Polynitro‐Functionalized Dipyrazolo‐1,3,5‐triazinanes: Energetic Polycyclization toward High Density and Excellent Molecular Stability

A new fused N‐heterocyclic framework, dipyrazolo‐1,3,5‐triazinane, was synthesized and the physiochemical properties of its derivatives were investigated to evaluate the integrated energetic performance. In contrast to 1,3,5‐trinitro‐1,3,5‐triazinane (RDX) featuring a distorted chair confirmation, polynitro‐functionalized dipyrazolo‐1,3,5‐triazinanes have nearly planar backbones, thereby enhancing the density and thermal stability. Among these new energetic tricyclic compounds, 5 a and 12 show favorable crystal densities of 1.937 g cm⁻³ and 1.990 g cm⁻³ at 150 K, respectively, which rank highest in triazinane‐based energetic compounds. Additionally, this synthetic approach was carried out to form seven‐membered and eight‐membered rings, giving rise to tetranitro dipyrazolo‐1,3,5‐triazepane ( 5 b ) and tetranitro dipyrazolo‐1,3,5‐triazocane ( 5 c ), respectively.     

Photoelectron Spectroscopy and Theoretical Studies of PCSe−, AsCS−, AsCSe−, and NCSe−: Insights into the Electronic Structures of the Whole Family of ECX− Anions (E=N,P, As; X=O,S, Se)

The newly synthesized phosphorus‐ and arsenic‐containing analogues of the thio‐ and seleno‐cyanate anions, PCSe^?, AsCS^?, and AsCSe^?, as well as the known ion NCSe^? were investigated in the gas phase by negative‐ion photoelectron spectroscopy (NIPES), velocity‐map imaging (VMI) spectroscopy, and quantum‐chemical computations. The electron affinities (EA), spin–orbit (SO) splittings, and “symmetric”/“asymmetric” stretching frequencies of the neutral radicals ECX^. (E=N, P, As; X=S, Se), generated by electron detachment from the corresponding anions, were obtained from the spectra. The calculated EAs, SO splittings, and vibrational frequencies are in excellent agreement with the experimental measurements. These newly obtained values, when combined with those previously determined for the lighter analogues, show interesting trends on descending the pnictogen and chalcogen series. These trends are rationalized based on electronegativity arguments, the electron distributions in the HOMOs, and NBO/NRT analyses.     

Ferroelasticity in an Organic Crystal: A Macroscopic and Molecular Level Study

Ferroelasticity has been relatively well‐studied in mechanically robust inorganic atomic solids but poorly investigated in organic crystals, which are typically inherently fragile. The absence of precise methods for the mechanical analysis of small crystals has, no doubt, impeded research on organic ferroelasticity. The first example of ferroelasticity in an organic molecular crystal of 5‐chloro‐2‐nitroaniline is presented, with thorough characterization by macro‐ and microscopic methods. The observed cyclic stress–strain curve satisfies the requirements of ferroelasticity. Single‐crystal X‐ray structure analysis provides insight into lattice correspondence at the twining interface, which enables substantial crystal bending by a large molecular orientational shift. This deformation represents the highest maximum strain (115.9 %) among reported twinning materials, and the associated dissipated energy density of 216 kJ m⁻³ is relatively large, which suggests that this material is potentially useful as a mechanical damping agent.     

Unique Bora[1]ferrocenophanes with Sterically Protected Boron: A Potential Gateway to Helical Polyferrocenes

Silicon‐bridged [1]ferrocenophanes are a versatile class of monomers to obtain well‐defined metallopolymers, however, their boron‐bridged analogues are far less utilized despite being significantly higher strained. We assumed that the reactivity of known bora[1]ferrocenophanes towards ring‐opening polymerization is hampered by π‐donating R₂N groups at the bridging boron atom and therefore prepared the first bora[1]ferrocenophanes lacking such electronic stabilization. The new, isolated ferrocenophane with a 2,4,6‐triisopropylphenyl group attached to the bridging boron atom exhibits the most tilted Cp rings among all isolated strained sandwich compounds [α(DFT)=33.3°] with a measured record value of the bathochromic shift (λ_max=516 nm). Attempts to purify the mesityl analogue by vacuum sublimation transformed this monomer to a purple‐colored polymer that resulted in Cotton effects in circular dichroism spectroscopy. DFT calculations revealed a left‐handed helical structure for this polymer. This is the first evidence for a polyferrocene with a chiral secondary structure.     

Shaping Antiaromatic π‐Systems by Metalation: Synthesis of a Bowl‐Shaped Antiaromatic Palladium Norcorrole

The synthesis of a bowl‐shaped antiaromatic molecule was achieved through the deformation of a planar antiaromatic porphyrinic π‐conjugation system by insertion of palladium into the small cavity of a metal‐free norcorrole. The bowl‐to‐bowl inversion dynamics of the antiaromatic Pd‐coordinated norcorrole was determined by variable‐temperature ¹H NMR spectroscopy. The metal‐free norcorrole was prepared from acid‐induced demetalation of a copper norcorrole, which was obtained from the intramolecular coupling of a bis(diiododipyrrin) copper complex with copper thiophenecarboxylate.     

