Understanding the motional dynamics of the ammonium ion in the mechanism of multiferroicity of Cr(V) peroxychromates: a H NMR study.

Cr(5+)-based peroxychromates, MCr(O), with M = NH or a mixed NH-alkali metal are a new class of multiferroics for potential use in molecular memory devices, with the NH being a key element, but the underlying chemical mechanism is not fully understood. The NH ion occupies two different sites, but their specific roles are not known. We thus performed detailed H NMR spin-relaxation () measurements on (NH)Cr(O) over a wide temperature range (120-300 K) to probe the displacive as well as hindered rotational dynamics of the NH ions with the view of understanding their specific roles in the phase transitions.

Arsenic(III)-Capped 12-Tungsto-2-Arsenates(III) [M(AsWO)(AsOH)] (M = Cr, Fe, Sc, In, Ti, Mn) and Their Magnetic Properties.

Six arsenic(III)-capped 12-tungsto-2-arsenates(III) of the type [M(AsWO)(AsOH)] (M = Cr, ; Fe, ; Sc, ; In, ; Ti, ; Mn, ) have been synthesized in aqueous medium by direct reaction of the elements using a one-pot strategy and structurally characterized by FT-IR spectroscopy, single-crystal XRD, and elemental analysis. Polyanions - are comprised of two octahedrally coordinated guest metal ions M sandwiched between two {AsW} units, resulting in a structure with point-group symmetry. Polyanions - contain tri- and tetravalent metal ion guests M (M = Cr, Fe, Sc, In, and Ti, respectively), and they have one {AsOH} group grafted on each {AsW} unit, whereas the divalent Mn-containing derivative has two such {AsOH} groups grafted on each {AsW} unit.

Synthesis, structure, electrochemistry and magnetism of cobalt-, nickel- and zinc-containing [M(OH)(HO)(α-SiWO)] (M = Co, Ni, and Zn).

Interaction of the trilacunary 9-tungstosilicate [A-α-SiWO] with cobalt(ii), nickel(ii) and zinc(ii) ions in pH 9 aqueous medium at room temperature led to the formation of the respective M-containing heteropolytungstates [M(OH)(HO)(α-SiWO)] (M = Co (1), Ni (2), and Zn (3)). Polyanions 1-3 were characterized in the solid state by single-crystal XRD, FT-IR spectroscopy, and thermogravimetric and elemental analyses. Electrochemical studies showed that the Co ions in 1 can be oxidized to Co and the CVs of the W centers of the polyanions feature well-defined and chemically reversible reduction waves.

Tetra-Mn-Containing 30-Tungsto-4-phosphate, [Mn(HO)(PWO)]: Synthesis, Structure, XPS, Magnetism, and Electrochemical Study.

Reaction of the mixed-valent Mn-acetato complex [MnMnO(CHCOO)(HO)] with the trilacunary Wells-Dawson-type heteropolytungstate [PWO] in acidic acetate solution (pH 1.1) resulted in the tetra-Mn-containing polyanion [Mn(HO)(PWO)] (). Single-crystal XRD on Na[Mn(HO)(PWO)]·84HO () revealed that four Mn ions form a rhombic MnO core encapsulated by two [PWO] units.

Fe -Containing 96-Tungsto-16-Phosphate: Synthesis, Structure, Magnetism and Electrochemistry.

The 48-Fe -containing 96-tungsto-16-phosphate, [Fe (OH) (H O) (HP W O ) ] (Fe ), has been synthesized and structurally characterized. This polyanion comprises eight equivalent {Fe P W } units that are linked in an end-on fashion forming a macrocyclic assembly that contains more iron centers than any other polyoxometalate (POM) known to date. The novel Fe was synthesized by a simple one-pot reaction of an {Fe } coordination complex with the hexalacunary {P W } POM precursor in water.

Developing the Pressure-Temperature-Magnetic Field Phase Diagram of Multiferroic [(CH)NH]Mn(HCOO).

We combined Raman scattering and magnetic susceptibility to explore the properties of [(CH)NH]Mn(HCOO) under compression. Analysis of the formate bending mode reveals a broad two-phase region surrounding the 4.2 GPa critical pressure that becomes increasingly sluggish below the order-disorder transition due to the extensive hydrogen-bonding network.

Viewpoint: Atomic-Scale Design Protocols toward Energy, Electronic, Catalysis, and Sensing Applications.

