An Organic Spin Crossover Material in Water from a Covalently Linked Radical Dyad

A covalently linked viologen radical cation dyad acts as a reversible thermomagnetic switch in water. Cycling between diamagnetic and paramagnetic forms by heating and cooling is accompanied by changes in optical and magnetic properties with high radical fidelity. Thermomagnetic switches in water may eventually find use as novel biological thermometers and in temperature-responsive organic materials where the changes in properties originate from a change in electronic spin configuration rather than a change in structure

Time-resolved single-crystal X-ray crystallography

In this chapter the development of time-resolved crystallography is traced from its beginnings more than 30 years ago. The importance of being able to “watch” chemical processes as they occur rather than just being limited to three-dimensional pictures of the reactant and final product is emphasised, and time-resolved crystallography provides the opportunity to bring the dimension of time into the crystallographic experiment. The technique has evolved in time with developments in technology: synchrotron radiation, cryoscopic techniques, tuneable lasers, increased computing power and vastly improved X-ray detectors. The shorter the lifetime of the species being studied, the more complex is the experiment. The chapter focusses on the results of solid-state reactions that are activated by light, since this process does not require the addition of a reagent to the crystalline material and the single-crystalline nature of the solid may be preserved. Because of this photoactivation, time-resolved crystallography is often described as “photocrystallography”. The initial photocrystallographic studies were carried out on molecular complexes that either underwent irreversible photoactivated processes where the conversion took hours or days. Structural snapshots were taken during the process. Materials that achieved a metastable state under photoactivation and the excited (metastable) state had a long enough lifetime for the data from the crystal to be collected and the structure solved. For systems with shorter lifetimes, the first time-resolved results were obtained for macromolecular structures, where pulsed lasers were used to pump up the short lifetime excited state species and their structures were probed by using synchronised X-ray pulses from a high-intensity source. Developments in molecular crystallography soon followed, initially with monochromatic X-ray radiation, and pump-probe techniques were used to establish the structures of photoactivated molecules with lifetimes in the micro- to millisecond range. For molecules with even shorter lifetimes in the sub-microsecond range, Laue diffraction methods (rather than using monochromatic radiation) were employed to speed up the data collections and reduce crystal damage. Future developments in time-resolved crystallography are likely to involve the use of XFELs to complete “single-shot” time-resolved diffraction studies that are already proving successful in the macromolecular crystallographic field.</p

Pyridinium bis(pyridine-κN)tetrakis(thiocyanato-κN)ferrate(III) -pyrazine-2-carbonitrile-pyridine (1/4/1)

In the title compound, (C5H6N)[Fe(NCS)4(C5H5N)2]- 4C5H3N3C5H5N, the FeIII ion is located on an inversion centre and is six-coordinated by four N atoms of the thiocyanate ligands and two pyridine N atoms in a trans arrangement, forming a slightly distorted octahedral geometry. A half-occupied H atom attached to a pyridinium cation forms an N—HN hydrogen bond with a centrosymmetrically-related pyridine unit. Four pyrazine-2-carbonitrile molecules crystallize per complex anion. In the crystal, – stacking interactions are present [centroid–centroid distances = 3.6220 (9), 3.6930 (9), 3.5532 (9), 3.5803 (9) and 3.5458 (8) A˚ ].peerReviewe

Spin Crossover in Fe(II)–M(II) Cyanoheterobimetallic Frameworks (M = Ni, Pd, Pt) with 2‑Substituted Pyrazines

