Confined Lewis Pairs: Investigation of the X−→Si20 Interaction in Halogen-Encapsulating Silafulleranes

A joint theoretical and experimental study on 32 endohedral silafullerane derivatives [X@Si₂₀Y₂₀]⁻ (X=F-I; Y=F-I, H, Me, Et) and -[Cl@Si₂₀H₁₂Y₈]⁻ (Y=F-I) is presented. First, we evaluated the structure-determining template effect of Cl⁻ in a systematic series of concave silapolyquinane model systems. Second, we investigated the X⁻→Si₂₀ interaction energy ( ) as a function of X⁻ and Y and found the largest values for electron-withdrawing exohedral substituents Y. Given that X⁻ ions can be considered as Lewis bases and empty Si₂₀Y₂₀ clusters as Lewis acids, we classify our inseparable host–guest complexes [X@Si₂₀Y₂₀]⁻ as “confined Lewis pairs”. Third, ³⁵Cl NMR spectroscopy proved to be highly diagnostic for an experimental assessment of the Cl⁻→Si₂₀ interaction as the paramagnetic shielding and, in turn, (³⁵Cl) of the endohedral Cl⁻ ion correlate inversely with . Finally, we disclose the synthesis of [PPN][Cl@Si₂₀Y₂₀] (Y=Me, Et, Br) and provide a thorough characterization of these new silafulleranes.     

A Cationic Unsaturated Platinum(II) Complex that Promotes the Tautomerization of Acetylene to Vinylidene

Complex [PtMe₂(PMe₂Ar )] ( 1 ), which contains a tethered terphenyl phosphine (Ar =2,6‐(2,6‐ⁱ Pr₂C₆H₃)₂C₆H₃), reacts with [H(Et₂O)₂]BAr_F (BAr_F⁻=B[3,5‐(CF₃)₂C₆H₃]₄⁻) to give the solvent (S) complex [PtMe(S)(PMe₂Ar )]⁺ ( 2⋅S ). Although the solvent molecule is easily displaced by a Lewis base (e.g., CO or C₂H₄) to afford the corresponding adducts, treatment of 2⋅S with C₂H₂ yielded instead the allyl complex [Pt(η³‐C₃H₅)(PMe₂Ar )]⁺ ( 6 ) via the alkyne intermediate [PtMe(η²‐C₂H₂)(PMe₂Ar )]⁺ ( 5 ). Deuteration experiments with C₂D₂, and kinetic and theoretical investigations demonstrated that the conversion of 5 into 6 involves a Pt^II‐promoted HC≡CH to :C=CH₂ tautomerization in preference over acetylene migratory insertion into the Pt−Me bond.     

A Modular Approach to Inorganic Phosphazane Macrocycles

Inorganic macrocycles, based on non‐carbon backbones, present exciting synthetic challenges in the systematic assembly of inorganic molecules, as well as new avenues in host–guest and supramolecular chemistry. Here we demonstrate a new high‐yielding modular approach to a broad range of trimeric and hexameric S‐ and Se‐bridged inorganic macrocycles based on cyclophosphazane frameworks, using the building blocks [S=(H)P(μ‐NR)]₂. The method involves the in situ generation of the key intermediate [E (S )P(μ‐NR)]₂²⁻(E=S, Se) dianion, which can be reacted with electrophilic [ClP(μ‐NR)]₂ to give P^III/P^V hexameric rings or reacted with I₂ to give trimeric P^V variants. Important issues which are highlighted in this work are the competitive bridging ability of S versus Se in these systems and the synthesis of the first air‐stable and chiral inorganic macrocycles.     

Ni‐Catalyzed Stannylation of Aryl Esters via C−O Bond Cleavage

A Ni‐catalyzed stannylation of aryl esters with air‐ and moisture‐insensitive silylstannyl reagents via C −O cleavage is described. This protocol is characterized by its wide scope, including challenging combinations, thus enabling access to versatile building blocks and orthogonal C−heteroatom bond formations.     

General build up of basis and matrix in the diagonalization approach. Determination of Kramers configuration state functions

Algorithms to build the basis and matrix representation to obtain the Kramers configuration space functions (KCSFs) via diagonalization will be formally generalized to an arbitrary number of unpaired (open shell) fermions. Effective build up of the matrix representation will be outlined (including threading and graphical processing unit parallelism) to subsequently obtain the KCSFs via calling external/numerical library routines for diagonalization. The effective build up of the matrix representation relays on a binary tree search algorithm to allow evaluation the action on a given basis vector. The binary tree search avoids the treatment of zero matrix elements which leads to an exponential acceleration. The implementation ( basis creation, matrix representation, and matrix diagonalization) will be done in an all in core and all at once manner, hence the available core memory sets the physical limits in practical applications. Memory limitations, sparsity of the matrix, general case of n fermions in m spinors, and the application of KCSFs will be put into further perspective.     

