Analysis of polarization mode dispersion fluctuations in single mode fibres due to temperature

We have studied the effect of temperature on the birefringence and polarization mode dispersion PMD in standard single mode fibre (SSMF) with elliptical core cross section by using numerical computations. On the basis of simulation we have concluded that PMD fluctuates more rapidly than the stress-induced birefringence. In addition, DGD is inversely proportional to temperature.     

Fe(II)(TRIM)(2)]F(2), the First Example of Spin Conversion Monitored by Molecular Vibrations

The new [Fe(II)(TRIM)(2)]F(2) spin-crossover complex (TRIM = 4-(4-imidazolylmethyl)-2-(2-imidazolylmethyl)imidazole) has been synthesized, crystallizing in the monoclinic system, space group P2/n, with Z = 2, a = 9.798(2) ?, b = 8.433(2) ?, c = 14.597(3) ?, and beta = 90.46(1) degrees. The structure was solved by direct methods and refined to conventional agreement indices R = 0.032 and R(w) = 0.034 with 1378 unique reflections for which I > 3sigma(I). The molecular structure consists of [Fe(TRIM)(2)](2+) complex cations hydrogen-bonded to six fluoride anions. The crystal packing results from this highly symmetrical and dense 3D network of hydrogen bonds. The coordination geometry of the iron(II) center can be described as a weakly distorted octahedron, including six nitrogen atoms originating from the two TRIM ligands coordinated to Fe(II) through their imine nitrogen atoms. Investigation of [Fe(II)(TRIM)(2)]F(2) by magnetic susceptibility measurements and M?ssbauer spectroscopy as a function of temperature indicates a 5% thermal variation of the spin fraction between 50 and 150 K, at variance with all previous litterature data. The spin conversion is gradual with 6% LS fraction below 50 K and less than 1% above 150 K. A theoretical approach based on the Ising-like model, completed with harmonic oscillators associated with the 15 vibration modes of the FeN(6) coordination octahedron, successfully fits the data with an energy gap of approximately 40 K between the lowest LS and HS electrovibrational states, an average vibration frequency omega(LS) of 232 K in the LS state, and an average omega(LS)/omega(HS) ratio of 1.3. Taking these results into account, the computed molar entropy change DeltaS associated with a complete conversion between the HS and LS states of Fe(II)(TRIM)(2)F(2) ( approximately 40 J.K(-)(1).mol(-)(1)) is in fair agreement with the expected value.     

Light induced excited spin state trapping in the binuclear spin crossover compound [Fe(bpym)(NCS)2]2(bpym) exhibiting a high-spin ground state

A photo-magnetic effect is evidenced using near-infrared light in the binuclear complex [Fe(bpym)(NCS)₂]₂(bpym). This compound has a ⁵T_2g–⁵T_2g ground state and exhibits no thermal spin crossover – in contrast to the analogous [Fe(bpym)(NCSe)₂]₂(bpym). The estimated photo-conversion ratio is ca. 30%. By means of magnetic susceptibility measurements as well as Raman and infrared absorption spectroscopies, the nature of the photo-induced phase was established as the ⁵T_2g–¹A_1g state, which means that only one iron center is converted to low-spin. The photo-induced state was completely converted back to the ground state either by visible light excitation or by heating.     

On bistability in molecular systems: Photomagnetic studies of inorganic complexes

Photo‐induced effects have been detected by magnetic measurements, Mössbauer spectroscopy and reflectivity. The LIESST effect has been achieved in the spin‐crossover system [Fe_xCo_1-x(btr)₂(NCS)₂]·H₂O. We investigated the purely photo‐induced magnetism of a Prussian Blue analogue Rb_0.52Co[Fe(CN)₆]_0.84, 2.31 H₂O, involving an optical electron transfer from Fe^II to Co^III. Inherent aspects of photomagnetic experiments are described: bulk and surface effects, magnetic and electronic metastabilities of the photo‐excited state.     

