Montmorillonite alignment induced by magnetic field: evidence based on the diffusion anisotropy of water molecules

Diffusion coefficients of water in Na-montmorillonite (Na-mon) suspensions have been determined by pulsed-field gradient spin-echo (PGSE) NMR spectroscopy for three directions (x, y, and z), where x and y mean the directions perpendicular to the static magnetic field, and z the direction parallel to it. Diffusion anisotropy was observed in the suspensions with Na-mon weight fractions of 0.63, 1.82, and 3.32%; i.e., the diffusivity of water in the z direction is faster than that in the x or y direction. The largest diffusion anisotropy of water was observed at the Na-mon fraction of 3.32%. However, diffusion anisotropy disappeared in the suspensions with Na-mon fraction more than 5.02%. The fast diffusivity in the z direction was slightly enhanced in a stronger static magnetic field (14.1 T). These results indicate that the platelike Na-mon particles are aligned with their platelike faces parallel to the static magnetic field of NMR. We also measured diffusion coefficients of water for the z direction in the temperature range from 24 to 85 degrees C. The plot of diffusion coefficients of water against reciprocal temperature showed a refraction point at 65 degrees C. This phenomenon explicitly means that the alignment is gradually relaxed at higher temperatures.     

Magnetic alignment of the chiral nematic phase of a cellulose microfibril suspension

Stable suspensions of tunicate cellulose microfibrils were prepared by acid hydrolysis of the cellulosic mantles of tunicin. They formed a chiral nematic phase above a critical concentration. External magnetic fields were applied to the chiral nematic phase in two different manners to control its phase structure. (i) Static magnetic fields ranging 1-28 T were used to align the chiral nematic axis (helical axis) in the field direction. (ii) A rotating magnetic field (5 T, 10 rpm) was applied to unwind the helices and to form a nematic phase. These phenomena were interpreted in terms of the anisotropic diamagnetic susceptibility of the cellulose microfibril. The diamagnetic susceptibility of the microfibril is smaller in the direction parallel (chi( parallel)) to the fiber axis than in the direction perpendicular (chi( perpendicular)) to the fiber axis, that is, chi( parallel) < chi( perpendicular) < 0. Because the helical axis coincides with the direction normal ( perpendicular) to the fiber axis, the helical axis aligned parallel to the applied field. On the other hand, the rotating magnetic field induced the uniaxial alignment of the smallest susceptibility axis, that is, chi( parallel) in the present case, and brought about unwinding of the helices.     

Uniaxial alignment of the smallest diamagnetic susceptibility axis using time-dependent magnetic fields

A diamagnetic particle with magnetic susceptibilities chi3 < chi2 = chi1 < 0 was subjected to a rotating magnetic field to obtain an alignment of the chi3 axis (the smallest susceptibility axis) in the direction perpendicular to the plane of the rotating magnetic field. A polymer short fiber, whose fiber axis coincides with the chi3 axis, was suspended in a fluid with the same density, and then a rotating magnetic field generated by a rotation of a pair of permanent magnets was applied. The fiber axis, rotating following the applied field, finally ended up with an alignment perpendicular to the plane of the rotating magnetic field. The experimental data on the time course of the alignment was in good agreement with the numerical calculation based on the equation of rotation.     

PDMS melts on mica studied by confocal Raman scattering

We report surprising surface-induced torsional alignment of polydimethylsiloxane (PDMS) chains in contact with the muscovite (001) mica surface with and without confinement. The alignment was measured by polarized confocal Raman spectroscopy over diffraction-limit circular spots with approximately 0.3 microm diameter. Our discussion here focuses on the intense symmetric methyl-group vibration centered at 2907 cm(-1), whose Raman scattering intensity is found to depend on whether incident light is polarized in the x or y direction of the surface, the x direction being parallel to one of the mica optical axes. Furthermore, the Raman peak broadens significantly relative to that of bulk PDMS while remaining Lorentzian in shape, implying slower but homogeneous vibrational dephasing. However, the preferred orientation differs, apparently stochastically, from spot to spot on the surface. Possible origins of this heterogeneous surface-induced structure are discussed.     

