Interpenetrated Lattices of Quaternary Chalcogenides Displaying Magnetic Frustration, High Na-Ion Conductivity, and Cation Redox in Na-Ion Batteries.

A series of quaternary selenides, NaxMGaSe4 (M = Mn, Fe, and mixed Zn/Fe), have been synthesized for the first time employing a high-temperature solid-state synthesis route through stochiometric or polychalcogenide flux reactions. Along with the selenides, a previously reported sulfide analogue, NaxFeGaS4, is also revisited with new findings. These compounds form an interpenetrated structure made up of a supertetrahedral unit. The electrochemical evaluations exhibit a reversible (de)intercalation of ∼0.6 and ∼0.45 Na-ions, respectively, from Na2.87FeGaS4 (1a) and Na2.5FeGaSe4 (2) involving Fe2+/Fe3+ redox when cycled between 1.5 and 2.5 V. Mössbauer spectroscopy of 1a shows the existence of a mixed oxidation state of Fe2+/3+ in the pristine compound and reversible oxidation of Fe2+ to Fe3+ during the electrochemical cycles. Na2.79Zn0.6Fe0.4GaSe4 possesses a reasonably high room temperature ionic conductivity of 0.077 ms/cm with an activation energy of 0.30 eV. The preliminary magnetic measurements show a bifurcation of FC-ZFC at 4.5 and 2.5 K, respectively, for 1a and Na3MnGaSe4 (4) arising most likely from a spin-glass like transition. The high negative values of the Weiss constants -368.15 and -308.43 K for 1a and 4, respectively, indicate strong antiferromagnetic interactions between the magnetic ions and also emphasize the presence of a high degree of magnetic frustration in these compounds.

3D Cyclophane for the Selective Conversion of Epoxide to Cyclic Carbonate.

A novel three-dimensional (3D) cyclophane molecule 1 was synthesized and fully characterized. Cyclophane 1, which can form a N heterocyclic carbene, was tested for conversion of certain epoxides (3-6) [scheme 2] to cyclic carbonates in the presence of CO2. Propylene oxide (3) was found to have more reactivity with cyclophane 1 compared to the other epoxides. The theoretical calculations based on N,N'-disubstituted imidazol(in)ium-2-carboxylates derived from N,N' disubstituted imidazole as the source of N-heterocyclic carbene show lower activation energy in the case of the reactivity of epoxides 5 and 6 as compared to 3 and 4. However, cyclophane 1, which possesses a 3D geometry, can form the open intermediate with CO2 and propylene oxide more feasibly than the other three epoxides, which have larger sizes as compared to propylene oxide. Hence, the reaction of propylene oxide, CO2, and cyclophane 1 can follow the mechanistic path 1, whereas the epoxides 4-6 can follow a different mechanistic path 2. Cyclophane 1 is the first example of a cyclophane to act as an organocatalyst for the conversion of CO2 and epoxide to cyclic carbonate via the N heterocyclic carbene pathway.

Cationic Divalent Metal Sites (M = Mn, Fe, Co) Operating as Both Nitrene-Transfer Agents and Lewis Acids toward Mediating the Synthesis of Three- and Five-Membered N-Heterocycles.

The tripodal compounds [(TMG3trphen)MII-solv](PF6)2 (M = Mn, Fe, Co; solv = MeCN, DMF) and bipodal analogues [(TMG2biphen)MII(NCMe)x](PF6)2 (x = 3 for Mn, Fe; x = 2 for Co) and [(TMG2biphen)MIICl2] have been synthesized with ligands that feature a triaryl- or diarylmethyl-amine framework and superbasic tetramethylguanidinyl residues (TMG). The dicationic M(II) sites mediate catalytic nitrene-transfer reactions between the imidoiodinane PhI═NTs (Ts = tosyl) and a panel of styrenes in MeCN to afford aziridines and low yields of imidazolines (upon MeCN insertion) with an order of productivity that favors the bipodal over the tripodal reagents and a metal preference of Fe > Co ≥ Mn. In CH2Cl2, the more acidic Fe(II) sites favor formation of 2,4-diaryl-N-tosylpyrrolidines by means of an in situ (3 + 2) cycloaddition of the initially generated 2-aryl-N-tosylaziridine with residual styrene. In the presence of ketone, 1,3-oxazolidines can be formed in practicable yields, involving a single-pot cycloaddition reaction of alkene, nitrene, and ketone (2 + 1 + 2). Mechanistic studies indicate that the most productive bipodal Fe(II) site mediates stepwise addition of nitrene to olefins to generate aziridines with good retention of stereochemistry and further enables aziridine ring opening to unmask a 1,3-zwitterion that can undergo cycloaddition with dipolarophiles (MeCN, alkene, ketone) to afford five-membered N-heterocycles.

