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Chalcogen-Bonded Se–Nsub.2 Cyclic Supramolecular Synthons Enhanced by Halogen Bonds: Studies in the Gas Phase and Crystalline Phase
Chalcogen-bonded [Se–N][sub.2] is a strong cyclic supramolecular synthon in supramolecular chemistry. Selenadiazole is commonly used in the synthesis of [Se–N][sub.2]. One nitrogen atom in a selenadiazole molecule participates in the formation of [Se–N][sub.2], while the other nitrogen atom can participate in the formation of other types of noncovalent bonds. Investigating the effect of neighboring noncovalent bonds on [Se–N][sub.2] is beneficial for its further synthesis and application. In this study, we combined theoretical calculations and crystallography to explore the effect of I···N halogen bonds on [Se–N][sub.2] in both the gas phase and the crystalline phase. Gas-phase calculations show that the formation of halogen bonds increases the strength of [Se–N][sub.2], and the strength of the halogen bond is directly proportional to the strength of [Se–N][sub.2]. In the crystalline phase, [Se–N][sub.2] is influenced by more noncovalent bonds in addition to halogen bonds, making the results more complex. However, if the effect of other noncovalent bonds is relatively small, the strength of the halogen bond remains directly proportional to the strength of [Se–N][sub.2]. It is believed that the conclusions drawn from halogen bonds are also applicable to other types of noncovalent bonds.
Journal Article
Synthesis and Characterization of Iron Bispyridine Bisdicyanamide, FeCsub.5Hsub.5Nsub.2Nsub.2sub.2
Fe[C[sub.5]H[sub.5]N][sub.2][N(CN)[sub.2]][sub.2] (1) was synthesized from a reaction of stoichiometric amounts of NaN(CN)[sub.2] and FeCl[sub.2]·4H[sub.2]O in a methanol/pyridine solution. Single-crystal and powder diffraction show that 1 crystallizes in the monoclinic space group I2/m (no. 12), different from Mn[C[sub.5]H[sub.5]N][sub.2][N(CN)[sub.2]][sub.2] (P2[sub.1]/c, no. 14) due to tilted pyridine rings, with a = 7.453(7) Å, b = 13.167(13) Å, c = 8.522(6) Å, β = 114.98(6)° and Z = 2. ATR-IR, AAS, and CHN measurements confirm the presence of dicyanamide and pyridine. Thermogravimetric analysis shows that π-stacking interactions of the pyridine rings play an important role in structural stabilization. Based on DFT-optimized structures, a chemical bonding analysis was performed using a local-orbital framework by projection from a plane-wave basis. The resulting bond orders and atomic charges are in good agreement with the expectations based on the structure analysis. SQUID magnetic susceptibility measurements show a high-spin state Fe[sup.II] compound with predominantly antiferromagnetic exchange interactions at lower temperatures.
Journal Article
The California nitrogen assessment : challenges and solutions for people, agriculture, and the environment
\"Nitrogen is indispensable to all life on Earth. However, humans now dominate the nitrogen cycle and nitrogen emissions resulting from human activity involve real costs: water and air pollution, climate change, and detrimental effects for human health, biodiversity, and natural habitat. Too little nitrogen limits ecosystem processes, while too much nitrogen transforms ecosystems profoundly. The California Nitrogen Assessment is the first comprehensive accounting of nitrogen flows, practices, and policies for California; encompassing all nitrogen flows--not just those associated with agriculture--and their impacts on ecosystem services and human wellbeing. How California handles issues of nitrogen will be of interest nationally and internationally, and the goal of the assessment is to more effectively link science with action and to produce information that informs both future policy and solutions to nitrogen pollution. This book also provides a model for application of integrated ecosystem assessment methods at regional and state (sub-national) levels.\"--Provided by publisher.
Book
Too Much of a Good Thing
All biological systems need reactive nitrogen, but historically it has been in short supply. [...] the end of the nineteenth century, the main agricultural source was fixation of N2 by symbiotic bacteria in legumes planted for that purpose, combined with careful recycling of the limited amount of nitrogen in manure.
Publication
The nitrogen cycle
\"Nitrogen is a common element found as a gas in the air we breathe as well as in other forms in water and soil. Nitrogen is essential for all life on Earth. This informative book explains how the Earth's supply of nitrogen moves in different forms in a cycle from the air to the soil to living things. Highly readable text and supportive images help explain such processes as fixation, nitrification, and dentrification, as well as the important role of bacteria in the nitrogen cycle. Feature boxes highlight examples of the ways in which human activity, such as adding more nitrogen to the soil to make plants grow faster, releases harmful greenhouse gases into the air interfering with the nitrogen cycle. Readers are encouraged to find ways to take action and find solutions\"-- Provided by publisher.
Book
Responses of ecosystem nitrogen cycle to nitrogen addition: a meta-analysis
Anthropogenic nitrogen (N) addition may substantially alter the terrestrial N cycle. However, a comprehensive understanding of how the ecosystem N cycle responds to external N input remains elusive. Here, we evaluated the central tendencies of the responses of 15 variables associated with the ecosystem N cycle to N addition, using data extracted from 206 peer-reviewed papers. Our results showed that the largest changes in the ecosystem N cycle caused by N addition were increases in soil inorganic N leaching (461%), soil NO₃⁻ concentration (429%), nitrification (154%), nitrous oxide emission (134%), and denitrification (84%). N addition also substantially increased soil NH₄⁺ concentration (47%), and the N content in belowground (53%) and aboveground (44%) plant pools, leaves (24%), litter (24%) and dissolved organic N (21%). Total N content in the organic horizon (6.1%) and mineral soil (6.2%) slightly increased in response to N addition. However, N addition induced a decrease in microbial biomass N by 5.8%. The increases in N effluxes caused by N addition were much greater than those in plant and soil pools except soil NO₃⁻, suggesting a leaky terrestrial N system.
Journal Article