Discovery of spin-crossover (SCO) behavior in the family of Fe^II-based Hofmann clathrates has led to a “new rush” in the field of bistable molecular materials. To date this class of SCO complexes is represented by several dozens of individual compounds, and areas of their potential application steadily increase. Starting from Fe²⁺, square planar tetracyanometalates M^II(CN)₄^2– (M^II = Ni, Pd, Pt) and 2-substituted pyrazines Xpz (X = Cl, Me, I) as coligands we obtained a series of nine new Hofmann clathrate-like coordination frameworks. X-ray diffraction reveals that in these complexes Fe^II ion has a pseudo-octahedral coordination environment supported by four μ₄-tetracyanometallates forming its equatorial coordination environment. Depending on the nature of X and M, axial positions are occupied by two 2X-pyrazines (X = Cl and M^II = Ni (<b>1</b>), Pd (<b>2</b>), Pt (<b>3</b>); X = Me and M^II = Ni (<b>4</b>), Pd (<b>5</b>)) or one 2X-pyrazine and one water molecule (X = I and M^II = Ni (<b>7</b>), Pd (<b>8</b>), Pt (<b>9</b>)), or, alternatively, two distinct Fe^II positions with either two pyrazines or two water molecules (X = Me and M^II = Pt (<b>6</b>)) are observed. Temperature behavior of magnetic susceptibility indicates that all compounds bearing FeN₆ units (<b>1</b>–<b>6</b>) display cooperative spin transition, while Fe^II ions in N₅O or N₄O₂ surrounding are high spin (HS). Structural changes in the nearest Fe^II environment upon low-spin (LS) to HS transition, which include ca. 10% Fe–N distance increase, lead to the cell expansion. Mössbauer spectroscopy is used to characterize the spin state of all HS, LS, and intermediate phases of <b>1</b>–<b>9</b> (see abstract figure). Effects of a pyrazine substituent and M^II nature on the hyperfine parameters in both spin states are established

Spin Crossover in Fe(II)–M(II) Cyanoheterobimetallic Frameworks (M = Ni, Pd, Pt) with 2‑Substituted Pyrazines

Discovery of spin-crossover (SCO) behavior in the family of Fe^II-based Hofmann clathrates has led to a “new rush” in the field of bistable molecular materials. To date this class of SCO complexes is represented by several dozens of individual compounds, and areas of their potential application steadily increase. Starting from Fe²⁺, square planar tetracyanometalates M^II(CN)₄^2– (M^II = Ni, Pd, Pt) and 2-substituted pyrazines Xpz (X = Cl, Me, I) as coligands we obtained a series of nine new Hofmann clathrate-like coordination frameworks. X-ray diffraction reveals that in these complexes Fe^II ion has a pseudo-octahedral coordination environment supported by four μ₄-tetracyanometallates forming its equatorial coordination environment. Depending on the nature of X and M, axial positions are occupied by two 2X-pyrazines (X = Cl and M^II = Ni (<b>1</b>), Pd (<b>2</b>), Pt (<b>3</b>); X = Me and M^II = Ni (<b>4</b>), Pd (<b>5</b>)) or one 2X-pyrazine and one water molecule (X = I and M^II = Ni (<b>7</b>), Pd (<b>8</b>), Pt (<b>9</b>)), or, alternatively, two distinct Fe^II positions with either two pyrazines or two water molecules (X = Me and M^II = Pt (<b>6</b>)) are observed. Temperature behavior of magnetic susceptibility indicates that all compounds bearing FeN₆ units (<b>1</b>–<b>6</b>) display cooperative spin transition, while Fe^II ions in N₅O or N₄O₂ surrounding are high spin (HS). Structural changes in the nearest Fe^II environment upon low-spin (LS) to HS transition, which include ca. 10% Fe–N distance increase, lead to the cell expansion. Mössbauer spectroscopy is used to characterize the spin state of all HS, LS, and intermediate phases of <b>1</b>–<b>9</b> (see abstract figure). Effects of a pyrazine substituent and M^II nature on the hyperfine parameters in both spin states are established

Spin Crossover in Fe(II)–M(II) Cyanoheterobimetallic Frameworks (M = Ni, Pd, Pt) with 2‑Substituted Pyrazines

Discovery of spin-crossover (SCO) behavior in the family of Fe^II-based Hofmann clathrates has led to a “new rush” in the field of bistable molecular materials. To date this class of SCO complexes is represented by several dozens of individual compounds, and areas of their potential application steadily increase. Starting from Fe²⁺, square planar tetracyanometalates M^II(CN)₄^2– (M^II = Ni, Pd, Pt) and 2-substituted pyrazines Xpz (X = Cl, Me, I) as coligands we obtained a series of nine new Hofmann clathrate-like coordination frameworks. X-ray diffraction reveals that in these complexes Fe^II ion has a pseudo-octahedral coordination environment supported by four μ₄-tetracyanometallates forming its equatorial coordination environment. Depending on the nature of X and M, axial positions are occupied by two 2X-pyrazines (X = Cl and M^II = Ni (<b>1</b>), Pd (<b>2</b>), Pt (<b>3</b>); X = Me and M^II = Ni (<b>4</b>), Pd (<b>5</b>)) or one 2X-pyrazine and one water molecule (X = I and M^II = Ni (<b>7</b>), Pd (<b>8</b>), Pt (<b>9</b>)), or, alternatively, two distinct Fe^II positions with either two pyrazines or two water molecules (X = Me and M^II = Pt (<b>6</b>)) are observed. Temperature behavior of magnetic susceptibility indicates that all compounds bearing FeN₆ units (<b>1</b>–<b>6</b>) display cooperative spin transition, while Fe^II ions in N₅O or N₄O₂ surrounding are high spin (HS). Structural changes in the nearest Fe^II environment upon low-spin (LS) to HS transition, which include ca. 10% Fe–N distance increase, lead to the cell expansion. Mössbauer spectroscopy is used to characterize the spin state of all HS, LS, and intermediate phases of <b>1</b>–<b>9</b> (see abstract figure). Effects of a pyrazine substituent and M^II nature on the hyperfine parameters in both spin states are established

