Marilyn Morgan Olmstead (1943–2020) Roy, Mrittika; Balch, Alan L.; Carey, Janis M. ...
Journal of applied crystallography,
December 2020, 2020-12-01, 20201201, Letnik:
53, Številka:
6
Journal Article
The “New History of Capitalism” grounds the rise of industrial capitalism on the production of raw cotton by American slaves. Recent works include Sven Beckert's Empire of Cotton, Walter Johnson's ...River of Dark Dreams, and Edward Baptist's The Half Has Never Been Told. All three authors mishandle historical evidence and mis-characterize important events in ways that affect their major interpretations on the nature of slavery, the workings of plantations, the importance of cotton and slavery in the broader economy, and the sources of the Industrial Revolution and world development.
Gadolinium-containing endohedral fullerenes represent a new class of effective relaxation agents for magnetic resonance imaging (MRI). The range of different structures possible for this class of ...molecules and their properties as MRI agents are reviewed here.
The Intergovernmental Panel on Climate Change projects that temperatures in the major grain-growing areas of North America will rise by 3–4 °C by 2100. Such abrupt changes will create major ...challenges, significantly altering the area suitable for wheat. The historical record offers insight into the capability of agriculture to adapt to climatic challenges. Using a new county-level dataset on wheat production and climate norms, we show that during the 19th and 20th centuries North American grain farmers pushed wheat production into environments once considered too arid, too variable, and too harsh to cultivate. As summary measures, the median annual precipitation norm of the 2007 distribution of North American wheat production was one-half that of the 1839 distribution, and the median annual temperature norm was 3.7 °C lower. This shift, which occurred mostly before 1929, required new biological technologies. The Green Revolution associated with the pioneering work of Norman Borlaug represented an important advance in this longer process of biological innovation. However, well before the Green Revolution, generations of North American farmers overcame significant climatic challenges.
Although fullerenes were discovered nearly three decades ago, the mechanism of their formation remains a mystery. Many versions of the classic 'bottom-up' formation mechanism have been advanced, ...starting with C2 units that build up to form chains and rings of carbon atoms and ultimately form those well-known isolated fullerenes (for example, I(h)-C60). In recent years, evidence from laboratory and interstellar observations has emerged to suggest a 'top-down' mechanism, whereby small isolated fullerenes are formed via shrinkage of giant fullerenes generated from graphene sheets. Here, we present molecular structural evidence for this top-down mechanism based on metal carbide metallofullerenes M2C2@C1(51383)-C84 (M = Y, Gd). We propose that the unique asymmetric C1(51383)-C84 cage with destabilizing fused pentagons is a preserved 'missing link' in the top-down mechanism, and in well-established rearrangement steps can form many well-known, high-symmetry fullerene structures that account for the majority of solvent-extractable metallofullerenes.
Endohedral metallofullerenes (EMFs) have novel structures and properties that are closely associated with the internal metallic species. Benzyl radical additions have been previously shown to form ...closed‐shell adducts by attaching an odd number of addends to open‐shell EMFs (such as Sc3C2@Ih‐C80) whereas an even number of groups are added to closed‐shell EMFs (for example Sc3N@Ih‐C80). Herein we report that benzyl radical addition to the closed‐shell La2@Ih‐C80 forms a stable, open‐shell monoadduct instead of the anticipated closed‐shell bisadduct. Single‐crystal X‐ray diffraction results show the formation of a stable radical species. In this species, the La−La distance is comparable to the theoretical value of a La−La covalent bond and is shorter than reported values for other La2@Ih‐C80 derivatives, providing unambiguous evidence for the formation of direct La−La bond.
A stable fullerene radical La2@Ih‐C80(C7H7) was synthesized and fully characterized. The stability of the radical is attributed to the localization of the unpaired electron inside the cage, as suggested by EPR spectroscopy and DFT calculations. Metal–metal bonding is indicated by the La−La distance, which is consistent with the calculated distance, and the localization of the SOMO on the La2 unit.
A series of di-gadolinium endohedrals that extends from Gd(2)C(90) to Gd(2)C(124) has been detected by mass spectrometry of the o-dichlorobenzene extract of the carbon soot produced by direct current ...arcing of graphite rods filled with a mixture of Gd(2)O(3) and graphite powder. Chromatographic separation has led to the isolation of pure samples of two isomers of Gd(2)C(94) and the complete series from Gd(2)C(96) to Gd(2)C(106). Endohedral fullerenes of the type M(2)C(2n) can exist as the conventional endohedral, M(2)@C(2n), or as the carbide-containing endohedral, M(2)C(2)@C(2n-2). Crystallographic characterization of the more rapidly eluting isomer of Gd(2)C(94) reveals that it possesses the carbide structure, Gd(2)C(2)@D(3)(85)-C(92). Computational studies suggest that the more slowly eluting isomer of Gd(2)C(94) may be a conventional endohedral, Gd(2)@C(2)(121)-C(94).
