Metal Transition in Sodium–Ammonia Nanodroplets

The famous nonmetal‐to‐metal transition in Na–ammonia solutions is investigated in nanoscale solution droplets by photoelectron spectroscopy. In agreement with the bulk solutions, a strong indication for a transition to the metallic state is found at an average metal concentration of 8.8±2.2 mole%. The smallest entity for the phase transition to be observed consists of approximately 100–200 solvent molecules. The quantification of this critical entity size is a stepping stone toward a deeper understanding of these quantum–classical solutions through direct modeling at the molecular level.     

The tropolone–isobutylamine complex: a hydrogen‐bonded troponoid without dominant π–π interactions

Tropolone long has served as a model system for unraveling the ubiquitous phenomena of proton transfer and hydrogen bonding. This molecule, which juxtaposes ketonic, hydroxylic, and aromatic functionalities in a framework of minimal complexity, also has provided a versatile platform for investigating the synergism among competing intermolecular forces, including those generated by hydrogen bonding and aryl coupling. Small members of the troponoid family typically produce crystals that are stabilized strongly by pervasive π–π, C—H…π, or ion–π interactions. The organic salt (TrOH·iBA) formed by a facile proton‐transfer reaction between tropolone (TrOH) and isobutylamine (iBA), namely isobutylammonium 7‐oxocyclohepta‐1,3,5‐trien‐1‐olate, C₄H₁₂N⁺·C₇H₅O₂⁻, has been investigated by X‐ray crystallography, with complementary quantum‐chemical and statistical‐database analyses serving to elucidate the nature of attendant intermolecular interactions and their synergistic effects upon lattice‐packing phenomena. The crystal structure deduced from low‐temperature diffraction measurements displays extensive hydrogen‐bonding networks, yet shows little evidence of the aryl forces (viz. π–π, C—H…π, and ion–π interactions) that typically dominate this class of compounds. Density functional calculations performed with and without the imposition of periodic boundary conditions (the latter entailing isolated subunits) documented the specificity and directionality of noncovalent interactions occurring between the proton‐donating and proton‐accepting sites of TrOH and iBA, as well as the absence of aromatic coupling mediated by the seven‐membered ring of TrOH. A statistical comparison of the structural parameters extracted for key hydrogen‐bond linkages to those reported for 44 previously known crystals that support similar binding motifs revealed TrOH·iBA to possess the shortest donor–acceptor distances of any troponoid‐based complex, combined with unambiguous signatures of enhanced proton‐delocalization processes that putatively stabilize the corresponding crystalline lattice and facilitate its surprisingly rapid formation under ambient conditions.     

Synthesis, structure, redox properties and azide binding for a series of biphenyl-based Cu(II) complexes

A series of biphenyl-based N(3)O ligands, 2, 4, 6, and 8 were synthesized and their Cu(II) complexes prepared. These complexes were characterized by a combination of elemental analysis, FAB-MS, UV-vis spectroscopy and electrochemistry. The structure of [Cu(N(3)O-mpy-NO2)Cl2], 12 [N(3)O-mpy = 2-(3-pyridylmethylimino)-2'-(2-methylaminophenol)biphenyl], was solved and showed that the ligand coordinates through the three nitrogens with the phenol oxygen uncoordinated. Titration of azide anion into solutions of the complexes in methanol resulted in the appearance of a new band between 485-495 nm at the expense of the starting peak at 380 nm. Cyclic voltammetry studies indicated that the complexes undergo quasi-reversible one-electron reductions in acetonitrile at potentials between 0.13-0.58 V vs. Ag/AgCl. The complexes were found to be weakly active for the oxidation of di-tert-butyl catechol (DTBC).     

Generating Self-Map Monoids of Infinite Sets

Let be a countably infinite set, the group of permutations of , and the monoid of self-maps of . Given two subgroups , let us write if there exists a finite subset such that the groups generated by and are equal. Bergman and Shelah showed that the subgroups which are closed in the function topology on S fall into exactly four equivalence classes with respect to . Letting denote the obvious analog of for submonoids of E, we prove an analogous result for a certain class of submonoids of E, from which the theorem for groups can be recovered. Along the way, we show that given two subgroups which are closed in the function topology on S, we have if and only if (as submonoids of E), and that for every subgroup (where denotes the closure of G in the function topology in S and its closure in the function topology in E).     

Discovery of beta-LnNiSb3 (Ln = La, Ce): crystal growth, structure, and magnetic and transport behavior

A new polymorph of CeNiSb3 has been grown from a Sn flux and characterized by single-crystal X-ray diffraction. beta-CeNiSb3 crystallizes in the orthorhombic space group Pbcm (No. 57) with Z = 8. The unit cell parameters are a = 12.9170(2) A, b = 6.1210(5) A, c = 12.0930(6) A, and V = 956.13(9) A3. Its layered structure contains structural motifs similar to that of the first form of CeNiSb3 and consists of Ce atoms inserted between anionic layers of nearly square infinity2[Sb] nets and distorted infinity2[NiSb2] octahedra. We report the synthesis, magnetization, electrical resistivity, and specific heat of the new form of CeNiSb3 and compare the structures and physical properties of both polymorphs.     

Switchable Ambient‐Temperature Singlet–Triplet Dual Emission in Nonconjugated Donor–Acceptor Triarylboron–PtII Complexes

Double the fun! Singlet–triplet dual emission at ambient temperature has been achieved in compounds containing a triarylboron acceptor and an N‐(2′‐pyridyl)‐7‐azaindolyl donor group bridged by a tetrahedral Si linker (see figure). Pt^II chelation and chelate‐mode switching from N,N to N,C have been found to greatly enhance phosphorescent emission. Furthermore, both singlet and triplet emission bands are responsive to fluoride ions.