Magnetic split-flow thin fractionation of magnetically susceptible particles.

We recently built a magnetic separation system to extend the applications of split-flow thin (SPLITT) fractionation to magnetically susceptible particles. Here, we characterize the magnetic SPLITT system using magnetically susceptible particles and ion-labeled particles. The flow axis of separation channel was orientated parallel and perpendicular to gravitational forces to exclude and include, respectively, gravitational effects on separation. Both operating modes were used to test the theory experimentally, with emphasis on the parallel mode. The magnetic susceptibilities of carrier and ion-labeled particles were varied, and various ion-labeled and unlabeled particles were studied experimentally, resulting in successful separation of labeled particles, yeasts, and cells from unlabeled ones. The minimal difference in magnetic susceptibility (delta(chi)) required for complete particle separation was about 1.75 x 10(-5) [cgs], corresponding to about 10(9) labeling ions per particle in this study. The throughput was around 7.2 x 10(8) particles/h using the present setup. Magnetic SPLITT fractionation shows good potential for use in obtaining particles magnetic susceptibilities from a simple theoretical treatment.     

Magneto-optics of Ferritin

Measurements of Rayleigh light scattering, nonlinear light scattering in DC magnetic fields, and the Cotton-Mouton effect were carried out for 15 mM NaCl and water solutions of ferritin at room temperature. The spherical geometry of the molecule implies that it is optically isotropic. Such a macromolecule should not manifest magnetic anisotropy; however, in solution it shows induced magnetic birefringence (Cotton-Mouton effect) and changes in the intensity of the scattered light components. The analysis of the obtained results indicates the deformation of linear optical polarizability induced in the ferritin by a magnetic field as the main source of the magneto-optical phenomena observed. Light scattering and the CM effects theoretically depend on the linear magneto-optical polarizability, chi, and the nonlinear magneto-optical polarizability, eta. Using the theory describing the phenomena as well as the experimental data, the values of the anisotropy of linear magneto-optical polarizability components, chi(parallel) - chi(perpendicular) = -(1.3 +/- 0.7) x 10(-22) [cm3] (in SI units chi(parallel) - chi(perpendicular) = -(2.0 +/- 1.2) x 10(-33) [m3]), the linear optical polarizability, alpha = (alpha(parallel) + 2alpha(perpendicular))/3 = (3.9 +/- 1.0) x 10(-20) [cm3] (in SI units alpha = (3.52 +/- 0.09)x10(-4) [Cm2 V(-1)]), and its anisotropy, kappa(alpha) = (alpha(parallel) - alpha(perpendicular))/3alpha = -(0.06+/-0.03), nonlinear magneto-optical polarizability, eta = (eta(parallel) + 2eta(perpendicular))/3 = -(4.7 +/- 0.9) x 10(-30) [cm3 Oe(-2)] (in SI units eta = -(6.7 +/- 1.3) x 10(-18) [Cm4 V(-1) A(-2)]) and its anisotropy, kappa(eta) = (eta[parallel) - eta(perpendicular))/3eta = -(0.15 +/- 0.10), were deduced. Here alpha(parallel), eta(parallel), alpha(perpendicular), eta(perpendicular) are the optical and magneto-optical polarizability components along the parallel and the perpendicular axes of the axially symmetric molecule, respectively.     

Magnetic orientation of 1,3,5-triphenyl-6-oxoverdazyl radical crystals

The magnetic orientation has been studied for paramagnetic organic radical crystals 1,3,5-triphenyl-6-oxoverdazyl and 1,5-di-p-tolyl-3-phenyl-6-oxoverdazyl in magnetic fields of 2-80 kOe at temperatures of 77-343 K. The X-ray diffraction measurement has revealed that the crystals are oriented with the crystallographic c axis perpendicular to the field. The anisotropic diamagnetic susceptibility arising from the benzene rings has been estimated for the crystals along the principal magnetic chi 1, chi 2, and chi 3 axes. (The chi 1 axis is at a small angle to the a axis in the monoclinic ac plane, and the chi 3 axis is along the b axis.) Since the paramagnetic susceptibility originating from the verdazyl ring is isotropic (though a large absolute value), it is shown that the magnetic orientation occurs by the anisotropy of the diamagnetic susceptibility in the crystals. The diamagnetic susceptibility is found to have a relation of chi 2 < chi 1 < chi 3 < 0.     

