Search results for "cross"
showing 10 items of 8498 documents
Enhancement of the Multipactor Threshold Inside Nonrectangular Iris
2018
Multipactor breakdown is studied inside the capacitive iris of a rectangular waveguide with a skewed slot along its longitudinal cross section. Both the iris length and height are assumed to be small compared to the electromagnetic wavelength. Therefore, the quasi-static approximation is applied so as to describe the RF field distribution inside the iris gap, whereas a 2-D model is used to analyze the electron motion. The peculiarities of RF field structure are studied using the conformal mapping approach, which shows that the electric field lines can be approximated by circular arcs when the iris length is much larger than its height. The electron motion inside the iris gap is analyzed usi…
Gas-Phase Synthesis of the Elusive Trisilicontetrahydride Species (Si3H4)
2016
The bimolecular gas-phase reaction of ground-state atomic silicon (Si; 3P) with disilane (Si2H6; 1A1g) was explored under single-collision conditions in a crossed molecular beam machine at a collision energy of 21 kJ mol–1. Combined with electronic structure calculations, the results suggest the formation of Si3H4 isomer(s) along with molecular hydrogen via indirect scattering dynamics through Si3H6 collision complex(es) and intersystem crossing from the triplet to the singlet surface. The nonadiabatic reaction dynamics can synthesize the energetically accessible singlet Si3H4 isomers in overall exoergic reaction(s) (−93 ± 21 kJ mol–1). All reasonable reaction products are either cyclic or …
Computational study of the spin-forbidden H 2 oxidative addition to 16-electron Fe(0) complexes
2003
International audience; The spin-forbidden oxidative addition of H2 to Fe(CO)4, Fe(PH3)4, Fe(dpe)2 and Fe(dmpe)2 [dpe = H2PCH2CH2PH2, dmpe = (CH3)2PCH2CH2P(CH3)2] has been investigated by density functional theory using a modified B3PW91 functional. All 16-electron fragments are found to adopt a spin triplet ground state. The H2 addition involves a spin crossover in the reagents region of configurational space, at a significantly higher energy relative to the triplet dissociation asymptote and, for the case of Fe(CO)4·H2, even higher than the singlet dissociation asymptote. After crossing to the singlet surface, the addition proceeds directly to the classical cis-dihydride product. Only for…
Spin crossover (SCO) iron(II) coordination polymer chain: Synthesis, structural and magnetic characterizations of [Fe(abpt)2(μ-M(CN)4)] (M=PtII and N…
2013
Abstract New iron(II) coordination polymeric neutral chain of formula [Fe(abpt) 2 (μ-M(CN) 4 )], with M = Pt II ( 1 ), Ni II ( 2 ) and abpt = 4-amino-3,5-bis(pyridin-2-yl)-1,2,4-triazole, have been synthesized and characterized by infrared spectroscopy, X-ray diffraction and magnetic measurements. The two compounds are isostructural as deduced from a Rietveld analysis of X-ray powder diffraction data of 2 simulated from the single crystal structure of 1 . The crystal packing of 1 is formed by regular chains running along the crystallographic [−1 0 1] direction where the planar [Pt(CN) 4 ] 2− anion acts as a μ 2 -bridging ligand via two nitrogen atoms of two different trans cyano groups, whi…
Hydrogen-bonded networks of [Fe(bpp)2]2+spin crossover complexes and dicarboxylate anions: structural and photomagnetic properties
2016
The paper reports the syntheses, crystal structures, thermal and (photo)magnetic properties of spin crossover salts of formula [Fe(bpp)2](C6H8O4)·4H2O (1·4H2O), [Fe(bpp)2](C8H4O4)·2CH3OH·H2O (2·2MeOH·H2O) and [Fe(bpp)2](C8H4O4)·5H2O (2·5H2O) (bpp = 2,6-bis(pyrazol-3yl)pyridine; C6H8O4 = adipate dianion; C8H4O4 = terephthalate dianion). The salts exhibit an intricate network of hydrogen bonds between low-spin iron(II) complexes and carboxylate dianions, with solvent molecules sitting in the voids. Desolvation is accompanied by a low-spin (LS) to high-spin (HS) transformation in the materials. The dehydrated phase 2 undergoes a two-step transition with a second step showing thermal hysteresis…
