Deep Green
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Item Open Access Pressure-temperature-time evolution of a polymetamorphic paragneiss with pseudomorphs after jadeite from the HP-UHP gneiss‐eclogite unit of the Variscan Erzgebirge crystalline complex, Germany(2024) Massonne, Hans‐JoachimA quartz‐rich paragneiss from the Variscan Erzgebirge Crystalline Complex (ECC) was studied in detail because of abundant millimetre‐sized and clearly oriented pseudomorphs after a sodic mineral interpreted to have been jadeite. This mineral, or pseudomorphs after it, is rarely found in extensive high‐pressure (HP)-ultrahigh‐pressure (UHP) terranes worldwide despite reported pressure-temperature (P-T) conditions suitable for the formation of jadeite in common paragneisses and orthogneisses. In the studied rock, which contains abundant large and oriented potassic white mica flakes and minor millimetre‐sized garnet grains, the pseudomorphs consist of clusters of small albite grains with thin phengitic muscovite flakes in between. X‐ray maps for Ca and Mg in garnet demonstrate that an early generation of this mineral (Gt1) was corroded and subsequently overgrown by a Ca‐richer generation (Gt2). White mica is phengite with maximum Si contents of 3.42 atoms per formula unit. P-T conditions of 0.85 GPa and 650°C and 1.7 GPa and 660°C were derived for the formation of Gt1 and Gt2 rim + Si‐rich phengite, respectively, using pseudosection modelling. The latter conditions representing the pressure peak experienced by the paragneiss are compatible with the original presence of jadeite and possibly paragonite as well. This metamorphic peak occurred at 338.4 ± 2.3 (2σ) Ma based on in situ dating of monazite grains with the electron microprobe. A single monazite age of 386.4 ± 10.5 (2σ) Ma is related to the formation of Gt1. Thus, a Late Devonian metamorphism is suggested here for the first time to have occurred in ECC gneisses before the major HP event in the Early Carboniferous. Furthermore, the study demonstrates that the eclogite‐facies gneisses of the Gneiss‐Eclogite Unit of the ECC experienced peak pressures of not more than 2 GPa in contrast to recent proposals of an extensive UHP area in this unit. In addition, it is suggested that the localized occurrence of UHP rocks surrounded by other lithologies otherwise lacking evidence for UHP conditions should be interpreted with caution with respect to their regional extent and significance.Item Open Access Crystal structure of rac-(6R,1'R)-6-(1',2'-diacetoxyethyl)-2-phenyl-5,6-dihydro-4H-1,3-oxazine, (C6H5)C4H5NO[C2H3(OCOCH3)2](2014) Peters, K.; Peters, E.-M.; Kugler, Rolf; Jäger, VolkerC16H19NO5, triclinic, P‾1 (No. 2), a = 9.211(1) Å, b = 9.259(2) Å, c = 9.796(2) Å, α = 84.36(1)°, β = 85.26(1)°, γ = 69.21(1)°, V = 776.2 Å3, Ζ = 2, Rgt(F) = 0.069, Rw(F) = 0.069, Τ = 293 Κ.Item Open Access The role of spacer length in macrocyclization reactions under confinement(2024) Nandeshwar, Muneshwar; Weisser, Kilian; Ziegler, Felix; Frey, Wolfgang; Buchmeiser, Michael R.We studied the influence of the distance of olefin metathesis catalysts from the inner surface of a mesoporous support on macrocyclization and Z‐selectivity under confinement. For these purposes, the cationic molybdenum imido alkylidene N‐heterocyclic carbene (NHC) catalysts [Mo(N‐(2‐tBu‐C6H4)(1‐mesityl‐3‐(3‐trimethoxysilylprop‐1‐yl)‐imidazol‐2‐ylidene)(CHCMe2Ph)(MeCN)Br+ B(ArF)4-] Mo2, [Mo(N‐(2‐tBu‐C6H4)(1‐mesityl‐3‐(3‐trimethoxysilylprop‐1‐yl)‐imidazol‐2‐ylidene)(CHCMe2Ph)(MeCN)OTf+ B(ArF)4-] Mo3, [Mo(N‐(2,6‐Me2‐C6H3)(1‐mesityl‐3‐(3‐trimethoxysilylprop‐1‐yl)‐imidazol‐2‐ylidene)(CHCMe2Ph)(MeCN)Br+ B(ArF)4-] Mo5, and [Mo(N‐(2,6‐iPr2‐C6H3)(1‐mesityl‐3‐(3‐trimethoxysilylprop‐1‐yl)‐imidazol‐2‐ylidene)(CHCMe2Ph)(MeCN)+Br B(ArF)4-] Mo7 (B(ArF)4 = tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate), all containing a trimethoxysilylpropyl tether, were selectively immobilized inside the mesopores of SBA‐15. Under confinement, both macro(mono)cyclization (MMC) and