Single crystal X- and Q-band EPR spectroscopy of a binuclear Mn(2)(III,IV) complex relevant to the oxygen-evolving complex of photosystem II

The anisotropic g and hyperfine tensors of the Mn di-micro-oxo complex, [Mn(2)(III,IV)O(2)(phen)(4)](PF(6))(3).CH(3)CN, were derived by single-crystal EPR measurements at X- and Q-band frequencies. This is the first simulation of EPR parameters from single-crystal EPR spectra for multinuclear Mn complexes, which are of importance in several metalloenzymes; one of them is the oxygen-evolving complex in photosystem II (PS II). Single-crystal [Mn(2)(III,IV)O(2)(phen)(4)](PF(6))(3).CH(3)CN EPR spectra showed distinct resolved (55)Mn hyperfine lines in all crystal orientations, unlike single-crystal EPR spectra of other Mn(2)(III,IV) di-micro-oxo bridged complexes. We measured the EPR spectra in the crystal ab- and bc-planes, and from these spectra we obtained the EPR spectra of the complex along the unique a-, b-, and c-axes of the crystal. The crystal orientation was determined by X-ray diffraction and single-crystal EXAFS (Extended X-ray Absorption Fine Structure) measurements. In this complex, the three crystallographic axes, a, b, and c, are parallel or nearly parallel to the principal molecular axes of Mn(2)(III,IV)O(2)(phen)(4) as shown in the crystallographic data by Stebler et al. (Inorg. Chem. 1986, 25, 4743). This direct relation together with the resolved hyperfine lines significantly simplified the simulation of single-crystal spectra in the three principal directions due to the reduction of free parameters and, thus, allowed us to define the magnetic g and A tensors of the molecule with a high degree of reliability. These parameters were subsequently used to generate the solution EPR spectra at both X- and Q-bands with excellent agreement. The anisotropic g and hyperfine tensors determined by the simulation of the X- and Q-band single-crystal and solution EPR spectra are as follows: g(x) = 1.9887, g(y) = 1.9957, g(z) = 1.9775, and hyperfine coupling constants are A(III)(x) = |171| G, A(III)(y) = |176| G, A(III)(z) = |129| G, A(IV)(x) = |77| G, A(IV)(y) = |74| G, A(IV)(z) = |80| G.     

The use of IR, magnetism, reflectance, and mass spectra together with thermal analyses in structure investigation of codeine phosphate complexes of d-block elements

Codeine is an analgesic with uses similar to morphines, but it is of much less effect, i.e., it had a mild sedative effect; codeine is usually used as the phosphate form (Cod.P) and is often administrated by mouth with aspirin of paracetamol. Due to its serious use, if it is in large dose, attention is paid in this research to the synthesis and stereochemistry of new iron, cobalt, nickel, copper, and zinc complexes of this drug in both solution and the solid states. The spectra of these complexes in solution and the study of their stoichiometry refer to the formation of 1:1 ratio of metal (M) to ligand (L). The steriochemical structures of the solid complexes were studied on the basis of their analytical, spectroscopic, magnetic, and thermal data. Infrared spectra proved the presence of MO bonds. Magnetic susceptibility and solid reflectance spectral measurements were used to infer the structures. The prepared complexes were found to have the general formulae [ML(OH)(x)(H2O)(y)](H2O)(z)H3PO4, M: Co(II), Ni(II), and Cu(II), x = 1, y = 0, z = 0; M: Fe(II), x = 1, y = 2, z = 1; Fe(III), x = 2, y = 1, z = 0; Co(III), x = 0, y = 2, z = 1; Zn(II), x = 1, y = 0, z = 3; and L: (Cod.P) of the general formula C18H24NO7P (anhydrate). Octahedral, tetrahedral, and square planer structures were proposed for these complexes depending upon the magnetic and reflectance data and were confirmed by detailed mass and thermal analyses comparative studies.     

