Laboratory simulation of Hg<Superscript>0</Superscript> emissions from a snowpack

Snow surfaces play an important role in the biogeochemical cycle of mercury in high-latitude regions. Snowpacks act both as sources and sinks for gaseous compounds. Surprisingly, the roles of each environmental parameter that can govern the air–surface exchange over snow are not well understood owing to the lack of systematic studies. A laboratory system called the laboratory flux measurement system was used to study the emission of gaseous elemental mercury from a natural snowpack under controlled conditions. The first results from three snowpacks originating from alpine, urban and polar areas are presented. Consistent with observations in the field, we were able to reproduce gaseous mercury emissions and showed that they are mainly driven by solar radiation and especially UV-B radiation. From these laboratory experiments, we derived kinetic constants which show that divalent mercury can have a short natural lifetime of about 4–6 h in snow.     

Syntheses and crystal structures of [Bu3SbCr(CO)5], [Bu3BiM(CO)5] (M = Cr, W), and [Bu3BiMnCp′(CO)2] (Cp′ = η-C5H4CH3)

Syntheses and crystal structures of [^tBu₃SbCr(CO)₅] (1), [^tBu₃BiM(CO)₅] [M = Cr (2), W (3)] and [^tBu₃BiMnCp′(CO)₂] (4) (Cp′ = η⁵-C₅H₄CH₃) are reported.     

[μ‐(Me3SiCH2Sb)5–Sb1,Sb3–{W(CO)5}2] und [{(Me3Si)2CHSb}3Fe(CO)4] – zwei cyclische Komplexe mit Antimon‐Liganden

Syntheses and Crystal Structures of [μ‐(Me₃SiCH₂Sb)₅–Sb¹,Sb³–{W(CO)₅}₂] and [{(Me₃Si)₂CHSb}₃Fe(CO)₄] – Two Cyclic Complexes with Antimony Ligands cyclo‐(Me₃SiCH₂Sb)₅ reacts with [(THF)W(CO)₅] (THF = tetrahydrofuran) to form cyclo‐[μ‐(Me₃SiCH₂Sb)₅–Sb¹,Sb³–{W(CO)₅}₂] ( 1 ). The heterocycle cyclo‐ [{(Me₃Si)₂CHSb}₃Fe(CO)₄] ( 2 ) is formed by an insertion reaction of cyclo‐[(Me₃Si)₂CHSb]₃ and [Fe₂(CO)₉]. The crystal structures of 1 and 2 are reported.     

Reaktionen von R4Sb2 (R = Me,Et) mit (Me3SiCH2)3M (M = Ga,In) und Kristallstrukturen von [(Me3SiCH2)2InSbMe2]3 und [(Me3SiCH2)2GaOSbEt2]2

Reactions of R₄Sb₂ (R = Me, Et) with (Me₃SiCH₂)₃M (M = Ga, In) and Crystal Structures of [(Me₃SiCH₂)₂InSbMe₂]₃ and [(Me₃SiCH₂)₂GaOSbEt₂]₂ The reaction of (Me₃SiCH₂)₃In with Me₂SbSbMe₂ gives [(Me₃SiCH₂)₂InSbMe₂]₃ ( 1 ) and Me₃SiCH₂SbMe₂. [(Me₃SiCH₂)₂GaOSbEt₂]₂ ( 2 ) is formed by the reaction of (Me₃SiCH₂)₃Ga with Et₂SbSbEt₂ and oxygen. The syntheses and the crystal structures of 1 and 2 are reported.     

Reaction of 2‐(Polyfluoroacyl)cycloalkanones with Hydroxylamine

The 2‐acylcycloalkanones 1a – g and 3a – c , possessing a polyfluoroalkyl group, react with hydroxylamine regio‐ and stereoselectively to yield 4,5‐dihydroisoxazol‐5‐ols 2a – g and 4a – c , respectively, i.e., products of N‐addition to the oxo group at the cycloalkane ring (Schemes 1 and 2). The products 2 and 4 can be dehydrated under drastic conditions only (Schemes 3 and 4). The structure of one of the 4,5‐dihydroisoxazol‐5‐ols was confirmed by X‐ray crystal‐structure analysis.     

