The union of structural and spectroscopic modeling can accelerate the discovery and improvement of phosphor materials if guided by an appropriate principle. Herein, we describe the concept of "chemical unit cosubstitution" as one such potential design scheme. We corroborate this strategy experimentally and computationally by applying it to the Ca2(Al(1-x)Mg(x))(Al(1-x)Si(1+x))O7:Eu(2+) solid solution phosphor. The cosubstitution is shown to be restricted to tetrahedral sites, which enables the tuning of luminescent properties. The emission peaks shift from 513 to 538 nm with a decreasing Stokes shift, which has been simulated by a crystal-field model. The correlation between the 5d crystal-field splitting of Eu(2+) ions and the local geometry structure of the substituted sites is also revealed. Moreover, an energy decrease of the electron-phonon coupling effect is explained on the basis of the configurational coordinate model.

Mechanistic studies indicate that the oxomolybdenum(vi) bis(3,5-di-tert-butylcatecholate) fragment deoxygenates pyridine-N-oxides in a reaction where the oxygen is delivered to molybdenum but the electrons for substrate reduction are drawn from the bound catecholate ligands, forming 3,5-di-tert-butyl-1,2-benzoquinone.

No abstract

To efficiently capture the energy of the nuclear bond, advanced nuclear reactor concepts seek solid fuels that must withstand unprecedented temperature and radiation extremes. In these advanced fuels, thermal energy transport under irradiation is directly related to reactor performance as well as reactor safety. The science of thermal transport in nuclear fuel is a grand challenge due to both computational and experimental complexities. Here, we provide a comprehensive review of thermal transport research on two actinide oxides: one currently in use in commercial nuclear reactors, uranium dioxide (UO2), and one advanced fuel candidate material, thorium dioxide (ThO2). In both materials, 5Concluding Remarks .

In the solid state, tris(3,5-di-tert-butylcatecholato)molybdenum(VI) forms a dimer with seven-coordinate molybdenum and bridging catecholates. NMR spectroscopy indicates that the dimeric structure is retained in solution. The molybdenum center has a high affinity for Lewis bases such as pyridine or pyridine-N-oxide, forming seven-coordinate monomers with a capped octahedral geometry, as illustrated by the solid-state structure of (3,5-(t)Bu2Cat)3Mo(py). Structural data indicate that the complexes are best considered as Mo(VI) with substantial π donation from the nonbridging catecholates to molybdenum. Both the dimeric and the monomeric tris(catecholates) react rapidly with water to form free catechol and oxomolybdenum bis(catecholate) complexes. Monooxomolybdenum complexes are also obtained, more slowly, on reaction with dioxygen, with organic products consisting mostly of 3,5-di-tert-butyl-1,2-benzoquinone with minor amounts of the extradiol oxidation product 4,6-di-tert-butyl-1-oxacyclohepta-4,6-diene-2,3-dione. The pyridine-N-oxide complex reacts on heating (with excess pyO) to form initially (3,5-(t)Bu2Cat)2MoO(Opy) and ultimately MoO3(Opy), with quinone and free pyridine as the only organic products. The decay of (3,5-(t)Bu2Cat)3Mo(Opy) shows an accelerated, autocatalytic profile because the oxidation of its product, (3,5-(t)Bu2Cat)2MoO(Opy), produces an oxo-rich, catecholate-poor intermediate which rapidly conproportionates with (3,5-(t)Bu2Cat)3Mo(Opy), providing an additional pathway for its conversion to the mono-oxo product. The tris(catecholate) fragment Mo(3,5-(t)Bu2Cat)3 deoxygenates Opy in this nonclassical oxygen atom transfer reaction slightly less rapidly than does its oxidized product, MoO(3,5-(t)Bu2Cat)2.