Synthesis, characterization and electronic spectra of cefadroxil complexes of d-block elements

Cefadroxil (CD) is an essential pharmaceutical drug used in curing many diseases. Due to its popular use in many pharmaceutical forms, attention is paid in this research to the synthesis and stereochemistry of new iron, cobalt, nickel, copper, and zinc complexes of this drug both in solution and the solid states. The spectra of these complexes in solution and the study of their stoichiometry refer to the formation of 1:1 and 1:2 ratios of metal (M) to ligand (L). The calculated stability constants (Kf) of these complexes (1.5x10(7) to 5x10(13)) and the change in free energy of formation (deltaGf=2.5-12.5 kcal mol(-1) degree(-1)) are indicative of their high stability. The stereo chemical structure of the solid complexes was studied on the basis of their analytical, spectroscopic, magnetic, and thermal data. Infrared spectra proved the presence of M-N and M-O bonds. Magnetic susceptibility and solid reflectance spectral measurements were used to infer the structure. The prepared complexes were found to have the general formulae [ML(OH)x(H2O)y](H2O)z-M: Fe(II), x=0, y=2, z=1; M: Fe(III) and Co(III), x=1, y=2, z=1; M: Co(II) and Zn(II), x=0, y=1, z=0; M: Ni(II) and Cu(II), x=1, y=0, z=1; L: CD. Octahedral and tetrahedral structures were proposed for these complexes depending upon the magnetic and reflectance data and were confirmed by detailed mass and thermal analyses comparative studies.     

Mössbauer, electron paramagnetic resonance, and theoretical study of a high-spin, four-coordinate Fe(II) diketiminate complex

The iron(II) complex LFeCl 2Li(THF) 2 (L = beta-diketiminate), 1, has been studied with variable-temperature, variable-field Mossbauer spectroscopy and parallel mode electron paramagnetic resonance (EPR) spectroscopy in both solution and the solid state. In zero applied field the 4.2 K Mossbauer spectrum exhibits an isomer shift delta = 0.90 mm/s and quadrupole splitting Delta E Q = 2.4 mm/s, values that are typical for the high-spin ( S = 2) state anticipated for the iron in 1. Spectra recorded in applied magnetic fields yield an anisotropic magnetic hyperfine tensor with A x = +2.3 (+ 1.0) T, A y = A z = -21.5 T ( solution) and a nearly axial zero-field splitting of the spin quintet with D = D x approximately -14 cm (-1) and rhombicity E/ D approximately 0.1. The small, positive value for A x results from the presence of residual orbital angular momentum along x. The EPR analysis gives g x approximately 2.4 (and g y approximately g z approximately 2.0) and reveals a split " M S = +/- 2" ground doublet with a gap distributed around Delta = 0.42 cm (-1). The Mossbauer spectra of 1 show unusual features that arise from the presence of orientation-dependent relaxation and a distribution in the magnetic hyperfine field along x. The origin of the distribution has been analyzed using crystal field theory. The analysis indicates that the distribution in the magnetic hyperfine field originates from a narrow distribution, sigma phi approximately 0.5 degrees , in torsion angle phi between the FeN 2 and FeCl 2 planes, arising from minute inhomogeneities in the molecular environments.     

A justification for using NMR model-free methods when investigating the solution structures of rhombic paramagnetic lanthanide complexes

The detailed analysis of the 1H NMR hyperfine shifts according to the model-free methods shows that the semi-rigid monometallic complexes [Ln(L)(NO3)3] (Ln = Eu-Yb) are isostructural in solution. The associated separation of contact and pseudo-contact contributions to the hyperfine NMR shifts in each rhombic lanthanide complex at room temperature provides paramagnetic susceptibility tensors whose principal magnetic axes match the expected symmetry requirements. Moreover, both axial (Delta chi(ax)) and rhombic (Delta chi(rh)) paramagnetic anisotropies display satisfactory linear dependence on Bleaney's factors, a correlation predicted by the approximate high-temperature expansion of the magnetic susceptibility limited to T(-2). Consequently, the simple, and chemically attracting NMR model-free methods are not limited to axial systems, and can be safely used for the investigation of the solution structures of any lanthanide complexes. Molecular-based structural criteria for the reliable estimation of paramagnetic susceptibility tensors by NMR are discussed, together with the assignment of the labels of the crystal-field and magnetic axes within Bleaney's approach.     