A Ferroelectric Iron(II) Spin Crossover Material
2017
A dual-function material in which ferroelectricity and spin crossover coexist in the same temperature range has been obtained. Our synthetic strategy allows the construction of acentric crystal structures in a predictable way and is based on the high directionality of hydrogen bonds. The well-known iron(II) spin crossover complex [Fe(bpp)₂]²+ (bpp = 2,6-bis(pyrazol-3-yl)pyridine), a four-fold noncentrosymmetric H-bond donor, was combined with a disymmetric H-bond acceptor such as the isonicotinate (isonic) anion to afford [Fe(bpp)₂](isonic)₂·2H₂O. This low-spin iron(II) compound crystallises in the acentric nonpolar I-4 space group and shows piezoelectricity and SHG properties. Upon dehydra…
An investigation of photo- and pressure-induced effects in a pair of isostructural two-dimensional spin-crossover framework materials
2014
International audience; Two new isostructural iron(II) spin-crossover (SCO) framework (SCOF) materials of the type [Fe(dpms)2 (NCX)2 ] (dpms=4,4'-dipyridylmethyl sulfide; X=S (SCOF-6(S)), X=Se (SCOF-6(Se))) have been synthesized. The 2D framework materials consist of undulating and interpenetrated rhomboid (4,4) nets. SCOF-6(S) displays an incomplete SCO transition with only approximately 30 % conversion of high-spin (HS) to low-spin iron(II) sites over the temperature range 300-4 K (T1/2 =75 K). In contrast, the NCSe(-) analogue, SCOF-6(Se), displays a complete SCO transition (T1/2 =135 K). Photomagnetic characterizations reveal quantitative light- induced excited spin-state trapping (LIES…
Harnessing Fluorescence versus Phosphorescence Ratio via Ancillary Ligand Fine-Tuned MLCT Contribution
2016
A series of gold(I) alkynyl-diphosphine complexes (XC6H4C2Au)PPh2—spacer—PPh2(AuC2C6H4X); spacer = —C2(C6H4)nC2— (A1, n = 2, X = CF3; A2, n = 2, X = OMe; A3, n = 3, X = CF3; A4, n = 3, X = OMe), —(C6H4)n— (B5, n = 3, X = OMe; B6, n = 4, X = OMe) were prepared, and their photophysical properties were investigated. The luminescence behavior of the titled compounds is dominated by the diphosphine spacer, which serves as an emitting ππ* chromophore. The complexes exhibit dual emission, comprising low and high energy bands of triplet (phosphorescence) and singlet (fluorescence) origins, respectively. The electron-donating characteristics of ancillary groups X significantly affect the LLCT/MLCT c…
Effect of Guest Molecules on Spin Transition Temperature in Loaded Hofmann‐Like Clathrates with Improved Porosity
2020
The synthesis, crystal structure, magnetic and calorimetric studies of a new clathrate compound of the Hofmann-type spin crossover (SCO) metal-organic framework (MOF) {Fe(bpb)[MII(CN)4]}·xGuest (bpb = bis(4-pyridyl)butadiyne, and MII = Ni, Pt) with characteristic fsc topology is reported. The framework {Fe(bpb)[MII(CN)4]} can host up to 1.5 guest molecules of (trifluoromethyl)benzene and display complete one-step cooperative SCO behavior. Our systematic study on {Fe(bpb)[Pt(CN)4]}·xGuest shows a general reciprocal correlation between the SCO temperature with the volume of the guest molecules.
Chiral and Racemic Spin Crossover Polymorphs in a Family of Mononuclear Iron(II) Compounds
2017
[EN] Understanding the origin of cooperativity and the equilibrium temperature of transition (T1/2) displayed by the spin-crossover (SCO) compounds as well as controlling these parameters are of paramount importance for future applications. For this task, the occurrence of polymorphism, presented by a number of SCO complexes, may provide deep insight into the influence of the supramolecular organization on the SCO behavior. In this context, herein we present a novel family of mononuclear octahedral FeII complexes with formula cis- [Fe(bqen)(NCX)2], where bqen is the chelating tetradentate ligand N,N¿-bis(8-quinolyl)ethane-1,2-diamine and X = S, Se. Depending on the preparation method, these…