Pertechnetyl Fluorosulfate, [TcO3]+[SO3F]−

A one step synthesis of [TcO₃]⁺[SO₃F]^? is reported. The compound is volatile at room temperature and has according to calculations a tetrahedral coordination around Tc and a monodentate SO₃F group. In the solid state the [SO₃F]^? anion bridges three [TcO₃]⁺ cations, and vice versa. Space group P2₁/c, Z = 4, lattice dimensions at 173 K: a = 695.4(11), b = 808.6(12), c = 893.3(14) pm, β = 97.36(8)°.     

A Hexameric Cationic Copper(II) Metallacrown as a Pertechnetate and Perrhenate Scavenger

Materials based on the cationic copper(II) hexanuclear 18‐membered metallacrown [18‐MC ‐6]⁶⁺ (2phH=2‐piconyl hydrazide) and tetrafluoroborate, perchlorate, nitrate, sulfate, and perrhenate anions were prepared by an easy method in aqueous medium. Single‐crystal X‐ray characterization of six members of this new family of complexes showed that the anions are attached to the metallacrown by direct coordination to a copper cation or by hydrogen‐bonding interaction with the center of the hexamer. The stable cationic nature of the complexes and their ability to bind different anions allows them to adsorb and immobilize environmentally relevant anions such as MO₄^? (M=Tc, Re). The MO₄^? trapping capacities suggest that these materials would be useful in the treatment of oxoanionic contaminants in water.     

Solid state molecular structures of transition metal hexafluorides

Single-crystal structure determinations of all nine transition metal hexafluorides (Mo, Tc, Ru, Rh, W, Re, Os, Ir, and Pt) at -140 degrees C are presented. All compounds crystallize alike and have the same molecular structure. The bond length sequence r(w-F) congruent with r(Re-F) congruent with r(Os-F) < r(Ir-F) < r(Pt-F) is confirmed and paralleled by the sequence r(Mo-F) congruent with r(Tc-F) congruent with r(Ru-F) < r(Rh-F). Within the limits of precision, no systematic deviation from octahedral symmetry can be established. DFT and ab initio calculations predict octahedral structures for MoF6 and RhF6 and tetragonally distorted structures for ReF6 and RuF6. The energy barrier toward octahedral structures is only 2.5 kJ mol(-1) in the two latter cases. Calculated electron affinities are in the sequence MoF6 < TcF6 < RhF6 < RuF6 with a value of 6.98 eV for the latter. O2+RhF6- crystallized in an undisordered manner in P, isostructural to the low-temperature form of O2+AuF6-. RhF6- has a D4h compressed octahedral structure, while AuF6- is essentially octahedral. The absorption spectrum of TcF6 and the 19F and 195NMR spectra of PtF6 are presented.     

Post-synthetic modification of Zr-metal-organic frameworks through cycloaddition reactions

Cycloaddition reactions are highly attractive for post-synthetic modification of metal-organic frameworks (MOFs). We report herein on cycloaddition reactions with PIZOF(R(1),R(2))s, which are porous interpenetrated Zr-based MOFs with Zr(6)O(4)(OH)(4)(CO(2))(12) as the nodes and the dicarboxylates (-)O(2)C[PE-P(R(1),R(2))-EP]CO(2)(-) (P: phenylene, E: ethynylene; R(1), R(2): side chains at the central phenylene unit) as the linkers. 1,3-Dipolar cycloaddition between the pendant ethyne moieties of PIZOF(OMe,OCH(2)C≡CH) and 4-methylbenzyl azide resulted in 98% conversion of the ethyne groups. Reactions of PIZOF(OMe,O(CH(2))(3)furan) with maleimide, N-methylmaleimide, and N-phenylmaleimide converted 98, 99, and 89% of the furan moieties into the Diels-Alder adducts. However, no reaction occurred with maleic anhydride. High-resolution (1)H NMR spectra were crucial in determining the conversion and identifying the reaction products. Of all the reagents (NaOD/D(2)O, D(2)SO(4), Bu(4)NF, CsF, CsF/DCl, and KHF(2)) tested for the disassembly of the PIZOFs in [D(6)]DMSO, the combination of CsF and DCl was found to be the best. The disassembly at room temperature was fast (5-15 min), and after the addition of K(2)CO(3) the (1)H NMR data were identical to those of the diacids (=protonated linkers) dissolved in pure DMSO. This allowed for simple structure elucidation through data comparison. CsF/DCl dissolves not only PIZOFs but also the hydrolytically very stable UiO-66.     