Z‐selectivity were higher than in solution but lower than with catalysts directly bound to the surface of the mesoporous supports. These findings are in agreement with existing theoretical models on substrate and product distribution in mesopores, which suggest that the highest substrate concentration is found at the pore wall and that it increases with decreasing pore diameter.Item Open Access The impact of donor‐orientation on the emission properties of chlorinated trityl radicals(2025) Arnold, Mona E.; Toews, Robert; Schneider, Lars; Schmid, Jonas; Putra, Miftahussurur Hamidi; Busch, Michael; Groß, Axel; Deschler, Felix; Köhn, Andreas; Kuehne, Alexander J. C.Chlorinated trityl radicals functionalized with electron‐donating groups are promising red‐emitting materials for optoelectronic and spintronic applications, overcoming the spin‐statistical limit of conventional emitters. Donor functionalization induces charge transfer character, enhancing photoluminescence quantum yield, which depends on the donor strength and its orientation. However, donor‐functionalized tris(trichlorophenyl)methyl radicals often show lower quantum yield than their perchlorinated derivatives, likely due to weaker donor‐acceptor electronic coupling and enhanced non‐radiative decay. A novel trityl derivative is presented with two additional chlorines that restrict the orientation of the donor to a nearly perpendicular arrangement toward the trityl plane, minimizing vibronic coupling and non‐radiative losses. Spectroscopic and computational studies reveal that this steric constraint improves the photoluminescence quantum yield compared to the tris(trichlorophenyl)methyl analogs. These findings highlight the potential of donor‐acceptor decoupling to enable efficient, redshifted emission, offering a design strategy for high‐performance radical emitters.Item Open Access Polycondensation‐derived high‐molecular weight lignin as nonblended precursor for carbon fibers(2024) Clauss, Manuel M.; Frank, Erik; Bauch, Volker; Kuske, Lisa; Buchmeiser, Michael R.A new concept for the controlled chain‐extension of lignin has been developed. A mixture of trioxane as formaldehyde source, resorcinol as chain extender, and lignin allows to prepare high molecular weight precursor fibers by melt‐spinning, which can be spun on a semitechnical scale. Chain extension with resorcinol bridged by methylene groups is achieved during the stabilization process of the precursor fiber. After carbonization, carbon fibers (CFs) with an average diameter of 18 µm show an average tensile strength of 0.78 GPa and a Young's modulus of 106 GPa. A maximum tensile strength of 2.44 GPa and a Young's modulus of 294 GPa are reached with fibers 9.7 µm in diameter.Item Open Access What makes a branched aromatic compound a crystallization chaperone? Insights from a comparison of three organic scaffolds(2025) Hartenfels, Jan; Berking, Tim; Rebelo, Ruben Pereira; Tsimopoulou, Katerina; Schiele, Stefanie; Stark, Leon; Frey, Wolfgang; Richert, ClemensSome tetraaryladamantane (TAA) octa‐ and tetraethers have the ability to crystallize into well‐ordered lattices without full desolvation. In many cases, the solvates then yield high‐resolution X‐ray crystal structures of the encapsulated liquids. To shed light on this unusual effect of TAAs as crystallization chaperones, we have synthesized a series of spirobiflourene and porphyrin derivatives with four phenyl arms also found in TAA chaperones. Despite the structural similarity, neither of the non‐TAA compounds showed promising crystallization properties. Six new X‐ray crystal structures were obtained, but neither gave a high‐resolution structure of an encapsulated guest. Quantum chemical computations suggest that conformational changes have low activation barriers for the TAAs, which may help to adapt to the structures of guest molecules in tightly packed arrangements. These findings on supramolecular chemistry in the crystalline state may help to design new chaperones with improved properties.