion into cauferin, the structure and relative configuration (I) has been put forward for cauferinin.Institute of the Chemistry of Plant Substances, Academy of Sciences of the Uzbek SSR, Tashkent. Orginal article translated from Khimiya Prirodnykh Soedinenii, No. 2, pp. 151–154, March–April, 1979.