The mono‐ and di‐chloroform solvates of Au2(μ‐1,2‐bis(diphenylarsino)ethane)2(AsF6)2 undergo single‐crystal‐to‐single‐crystal transformations that result in gain (over 12 hours) or slow loss (over ...five years) of only one chloroform molecule. The change in solvation results in changes in the structure and luminescence of the digold cation. The cation consists of a pair of slightly bent As‐Au‐As units that are connected through the two bridging dpae ligands and by aurophilic interactions with Au⋅⋅⋅Au contacts of 3.05152(15) Å in the disolvate or 2.9570(5) Å in the monosolvate.
Going for gold: The mono‐ and di‐chloroform solvates of Au2(μ‐1,2‐bis(diphenylarsino)ethane)2(AsF6)2 undergo single‐crystal‐to‐single‐crystal transformations that result in gain or loss of only one chloroform molecule and changes in the structure and luminescence of the digold cation.
Non-luminescent, isostructural crystals of (C
6
H
11
NC)
2
Au(EF
6
)·C
6
H
6
(E = As, Sb) lose benzene upon standing in air to produce green luminescent (E = As) or blue luminescent (E = Sb) powders. ...Previous studies have shown that the two-coordinate cation, (C
6
H
11
NC)
2
Au
+
, self-associates to form luminescent crystals that contain linear or nearly linear chains of cations and display unusual polymorphic, vapochromic, and/or thermochromic properties. Here, we report the formation of non-luminescent crystalline salts in which individual (C
6
H
11
NC)
2
Au
+
ions are isolated from one another. In (C
6
H
11
NC)
2
Au(BArF
24
) ((BArF
24
)
−
is tetrakis3,5-bis(trifluoromethyl)phenylborate) each cation is surrounded by two anions that prohibit any close approach of the gold ions. Crystallization of (C
6
H
11
NC)
2
Au(EF
6
) (E = As or Sb, but not P) from benzene solution produces colorless, non-emissive crystals of the solvates (C
6
H
11
NC)
2
Au(EF
6
)·C
6
H
6
. These two solvates are isostructural and contain columns in which cations and benzene molecules alternate. With the benzene molecules separating the cations, the shortest distances between gold ions are 6.936(2) Å for E = As and 6.9717(19) Å for E = Sb. Upon removal from the mother liquor, these crystals crack due to the loss of benzene from the crystal and form luminescent powders. Crystals of (C
6
H
11
NC)
2
Au(SbF
6
)·C
6
H
6
that powder out form a pale yellow powder with a blue luminescence with emission spectra and powder X-ray diffraction data that show that the previously characterized (C
6
H
11
NC)
2
Au(SbF
6
) is formed. In the process, the distances between the gold(
i
) ions decrease to ∼3 Å and half of the cyclohexyl groups move from an axial orientation to an equatorial one. Remarkably, when crystals of (C
6
H
11
NC)
2
Au(AsF
6
)·C
6
H
6
stand in air, they lose benzene and are converted into the yellow, green-luminescent polymorph of (C
6
H
11
NC)
2
Au(AsF
6
) rather than the colorless, blue-luminescent polymorph. Paradoxically, the yellow, green-luminescent powder that forms as well as authentic crystals of the yellow, green-luminescent polymorph of (C
6
H
11
NC)
2
Au(AsF
6
) are sensitive to benzene vapor and are converted by exposure to benzene vapor into the colorless, blue-luminescent polymorph.
Non-luminescent crystals of (C
6
H
11
NC)
2
Au(AsF
6
)·C
6
H
6
readily lose benzene to form the green-luminescent polymorph of (C
6
H
11
NC)
2
Au(AsF
6
) rather than the blue-luminescent polymorph.
Fullerenyl radicals can be generated by addition of a free radical to a fullerene surface, by nucleophilic addition followed by one-electron oxidation, or by thermal dissociation of singly bonded ...fullerene dimers. However, fullerenyl radicals are usually very reactive and generally cannot be isolated. On the contrary, we have found that the reactions of the dimetallic endofullerenes, La2@Ih-C80 and La2@D5h-C80, with 3-chloro-5,6-diphenyltriazine resulted in mono-addition of the triazinyl radical to the fullerene cages to yield isolable fullerenyl radicals. The unusual stability of these fullerenyl radicals arises from the confinement of the unpaired electron to an internal, metal-metal bonding orbital. Accordingly, the fullerene cage protects the radical center from other reactive species. Furthermore, we demonstrate that the fullerenyl radical adduct of La2@Ih-C80 reacts with toluene to afford additional benzylation. Interestingly, the benzylated derivative is diamagnetic in solution, while it forms a paramagnetic dimer when crystallized.
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