The Trifluoromethyl Anion: Evidence for [K(crypt‐222)]+

[K(crypt‐222)]⁺ ( 1 ) and [K(crypt‐222)]⁺ ( 3 ) are isostructural, displaying nearly identical unit cell parameters. The two structures are similar to the extent that the previously reported [K(crypt‐222)]⁺ model can be refined against the new data for [K(crypt‐222)]⁺ , with extra electron density being observed from the fourth fluorine atom of the . In agreement with experimental observations, theoretical calculations suggest that deprotonated [K(crypt‐222)]⁺ is highly unstable even at as low as 195 K. The previously considered 1:1 CHF ₃ clathrate of deprotonated [K(crypt‐222)]⁺ (crystallographically indistinguishable from 1 ) is ruled out on the basis of all available data.     

Tunable Self‐Assembly of Diblock Copolymers into Colloidal Particles with Triply Periodic Minimal Surfaces

We herein report the tunable self‐assembly of simple block copolymers, namely polystyrene‐block‐poly(ethylene oxide) (PS‐b‐PEO) diblock copolymers, into porous cubosomes with inverse or mesophases of controlled unit cell parameters as well as hexasomes with an inverse hexagonal (p 6mm ) structure, which have been rarely observed in polymer self‐assembly. A new morphological phase diagram was constructed for the solution self‐assembly of PS‐b‐PEO based on the volume fraction of the PS block against the initial copolymer concentration. The formation mechanisms of the cubosomes and hexasomes have also been revealed. This study not only affords a simple system for the controllable preparation and fundamental studies of ordered bicontinuous structures, but also opens up a new avenue towards porous architectures with highly ordered pores.     

Geometric and electronic structures of silicon fluorides (N = 4 – 6) and potential energy surfaces for dissociation reactions → SiF4 + F– and → + F–

The geometric and electronic structures of a series of silicon fluorides (n = 4 ? 6) were computationally studied with the aid of density functional theory (DFT) method with B3LYP and M06‐2X functionals and coupled cluster (CCSD and CCSD(T)) methods with 6‐311++G(d,p) basis set. The nature of the Si‐F bonds in these compounds was analyzed in the framework of the natural bond orbital theory and natural resonance theory. Energy characteristics (heats of reactions and energy barriers) of the dissociation reactions → SiF₄ + F^– and → + F^– were calculated using the DFT and CCSD methods. The potential energy surface of elimination of a fluoride anion from has a specific topology with valley‐ridge inflection points corresponding to bifurcations of the minimal energy reaction path. © 2016 Wiley Periodicals, Inc.     

Ritz variational method for the high‐lying nonautoionizing doubly excited 1,3Fe states of two‐electron atoms

Energy eigenvalues of nonautoionizing doubly excited states originating from 2pnf ( ) configuration of two‐electron atoms have been calculated by expanding the basis set in explicitly correlated Hylleraas coordinates under the framework of Ritz variational method. A detailed discussion on the evaluation of correlated basis integrals is given. The energy eigenvalues of a number of these doubly excited states are being reported for the first time especially for the high lying states. The effective quantum numbers ( ) for the states mentioned above have been calculated by using the theory of quantum defect.     

Universality in Branching Frequencies and Molecular Dimensions during Hyperbranched Polymer Formation: Step Polymerization of AB2 Type Monomer with Equal Reactivity

Hyperbranched polymer formation during step polymerization of AB₂ type monomer with equal reactivity of two B's is investigated theoretically, focusing the attention to the degree of branching (DB) and the mean square radius of gyration for the unperturbed chains, . It is found that the DB‐value at large degree of polymerization (P) limit, = 0.5 is unchanged during the whole course of polymerization. The average value of having the same P is invariant throughout the polymerization. The universal curve between and P agrees perfectly with that for the self‐condensing vinyl polymerization (SCVP), another method to synthesize hyperbranched polymers, when the reactivity ratio for SCVP, r_SCVP, is 2.589 that gives = 0.5. The power law, is found for large values of P.

     

A T‐Shaped Nickel(I) Metalloradical Species

A T‐shaped Ni^I complex was synthesized using a rigid acridane‐based pincer ligand to prepare a metalloradical center. Structural data displays a nickel ion is embedded in the plane of a PNP ligand. Having a sterically exposed half‐filled orbital, this three‐coordinate Ni^I species reveals unique open‐shell reactivity including the homolytic cleavage of various σ‐bonds, such as H−H, N−N, and C−C.     