High sensitivity and versatility of the DEER experiment on nitroxide radical pairs at Q-band frequencies

Measurement of distances with the Double Electron-Electron Resonance (DEER) experiment at X-band frequencies using a pair of nitroxides as spin labels is a popular biophysical tool for studying function-related conformational dynamics of proteins. The technique is intrinsically highly precise and can potentially access the range from 1.5 to 6-10 nm. However, DEER performance drops strongly when relaxation rates of the nitroxide spin labels are high and available material quantities are low, which is usually the case for membrane proteins reconstituted into liposomes. This leads to elevated noise levels, very long measurement times, reduced precision, and a decrease of the longest accessible distances. Here we quantify the performance improvement that can be achieved at Q-band frequencies (34.5 GHz) using a high-power spectrometer. More than an order of magnitude gain in sensitivity is obtained with a homebuilt setup equipped with a 150 W TWT amplifier by using oversized samples. The broadband excitation enabled by the high power ensures that orientation selection can be suppressed in most cases, which facilitates extraction of distance distributions. By varying pulse lengths, Q-band DEER can be switched between orientationally non-selective and selective regimes. Because of suppression of nuclear modulations from matrix protons and deuterons, analysis of the Q-band data is greatly simplified, particularly in cases of very small DEER modulation depth due to low binding affinity between proteins forming a complex or low labelling efficiency. Finally, we demonstrate that a commercial Q-band spectrometer can be readily adjusted to the high-power operation.     

Zur Kenntnis der Schmelzdiagramme gesättigter Fettsäuren

Zusammenfassung Im Schmelzdiagramm von Palmitinsäure: Stearinsäure wurde auf mikroskopischem Wege das Auftreten dreier Mischkristallphasen festgestellt, wovon die Mischphase des mittleren Konzentrationsbereiches nicht wie bisher in der Regel üblich als Verbindung, sondern als stabilisierte Zwischenphase betrachtet wird. Der für das genannte System gefundene Aufbau des Diagramms gilt im allgemeinen für alle Systeme geradzahliger gesättigter Fettsäuren, die sich in ihrer Kettenlänge um 2 bis 4 C-Atome unterscheiden.

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Summary By microscopic procedure the fusion diagram of palmitic acid: stearic acid was shown to contain three mixed crystal phases. The mixed crystal phase of the middle concentration ranges is to be considered not a compound, as was the former belief, but rather as a stabilized intermediate phase. The structure of the diagram found for this particular system holds in general for all systems of even-numbered saturated fatty acids, which differ by 2 to 4 carbon atoms in their chain lengths.

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Résumé On montre microscopiquement, dans le diagramme de fusion acide stéarique-acide palmitique, l'existence de trois sortes de cristaux mixtes dont la phase mixte du domaine de concentration intermédiaire est considérée comme une phase stable intermédiaire, mais pas comme un composé, étant jusqu'ici considérée en règle générale. La structure trouvée pour le diagramme ci-dessus s'accorde, en général, avec tous les systèmes d'acides gras saturés à nombre pair qui diffèrent par deux à quatre atomes de carbone.

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Herrn Universitätsprofessor Dr.L. Ebert zum 60. Geburtstag gewidmet.     

Synthesis of Model Compounds for the Structure Elucidation of a Ladder Polymer from Benzo[1,2-c:4,5-c']difuran and a Diquinone Derivative

The high yield synthesis of the fully soluble acenequinone model compounds 6 and 7 as well as of the corresponding poly(acene quinone) derivative 4 is reported. Some of the diastereomers of 6 and 7 have been isolated and their structures clarified by NMR spectroscopy. This information was used as a basis for assigning the polymer's structure.