We review theories and experiments on the effects of shear in fluids undergoing phase transitions. We put emphasis on near-critical fluids and polymer solutions as representative examples, but also discuss related problems in polymer blends, gels, and surfactant systems, etc. In near-critical fluids, convective deformations can drastically alter the critical behaviour, spinodal decomposition, and nucleation. In this case the hydrodynamic interaction suppresses the fluctuations and gives rise to a downward shift of the critical temperature (shear-induced mixing). The rheology in two-phase states, and effects of random stirring are also reviewed. In semidilute polymer solutions near the coexistence curve, on the other hand, the composition fluctuations can be strongly influenced by the viscoelastic stress. In shear flow, this dynamical coupling results in enhancement of the composition fluctuations (shear-induced demixing). They grow, but are eventually disrupted by convective deformations, yielding chaotic dynamical steady states where phase separation is incompletely taking place. Such nonlinear shear regimes are examined using computer simulations based on a viscoelastic Ginzburg - Landau model.

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Phase transitions of fluids in shear flow

The reaction of the tris(tetradentate) triplesalen ligand H6talent-Bu2, which provides three salen-like coordination environments bridged in a meta-phenylene arrangement by a phloroglucinol backbone, with MnII salts under aerobic conditions affords, in situ, the trinuclear MnIII triplesalen complexes [(talent-Bu2){MnIII(solv)n}3]3+. These can be used as molecular building blocks in the reaction with [Fe(CN)6]3− as a hexaconnector to form the heptanuclear complex [{(talent-Bu2){MnIII(solv)n}3}2{FeIII(CN)6}]3+ ([MnIII6FeIII]3+). The regular ligand folding observed in the trinuclear triplesalen complexes preorganizes the three metal ions for the reaction of three facially coordinated nitrogen atoms of a hexacyanometallate and provides a driving force for the formation of the heptanuclear complexes [Mt6Mc]n+ (Mt, terminal metal ion of the triplesalen building block; Mc, central metal ion of the hexacyanometallate) by molecular recognition, as has already been demonstrated for the single-molecule magnet [MnIII...

Exchange Interactions and Zero-Field Splittings in C3-Symmetric MnIII6FeIII: Using Molecular Recognition for the Construction of a Series of High Spin Complexes Based on the Triplesalen Ligand

The syntheses, crystal structures, and magnetic properties of three novel cyano-bridged bimetallic assemblies, [Ni(bpm)(2)](3)[Co(CN)(6)](2)x3.5H(2)O (1), [Co(bpm)(2)][Fe(CN)(5)NO]x2H(2)O (2), and [Co(bpm)(2)][Ni(CN)(4)] (3) (bpm = bis(1-pyrazolyl)methane), are reported. Complex 1 crystallizes in the tetragonal space group P4(3)2(1)2 with a = 12.800(5) A, b = 12.800(5) A, c = 42.80(3) A, V = 7012(6) A(3), and Z = 8. Complex 2 crystallizes in the chiral trigonal space group P3(2)21 with a = 11.9961(19) A, b = 11.9961(19) A, c = 16.062(5) A, gamma = 120 degrees , V = 2001.7(8) A(3), and Z = 3. Complex 1 is a trigonal bipyramidal complex in which three [Ni(bpm)(2)](2+) units are situated in the equatorial plane and are connected to the two apical [Co(CN)(6)](3)(-) units via three N ends of the cyanide groups. Complex 2 possesses a triangular left-handed helical chain structure composed of [Co(bpm)(2)](2+) linked by [Fe(CN)(5)NO](2)(-); the shortest intramolecular Co...Fe distance is 5.162 A. To the best of our knowledge, this is the first observation of a heteronuclear helical chain structure based on pentacyanonitrosylferrate(II). The structure of complex 3 is roughly determined by X-ray crystallograhy analysis to be a 1D zigzag chain. These structure variations, from a discrete cluster to a 1D helical chain and a 1D zigzag chain, rely on the semirigidity of the capping ligand bpm. Magnetic susceptibility measurements indicate that complex 1 has an intramolecular ferromagnetic interaction (J = 4.06 cm(-)(1)) between the nickel(II) ions; this is further confirmed by the magnetization measurements. In complexes 2 and 3, the cobalt(II) ions are located in a moderately strong field.

