Search results for "spin [structure function]"

Pressure effect studies in molecular magnetism

2004

We report on temperature dependent magnetic susceptibility and Mossbauer effect studies of the influence of hydrostatic pressure (up to 1.2 GPa) on dynamic electronic structure phenomena in 3d transition metal coordination compounds. The systems under investigation are mononuclear spin crossover compounds of iron (II) and chromium (II), dinuclear complexes of iron (II) exhibiting coexistence of intramolecular antiferromagnetic coupling and thermal spin crossover, 1D, 2D and 3D polynuclear spin crossover complexes of iron (II), a valence tautomeric system of cobalt (II) showing a thermal transition from a high spin [CoII (semiquinone)] to a low spin [CoII (catecholate)] species on lowering t…

Molecular magnetism, quo vadis? A historical perspective from a coordination chemist viewpoint☆

2017

Abstract Molecular magnetism has travelled a long way from the pioneering studies on electron exchange and double exchange or spin crossover and valence tautomerism in small oligonuclear complexes, from mono- to di- and tetranuclear species, to the current investigations about magnetic anisotropy and spin dynamics or quantum coherence of simple mono- or large polynuclear complexes, behaving as switchable bistable molecular nanomagnets for potential applications in information data storage and processing. In this review, we focus on the origin and development of the research in the field of molecular magnetism from a coordination chemistry viewpoint, which dates back to the establishment of …

Oxotris(oxalato)niobate(V) as counterion in cobalt(II) spin-crossover systems

2016

Abstract This work is devoted to the investigation of the thermally induced spin-crossover behavior from a high-spin state (HS, S = 3/2) at higher temperatures to a low-spin phase (LS, S = 1/2) at lower temperatures of the six-coordinate cobalt(II) complex in the compound [Co(terpy)2]3[NbO(C2O4)3]2·3CH​3OH·4H2O (2). The crystal structure of 2 together with that of its counterion as tetraphenylarsonium(V) salt (AsPh4)3[NbO(C2O4)3]·9H2O (1) are also included. The spin-crossover process was followed by the thermal variation of the χMT product between 2.0 and 400 K under the warming mode, with the LS configuration being achieved at T ⩽ 200 K and the LS → HS interconversion being incomplete at 4…

Strong Field Iron(II) Complex Converted by Light into a Long-Lived High-Spin State

2000

Spin transition in heptanuclear star-shaped iron(III)–antimony(V) NCS- and CN-bridged compounds

2009

Abstract The precursor [FeIII(L)Cl] (LH2 = N,N′-bis(2′-hydroxy-benzyliden)-1,6-diamino-3-azahexane) has been prepared and Mossbauer spectroscopy assigned a high-spin (S = 5/2) state at room temperature. The precursor is combined with the bridging units [SbV(X)6]− (X = CN−, NCS−) to yield star-shaped heptanuclear clusters [(LFeIII–X)6SbV]Cl5. The star-shaped compounds are in general high-spin systems at room temperature. On cooling to 20 K some of the iron(III) centers switch to the low-spin state as indicated by Mossbauer spectroscopy, i.e. multiple electronic transitions. While the cyano-bridged complex performs a multiple spin transition the thiocyanate-compound shows no significant popul…

Spin Switching with Triazolate-Strapped Ferrous Porphyrins

2019

Fe(III) porphyrins bridged with 1,2,3-triazole ligands were synthesized. Upon deprotonation, the triazolate ion coordinates to the Fe(III) ion, forming an overall neutral high-spin Fe(III) porphyrin in which the triazolate serves both as an axial ligand and as the counterion. The second axial coordination site is activated for coordination and binds p-methoxypyridine, forming a six-coordinate low-spin complex. Upon addition of a phenylazopyridine as a photodissociable ligand, the spin state of the complex can be reversibly switched with ultraviolet and visible light. The system provides the basis for the development of switchable catalase- and peroxidase-type catalysts and molecular spin sw…

Spin-Transition in [Fe(II)(2,6-Bis-(Benzimidazol-2′-yl)pyridine)2] (CIO4)2: Hysteresis Effect Dependent on the Matrix

1999

Abstract Far-Infrared spectroscopical investigation of the spin-crossover in [Fe(II)(2,6-bis-(benzimidazol-2′-yl)-pyridine)2] (CIO4)2 exhibits a hysteresis in both CsI and polyethylene matrices within temperature cycles between 100K and 520K. The hysteresis broadening is dependent on the matrix and bigger in CsI. This can be explained due to polarity and hydrogen bonding. Two low spin vibrations, LS1 at 437 cm−1 and LS2 at 424cm−1, are observed. On heating from 100K to 520K: during LS1 decreases, the LS2 raises temporarily, until both LS1 and LS2 disappear; for the HS only one raising species was observed. This gives raise to assume two different sub-lattices.

Spin crossover in mononuclear and binuclear iron(III) complexes with pentadentate Schiff-base ligands

2000

Abstract A series of mononuclear hexacoordinate iron(III) complexes, [Fe( 5 L )(py)]BPh 4 , and binuclear hexacoordinate iron(III) complexes, [( 5 L )Fe(μ 2 -bpy)Fe( 5 L )](BPh 4 ) 2 , has been prepared and their magnetic properties were investigated; the pentadentate ligands were derivatives of 5 L =saldptn=N,N′-bis(2-hydroxybenzyliden)-1,7-diamino-4-azaheptane. Temperature variation of the effective magnetic moment for them shows that a spin transition from the low-spin to the high-spin state occurs. The magnetic data were fitted to an Ising-like model appropriate for the mono- and binuclear systems.

Development of MR active contrast agents via Parahydrogen Induced Polarization

2009

Parahydrogen Induced Polarization provides dramatic MR signal enhancement that can be exploited for molecular imaging. This method allows amongst others for Magnetic Resonance Imaging of 13C and 15N, which is usually constrained by the low MR sensitivity of these nuclei. By combining hydrogenation of barbiturates with parahydrogen under special experimental conditions (PASADENA under pressure) with a polarization transfer sequence we demonstrate the transfer of the initial 1H polarization to 13C. The polarization transfer yields a signal increase for 13C of more than 1000. Hence, the role of certain target compounds such as anesthetics like the barbituric acid derivatives could be investiga…

Synthesis of Lead Zirconate Antiferroelectric Thin Films by Sol-Gel Processing

2000

A modified methoxyethanol sol-gel process was used for the production of PbZrO3 thin films. The new route uses lead oxide [PbO] instead of lead acetate [Pb(OAc)2]. Through the use of this method it is possible to prepare single-phase perovskite materials with improved properties. Examples are given for PbZrO3 thin layers deposited by the spin coating process on TiO2/Pt/TiO2/SiO2/Si substrates from various sols where lead acetate or lead oxide are used as the starting lead compound. The preferred orientation and the perovskite phase content of the films were studied using X-ray diffraction analysis (XRD). Scanning electron microscopy (SEM) was used for microstructural characterization of the…