scholarly journals Iron(ii) complexes of 4-sulfanyl-, 4-sulfinyl- and 4-sulfonyl-2,6-dipyrazolylpyridine ligands. A subtle interplay between spin-crossover and crystallographic phase changes

2015 ◽  
Vol 2 (7) ◽  
pp. 662-670 ◽  
Author(s):  
Laurence J. Kershaw Cook ◽  
Rafal Kulmaczewski ◽  
Simon A. Barrett ◽  
Malcolm A. Halcrow
Keyword(s):  
Phase Change ◽  
Spin Crossover ◽  
Spin Transition ◽  
Phase Changes ◽  
Lower Temperature ◽  
Susceptibility Curve

The compound shown exhibits an abrupt thermal spin-transition, with an accompanying crystallographic phase change at slightly lower temperature which is visible as a shoulder on the susceptibility curve.

Influence of Metal Substitution on the Pressure-Induced Phase Change in Flexible Zeolitic Imidazolate Frameworks

2018 ◽  
Author(s):  
C. Michael McGuirk ◽  
Tomče Runčevski ◽  
Julia Oktawiec ◽  
Ari Turkiewicz ◽  
mercedes K. taylor ◽  
...  
Keyword(s):  
Phase Change ◽  
Single Crystal ◽  
Gas Adsorption ◽  
High Capacity ◽  
Phase Changes ◽  
Zeolitic Imidazolate Frameworks ◽  
Metal Substitution ◽  
Heat Management ◽  
Metal Organic ◽  
First Time

<p>Metal–organic frameworks that display step-shaped adsorption profiles arising from discrete pressure-induced phase changes are promising materials for applications in both high-capacity gas storage and energy-efficient gas separations. The thorough investigation of such materials through chemical diversification, gas adsorption measurements, and <i>in situ </i>structural characterization is therefore crucial for broadening their utility. We examine a series of isoreticular, flexible zeolitic imidazolate frameworks (ZIFs) of the type M(bim)<sub>2</sub> (SOD; M = Zn<sup> </sup>(ZIF-7), Co (ZIF-9), Cd (CdIF-13); bim<sup>–</sup> = benzimidazolate), and elucidate the effects of metal substitution on the pressure-responsive phase changes and the resulting CO<sub>2</sub> and CH<sub>4</sub> step positions, pre-step uptakes, and step capacities. Using ZIF-7 as a benchmark, we reexamine the poorly understood structural transition responsible for its adsorption steps and, through high-pressure adsorption measurements, verify that it displays a step in its CH<sub>4 </sub>adsorption isotherms. The ZIF-9 material is shown to undergo an analogous phase change, yielding adsorption steps for CO<sub>2</sub> and CH<sub>4</sub> with similar profiles and capacities to ZIF-7, but with shifted threshold pressures. Further, the Cd<sup>2+</sup> analogue CdIF-13 is reported here for the first time, and shown to display adsorption behavior distinct from both ZIF-7 and ZIF-9, with negligible pre-step adsorption, a ~50% increase in CO<sub>2</sub> and CH<sub>4</sub> capacity, and dramatically higher threshold adsorption pressures. Remarkably, a single-crystal-to-single-crystal phase change to a pore-gated phase is also achieved with CdIF-13, providing insight into the phase change that yields step-shaped adsorption in these flexible ZIFs. Finally, we show that the endothermic phase change of these frameworks provides intrinsic heat management during gas adsorption. </p>

Abrupt spin crossover in iron(iii) complexes with aromatic anions

2019 ◽  
Vol 48 (41) ◽  
pp. 15515-15520 ◽  
Author(s):  
Sharon E. Lazaro ◽  
Adil Alkaş ◽  
Seok J. Lee ◽  
Shane G. Telfer ◽  
Keith S. Murray ◽  
...  
Keyword(s):  
Transition Temperature ◽  
Spin Crossover ◽  
Spin Transition ◽  
Halogen Bonds ◽  
Aromatic Anions

