Affine spherical homogeneous spaces with good quotient by a maximal unipotent subgroup

For an affine spherical homogeneous space G/H of a connected semisimple algebraic group G, we consider the factorization morphism by the action on G/H of a maximal unipotent subgroup of G. We prove that this morphism is equidimensional if and only if the weight semigroup of G/H satisfies some simple condition.Comment: v2: title and abstract changed; v3: 16 pages, minor correction

Purification of NaYF₄‑Based Upconversion Phosphors

Applications of upconversion phosphors have grown extensively in number during the past decade. Hexagonal sodium yttrium fluoride (β-NaYF₄) is known to be one of the best host lattices for upconversion materials. We developed a novel technique for transforming cubic sodium yttrium fluoride (α-NaYF₄) phosphors into the hexagonal modification and remove oxygen impurities that hinder the upconversion luminescence. We transformed cubic α-NaYF₄ nanoparticles from flame-spray synthesis with a particle size less than 50 nm into more efficient β-NaYF₄ phosphors. The application of SnF₂ and ZnF₂ as oxygen scavengers allowed the formation of the pure hexagonal phase and improved the upconversion luminescence intensity. The developed process utilizes no free HF gas in the production and does not contaminate the upconversion phosphors with scavenger material. The treatment increases the particle size to between approximately 500 nm and 1 μm. Upconversion luminescence spectra revealed the characteristic blue Tm³⁺ and green Er³⁺ emissions of β-NaYF₄: Yb,Tm and Yb,Er, respectively

A Homologous Series of First-Row Transition-Metal Complexes of 2,2′-Bipyridine and their Ligand Radical Derivatives: Trends in Structure, Magnetism, and Bonding

The organometallic first-row transition-metal complexes [M­(2,2′-bipy)­(mes)₂] (M = Cr (<b>1</b>), Mn (<b>2</b>), Co (<b>4</b>), Ni (<b>5</b>); 2,2′-bipy = 2,2′-bipyridine; mes = 2,4,6-Me₃C₆H₂) were reacted with potassium and a suitable alkali-metal sequestering agent to yield salts of the anionic species [M­(2,2′-bipy)­(mes)₂]⁻. The neutral parent compounds and their corresponding anionic congeners were characterized by single-crystal X-ray diffraction in [Cr­(2,2′-bipy)­(mes)₂]·1.5C₆H₆, [Mn­(2,2′-bipy)­(mes)₂], [Co­(2,2′-bipy)­(mes)₂]·THF, [Ni­(2,2′-bipy)­(mes)₂], [K­(dibenzo-18-crown-6)·THF]­[Cr­(2,2′-bipy)­(mes)₂]·2THF, [K­(18-crown-6)]­[Mn­(2,2′-bipy)­(mes)₂]·2THF, [K­(18-crown-6)]­[Mn­(2,2′-bipy)­(mes)₂]·0.67py·0.67tol, [K­(2,2,2-crypt)]­[Co­(2,2′-bipy)­(mes)₂], and [K­(2,2,2-crypt)]­[Ni­(2,2′-bipy)­(mes)₂]. These species, along with the previously reported neutral and anionic iron complexes [Fe­(2,2′-bipy)­(mes)₂]^0/– (<b>3</b>/<b>3</b>^<b>–</b>), form a homologous series of compounds which allow for an in-depth study of the interactions between metals and ligands. Single-crystal X-ray diffraction data, DFT calculations, and various spectroscopic and magnetic measurements indicate that the anionic complexes (<b>1</b>^<b>–</b>–<b>5</b>^<b>–</b>) can be best formulated as M­(II) complexes of the 2,2′-bipyridyl radical anion. These findings complement recent studies which indicate that bond metric data from single-crystal X-ray diffraction may be employed as an important diagnostic tool in determining the oxidation states of bipyridyl ligands in transition-metal complexes

A Homologous Series of First-Row Transition-Metal Complexes of 2,2′-Bipyridine and their Ligand Radical Derivatives: Trends in Structure, Magnetism, and Bonding

The organometallic first-row transition-metal complexes [M­(2,2′-bipy)­(mes)₂] (M = Cr (<b>1</b>), Mn (<b>2</b>), Co (<b>4</b>), Ni (<b>5</b>); 2,2′-bipy = 2,2′-bipyridine; mes = 2,4,6-Me₃C₆H₂) were reacted with potassium and a suitable alkali-metal sequestering agent to yield salts of the anionic species [M­(2,2′-bipy)­(mes)₂]⁻. The neutral parent compounds and their corresponding anionic congeners were characterized by single-crystal X-ray diffraction in [Cr­(2,2′-bipy)­(mes)₂]·1.5C₆H₆, [Mn­(2,2′-bipy)­(mes)₂], [Co­(2,2′-bipy)­(mes)₂]·THF, [Ni­(2,2′-bipy)­(mes)₂], [K­(dibenzo-18-crown-6)·THF]­[Cr­(2,2′-bipy)­(mes)₂]·2THF, [K­(18-crown-6)]­[Mn­(2,2′-bipy)­(mes)₂]·2THF, [K­(18-crown-6)]­[Mn­(2,2′-bipy)­(mes)₂]·0.67py·0.67tol, [K­(2,2,2-crypt)]­[Co­(2,2′-bipy)­(mes)₂], and [K­(2,2,2-crypt)]­[Ni­(2,2′-bipy)­(mes)₂]. These species, along with the previously reported neutral and anionic iron complexes [Fe­(2,2′-bipy)­(mes)₂]^0/– (<b>3</b>/<b>3</b>^<b>–</b>), form a homologous series of compounds which allow for an in-depth study of the interactions between metals and ligands. Single-crystal X-ray diffraction data, DFT calculations, and various spectroscopic and magnetic measurements indicate that the anionic complexes (<b>1</b>^<b>–</b>–<b>5</b>^<b>–</b>) can be best formulated as M­(II) complexes of the 2,2′-bipyridyl radical anion. These findings complement recent studies which indicate that bond metric data from single-crystal X-ray diffraction may be employed as an important diagnostic tool in determining the oxidation states of bipyridyl ligands in transition-metal complexes