Effect of the semirigid capping ligand on the structure formation of cyano-bridged bimetallic assemblies: syntheses, crystal structures, and magnetic properties.

We present the results of calculations of the {[FeCl6-n(CN)n]m-×(VNa)5-m}5- impurity complex incorporated in the NaCl crystal lattice. A number of characteristic defect configurations are calculated quantum mechanically using an embedded cluster method, and compared with the results of Mott-Littleton (ML) calculations. We investigate the electron affinity and the orientation of CN- ligands. The dependence of vibrational frequencies of the CN stretching mode on the ligand orientation, charge of the impurity and the relative position of the ligands and the charge compensating vacancies are calculated. Analysis of these results demonstrates the ability of ML calculations to predict the relative stability of different configurations of this particular family of defects. Comparison of the ML and embedded cluster calculations reveals the contributions to the defect energy and stability.

Embedded cluster calculations of metal complex impurity defects: properties of the iron cyanide in NaCl

A Na4Fe(CN)6/NaCl solid solution was synthesized and investigated as a cathode material for sodium ion batteries. Pure Na4Fe(CN)6 and NaCl do not work as cathode materials for sodium ion batteries, while a sample of Na4Fe(CN)6/NaCl demonstrated a remarkably enhanced Na+ insertion/extraction capability and electrochemical performance, due to the cation vacancies and interconnected cages generated in the solid solution framework.

A Na4Fe(CN)6/NaCl solid solution cathode material with an enhanced electrochemical performance for sodium ion batteries

Ten absorption bands are observed in the electronic spectra of NaCl and KCl crystals doped with Fe(CN)63- ions in the range 50000-20000 cm-1. Six of these bands are assigned to the ligand to metal charge transfer transitions (t1u6t2g5 to t1u5t2g6 and t1u5t2g5eg1 and a1g2t2g5 to a1g1t2g6). The positions of these bands agree with those calculated using Dq=1944 cm-1, B=623 cm-1 and C=3270 cm-1 for d6 configuration. The remaining four bands are assigned to crystal field transitions for d5 configuration and agree with the calculated peak positions for Dq=3450 cm-1, B=700 cm-1 and C=2400 cm-1. Vibration spectrum in the (C identical to N) stretch region shows that the Fe(CN)63- ion is present predominantly in the Cs site symmetry.

https://iopscience.iop.org/article/10.1088/0022-3719/6/1/029/pdf

Electronic and vibrational spectra of ferricyanide ions doped in NaCl and KCl crystals

The IR spectra of solution grown crystals of NaCl and KCl doped with Co(CN)63- show a multiplet in the v6 stretch frequency region of CN-. Apparently the multiplet consists of four components in NaCl and three in KCl. However, a detailed examination of the results shows that the multiplet consists of several components due to different site symmetries in which Co(CN)63- is present in the crystal. The most probable symmetries are D2h and C8. On x irradiation the multiplet characteristic of Co(CN)63- appear on the low energy side. On heating the crystals, irreversible changes in the spectra occur. The spectra consist of many lines but only the line corresponding to NCO- could be identified. The electronic spectra of the impurity show seven bands in the wavelength region 600 nm to 200 nm as compared with only three bands observed in the solution in this region. The bands are interpreted as being due to transitions of the split components of crystal field levels in Oh symmetry. Both peak positions and intensities are consistent with the assignment.

http://iopscience.iop.org/article/10.1088/0022-3719/5/12/026/pdf

H K Sehgal

Papers

Electronic and vibrational spectra of ferricyanide ions doped in NaCl and KCl crystals

Vibrational and electronic properties of Co(CN)63- doped in alkali halides