Conformational Fixation of a Rectangular Antiaromatic [28]Hexaphyrin Using Rationally Installed Peripheral Straps

A rectangular [28]hexaphyrin bearing outer straps at the long side has been synthesized by S_NAr reaction of [26]hexaphyrin with allyl alcohol, intramolecular olefin metathesis by using Hoveyda–Grubbs second‐generation catalyst, and reduction with NaBH₄. The peripheral straps enforce a rectangular conformation for the [28]hexaphyrin, which shows Hückel antiaromatic character, as confirmed by its planar X‐ray structure, a strong paratropic ring current, characteristic UV/Vis/NIR absorption features, small electrochemical HOMO–LUMO gap, and very fast S₁ decay.     

Magnetless Device for Conducting Three‐Dimensional Spin‐Specific Electrochemistry

Electron spin states play an important role in many chemical processes. Most spin‐state studies require the application of a magnetic field. Recently it was found that the transport of electrons through chiral molecules also depends on their spin states and may also play a role in enantiorecognition. Electrochemistry is an important tool for studying spin‐specific processes and enantioseparation of chiral molecules. A new device is presented, which serves as the working electrode in electrochemical cells and is capable of providing information on the correlation of spin selectivity and the electrochemical process. The device is based on the Hall effect and it eliminates the need to apply an external magnetic field. Spin‐selective electron transfer through chiral molecules can be monitored and the relationship between the enantiorecognition process and the spin of electrons elucidated.     

Twisted N‐Doped Nano‐Graphenes: Synthesis,Characterization, and Resolution

Two diastereoisomeric N‐doped nanographene derivatives have been efficiently prepared in two synthetic steps starting from an ethynylated hexaazatriphenylene building block. The first derivative adopts a D₃‐symmetrical propeller‐shaped structure with three equivalent nanographene foils. The structure of the second diastereoisomer is C₂‐symmetrical and differs from the first one by the way two peripheral nanographene foils overlap. Owing to their intertwined structures, the two N‐doped nanographenes are soluble in organic solvents and could be characterized by a combination of several analytical tools. Resolution of the D₃‐symmetrical derivative has been achieved and CD measurements revealed extremely strong Cotton effects.     

Selective Autonomous Molecular Transport and Collection by Hydrogel‐Embedded Supramolecular Chemical Gradients

Selective transport and concentration of molecules to specified regions on a substrate both enhances the potential to detect such molecules and provides a path to spatially localize such molecules prior to initiation of subsequent chemical reactions. Here, we first embed radially symmetric α‐, β‐, and γ‐cyclodextrin gradients in a hydrogel matrix. Driven by host‐guest interactions between the cyclodextrins and the target molecule, we observe these gradients can serve to direct 2D molecular transport. Using xanthene dyes and organophosphates as target molecules, we found the transport metrics, e.g., selectivity, rate, and concentration limits, are strongly dependent on the specific cyclodextrin forming the gradient. In all cases, as the concentrating power of the gradient increased, the rate of target concentration slowed, which we hypothesize is because stronger interactions between the target and the cyclodextrin decrease the rate of target diffusion. The concentration enhancement for the nerve agent simulant 4‐methylumbelliferyl phosphate (15.8) is the greatest when the gradient is formed using β‐cyclodextrin while directed concentration of cyanomethyl phosphonate, a smaller non‐aromatic organophosphate, is observed only for the smaller α‐CD. To provide a near real‐time read‐out of the concentration of the analyte, we used an array of IR resonant metallic nanoantennas tuned to a specific IR absorption band of the analyte to enhance the IR signal generated by the analyte.     

A Twisted Nanographene Consisting of 96 Carbon Atoms

Herein we report synthesis, structure and properties of a new type of twisted nanographene, which contains an [8]circulene moiety in a polycyclic framework of 96 sp² carbon atoms. The key steps in this synthesis are the Diels–Alder reaction of a macrocyclic diyne and the subsequent Scholl reaction forming the [8]circulene moiety. Two incompletely cyclized products were isolated from the Scholl reaction, providing insight into the cyclization of the strained octagon. This nanographene is twisted along two directions with end‐to‐end twists of 142.4° and 140.2° as revealed by X‐ray crystallography, and is flexible at room temperature as found from the computational and experimental studies.     

Contractive Annulation: A Strategy for the Synthesis of Small,Strained Cyclophanes and Its Application in the Synthesis of [2](6,1)Naphthaleno[1]paracyclophane

A new synthetic strategy (contractive annulation) for the synthesis of highly strained cyclophanes has been conceived and its viability has been demonstrated through a nine‐step synthesis of [2](6,1)naphthaleno[1]paracyclophane from [2.2]paracyclophane.     