Spherical actions on flag varieties

For every finite-dimensional vector space V and every V-flag variety X we list all connected reductive subgroups in GL(V) acting spherically on X.Comment: v2: 39 pages, revised according to the referee's suggestion

Potential Oscillations in Galvanostatic Cu Electrodeposition: Antagonistic and Synergistic Effects among SPS, Chloride, and Suppressor Additives

Polymerizates of imidazole and epichlorohydrin (Imep) serve as one of the benchmarks for today's chemistry development of leveler additives in context of the industrial copper Damascene process. We therefore studied the synergistic and antagonistic interplay of the Imep polymer with other additives, commonly present in copper plating baths used for the state-of-the-art IC manufacturing. Characteristic oscillations in the applied electrode potential appear in galvanostatic copper electrodeposition when Imep is used in combination with SPS (bis­(sodium sulfopropyl) disulfide). We identified the reversible Cu­(I) coordination chemistry of the Imep polymer as a second prospective driving force beyond interfacial anion/cation pairing toward the formation of such suppressor/leveler ensembles at the interface. OH groups of the pristine Imep polymer coordinate with H₂O-Cu­(I)-MPS units (primary effect) that appear as side products of the copper electrodeposition in the presence of SPS. The latter transforms during copper deposition into monomeric MPS (mercaptopropanesulfonic acid/sulfonate) as result of the adsorptive SPS dissociation on the copper surface. Electrostatic coupling between the anionic sulfonate of the MPS and the cationic imidazolium group in the formed linear, bidentate Imep-Cu­(I)-MPS complex results into a neutral, hydrophobic species that finally precipitates (secondary effect). The presence of diamagnetic Cu­(I) species in those precipitates is proven by elementary analysis in combination with magnetic SQUID measurements. The observed potential oscillations under galvanostatic conditions are discussed in terms of an alternating precipitation and dissolution of the Imep-Cu­(I)-MPS suppressor ensemble at the copper/electrolyte interface. Linear sweep experiments prove a partially hidden, N-shaped negative differential resistance (HN-NDR) as physical origin for the observed instabilities under galvanostatic conditions. SIMS (secondary ion mass spectroscopy) depth profiling of copper films deposited under such oscillatory conditions reveals periodic modulations in the contamination level parallel to the surface normal. Cross-sectional FIB analysis of the grown copper deposit reveals periodically repeating lines of grain boundaries in the copper deposit

[V₁₆O₃₈(CN)]^9–: A Soluble Mixed-Valence Redox-Active Building Block with Strong Antiferromagnetic Coupling

A new discrete [V₁₆O₃₈(CN)]^9– cluster, which displays the hitherto unknown 8– charge on the cluster shell and is the first to encapsulate the cyanide anion, has been synthesized and characterized by IR and UV/vis/near-IR spectroscopy, electrochemistry, and magnetic susceptibility measurements. Bond valence sum calculations conducted on the basis of the crystal structure analysis of K₉[V₁₆O₃₈(CN)]·13H₂O confirm that this new member of the polyoxovanadate series is a mixed-valence complex. The intervalence charge transfer bands arising from intrametal interactions reveal that a localized (class II) assignment is appropriate for the cluster; however, a small degree of electronic delocalization is present. Interesting possibilities exist for the incorporation of this unit into higher dimensionality framework structures, where the redox, optical, and magnetic properties can be exploited and tuned

Pulsed Electron Paramagnetic Resonance Spectroscopy of ³³S‑Labeled Molybdenum Cofactor in Catalytically Active Bioengineered Sulfite Oxidase

Molybdenum enzymes contain at least one pyranopterin dithiolate (molybdopterin, MPT) moiety that coordinates Mo through two dithiolate (dithiolene) sulfur atoms. For sulfite oxidase (SO), hyperfine interactions (<i>hfi</i>) and nuclear quadrupole interactions (<i>nqi</i>) of magnetic nuclei (<i>I</i> ≠ 0) near the Mo­(V) (d¹) center have been measured using high-resolution pulsed electron paramagnetic resonance (EPR) methods and interpreted with the help of density functional theory (DFT) calculations. These have provided important insights about the active site structure and the reaction mechanism of the enzyme. However, it has not been possible to use EPR to probe the dithiolene sulfurs directly since naturally abundant ³²S has no nuclear spin (<i>I</i> = 0). Here we describe direct incorporation of ³³S (<i>I</i> = 3/2), the only stable magnetic sulfur isotope, into MPT using controlled <i>in vitro</i> synthesis with purified proteins. The electron spin echo envelope modulation (ESEEM) spectra from ³³S-labeled MPT in this catalytically active SO variant are dominated by the “interdoublet” transition arising from the strong nuclear quadrupole interaction, as also occurs for the ³³S-labeled exchangeable equatorial sulfite ligand [Klein, E. L., et al. Inorg. Chem. 2012, 51, 1408−1418]. The estimated experimental <i>hfi</i> and <i>nqi</i> parameters for ³³S (<i>a</i>_iso = 3 MHz and <i>e</i>²<i>Qq</i>/<i>h</i> = 25 MHz) are in good agreement with those predicted by DFT. In addition, the DFT calculations show that the two ³³S atoms are indistinguishable by EPR and reveal a strong intermixing between their out-of-plane p_<i>z</i> orbitals and the d_<i>xy</i> orbital of Mo­(V)