Inelastic neutron scattering on three mixed-valence dodecanuclear polyoxovanadate clusters

The magnetic exchange interactions in the mixed-valence dodecanuclear polyoxovanadate compounds Na(4)[V(IV)(8)V(V)(4)As(III)(8)O(40)(H(2)O)].23H(2)O, Na(4)[V(IV)(8)V(V)(4)As(III)(8)O(40)(D(2)O)].16.5D(2)O, and (NHEt(3))(4)[V(IV)(8)V(V)(4)As(III)(8)O(40)(H(2)O)].H(2)O were investigated by an inelastic neutron scattering (INS) study using cold neutrons. In addition, the synthesis procedures and the single-crystal X-ray structures of these compounds have been investigated together with the temperature dependence of their magnetic susceptibilities. The magnetic properties below 100 K can be described by simply taking into account an antiferromagnetically exchange coupled tetramer, consisting of four vanadium(IV) ions. Up to four magnetic transitions between the cluster S = 0 ground state and excited states could be observed by INS. The transition energies and the relative INS intensities could be modeled on the basis of the following exchange Hamiltonian: H(ex) = -2J(12)(xy)[S(1x)S(2x)+ S(3x)S(4x)+ S(1y)S(2y)+ S(3y)S(4y)] - 2J(12)(z)[(S(1z)S(2z)+ S(3z)S(4z)] - 2J(23)(xy)[(S(2x)S(3x)+ S(1x)S(4x)+ S(2y)S(3y)+ S(1y)S(4y)] - 2J(23)(z)[(S(2z)S(3z)+ S(1z)S(4z)]. The following sets of parameters were derived: for Na(4)[V(12)As(8)O(40)(H(2)O)].23H(2)O, J(12)(xy)() = J(12)(z)= -0.80 meV, J(23)(xy) = J(23)(z) = -0.72 meV; for Na(4)[V(12)As(8)O(40)(D(2)O)].16.5D(2)O, J(12)(xy) = J(12)(z) = J(23)(xy) = J(23)(z = -0.78 meV; for (NHEt(3))(4)[V(12)As(8)O(40)(H(2)O)].H(2)O, J(12)(xy) = -0.80 meV, J(12)(z) = -0.82 meV, J(23)(xy)() = -0.67 meV, J(23)(z) = -0.69 meV. This study of the same [V(12)As(8)]-type cluster in three different crystal environments allows us to draw some conclusions concerning the applicability on INS in the area of nondeuterated molecular spin clusters. In addition, the effects of using nondeuterated samples and different sample container shapes for INS were evaluated.     

Magnetic polyoxometalates: anisotropic exchange interactions in the moiety of [(NaOH2)Co3(H2O)(P2W15O56)2]17-

The magnetic exchange interactions in a C0(3)(11) moiety encapsulated in Na(17) [(NaOH(2))Co(3)(H(2)O)(P(2)W(15)O(56))(2)] (NaCo(3)) were studied by a combination of magnetic measurements (magnetic susceptibility and low-temperature magnetization), with a detailed Inelastic Neutron Scattering (INS) investigation. The novel structure of the salt was determined by X-ray crystallography. The ferromagnetic Co(3)O(14) triangular cluster core consists of three octahedrally oxo-coordinated Co(II) ions sharing edges. According to the single-ion anisotropy and spin-orbit coupling usually assumed for octahedral Co(II) ions, the appropiate exchange Hamiltonian to describe the ground-state properties of the isosceles triangular Co(3) spin cluster is anisotropic and is expressed as H = - 2sigma(alpha)(=)(x,y,z)(J(alpha)(12)S(1alpha)S(2alpha) + J(alpha)(23)S(2alpha)S(3alpha) + J(alpha)(13)S(1alpha)S(3alpha)), where J(alpha) are the components of the exchange interactions between the Co(II) ions. To reproduce the INS data, nonparallel anisotropic exchange tensors needed to be introduced, which were directly connected to the molecular symmetry of the complex. The following range of parameters (value +/- 0.5 cm(-1)) was found to reproduce all experimental information while taking magnetostructural relations into account: J(x)(12) = J(y)(13) = 8.6 cm(-1); J(y)(12) = J(x)(13) = 1.4 cm(-1); J(z)(12) = J(z)(13) = 10.0 cm(-1); J(x)(23) = J(y)(23) = 6.5 cm(-1) and = 3.4 cm(-1).     