Diamagnetic Raman Optical Activity of Chlorine,Bromine, and Iodine Gases

Magnetic Raman optical activity of gases provides unique information about their electric and magnetic properties. Magnetic Raman optical activity has recently been observed in a paramagnetic gas (Angew. Chem. Int. Ed. 2012 , 51, 11058; Angew. Chem. 2012 , 124, 11220). In diamagnetic molecules, it has been considered too weak to be measurable. However, in chlorine, bromine and iodine vapors, we could detect a significant signal as well. Zeeman splitting of electronic ground‐state energy levels cannot rationalize the observed circular intensity difference (CID) values of about 10⁻⁴. These are explicable by participation of paramagnetic excited electronic states. Then a simple model including one electronic excited state provides reasonable spectral intensities. The results suggest that this kind of scattering by diamagnetic molecules is a general event observable under resonance conditions. The phenomenon sheds new light on the role of excited states in the Raman scattering, and may be used to probe molecular geometry and electronic structure.     

Ag8Ca19N7 – Nitrogen Bridged Ca19N7 Superoctahedra surrounded by Silver Tetrahedra

By reacting Ca₃N₂ and silver powder at a temperature of 1300 K the subnitride Ag₈Ca₁₉N₇ was obtained. The title compound crystallizes in the space group Fm3m (No. 225) and has the lattice constant a = 1472.0(2) pm at T = 210 K and a = 1474.43(3) pm at T = 295 K. Ag₈Ca₁₉N₇ combines two very interesting, but rather different structural features, Ag₄ tetrahedra and Ca₁₉N₇ superoctahedra. An analysis of the bonding situation has been performed by means of Extended‐Hückel calculations.     

Violations of the Hückel (4n + 2) Rule

In polycyclic conjugated hydrocarbons the Hückel (4n + 2)-rule may be violated, so that certain (4n + 2)-membcred rings cause thermodynamic destabilization. The structural conditions for the occurrence of such an effect are analyze d. Eight examples (of which seven are new) of non-b enzenoid hydrocarbons are put forward, in which the Hückel rule is disobeyed.     

Synthesis,Characterization, Structural and Theoretical Analysis of a New Rare‐Earth Boride Carbide: Lu3BC3

Lu₃BC₃ is prepared by arc‐melting of the elements. The silver colored compound crystallizes in the space group Cmcm (Z = 4, a = 4.9788(3) Å, b = 5.0109(3) Å, c = 15.669(1) Å). The crystal structure contains discrete carbon atoms and CBC units in octahedra and bicapped cubes of metal atoms, respectively. The structural analysis is consistent with the group oxidation states (Lu³⁺)₃(C^4–)(CBC^5–). Extended Hückel and LAPW calculations have been performed. Although a semiconducting behavior could be anticipated, the valence band and the conduction band are touching according to LAPW calculations in agreement with the observed metallic conductivity of the compound.     

Regiodivergent and Diastereoselective CuH‐Catalyzed Allylation of Imines with Terminal Allenes

A copper‐catalyzed, chemoselective hydrometalation process enables the use of simple allenes as allylmetal nucleophile surrogates in imine allylation reactions. By modulating the nitrogen‐protecting group, either highly branched‐ or linear‐selective addition can be achieved from the same allene. Both reactions exhibit excellent diastereoselectivity and broad functional‐group tolerance. Preliminary results indicate that good enantioselectivity can also be achieved in the linear‐selective reaction. Finally, a mechanistic model for the regiodivergence is proposed on the basis of density functional theory calculations.     

Chiral Phosphoric Acids in Metal–Organic Frameworks with Enhanced Acidity and Tunable Catalytic Selectivity

Chiral phosphoric acids are incorporated into indium‐based metal–organic frameworks (In‐MOFs) by sterically preventing them from coordination. This concept leads to the synthesis of three chiral porous 3D In‐MOFs with different network topologies constructed from three enantiopure 1,1′‐biphenol‐phosphoric acid derived tetracarboxylate linkers. More importantly, all the uncoordinated phosphoric acid groups are periodically aligned within the channels and display significantly enhanced acidity compared to the non‐immobilized acids. This facilitates the Brønsted acid catalysis of asymmetric condensation/amine addition and imine reduction. The enantioselectivities can be tuned (up to >99 % ee) by varying the substituents to achieve a nearly linear correlation with the concentrations of steric bulky groups in the MOFs. DFT calculations suggest that the framework provides a chiral confined microenvironment that dictates both selectivity and reactivity of chiral MOFs.     

A simple alternative to the pseudo‐π method

In this work, we introduce an approximate method for the multicenter index calculation that is very simple in implementation and has the same computational cost as the pseudo‐π approach. In contrast to the latter, however, the newly proposed method does not require additional single‐point calculations and is capable of quantifying multicenter electron sharing in aromatic rings containing heteroatoms and transition metals.