Tetracarbonylchrom-Komplexe mit Me2SbESbMe2 (E = O,S) und MeSb(SSbMe2)2 als Liganden

Tetracarbonyl Chromium Complexes with Me₂SbESbMe₂ (E = O, S) and MeSb(SSbMe₂)₂ as Ligands Me₂SbOSbMe₂ reacts with nbdCr(CO)₄ (nbd = norbornadiene) to form cyclo-[Me₂SbOSbMe₂Cr(CO)₄]₂ ( 1 ). The reaction of Me₂SbSSbMe₂ with nbdCr(CO)₄ gives cis-[(Me₂SbSSbMe₂)₂Cr(CO)₄] ( 2 ), a complex stable only in solution. With excess nbdCr(CO)₄ also cyclo[Me₂SbSSbMe₂Cr(CO)₄]₂ ( 3 ) and cyclo[MeSb(SSbMe₂)₂Cr(CO)₄] ( 4 ) form in low yield. The crystal structures of 1 , 3 and 4 · nbdCr(CO)₄ are reported. The novel ligand MeSb(SSbMe₂)₂ is formed by elimination of Me₃Sb from Me₂SbSSbMe₂.     

Unexpectedly low affinity of aromatic disulfides for π-stacking interactions of the arene-polyfluoroarene type

1,2,3,4,5-Pentafluorodiphenyl disulfide (1) was synthesized from C₆F₅SCl and C₆H₅SSiMe₃ in quantitative yield. The homo-crystals of disulfide 1 and co-crystals of 1,1′,2,2′,3,3′,4,4′,5,5′-decafluorodiphenyl disulfide (2) with naphthalene (stoichiometry 1:2, complex 4) and diphenyl disulfide (3) with octafluoronaphthalene (stoichiometry 2:1, complex 5) were prepared followed by XRD characterization. In the crystal lattice of 1, face-to-face and face-to-edge Ph_H/Ph_F orientations of neighboring rings were observed together with face-to-edge Ph_F/Ph_F orientations. For the face-to-face Ph_H/Ph_F orientation, the large offset of Ph_H and Ph_F groups excludes their π-stacking interaction which is very non-typical of the field. The crystal lattice of 4 reveals standard π-stacking interactions of the arene-polyfluoroarene type. While in the lattice of 4 each Ph_F ring interacts alternating with naphthalenes, in 5 two disulfides 3 are bridged by one octafluoronaphthalene with only one of the Ph_H rings of each disulfide interacting with the polyfluoroarene π-system. The large offset of neighboring molecules excludes however their π-stacking interactions in complex 5. An attempt to prepare 2/3 co-crystals failed.     

Nondispersive solutions to the L 2-critical Half-Wave Equation

We consider the focusing L ²-critical half-wave equation in one space dimension, $$i \partial_t u = D u - |u|^2 u$$ , where D denotes the first-order fractional derivative. Standard arguments show that there is a critical threshold ${M_{*} > 0}$ such that all H ^1/2 solutions with ${\|u\|_{L^2} < M_*}$ extend globally in time, while solutions with ${\|u\|_{L^2} \geq M_*}$ may develop singularities in finite time. In this paper, we first prove the existence of a family of traveling waves with subcritical arbitrarily small mass. We then give a second example of nondispersive dynamics and show the existence of finite-time blowup solutions with minimal mass ${\|u_0\|_{L^2} = M_*}$ . More precisely, we construct a family of minimal mass blowup solutions that are parametrized by the energy E ₀ > 0 and the linear momentum ${P_0 \in \mathbb{R}}$ . In particular, our main result (and its proof) can be seen as a model scenario of minimal mass blowup for L ²-critical nonlinear PDEs with nonlocal dispersion.     

Low-Temperature High-Resolution Solid-State (cryoMAS) NMR of Han Purple BaCuSi2O6

We present low-temperature (low-T, sub-liquid-N₂) high-speed high-resolution ²⁹Si solid-state (cryoMAS) nuclear magnetic resonance studies on a model 2D-BEC quantum magnet BaCuSi₂O₆, known also as Han Purple. We observe broadened ²⁹Si lines below the well-established 100 K structural phase transition confirming the existence of inhomogeneities at low temperatures. Interestingly, the low-T spectra of \({\mathrm{BaCuSi}}_{2}{\mathrm{O}}_{6}\) closely resemble those of the novel compound Ba₂CoSi₂O₆Cl₂ taken at room temperature. This suggests that the Co compound features structural modulations or inhomogeneities already at room temperature. The low-T crystal structure and magnetism of \({\mathrm{BaCuSi}}_{2}{\mathrm{O}}_{6}\) are more complex than previously believed, and deserve further investigation.