Sodium-Stuffed Open-Framework Quaternary Chalcogenide Built with (Cu2Ga6S18)16- Ribbons Cross-Linked by Unusual Linear Cu(I) Pillars.

A quaternary compound, Na15Cu3Ga6S18, the first member in the A-Cu-Ga-S (A = alkali metal) series, has been synthesized from a solid-state metathesis reaction between Na6Ga2S6 and CuCl as well as from a combination of Na2S, Ga, Cu, and S. The compound crystallizes in a monoclinic crystal system, space group C2/c, and represents a unique open-framework structure with channels filled with eight crystallographically distinct Na ions. The anionic framework is built up of infinite chains of corner-shared GaS4 tetrahedra fused together by an edge-shared dimer of CuS4 tetrahedra forming one-dimensional ribbons of (Cu2Ga6S18)16-, which are cross-linked by linearly coordinated S-Cu-S linkages resulting in a three-dimensional network with tunnels filled with Na atoms. Optical band gap measurements show that the compound has a direct band gap of 3.00 eV that is in good agreement with the theoretical band gap derived from density functional theory calculations. Band structure calculations further indicate that the states near the Fermi level are dominated by tetrahedral Cu+(d) and S(p) states resulting from the antibonding interactions, while s-d hybridization is prevalent in linear Cu+ coordination. Ionic conductivity measurements show that the compound has a room-temperature Na ion conductivity of 2.72 × 10-5 mS/cm with an activation energy of 0.68 eV, which corroborates well the nudged elastic band calculations.

Is the Electrophilicity of the Metal Nitrene the Sole Predictor of Metal-Mediated Nitrene Transfer to Olefins? Secondary Contributing Factors as Revealed by a Library of High-Spin Co(II) Reagents.

Recent research has highlighted the key role played by the electron affinity of the active metal-nitrene/imido oxidant as the driving force in nitrene additions to olefins to afford valuable aziridines. The present work showcases a library of Co(II) reagents that, unlike the previously examined Mn(II) and Fe(II) analogues, demonstrate reactivity trends in olefin aziridinations that cannot be solely explained by the electron affinity criterion. A family of Co(II) catalysts (17 members) has been synthesized with the assistance of a trisphenylamido-amine scaffold decorated by various alkyl, aryl, and acyl groups attached to the equatorial amidos. Single-crystal X-ray diffraction analysis, cyclic voltammetry and EPR data reveal that the high-spin Co(II) sites (S = 3/2) feature a minimal [N3N] coordination and span a range of 1.4 V in redox potentials. Surprisingly, the Co(II)-mediated aziridination of styrene demonstrates reactivity patterns that deviate from those anticipated by the relevant electrophilicities of the putative metal nitrenes. The representative L4Co catalyst (-COCMe3 arm) is operating faster than the L8Co analogue (-COCF3 arm), in spite of diminished metal-nitrene electrophilicity. Mechanistic data (Hammett plots, KIE, stereocontrol studies) reveal that although both reagents follow a two-step reactivity path (turnover-limiting metal-nitrene addition to the C b atom of styrene, followed by product-determining ring-closure), the L4Co catalyst is associated with lower energy barriers in both steps. DFT calculations indicate that the putative [L4Co]NTs and [L8Co]NTs species are electronically distinct, inasmuch as the former exhibits a single-electron oxidized ligand arm. In addition, DFT calculations suggest that including London dispersion corrections for L4Co (due to the polarizability of the tert-Bu substituent) can provide significant stabilization of the turnover-limiting transition state. This study highlights how small ligand modifications can generate stereoelectronic variants that in certain cases are even capable of overriding the preponderance of the metal-nitrene electrophilicity as a driving force.

Magnetically Frustrated Quaternary Chalcogenides with Interpenetrating Diamond Lattices.

