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Self-assembly of nanocrystals (NCs) into superlattices is an intriguing multiscale phenomenon that may lead to materials with novel collective properties, in addition to the unique properties of individual NCs compared with their bulk counterparts. By using different dispersion solvents, we synthesized three types of PbSe NC superlattices—body-centered cubic (bcc), body-centered tetragonal (bct), and face-centered cubic (fcc)—as confirmed by synchrotron small-angle X-ray scattering. Solution calorimetric measurements in hexane show that the enthalpy of formation of the superlattice from dispersed NCs is on the order of −2 kJ/mol. The calorimetric measurements reveal that the bcc superlattice is the energetically most stable polymorph, with the bct being 0.32 and the fcc 0.55 kJ/mol higher in enthalpy. This stability sequence is consistent with the decreased packing efficiency of PbSe NCs from bcc (17.2%) to bct (16.0%) and to fcc (15.2%). The small enthalpy differences among the three polymorphs confirm a closely spaced energy landscape and explain the ease of formation of different NC superlattices at slightly different synthesis conditions.

Here we describe the synthesis of two imido analogs of the uranyl ion, UO²⁺₂, in which the oxygens are replaced by divalent alkyl or aryl nitrogen groups: U(N[superscript t]Bu)₂I₂(THF)₂ (1) and U(NPh)₂I₂(THF)₃ (2) (where [superscript t]Bu is tert-butyl and THF is tetrahydrofuran). Both compounds have been fully characterized by standard analytical techniques, including x-ray crystallography, and the chemical bonding between the metal center and the nitrogen ligands was quantified by using hybrid density functional theory calculations. As expected for a uranyl analog, these complexes exhibit linear N-U-N linkages and very short U-N bonds. In addition, the theoretical calculations show strong involvement of the 5f and 6d electrons in the U-N bonding.

The most common form of uranium in solution is notoriously unreactive, limiting the use of the element. But interactions of this complex with potassium ions unleash a potentially rich seam of unexpected chemistry.

The most common form of uranium in solution is notoriously unreactive, limiting the use of the element. But interactions of this complex with potassium ions unleash a potentially rich seam of unexpected chemistry Uranium on the move Uranium is present almost everywhere in the environment as the highly soluble and mobile uranyl dication UO 2 2+ , which is also a major radioactive pollutant from the nuclear power and mining industries. The compound is chemically inert because of unusually strong bonds between the uranium atom and its two oxo groups. Arnold et al . now report that one uranyl oxo group can be made to undergo radical reactions normally associated only with transition metal oxo groups, if the strong O=U=O bonding is disrupted by placing the dication within an appropriate rigid molecular framework. Once put in the spot, the uranyl dication undergoes both single-electron reduction and oxo-group functionalization to form unique pentavalent uranyl compounds. These transformations might lead to strategies for manipulating and processing uranium in its most common form in solution.

The first comprehensive general resource on state-of-the-art protocell research, describing current approaches to making new forms of life from scratch in the laboratory.