Nanostructured materials are essential building blocks for the fabrication of new devices for energy harvesting/storage, sensing, catalysis, magnetic, and optoelectronic applications. However, because of the increase of technological needs, it is essential to identify new functional materials and improve the properties of existing ones. The objective of this Viewpoint is to examine the state of the art of atomic-scale simulative and experimental protocols aimed to the design of novel functional nanostructured materials, and to present new perspectives in the relative fields.

Antiferroelectric Phase Transition in a Proton-Transfer Salt of Squaric Acid and 2,3-Dimethylpyrazine.

A proton-transfer reaction between squaric acid (Hsq) and 2,3-dimethylpyrazine (2,3-Mepyz) results in crystallization of a new organic antiferroelectric (AFE), (2,3-MepyzH)(Hsq)·HO (), which possesses a layered structure. The structure of each layer can be described as partitioned into strips lined with methyl groups of the MepyzH cations and strips featuring extensive hydrogen bonding between the Hsq anions and water molecules. Variable-temperature dielectric measurements and crystal structures determined through a combination of single-crystal X-ray and neutron diffraction reveal an AFE ordering at 104 K.

Structure-Property Relations in Multiferroic [(CH)NH] M(HCOO) ( M = Mn, Co, Ni).

We bring together magnetization, infrared spectroscopy, and lattice dynamics calculations to uncover the magnetic field-temperature ( B- T) phase diagrams and vibrational properties of the [(CH)NH] M(HCOO) ( M = Mn, Co, Ni) family of multiferroics. While the magnetically driven transition to the fully saturated state in [(CH)NH]Mn(HCOO) takes place at 15.3 T, substitution with Ni or Co drives the critical fields up toward 100 T, an unexpectedly high energy scale for these compounds.

15-Copper(ii)-containing 36-tungsto-4-silicates(iv) [CuO(OH)X(A-α-SiWO)] (X = Cl, Br): synthesis, structure, magnetic properties, and electrocatalytic CO reduction.

The 15-copper(ii)-containing 36-tungsto-4-silicates [Cu15O2(OH)10X(A-α-SiW9O34)4]25- (X = Cl, 1; Br, 2) have been prepared in 70% yield by reaction of the trilacunary 9-tungstosilicate precursor [A-α-SiW9O34]10- with Cu2+ ions in aqueous pH 8 medium. Both polyanions 1 and 2 were isolated as hydrated mixed potassium/sodium salts and characterized in the solid state by FT-IR, TGA, single-crystal XRD, and elemental analysis. DC magnetic susceptibility measurements from 1.

Structural and Optical Properties of Nanocrystalline TiO with Multiwalled Carbon Nanotubes and Its Photovoltaic Studies Using Ru(II) Sensitizers.

In this study, the sol-gel method has been deployed to prepare the titanium dioxide/multiwalled carbon nanotubes (TiO/MWCNTs) nanocomposite (NCs) powders with varying content of MWCNTs (0.01-1.0 wt %), to construct the dye-sensitized solar cells (DSSCs).

DNA mismatch repair protein Mlh1 is required for tetravalent chromium intermediate-induced DNA damage.

Hexavalent chromium (Cr[VI]) is associated with occupational lung cancer and poses a significant public health concern. When exposed to Cr[VI], cells rapidly internalize this compound and metabolize it to Cr[III]. Byproducts of Cr[VI] metabolism include unstable Cr[V] and Cr[IV] intermediates that are believed to be directly responsible for the genotoxicity and carcinogenicity caused by Cr[VI] exposure; however, the carcinogenic potential of the Cr intermediates and the mechanisms of Cr-induced carcinogenesis remain to be further defined.

Magic angle spinning NMR study of the ferroelectric transition of KHPO: definitive evidence of a displacive component.

Variable temperature magic angle spinning (MAS) NMR measurements are reported on H and P nuclei in KHPO (KDP) in the vicinity of its paraelectric-ferroelectric phase transition temperature, T , of 123 K, to examine the transition mechanism, in particular if this is a model order-disorder type or whether it also involves a displacive component. It has been well established that the temperature variation of the isotropic chemical shift, δ , in NMR measurements of the nuclei directly involved in the transition should remain constant or change smoothly through T for an order-disorder type transition but it should show an anomalous change for a displacive one. Here we demonstrate that the δ for both P and H nuclei in KDP show clear anomalies as a function of temperature around KDP's T , providing direct evidence of a displacive component for the phase transition of KDP in contrast to the generally accepted notion that it is a model order-disorder type.

