RESUMO
The "disappearing polymorph" phenomenon is well established in organic solids, and has had a profound effect in pharmaceutical materials science. The first example of this effect in metal-containing systems in general, and in coordination-network solids in particular, is here reported. Specifically, attempts to mechanochemically synthesize a known interpenetrated diamondoid (dia) mercury(II) imidazolate metal-organic framework (MOF) yielded a novel, more stable polymorph based on square-grid (sql) layers. Simultaneously, the dia-form was found to be highly elusive, observed only as a short-lived intermediate in monitoring solvent-free synthesis and not at all from solution. The destabilization of a dense dia-framework relative to a lower dimensionality one is in contrast to the behavior of other imidazolate MOFs, with periodic density functional theory (DFT) calculations showing that it arises from weak interactions, including structure-stabilizing agostic C-Hâ â â Hg contacts. While providing a new link between MOFs and crystal engineering of organic solids, these findings highlight a possible role for agostic interactions in directing topology and stability of MOF polymorphs.
RESUMO
Owing to the strength of the C-F bond, the 'direct' preparation of Grignard reagents, i.e., the interaction of elemental magnesium with an organic halide, typically in an ethereal solvent, fails for bulk magnesium and organofluorine compounds. Previously described mechanochemical methods for preparing Grignard reagents have involved ball milling powdered magnesium with organochlorines or bromines. Activation of the C-F bond through a similar route is also possible, however. For example, milling 1- and 2-fluoronaphthalene with an excess of magnesium metal for 2 h, followed by treatment with FeCl3 and additional milling, produces the corresponding binaphthalenes, albeit in low yields (ca. 20%). The yields are independent of the particular isomer involved and are also comparable to the yields from corresponding the bromonaphthalenes. These results may reflect similar charges that reside on the α-carbon in the naphthalenes, as indicated by density functional theory calculations.
Assuntos
Magnésio/química , Naftalenos/química , Teoria da Densidade FuncionalRESUMO
Valuing diversity leads to scientific excellence, the progress of science and most importantly, it is simply the right thing to do. We can value diversity not only in words, but also in actions.
RESUMO
Ball milling CaI2 and [KN(SiMe3)2] in a 1 : 1 ratio without solvent, and then extracting the ground material with toluene, yields the synthetically valuable neutral amide [Ca(N(SiMe3)2)2] in good yield, without the contamination by calciate species that complicates solution metathesis routes. The effects on yield of grinding time, milling frequency, and calcium halide identity are also examined.