Explicitly correlated variational estimates of the energy levels of negative hydrogen ion under spatial confinement

Comprehensive investigations on the structural modifications of negative hydrogen ion within an impenetrable spherical domain has been performed in the framework of Ritz variational method. Electron correlation plays a major role in the formation of H^– ion. The Hylleraas‐type basis set expansion of wave function considered here incorporates the effect of electron correlation in an explicit manner. Energy values of and 1sn states of H^– ion within confined domain have been calculated. Although the singly excited states do not exist for a “free” H^– ion, well converged energy values of such states have been found within a wide range of confinement radius. The thermodynamic pressure felt by the ion inside the sphere is also estimated. The general trend shows successive destabilization of the excited energy levels with increase of pressure. The contribution of angular correlation in the energy values have been estimated. Evolution of and energy levels of H^– ion as quasi‐bound states are being reported.     

Bending Vibrational Levels in the Electronic Spectra of Small Radicals

The role played by bending vibrations in the spectroscopy of small carbon‐containing radicals is illustrated by the patterns and effects shown by C₃, CCH, and C₃Ar. Because of the large change in the bending frequency between the ¹Σ⁺_g and ¹Π_u states of C₃, the ¹Π_u state provides one of the best known examples of the coupling of electronic and vibrational motion in linear molecules (the Renner–Teller effect). The ²Σ⁺ and ²Π states of CCH provide a classic instance of vibronic coupling between two close‐lying electronic states, which leads very rapidly to a chaotic pattern of mixed‐state vibrational energy levels, which can only be understood by extensive high‐quality ab initio calculations. C₃Ar is an approximately T‐shaped molecule with no less than four large‐amplitude vibrations. Its state provides a beautiful example of what happens to the angular momentum of a Π state of C₃ when the symmetry is lowered by complex formation.     

Energies for cyclic and acyclic aggregations of adamantane and diamantane units sharing vertices,edges, or six‐membered rings

Diamondoids are hydrocarbons having a carbon scaffold comprised from polymer‐like composites of adamantane cages. This article describes computed total energies and “SWB‐tension” energies (often referred to as “strain” energies) for species having n adamantane or diamantane units sharing pairwise: one carbon atom (spiro‐[n]adamantane or spiro‐[n]diamantane); one C? C bond (one‐bond‐sharing‐[n]adamantane or one‐bond‐sharing‐[n]diamantane); or one chair‐shaped hexagon of carbon atoms (1234‐helical‐cata‐[n]diamantanes). Each of the five investigated polymer‐like types is considered either as an acyclic or a cyclic chain of adamantane‐ or diamantane‐unit cages. With increasing n values, SWB‐tension energies for acyclic aggregates are found to increase linearly, while the net SWB‐tension energies of cyclic aggregates often go thru a minimum at a suitable value of . In all five cases, a limiting common energy per unit ( ) is found to be approached by both cyclic and acyclic chains as , as revealed from plots of versus 1/n for acyclic chains and of versus 1/n² for cyclic chains. © 2015 Wiley Periodicals, Inc.     

Development of a Perchlorate Chemical Sensor Based on Magnetic Nanoparticles and Silicon Nitride Capacitive Transducer

We report in this work the development of a novel capacitance electrochemical sensors based on silicon nitride substrate (Si₃N₄) chemically modified with a structure of Cobalt phthalocyanine, C,C,C,C‐tetracarboxylic acid‐Polyacrylamide (Co(II)Pc‐PAA). This sensitive layer was tested with and without magnetic nanoparticles (MNP) for perchlorate ( ) detection. The developed chemical sensor with Si₃N₄/APTES‐MNP/Co(II)Pc‐PAA structure has shown a better performance when compared to the other structure based on Si₃N₄/Co(II)Pc‐PAA. Contact angle measurements (CAM) and atomic force microscopy (AFM) characterizations have been performed to characterize the functionalization of the chemical sensors surface. Under the optimized structure of the chemical sensor, electrochemical measurements were carried out using Mott‐Schottky analysis for detection within the large range of 10⁻¹⁰ to 10⁻⁴ M with a very low detection limit of 2×10⁻¹⁰ M. The chemical sensor has demonstrated a high selectivity toward when compared to other interfering anions such as Cl⁻, SO₄²⁻, and CO₃²⁻. The present capacitive chemical sensor is very promising for sensitive and rapid detection of for environmental applications.     