Cr-Substituted Heteropoly-16-Tungstates [Cr(B-β-XWO)] (X = Si, Ge): Magnetic, Biological, and Electrochemical Studies.

The dichromium(III)-containing heteropoly-16-tungstates [Cr(B-β-SiWO)] (1) and [Cr(B-β-GeWO)] (2) were prepared via a one-pot reaction of the composing elements in aqueous, basic medium. Polyanions 1 and 2 represent the first examples of Cr-containing heteropolytungstates comprising the octatungstate unit {XWO} (X = Si, Ge). Magnetic studies demonstrated that, in the solid state, the two polyanions exhibit a weak antiferromagnetic interaction between the two Cr centers with J = -3.

Ion Environments in Mn(2+)-Doped Polyelectrolyte Complexes: Dilute Magnetic Saloplastics.

Amorphous hydrated complexes of the polyelectrolytes poly(styrene sulfonate) (PSS) and poly(diallyldimethylammonium) were doped with the spin-5/2 ion Mn(2+). X-band electron paramagnetic resonance (EPR) measurements of the Mn(2+) spins within these stoichiometric polyelectrolyte complexes (PECs) revealed an octahedral coordination environment, similar to that observed in aqueous solutions of Mn(2+). This octahedral symmetry of the [Mn(H2O)6](2+) complexes, observed in fully hydrated PECs, is somewhat distorted because of the wide range of ion pairs possible with the sulfonate group on PSS.

Enhancing the Magnetic Anisotropy of Linear Cr(II) Chain Compounds Using Heavy Metal Substitutions.

Magnetic properties of the series of three linear, trimetallic chain compounds Cr2Cr(dpa)4Cl2, 1, Mo2Cr(dpa)4Cl2, 2, and W2Cr(dpa)4Cl2, 3 (dpa = 2,2'-dipyridylamido), have been studied using variable-temperature dc and ac magnetometry and high-frequency EPR spectroscopy. All three compounds possess an S = 2 electronic ground state arising from the terminal Cr(2+) ion, which exhibits slow magnetic relaxation under an applied magnetic field, as evidenced by ac magnetic susceptibility and magnetization measurements. The slow relaxation stems from the existence of an easy-axis magnetic anisotropy, which is bolstered by the axial symmetry of the compounds and has been quantified through rigorous high-frequency EPR measurements.

Six-coordinate ferric porphyrins containing bidentate N-t-butyl-N-nitrosohydroxylaminato ligands: structure, magnetism, IR spectroelectrochemisty, and reactivity.

NONOates (diazeniumdiolates) containing the [X{N2O2}](-) functional group are frequently employed as nitric oxide (NO) donors in biology, and some NONOates have been shown to bind to metalloenzymes. We report the preparation, crystal structures, detailed magnetic behavior, redox properties, and reactivities of the first isolable alkyl C-NONOate complexes of heme models, namely (OEP)Fe(η(2)-ON(t-Bu)NO) (1) and (TPP)Fe(η(2)-ON(t-Bu)NO) (2) (OEP = octaethylporphyrinato dianion, TPP = tetraphenylporphyrinato dianion). The compounds display the unusual NONOate O,O-bidentate binding mode for porphyrins, resulting in significant apical Fe displacements (+0.

Cr(i)Cl as well as Cr are stabilised between two cyclic alkyl amino carbenes.

Cr(i)Cl is a very unstable species. The present work describes the stabilisation of Cr(i)Cl in the low coordinate environment of cyclic alkyl(amino) carbene ligands and its synthetic application to yield an unprecedented cationic complex with a two coordinate Cr(i). One electron reduction of (cAAC)CrCl () with equivalent amount of KC results in the formation of (cAAC)CrCl (), with a distorted trigonal planar configuration at the metal centre.

High field electron paramagnetic resonance characterization of electronic and structural environments for paramagnetic metal ions and organic free radicals in Deepwater Horizon oil spill tar balls.

In the first use of high-field electron paramagnetic resonance (EPR) spectroscopy to characterize paramagnetic metal-organic and free radical species from tar balls and weathered crude oil samples from the Gulf of Mexico (collected after the Deepwater Horizon oil spill) and an asphalt volcano sample collected off the coast of Santa Barbara, CA, we are able to identify for the first time the various paramagnetic species present in the native state of these samples and understand their molecular structures and bonding. The two tar ball and one asphalt volcano samples contain three distinct paramagnetic species: (i) an organic free radical, (ii) a [VO](2+) containing porphyrin, and (iii) a Mn(2+) containing complex. The organic free radical was found to have a disc-shaped or flat structure, based on its axially symmetric spectrum.