Synthesis, structures, and magnetic properties of novel mononuclear, tetranuclear, and 1D chain Mn(III) complexes involving three related asymmetrical trianionic ligands

The manganese(III) complexes studied in this report derive from asymmetrical trianionic ligands abbreviated H(3)L(i) (i = 4-6). These ligands are obtained through reaction of salicylaldehyde with "half-units", the latter resulting from monocondensation of different diamines with phenylsalicylate,. Upon deprotonation, L(i) (i = 4-6) possess an inner N(2)O(2) coordination site with one amido, one imine, and two phenoxo functions, and an outer amido oxygen donor. The trianionic character of such ligands yields original neutral complexes with the L/Mn stoichiometry. The crystal and molecular structures of three complexes have been determined at 190 K (1) or 180 K (2 and 3). Complex 1 crystallizes in the triclinic space group P (No. 2): a = 7.8582(14) A, b = 10.9225(16) A, c = 12.4882(18) A, alpha = 67.231(14) degrees, beta = 72.134(14) degrees, gamma = 82.589(13) degrees, V = 940.6(3) A(3), Z = 2. Complex 2 crystallizes in the orthorhombic space group Pbcn (Nuomicron. 60): a = 23.8283(15) A, b = 11.1605(7) A, c = 26.152(2) A, V = 6954.8(8) A(3), Z = 8, while complex 3 crystallizes in the monoclinic space group P2(1)/c (No. 14) with a = 11.7443(14) A, b = 7.5996(10) A, c = 18.029(2) A, beta = 100.604(10) degrees, V = 1581.6(3) A(3), Z = 4. Owing to hydrogen bonds and pi-pi stackings, the mononuclear neutral molecules of 1 are arranged in a 2D network while complexes 2 and 3 are tetranuclear and polymeric (1D chain) species, respectively, owing to the bridging ability of the oxygen atom of the amido function. The experimental magnetic susceptibilities of complexes 2 and 3 indicate the occurrence of similarly weak Mn(III)-Mn(III) antiferromagnetic interactions (J = -1.1 cm(-1)). Single ion zero-field splitting of manganese(III) must be taken into account for satisfactorily fitting the data by exact calculation of the energy levels associated to the spin Hamiltonian through diagonalization of the full matrix for axial symmetry in 2 (J = - 1.1 cm(-1), D(1) = 2.2 cm(-1), D(2) = -2.8 cm(-1)), D(1) and D(2) being associated to the six- and five-coordinate Mn ions, respectively. A weaker antiferromagnetic interaction (J = - 0.2 cm(-1)) operates through pi-pi stacking in complex 1. Complex 3 is a weak ferromagnet (ordering temperature approximately 7 K) as a result of the spin canting originating from the crystal packing.     

Spin crossover behavior in a family of iron(II) zigzag chain coordination polymers

The paper reports the synthesis and detailed characterization of two new Fe(II) compounds: [Fe(pyim)(2)(bpen)](ClO(4))(2).2C(2)H(5)OH (2) and [Fe(pyim)(2)(bpe)](ClO(4))(2).C(2)H(5)OH (3) (pyim = 2-(2-pyridyl)imidazole, bpen = 1,2-bis(4-pyridyl)ethane, and bpe = 1,2-bis(4-pyridyl)ethene). Both compounds and the earlier synthesized [Fe(pyim)(2)(bpy)](ClO(4))(2).2C(2)H(5)OH (1) (bpy = 4,4'-bipyridine) form a family of one-dimensional spin crossover coordination polymers. Variable-temperature magnetic susceptibility measurements and M?ssbauer spectroscopy have revealed rather gradual spin transitions centered at 176 and 198 K for 2 and 3, respectively. The fitting of magnetic properties with the regular solution model leads to the enthalpy and entropy of spin transitions and the cooperativity parameter equal to DeltaH = 12.3 kJ mol(-1), DeltaS = 68.5 J mol(-1) K(-1), Gamma = 1.80 kJ mol(-1) for 2 and DeltaH = 13.6 kJ mol(-1), DeltaS = 68.1 J mol(-1) K(-1), Gamma = 2.05 kJ mol(-1) for 3. The crystal structures of 2 and 3, resolved by X-ray diffraction at 293 K, belong to the monoclinic space group C2/c (Z = 4). Both compounds display a one-dimensional infinite zigzag-chain structure. The polymer chains are stacked into two-dimensional sheets through intermolecular pi-interactions. The crystal packing of both compounds encloses two kinds of channels in which the counter ions and ethanol molecules are inserted. The DFT calculations of binuclear fragments extracted from three polymers resulted in the energy gaps between the LS and HS states being ordered as the observed transition temperatures. The influence of bridging ligands in the studied family of compounds was found in the modulation of the energy gap between the LS and HS states, leading to different transition temperatures.