NMR observations of drawn polymers. VII. Nylon 66 fibers

Wide-line NMR spectra have been obtained on an oriented sample of drawn nylon 66 fibers at temperatures between ?196°C and 200°C and at alignment angles between the fiber axis and the magnetic field of 0°, 45°, and 90°. At ?196°C, 20°C, and 180°C, the complete angle dependence of the NMR spectrum has been measured. The second moments of these spectra have been compared to theoretical second moments calculated for various models of chain segmental motion in an attempt to elucidate the mechanisms involved in the low-temperature segmental motion (γ process) and the high-temperature segmental motion (α_c process). In agreement with earlier suggestions, the present results indicate that the γ process consists of segmental motion in noncrystalline regions. The overall decrease in second moment caused by the γ process is consistent with a model in which all noncrystalline segments rotate around axes nearly fixed in space. Furthermore, this decrease shows a pronounced dependence on the alignment angle. It is believed that this is due to tie molecules which become highly oriented along the fiber axis during drawing; their axes of rotation will therefore be nearly parallel to the fiber axis. The segments in noncrystalline entities such as chain folds and chain ends are less well oriented along the fiber axis and make an essentially isotropic contribution to the second moment decrease. The second moment at 180°C indicates the presence of considerable motion in the crystalline regions, and this motion is denoted the α_c process. The second moment S_c of the crystalline regions is strongly dependent on the alignment angle, the predominant feature being a relatively high value of the second moment when the fiber axis is directed parallel to the magnetic field. This is in qualitative, but not quantitative, agreement with the motional model recently advanced by McMahon, which assumes full rotation of the chains around their axes. Excellent quantitative agreement with experiment has been obtained by superimposition of rotational oscillation around the chain axis of amplitude roughtly 50°, and torsion of the chains with neighboring CH₂ groups oscillating around the C? C bond with a relative amplitude of about 40°. A model in which the chains perform rotational jumps of 60° between two equilibrium sites has also been considered (60° flip-flop motion). A distinction between this model and rotational oscillation has not been possible.     

NMR study of molecular motion in oriented long-chain alkanes. III. Oriented n-C32H66

The NMR second moment of a uniaxially oriented mat of single crystals of n-C₃₂H₆₆ (in the orthorhombic form) was measured at temperatures from ?170°C to 70°C and at various alignment angles γ between the orientation axis (preferential direction of the molecular chains) and the NMR magnetic field. Accurate expressions are given for the NMR second moment of an orthorhombic normal paraffin C_nH_2n+2 of arbitrary molecular chain length n for n ≥ 10, in the following states of molecular motion: no motion (a rigid lattice), rotation of CH₃ groups, and rotation of the chains around their axes with superimposed rotation of CH₃ groups. In addition to these well-known motions, n-C₃₂H₆₆ is found to exhibit an α process. The corresponding decrease of the NMR second moment shows the dependence on γ predicted for “flip-flop” motion, i.e., rotational jumps of the chain molecules around their axes through 180° and a simultaneous translation along these axes by one CH₂ group. The overall decrease in second moment occuring at the transition to the hexagonal rotator phase in n-C₃₂H₆₆ can be quantitatively accounted for. The dependence of this decrease on the alignment angle γ, however, is in disagreement with calculations based on a simple rotation of the chains around their axes. Considerable torsion of the chains superimposed on the rotation would improve agreement between theory and experiment.     