A series of quaternary sulfides of the composition Na3MGaS4 (M = Mn (1), Fe (2), and Co (3)) have been synthesized in sealed quartz ampules. In these compounds, divalent transition metal and Ga occupy the same crystallographic site in the Ga-S network, forming a supertetrahedral, T2 (adamantane) unit, through the corner-sharing of four M/GaS4 tetrahedra. The corner sulfur atoms of the T2 clusters are further connected to similar T2 units to form an open continuous three-dimensional (3D) anionic framework of composition {[Ga2M2S8]n}6-. The framework resembles a zinc blende structure type if each T2 cluster is considered as a single tetrahedron and two such frameworks are intertwined to generate channels wherein reside the extra-framework Na+ ions. Placement of transition metals (Mn or Fe or Co) in the corner of a perfect supertetrahedron, adamantane building unit, generates an ideal lattice for geometrical magnetic frustration, which, on dilution with nonmagnetic metal (Ga), creates an ideal case for random frustration. Preliminary magnetic measurements indicate high negative values of the Weiss constant (-200 to -400 K) and the absence of any magnetic ordering, reinforcing the presence of magnetic frustration in all of these compounds.

Metallic Ternary Telluride with Sphalerite Superstructure.

A new ternary compound with composition Cu5Sn2Te7 has been synthesized using the stoichiometric reaction of Cu, Sn, and Te. The compound crystallizes in C2 space group with unit cell parameters of a = 13.549(2) Å, b = 6.0521(11) Å, c = 9.568(2) Å, and ß = 98.121(2)°. Cu5Sn2Te7 is a superstructure of sphalerite and exhibits tetrahedral coordination of Cu, Sn, and Te atoms, containing a unique adamantane-like arrangement. The compound is formally mixed valent with a high electrical conductivity of 9.8 × 10(5) S m(-1) at 300 K and exhibits metallic behavior having p-type charge carriers as indicated from the positive Seebeck coefficient. Hall effect measurements further confirm holes as charge carriers with a carrier density of 1.39 × 10(21) cm(-3) and Hall mobility of 4.5 cm(2) V(-1) s(-1) at 300 K. The electronic band structure calculations indicate the presence of a finite density of states around the Fermi level and agree well with the p-type metallic conductivity. Band structure analysis suggests that the effective mass of the hole state is small and could be responsible for high electronic conductivity and Hall mobility. The high thermal conductivity of 15.1 W m(-1) K(-1) at 300 K coupled with the low Seebeck coefficient results in a poor thermoelectric figure of merit (ZT) for this compound. Theoretical calculations indicate that if Cu5Sn2Te7 is turned into a valence precise compound by substituting one Cu by a Zn, a semiconducting material, Cu4ZnSn2Te7, with a direct band gap of ∼ 0.5 eV can be obtained.

Flexible and rigid amine-functionalized microporous frameworks based on different secondary building units: supramolecular isomerism, selective CO(2) capture, and catalysis.

We report the synthesis, structural characterization, and porous properties of two isomeric supramolecular complexes of ([Cd(NH2 bdc)(bphz)0.5 ]⋅DMF⋅H2 O}n (NH2 bdc=2-aminobenzenedicarboxylic acid, bphz=1,2-bis(4-pyridylmethylene)hydrazine) composed of a mixed-ligand system. The first isomer, with a paddle-wheel-type Cd2 (COO)4 secondary building unit (SBU), is flexible in nature, whereas the other isomer has a rigid framework based on a µ-oxo-bridged Cd2 (µ-OCO)2 SBU. Both frameworks are two-fold interpenetrated and the pore surface is decorated with pendant -NH2 and NN functional groups. Both the frameworks are nonporous to N2 , revealed by the type II adsorption profiles. However, at 195 K, the first isomer shows an unusual double-step hysteretic CO2 adsorption profile, whereas the second isomer shows a typical type I CO2 profile. Moreover, at 195 K, both frameworks show excellent selectivity for CO2 among other gases (N2 , O2 , H2 , and Ar), which has been correlated to the specific interaction of CO2 with the -NH2 and NN functionalized pore surface. DFT calculations for the oxo-bridged isomer unveiled that the -NH2 group is the primary binding site for CO2 . The high heat of CO2 adsorption (ΔHads =37.7 kJ mol(-1) ) in the oxo-bridged isomer is realized by NH2 ⋅⋅⋅CO2 /aromatic π⋅⋅⋅CO2 and cooperative CO2 ⋅⋅⋅CO2 interactions. Further, postsynthetic modification of the -NH2 group into -NHCOCH3 in the second isomer leads to a reduced CO2 uptake with lower binding energy, which establishes the critical role of the -NH2 group for CO2 capture. The presence of basic -NH2 sites in the oxo-bridged isomer was further exploited for efficient catalytic activity in a Knoevenagel condensation reaction.