Spin Crossover in Fe(II)–M(II) Cyanoheterobimetallic Frameworks (M = Ni, Pd, Pt) with 2‑Substituted Pyrazines

Discovery of spin-crossover (SCO) behavior in the family of Fe^II-based Hofmann clathrates has led to a “new rush” in the field of bistable molecular materials. To date this class of SCO complexes is represented by several dozens of individual compounds, and areas of their potential application steadily increase. Starting from Fe²⁺, square planar tetracyanometalates M^II(CN)₄^2– (M^II = Ni, Pd, Pt) and 2-substituted pyrazines Xpz (X = Cl, Me, I) as coligands we obtained a series of nine new Hofmann clathrate-like coordination frameworks. X-ray diffraction reveals that in these complexes Fe^II ion has a pseudo-octahedral coordination environment supported by four μ₄-tetracyanometallates forming its equatorial coordination environment. Depending on the nature of X and M, axial positions are occupied by two 2X-pyrazines (X = Cl and M^II = Ni (<b>1</b>), Pd (<b>2</b>), Pt (<b>3</b>); X = Me and M^II = Ni (<b>4</b>), Pd (<b>5</b>)) or one 2X-pyrazine and one water molecule (X = I and M^II = Ni (<b>7</b>), Pd (<b>8</b>), Pt (<b>9</b>)), or, alternatively, two distinct Fe^II positions with either two pyrazines or two water molecules (X = Me and M^II = Pt (<b>6</b>)) are observed. Temperature behavior of magnetic susceptibility indicates that all compounds bearing FeN₆ units (<b>1</b>–<b>6</b>) display cooperative spin transition, while Fe^II ions in N₅O or N₄O₂ surrounding are high spin (HS). Structural changes in the nearest Fe^II environment upon low-spin (LS) to HS transition, which include ca. 10% Fe–N distance increase, lead to the cell expansion. Mössbauer spectroscopy is used to characterize the spin state of all HS, LS, and intermediate phases of <b>1</b>–<b>9</b> (see abstract figure). Effects of a pyrazine substituent and M^II nature on the hyperfine parameters in both spin states are established

Interaction of physical fields with nanostructured materials

Research results of several important material systems presented in this collective monograph demonstrate a number of characteristic features and unique effects. The main findings are listed below. 1. The interaction between molecules and semiconductor structures allows a new amplification effect to be registered and studied by utilizing a new parameter – characteristic time constant, which is extremely sensitive for the characterization of biomolecular quantity. 2. The effects of the interaction of magnetic, optical and electromagnetic fields with nanostructured composites, semiconductor structures, anisotropic media, magnetic fluid systems, layered structures, phonons of molecular nanocomplexes and nanoinhomogeneities of rough surfaces were established. 3. The fundamental nature of the interaction effects was found as a result of a careful comparison of modeling results with experimental data. The importance of the studies is underlined by the wide range of potential applications. For the reader’s convenience, the presentation of the material is structured as follows. The general content includes only the names of sections. The full content of each section is listed in the text. For the same reason, the list of references is given at the end of each section. The authors present the material in such a way that the reader can easily view the current state of research in these areas and be able to navigate freely in the text. Section 1 presents a number of effects registered in semiconductor structures with dielectric coatings as surface potential sensors. In particular, the effects of internal amplification in semiconductor (bio)sensors using single trap phenomena are revealed. The noise characteristics of semiconductor nanoscale sensor structures, the effect of γ-radiation on the noise and transport characteristics of the sensors mentioned above were analyzed. It is demonstrated that effects related to single traps can be used for the detection of troponin biomolecules as indicators of [...