EPR spectra from "EPR-silent" species: high-frequency and high-field EPR spectroscopy of pseudotetrahedral complexes of nickel(II)

High-frequency and high-field electron paramagnetic resonance (HFEPR) spectroscopy (using frequencies of approximately 90-550 GHz and fields up to approximately 15 T) has been used to probe the non-Kramers, S = 1, Ni(2+) ion in a series of pseudotetrahedral complexes of general formula NiL(2)X(2), where L = PPh(3) (Ph = phenyl) and X = Cl, Br, and I. Analysis based on full-matrix solutions to the spin Hamiltonian for an S = 1 system gave zero-field splitting parameters: D = +13.20(5) cm(-1), /E/ = 1.85(5) cm(-1), g(x) = g(y) = g(z) = 2.20(5) for Ni(PPh(3))(2)Cl(2). These values are in good agreement with those obtained by powder magnetic susceptibility and field-dependent magnetization measurements and with earlier, single-crystal magnetic susceptibility measurements. For Ni(PPh(3))(2)Br(2), HFEPR suggested /D/ = 4.5(5) cm(-1), /E/ = 1.5(5) cm(-1), g(x) = g(y) = 2.2(1), and g(z) = 2.0(1), which are in agreement with concurrent magnetic measurements, but do not agree with previous single-crystal work. The previous studies were performed on a minor crystal form, while the present study was performed on the major form, and apparently the electronic parameters differ greatly between the two. HFEPR of Ni(PPh(3))(2)I(2) was unsuccessful; however, magnetic susceptibility measurements indicated /D/ = 27.9(1) cm(-1), /E/ = 4.7(1), g(x) = 1.95(5), g(y) = 2.00(5), and g(z) = 2.11(5). This magnitude of the zero-field splitting ( approximately 840 GHz) is too large for successful detection of resonances, even for current HFEPR spectrometers. The electronic structure of these complexes is discussed in terms of their molecular structure and previous electronic absorption spectroscopic studies. This analysis, which involved fitting of experimental data to ligand-field parameters, shows that the halo ligands act as strong pi-donors, while the triphenylphosphane ligands are pi-acceptors.     

A tale of two metals: new cerium iron borocarbide intermetallics grown from rare-earth/transition metal eutectic fluxes

R(33)Fe(14-x)Al(x+y)B(25-y)C(34) (R = La or Ce; x ≤ 0.9; y ≤ 0.2) and R(33)Fe(13-x)Al(x)B(18)C(34) (R = Ce or Pr; x < 0.1) were synthesized from reactions of iron with boron, carbon, and aluminum in R-T eutectic fluxes (T = Fe, Co, or Ni). These phases crystallize in the cubic space group Im3m (a = 14.617(1) ?, Z = 2, R(1) = 0.0155 for Ce(33)Fe(13.1)Al(1.1)B(24.8)C(34), and a = 14.246(8) ?, Z = 2, R(1) = 0.0142 for Ce(33)Fe(13)B(18)C(34)). Their structures can be described as body-centered cubic arrays of large Fe(13) or Fe(14) clusters which are capped by borocarbide chains and surrounded by rare earth cations. The magnetic behavior of the cerium-containing analogs is complicated by the possibility of two valence states for cerium and possible presence of magnetic moments on the iron sites. Temperature-dependent magnetic susceptibility measurements and M?ssbauer data show that the boron-centered Fe(14) clusters in Ce(33)Fe(14-x)Al(x+y)B(25-y)C(34) are not magnetic. X-ray photoelectron spectroscopy data indicate that the cerium is trivalent at room temperature, but the temperature dependence of the resistivity and the magnetic susceptibility data suggest Ce(3+/4+) valence fluctuation beginning at 120 K. Bond length analysis and XPS studies of Ce(33)Fe(13)B(18)C(34) indicate the cerium in this phase is tetravalent, and the observed magnetic ordering at T(C) = 180 K is due to magnetic moments on the Fe(13) clusters.     