Two iron(iii) complexes, [Fe(qsal-X)2]OTs·nH2O, are found to exhibit abrupt spin crossover with the spin transition temperature substituent dependent, and X⋯O halogen bonds linking the spin centres.

scholarly journals Numerical Study of a Cooling System Using Phase Change of a Refrigerant in a Thermosyphon

Energies ◽  
2021 ◽  
Vol 14 (12) ◽  
pp. 3634
Author(s):  
Grzegorz Czerwiński ◽  
Jerzy Wołoszyn
Keyword(s):  
Mass Transfer ◽  
Phase Change ◽  
Heat Dissipation ◽  
Cooling System ◽  
Numerical Study ◽  
Relaxation Parameter ◽  
Phase Changes ◽  
Transfer Time ◽  
Two Phase ◽  
Time Relaxation

With the increasing trend toward the miniaturization of electronic devices, the issue of heat dissipation becomes essential. The use of phase changes in a two-phase closed thermosyphon (TPCT) enables a significant reduction in the heat generated even at high temperatures. In this paper, we propose a modification of the evaporation–condensation model implemented in ANSYS Fluent. The modification was to manipulate the value of the mass transfer time relaxation parameter for evaporation and condensation. The developed model in the form of a UDF script allowed the introduction of additional source equations, and the obtained solution is compared with the results available in the literature. The variable value of the mass transfer time relaxation parameter during condensation rc depending on the density of the liquid and vapour phase was taken into account in the calculations. However, compared to previous numerical studies, more accurate modelling of the phase change phenomenon of the medium in the thermosyphon was possible by adopting a mass transfer time relaxation parameter during evaporation re = 1. The assumption of ten-fold higher values resulted in overestimated temperature values in all sections of the thermosyphon. Hence, the coefficient re should be selected individually depending on the case under study. A too large value may cause difficulties in obtaining the convergence of solutions, which, in the case of numerical grids with many elements (especially three-dimensional), significantly increases the computation time.

scholarly journals Solvent-Induced Hysteresis Loop in Anionic Spin Crossover (SCO) Isomorph Complexes

2021 ◽  
Vol 7 (6) ◽  
pp. 75
Author(s):  
Emmelyne Cuza ◽  
Samia Benmansour ◽  
Nathalie Cosquer ◽  
Françoise Conan ◽  
Carlos J. Gómez-García ◽  
...  
Keyword(s):  
Metal Ion ◽  
Spin Crossover ◽  
Magnetic Behaviour ◽  
Magnetic Studies ◽  
Tridentate Ligands ◽  
Tripodal Ligand ◽  
Single Crystal Structures ◽  
One Step ◽  
Lower Temperature ◽  
Step Transition

Reaction of Fe(II) with the tris-(pyridin-2-yl)ethoxymethane (py3C-OEt) tripodal ligand in the presence of the pseudohalide ancillary NCSe- (E = S, Se, BH3) ligand leads to the mononuclear complex [Fe(py3C-OEt)2][Fe(py3C-OEt)(NCSe)3]2·2CH3CN (3), which has been characterised as an isomorph of the two previously reported complexes, Fe(py3C-OEt)2][Fe(py3C-OEt)(NCE)3]2·2CH3CN, with E = S (1), BH3 (2). X-ray powder diffraction of the three complexes (1–3), associated with the previously reported single crystal structures of 1–2, revealed a monomeric isomorph structure for 3, formed by the spin crossover (SCO) anionic [Fe(py3C-OEt)(NCSe)3]− complex, associated with the low spin (LS) [Fe(py3C-OEt)2]2+ cationic complex and two solvent acetonitrile molecules. In the [Fe(py3C-OEt)2]2+ complex, the metal ion environment involves two py3C-OEt tridentate ligands, while the [Fe(py3C-OEt)(NCSe)3]− anion displays a hexacoordinated environment involving three N-donor atoms of one py3C-OEt ligand and three nitrogen atoms arising from the three (NCSe)− coligands. The magnetic studies for 3 performed in the temperature range 300-5-400 K, indicated the presence of a two-step SCO transition centred around 170 and 298 K, while when the sample was heated at 400 K until its complete desolvation, the magnetic behaviour of the high temperature transition (T1/2 = 298 K) shifted to a lower temperature until the two-step behaviour merged with a gradual one-step transition at ca. 216 K.