Crossover between Tilt Families and Zero Area Thermal Expansion in Hybrid Prussian Blue Analogues

Materials in the family of Prussian blue analogues (C₃H₅N₂)₂K[ M (CN)₆], where C₃H₅N₂ is the imidazolium ion and M =Fe, Co, undergo two phase transitions with temperature; at low temperatures the imidazolium cations have an ordered configuration (C 2/c ), while in the intermediate‐ and high‐temperature phases (both previously reported as ) they are dynamically disordered. We show from high‐resolution powder neutron diffraction data that the high‐temperature phase has zero area thermal expansion in the ab ‐plane. Supported by Landau theory and single‐crystal X‐ray diffraction data, we re‐evaluate the space group symmetry of the intermediate‐temperature phase to . This reveals that the low‐to‐intermediate temperature transition is due to competition between two different tilt patterns of the [ M (CN)₆]³⁻ ions. Controlling the relative stabilities of these tilt patterns offers a potential means to tune the exploitable electric behaviour that arises from motion of the imidazolium guest.     

Spin–orbit effects on magnetically induced current densities in the () clusters

This study reports the spin–orbit effects on the aromaticity of the , , , , , and anionic clusters via the magnetically induced current‐density method. All‐electron density functional theory (DFT) calculations were carried out using the four‐component Dirac‐Coulomb (DC) hamiltonian, including scalar and spin–orbit relativistic effects. The magnetic index of aromaticity was calculated by numerical integration over the current flow between two atoms in the pentagonal ring. These values were compared to the spin‐free values (spin–orbit coupling switched off), in order to assess the spin–orbit effect on aromaticity. It was found that in the heavy anions, and , there is a significant influence of the spin–orbit coupling. © 2018 Wiley Periodicals, Inc.     

Synthesis and Structure of [Sn4Se11]6–, [Sn2Se52–], and [Sn3Se72–] – Model Anions for the Solventothermal Reaction Pathway to Lamellar Selenidostannates(IV)

Reaction of A₂CO₃ (A = K, Rb) with Sn and Se in an H₂O/CH₃OH mixture at 115–130°C affords the isotypic selenidostannates(IV) A₆Sn₄Se₁₁ _. xH₂O (A = K, x = 8) 1 and 2 whose discrete [Sn₄Se₁₁]^6– anions each contain two corner‐bridged ditetrahedral [Sn₂Se₆]^4– species. Similar reaction conditions with A = Cs afford Cs₂Sn₂Se₅ _. H₂O ( 3a ) and Cs₂Sn₂Se₅ ( 3b ) in which such [Sn₂Se₆]^4– building blocks are connected through common Se atoms into infinite [Sn₂Se₅^2–] chains. The [Sn₃Se₇^2–] ribbons of (Et₄N)₂Sn₃Se₇ ( 4 ), formed by treating (Et₄N)I with Sn and Se in methanol at 130°C, can be regarded as resulting from the condensation of [Sn₂Se₅^2–] chains with molecular [SnSe₄]^4– anions. The anions [Sn₄Se₁₁]^6–, [Sn₂Se₅^2–], and [Sn₃Se₇^2–] represent the products of individual reaction steps on the potential condensation pathway of [Sn₂Se₆]^4– to the lamellar selenidostannates(IV) [Sn₄Se₉^2–] or [Sn₃Se₇^2–].     

Full–dimensional quantum molecular dynamics calculations of the rovibrationally mediated X → 2 transition of nitrous oxide

A full dimensional time‐dependent quantum wavepacket approach is used to study the photodissociation dynamics of nitrous oxide for the X → 2 bound–bound transition based on new highly accurate potential energy and transition dipole moment surfaces. The computed 2 absorption spectra at room temperature are characterized by sharp vibrational structures that contribute slightly to the diffuse vibrational structures around the maximum peak at 180 nm of the first ultraviolet absorption band (from the contribution of 2 , 1 , and 2 states) of N₂O. Transitions from different initial rovibrational states reveal that the sharp structures arise mainly from N₂? O bending vibrations, whereas, at higher temperatures, the N₂? O and N? NO stretching vibrations are responsible for enhancing the intensity of the structures. At absorption wavelengths 166 nm and 179 nm, vibrational quantum state distributions of N₂ product fragments decrease monotonically with increasing vibrational quantum number v = 0, 1, 2. At 166 nm, rotational quantum state distributions of N₂ at fixed v = 0 and v = 1 display multimodal profiles with maximum peaks at j = 77 and j = 75, respectively, whereas, the distributions at the 179 nm absorption wavelength display bimodal profiles with maximum peaks at j = 73 and j = 71, respectively. Accordingly, the presence of rotationally hot N₂ from previous experimental and theoretical works in the first band strongly implies a significant influence of the 2 state in determining the final dissociation pathway of N₂ + O. © 2016 Wiley Periodicals, Inc.