Cyano-bridged homodinuclear copper(II) complexes

The synthesis and structural analysis (single crystal X-ray data) of two mononuclear ([Cu(L(1))(CN)]BF(4) and [Cu(L(3))(CN)](BF(4))) and three related, cyanide-bridged homodinuclear complexes ([{Cu(L(1))}(2)(CN)](BF(4))(3)·1.35 H(2)O, [{Cu(L(2))}(2)(CN)](BF(4))(3) and [{Ni(L(3))}(2)(CN)](BF(4))(3)) with a tetradentate (L(1)) and two isomeric pentadentate bispidine ligands (L(2), L(3); bispidines are 3,7-diazabicyclo[3.3.1]nonane derivatives) are reported, together with experimental magnetic, electron paramagnetic resonance (EPR), and electronic spectroscopic data and a ligand-field-theory-based analysis. The temperature dependence of the magnetic susceptibilities and EPR transitions of the dicopper(II) complexes, together with the simulation of the EPR spectra of the mono- and dinuclear complexes leads to an anisotropic set of g- and A-values, zero-field splitting (ZFS) and magnetic exchange parameters (Cu1: g(z) = 2.055, g(x) = 2.096, g(y) = 2.260, A(z) = 8, A(x) = 8, A(y) = 195 × 10(-4) cm(-1), Cu2: g and A as for Cu(1) but rotated by the Euler angles α = -6°, β = 100°, D(exc) = -0.07 cm(-1), E(exc)/D(exc) = 0.205 for [{Cu(L(1))}(2)(CN)](BF(4))(3)·1.35 H(2)O; Cu1,2: g(z) = 2.025, g(x) = 2.096, g(y) = 2.240, A(z) = 8, A(x) = 8, A(y) = 190 × 10(-4)cm(-1), D(exc) = -0.159 cm(-1), E(exc)/D(exc) = 0.080 for [{Cu(L(2))}(2)(CN)](BF(4))(3)). Thorough ligand-field-theory-based analyses, involving all micro states and all relevant interactions (Jahn-Teller and spin-orbit coupling) and DFT calculations of the magnetic exchange leads to good agreement between the experimental observations and theoretical predictions. The direction of the symmetric magnetic anisotropy tensor D(exc) in [{Cu(L(2))}(2)(CN)](BF(4))(3) is close to the Cu···Cu vector (22°), that is, nearly perpendicular to the Jahn-Teller axis of each of the two Cu(II) centers, and this reflects the crystallographically observed geometry. Antisymmetric exchange in [{Cu(L(1))}(2)(CN)](BF(4))(3)·1.35 H(2)O causes a mixing between the singlet ground state and the triplet excited state, and this also reflects the observed geometry with a rotation of the two Cu(II) sites around the Cu···Cu axis.     

Difference spatial distribution function analysis of aqueous solutions. III. Hydration structures of alcohol and ether solutions having straight chain and branched alkyl groups

Spatial distribution functions (SDFs), gOO(x,y,z) and gOH(x,y,z), obtained from Monte Carlo simulations at 298 K were applied to characterize the anisotropic structure of infinitely dilute aqueous solutions of alcohols and ethers having straight chain and branched alkyl groups. In spite of the different size and shape of the hydrophobic groups, the spatial orientation of the hydrogen-bonded water molecules was found to be of linear type with a triple layer structure in the hydrogen acceptor (HA) region and a double layer structure in the hydrogen donor (HD) region. The volumes and the coordination number (CN) in the HA region were essentially identical for all alcohol and ether solutions, but the volumes for the isopropyl alcohol (IPA) and isopropyl methyl ether (IPE) solutions were greater than those for the other solutions. In the hydrophobic hydration (HH) region, these values increased with increasing size and shape of hydrophobic groups, except in the case of IPA and IPE solutions. These results indicated that the hydration structures around the isopropyl group in alcohol and ether solutions differed from those in other solutions. From the results of the difference SDF (DSDF), AgOO(x,y,z), between SDFs gOO(x,y,z) for the two states, it was apparent that the distribution of hydration water molecules in the HA region for ether solution was characterized by the increase of the distribution in the direction of lone pair electrons on the oxygen atom of the solute molecule with increasing hydrophobicity.