Crossover behavior

Similar to the case of good solvent conditions, the complete coherent dynamic structure factor S(Q,t) is not available in the transition range of the regimes I and T. However, the crossover behavior becomes accessible via the initial slope as a function of Q and t [105]. Typical results of this treatment are shown in Fig. 39, where... 

Finally for Cfe(c) 1 the unperturbed (not self-entangled) single-chain re-laxationjust known from good solvent conditions, takes place. S(Q, t)/S(Q, 0) is a universal function of (Q(Q,t)2/3 with Q(Q) = QZ(Q) In Fig 58b a schematic plot of the crossover behavior of the segmental dynamics under 0-conditions is shown. 

The Fe(II) complex of this ligand shows crossover behavior both in solution and in the solid state. The complex has a distinct green color derived from the ligand field transition 2=620 nm) of the low-spin form of... 

Otsuka, H. Aotani, K. Higaki, Y. Takahara, A. A dynamic (reversible) covalent polymer Radical crossover behavior of TEMPO-containing poly(alkoxyamine ester)s. Chem. Commun. 2002, 2838-2839. 

Other crossover behavior can arise when one moves to a regime where the continuum picture is not valid. For examples, Giesen-Seibert et al. (1995) show that for PD, at very early times w behaves like t rather than t " because the dynamics are dominated by random walks of kinks. In their simulations the effective exponent decreases smoothly with increasing temperature, with no evident crossover in any of the fixed-Tlog-logplots of w vs. t. They also show how to take into account fast events, viz. rapid, inconsequential... 

As an essential feature of these theories, crossover behavior is governed by two physical parameters [317] (1) a scaled coupling constant u which reflects the strength and range of the intermolecular forces as represented by 0 and (2) a cutoff wave number A which is assumed to be inversely proportional to a structural length When = 0, one has only one length scale, and one recovers the Ginzburg number with Afa oc (wA)2. 

Matouzenko, G. S., Perrin, M., Le Guennic, B., et al., Spin crossover behavior in a family of iron(II) zigzag chain coordination polymers. Dalton Trans. 2007, 934-942. 

There are many examples of complexes where a high-spin (HS) and a low-spin (LS) are separated by only about the thermal energy prevailing at or below room temperature. The magnetic properties change anomously (that is, differently from ordinary Curie, or Curie-Weiss behavior) as a function of temperature they can change from LS to HS under special conditions (see below) giving rise to so-called spin-crossover behavior. ... 

Some complexes show a strong interdependence between crystal structure and spin-transition features. In the series of compounds [Fe(Rtz)6](BF4)2 (Rtz = 1-alkyltetrazole) the spin crossover behavior varies with the substituent R and is strongly influenced by cooperative effects. For example, the propyl derivative shows a quantitative spin transition, which is accompanied by a first-order crystallographic phase transition in the methyl and ethyl derivatives the Fe11 complexes occupy two nonequivalent lattice sites, only one of which shows a thermal spin transition.29... 

Only a few multinuclear cyanide complexes are known to exhibit spin crossover behavior. In all the cases described in Section IV.D, a gradual spin transition is observed, which can be explained by relatively weak intermolecular interactions in the crystal strucmres of these compounds. It is generally known that stronger interactions between individual SCO centers lead to cooperative behavior, abmpt spin transitions, and thermal hysteresis or bistability over a finite temperature range (276). The latter property renders SCO compounds attractive materials for the development of magnetic sensors and memory devices. It is expected that extended... 

A unique type of spin-crossover behavior is claimed for the mixed-valence dithiooxalate salt Pr4N[Fe Fe (dto)3]. Flere, the spin change is associated with electron transfer, equation (2), with the bridging dithiooxalate favoring Fe -S bonding at higher temperatures, Fe -0 bonding at lower temperatures ... 

However compelling, the scenario described above requires a rigorous justification that entails an understanding of the crossover behavior at a local level. This understanding prompts us to focus on the solvent environment of individual hydrogen bonds during the conformational exploration performed by the protein chain as the hydrophobic collapse takes place [12, 16, 17]. 

Narayanan, T., and Pitzer, K.S. Critical phenomena in ionic fluids A systematic investigation of the crossover behavior. J. Chem. Phys., 1995, 102, p. 8118-30. 

Symmetrical N2S2 tetradentate SBs incorporating pyrazole or isoxazole have been prepared and their complexes with different 3d metal ions investigated.111 A Co11 complex having a N3S2 environment was found to exhibit thermal-induced spin-crossover behavior and its structure was determined at two temperatures corresponding to the different spin states.112... 

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