Synthesis, detailed characterization, and theoretical understanding of mononuclear chromium(III)-containing polyoxotungstates [Cr(III)(HX(V)W₇O₂₈)₂]¹³⁻ (X = P, As) with exceptionally large magnetic anisotropy.

Two monochromium(III)-containing heteropolytungstates, [Cr(III)(HP(V)W7O28)2](13-) (1a) and [Cr(III)(HAs(V)W7O28)2](13-) (2a), were prepared via simple, one-pot reactions in aqueous, basic medium, by reaction of the composing elements, and then isolated as hydrated sodium salts, Na13[Cr(III)(HP(V)W7O28)2]·47H2O (1) and Na13[Cr(III)(HAs(V)W7O28)2]·52H2O (2). Polyanions 1a and 2a comprise an octahedrally coordinated Cr(III) ion, sandwiched by two {PW7} or {AsW7} units. Both compounds 1 and 2 were fully characterized in the solid state by single-crystal XRD, IR spectroscopy, thermogravimetric and elemental analyses, magnetic susceptibility, and EPR measurements.

Electronic structure and slow magnetic relaxation of low-coordinate cyclic alkyl(amino) carbene stabilized iron(I) complexes.

Cyclic alkyl(amino) carbene stabilized two- and three-coordinate Fe(I) complexes, (cAAC)2FeCl (2) and [(cAAC)2Fe][B(C6F5)4] (3), respectively, were prepared and thoroughly studied by a bouquet of analytical techniques as well as theoretical calculations. Magnetic susceptibility and Mössbauer spectroscopy reveal the +1 oxidation state and S = 3/2 spin ground state of iron in both compounds. 2 and 3 show slow magnetic relaxation typical for single molecule magnets under an applied direct current magnetic field.

Expansion of the rich structures and magnetic properties of neptunium selenites: soft ferromagnetism in Np(SeO3)2.

Two new neptunium selenites with different oxidation states of the metal centers, Np(IV)(SeO3)2 and Np(VI)O2(SeO3), have been synthesized under mild hydrothermal conditions at 200 °C from the reactions of NpO2 and SeO2. Np(SeO3)2 crystallizes as brown prisms (space group P21/n, a = 7.0089(5) Å, b = 10.

The usefulness of EPR spectroscopy in the study of compounds with metal-metal multiple bonds.

This Perspective reviews some of the contributions that EPR spectroscopy has made for the understanding of the bonding and electronic structure of molecular species with metal-to-metal multiple bonds. The goal is to show how useful this technique can be in (a) elucidating whether unpaired electrons reside in metal-based or ligand-based molecular orbitals, (b) providing information on the metal center's total electronic spin, an aspect that offers support to its oxidation state, (c) informing about the distribution of the unpaired electrons between the metals and the organic ligand, (d) detecting molecular dynamics and phase transitions to complement X-ray studies and (e) using high-frequency, high-field EPR for studying compounds that might be EPR-silent when only commonly available spectrometers are used. A brief comparison with NMR is provided in the ESI where it is noted that for typical laboratory magnetic fields, the energy gap between resonant states in EPR is in the microwave region of the electromagnetic spectrum (GHz) while for NMR it is in the radiofrequency range (MHz).

Di-, tri-, and tetranuclear nickel(II) complexes with oximato bridges: magnetism and catecholase-like activity of two tetranuclear complexes possessing rhombic topology.

Oxime-based tridentate Schiff base ligands 3-[2-(diethylamino)ethylimino]butan-2-one oxime (HL(1)) and 3-[3-(dimethylamino)propylimino]butan-2-one oxime (HL(2)) produced the dinuclear complex [Ni2L(1)2](ClO4)2 (1) and trinuclear complex [Ni3(HL(2))3(μ3-O)](ClO4)4·CH3CN (2), respectively, upon reaction with Ni(ClO4)2·6H2O. However, in a slightly alkaline medium, both of the ligands underwent hydrolysis and resulted in tetranuclear complexes [{Ni(deen)(H2O)}2(μ3-OH)2{Ni2(moda)4}](ClO4)2·2CH3CN (3) and [{Ni(dmpn)(CH3CN)2}2(μ3-OH)2{Ni2(moda)4}](ClO4)2·CH3CN (4), where deen = 2-(diethylamino)ethylamine, dmpn = 3-(dimethylamino)-1-propylamine, and modaH = diacetyl monoxime. All four complexes have been structurally characterized.