scholarly journals Electrical read-out of light-induced spin transition in thin film spin crossover/graphene heterostructures

2021 ◽  
Author(s):  
Nikita Konstantinov ◽  
Arthur Tauzin ◽  
Ulrich Nguetchuissi Noumbé ◽  
Diana Dragoe ◽  
Bohdan Kundys ◽  
...  
Keyword(s):  
Thin Film ◽  
Spin Crossover ◽  
Spin Transition ◽  
Switching Device ◽  
Electronic Switching ◽  
Spin Transitions

An opto-electronic switching device made from an evaporated spin crossover thin film over a graphene sensor is presented. The electrical transduction of both temperature and light-induced reversible spin transitions are demonstrated.

Phase changes and convection in the Earth’s mantle

1965 ◽  
Vol 258 (1088) ◽  
pp. 276-283 ◽  
Keyword(s):  
Temperature Gradient ◽  
Phase Change ◽  
Initial Temperature ◽  
Phase Changes ◽  
Homogeneous Layer ◽  
Transformation Zone ◽  
Earth’S Mantle ◽  
Transition Level ◽  
Transformation Rates

A phase change may hinder or enhance convection, depending on its characteristics. Univariant transformations such as may occur in the mantle constitute a barrier to convection unless the motion starts at some distance above or below the transition level; an initial temperature gradient in excess of the adiabatic value is also required. Multivariant transformations only require, in the transformation zone, an initial gradient slightly greater than the adiabatic value for a homogeneous layer. The effect on convection of transformation rates is not likely to be serious.

Spin-crossover in a trans-[FeL2(NCS)2] family (L = triaryltriazole): remote substituent effects on spin transition modes and temperature

2013 ◽  
Vol 42 (28) ◽  
pp. 10144 ◽  
Author(s):  
Guo-Ping Shen ◽  
Li Qi ◽  
Lei Wang ◽  
Yan Xu ◽  
Jing-Jing Jiang ◽  
...  
Keyword(s):  
Spin Crossover ◽  
Spin Transition ◽  
Substituent Effects ◽  
Transition Modes ◽  
Remote Substituent

COMPARING MALE AND FEMALE PRE-SERVICE TEACHERS‘ UNDERSTANDING OF THE PARTICULATE NATURE OF MATTER

2014 ◽  
Vol 13 (6) ◽  
pp. 821-827
Author(s):  
Frackson Mumba ◽  
Vivien Mweene Chabalengula ◽  
Asiana Banda
Keyword(s):  
Phase Change ◽  
Science Teachers ◽  
Teaching And Learning ◽  
Phase Changes ◽  
Particulate Nature Of Matter ◽  
Male And Female ◽  
Size Of Particles ◽  
Gender Groups ◽  
Key Words Gender ◽  
Number Of Particles

This study compared male and female pre-service science teachers’ understanding of the effect of phase changes and physical transformation of matter on the size of particles, spaces between particles, speed of particles, and number of particles. Data were collected using a questionnaire that has 36 items. Both gender groups had sound understanding of the effect of phase change on speed, spaces, and number of particles in a substance, and the effect of compression on speed, number, size and spaces between particles in solids and liquids. However, most female pre-service teachers had low understanding of the effect of phase change on the size of the particles in solids, liquids and gases as most of them incorrectly believed that heating increases the size of the particles and cooling decreases the size of particles. The results have implications for science teaching and learning and teacher education. Key words: gender, matter, particle, pre-service teachers, understanding.

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