Redox chemistry of [Fe2(CN)10]4−. Part 5. Reaction with thiourea

The reaction of the dimeric iron(III) complex [Fe2(CN)10]4– with a large excess of thiourea, tu, takes place in a series of stages, the first two of which have been examined in detail. The first stage is a one equivalent outer sphere electron transfer to form [Fe2– (CN)10]5– and the radical cation tu+· which dimerises to form the disulfide tu22+. There is kinetic evidence for the formation of a significant proportion of a precursor complex [Fe2(CN)10]4–·tu at high concentrations of tu. The second stage involves cleavage of the mixed valence dimer to yield [Fe(CN)5tu]2– and [Fe(CN)5H2O]3–. On standing, substitution of H2O by tu and oxidation by air occurs slowly, and finally all of the original iron is observed as [Fe(CN)5tu]2–.     

Wheel-shaped [Mn12] single-molecule magnets

The reaction of [Mn(12)O(12)(O(2)CCH(3))(16)(H(2)O)(4)].4H(2)O.2CH(3)COOH with n-methyldiethanol amine (H(2)mdea), n-ethyldiethanol amine (H(2)edea), or n-butyldiethanol amine (H(2)bdea) leads to the formation of wheel-shaped Mn(III)(6)Mn(II)(6) complexes with the general formula [Mn(12)(R)(O(2)CCH(3))(14)] (1, R = mdea; 2, R = edea; and 3, R = bdea). Complex 1 crystallizes in the triclinic space group P1, whereas complex 3 crystallizes in the monoclinic space group C(2/c). Complex 1a has the same molecular structure as complex 1 but crystallizes in the monoclinic space group P2(1/n). Complex 3a has the same molecular structure as complex 3 but crystallizes in the triclinic space group P1. Variable-temperature magnetic susceptibility data collected for complexes 1, 2, and 3 indicate that antiferromagnetic exchange interactions are present. The spin ground states of complexes 1, 2, and 3 were determined by fitting variable-field magnetization data collected in the 2-5 K temperature range. Fitting of these data yielded the spin ground-state parameters of S = 8, g = 2.0, and D = -0.47 cm(-1) for complex 1; S = 8, g = 2.0, and D = -0.49 cm(-1) for complex 2; and S = 8, g = 2, and D = -0.37 cm(-1) for complex 3. The ac magnetic susceptibility data were measured for complexes 1, 2, and 3 at temperatures between 1.8 and 10 K with a 3 G ac field oscillating in the range 50-1000 Hz. Slow kinetics of magnetization reversal relative to the frequency of the oscillating ac field were observed as frequency-dependent out-of-phase peaks for complexes 1, 2, and 3, and it can be concluded that these three complexes are single-molecule magnets.     

Mass spectrometry of metal compounds: II—mass spectrometric studies of [CF3EMn(CO)4]2, [CF3EFe(CO)3]2 (E = S,Se), CF3SeFe(CO)2C5H5 and CF3SCr(NO)2C5H5

The electron impact induced mass spectra of [CF₃SMn(CO)₄]₂, [CF₃SeMn(CO)₄]₂, [CF₃SFe(CO)₃]₂, [CF₃SeFe(CO)₃]₂, CF₃SeFe(CO)₂C₅H₅ and CF₃SCr(NO)₂C₅H₅ are reported. These compounds exhibit weak molecular ion peaks and undergo preferential loss of CO or NO groups. The CO or NO free fragments suffer typical loss of ECF₂(E = S, Se) with the simultaneous shift of F from carbon to metal. The ions [FFeC₅H₅]⁺ and [FCrC₅H₅]⁺ in the spectra of the cyclopentadienyl compounds prefer expulsion of π-cyclopentadienyls. The pyrolysis effects on the spectra of the compounds have been studied. An increase in temperature eases the expulsion of ECF₂ groups from all the compounds and favors the formation of [Fe(C₅H₅)₂]⁺ and [Cr(C₅H₅)₂]⁺ in the cyclopentadienyl compounds.     

Random phase approximation theory of higher surface plasma modes

Using the random phase approximation and analytical calculation we show that a higher surface plasma mode can exist near a plane metal-vacuum interface provided the oscillation is sufficiently localized. This conclusion is confirmed for the infinite potential barrier model of the surface where a mode with long-wavelength frequency _p in sodium is predicted.     

Kinematics of deformable media

We investigate the kinematics of deformations in two and three dimensional media by explicitly solving (analytically) the evolution equations (Raychaudhuri equations) for the expansion, shear and rotation associated with the deformations. The analytical solutions allow us to study the dependence of the kinematical quantities on initial conditions. In particular, we are able to identify regions of the space of initial conditions that lead to a singularity in finite time. Some generic features of the deformations are also discussed in detail. We conclude by indicating the feasibility and utility of a similar exercise for fluid and geodesic flows in a flat and curved spacetimes.     

Dynamics in quantum Ising chain driven by inhomogeneous transverse magnetization

We study the dynamics caused by transport of transverse magnetization in one dimensional transverse Ising chain at zero temperature. We observe that a class of initial states having product structure in fermionic momentum-space and satisfying certain criteria, produce spatial variation in transverse magnetization. Starting from such a state, we obtain the transverse magnetization analytically and then observe its dynamics in presence of a homogeneous constant field Γ. In contradiction with general expectation, whatever be the strength of the field, the magnetization of the system does not become homogeneous even after infinite time. At each site, the dynamics is associated with oscillations having two different timescales. The envelope of the larger timescale oscillation decays algebraically with an exponent which is invariant for all such special initial states. The frequency of this oscillation varies differently with external field in ordered and disordered phases. The local magnetization after infinite time also characterizes the quantum phase transition.     

Low-threshold operation of a 355-nm pumped nanosecond β-BaB2O4 optical parametric oscillator

We report the low-threshold operation of a nanosecond β-BaB₂O₄ optical parametric oscillator (OPO) pumped by the third harmonic of a Q-switched Nd:YAG laser. Using cylindrical focusing of the pump beam, a threshold pulse energy of 0.5 mJ is obtained at the signal wavelength of 560 nm, which is about sixteen times lower than that of a spherical focusing configuration. The importance of diffraction loss in the design of tightly focused OPOs is discussed in terms of a simple extension of the conventional OPO model.