A series of trifacial Pd6 molecular barrels with porphyrin walls.

Three new nanoscopic trigonal prisms, [(tmen)(6) Pd(6) (H(2)L)(3)](NO(3))(12) (1), [(Meen)(6) Pd(6)(H(2) L)(3)](NO(3))(12) (2), and [(2,2'-bipy)(6)Pd(6) (H(2)L)(3)](NO(3))(12) (3), have been synthesized in excellent yields through single-step metal-ligand-coordination-driven self-assembly using 5,10,15,20-tetrakis(3-pyridyl)porphyrin (H(2)L) as a donor and cis-blocked Pd(II) 90° acceptors. These complexes were fully characterized by spectroscopic studies and single-crystal X-ray diffraction. All of these barrels quantitatively bind Zn(II) ions in the N(4) pockets of the porphyrin walls at room temperature. Their corresponding zinc-embedded complexes, [(tmen)(6)Pd(6)(ZnL)(3)](NO(3))(12) (1 a), [(Meen)(6) Pd(6)(ZnL)(3)](NO(3))(12) (2 a), and [(2,2'-bipy)(6)Pd(6)(ZnL)(3)](NO(3))(12) (3 a), were synthesized under ambient conditions by the post-synthetic binding of Zn(II) ions into the H(2)N(4) pockets of the porphyrin walls of these complexes. These zinc-embedded complexes were characterized by electronic absorption, fluorescence emission, (1)H NMR spectroscopy, as well as elemental analysis. Complexes 1-3 exhibited considerable microporosity in their solid state. Complex 1 was an efficient adsorbent for nitrogen gas and EtOH, MeOH, and water vapors.

Terbium(III), europium(III), and mixed terbium(III)-europium(III) mucicate frameworks: hydrophilicity and stoichiometry-dependent color tunability.

Two 3D porous terbium(III) mucicate frameworks, {[Tb(2)(Mu(2-))(3)(H(2)O)(2)]·4H(2)O}(n) (1) and {[Tb(Mu(2-))(Ox(2-))(0.5)(H(2)O)]·H(2)O}(n) (2), have been synthesized under hydrothermal conditions by changing the pH of the reaction medium. Isostructural europium(III) and seven mixed terbium(III)-europium(III) mucicates were synthesized by doping different percentages of Eu(III) under similar reaction conditions and unveiling different emission colors ranging from green to red under the same wavelength. Both dehydrated Tb(III) metal-organic frameworks exhibit selective H(2)O vapor sorption over other solvent molecules (MeOH, MeCN, and EtOH) of less polarity and bigger size and have been correlated to the highly hydrophilic pore surfaces decorated with -OH groups and O atoms from the carboxyl groups of mucicate.

Guest-responsive reversible swelling and enhanced fluorescence in a super-absorbent, dynamic microporous polymer.

A swell idea! The guest-responsive reversible swelling and fluorescence enhancement of a dynamic, microporous polymer network is presented. Guest-induced breathing of hydrophobic pores imparts multi-functional properties, such as super-absorbency, phase-selective swelling of oil from water and encapsulation of C(60) (see figure), to this soft micro-porous organic polymer.

Facile synthesis of anion dependent versatile Cu(I) and mixed-valent porous Cu(I)/Cu(II) frameworks.

CuX(2) (X = ClO(4)(-), NO(3)(-), 0.5 SO(4)(2-), Cl(-)) and 2,3-dihydroxyfumaric acid (dhfa) undergo redox reaction in slightly basic aqueous solution forming Cu(I)X and 2,3-diketosuccinic acid. Pyrazine (pyz) and 1,2-bis(4-pyridyl)ethylene (bpee) linkers have been used for stabilizing and isolating the Cu(I) state in this reaction. The three different Cu(I)-frameworks, {Cu(pyz)(1.5)(ClO(4))}(n) (1), {Cu(pyz)(NO(3))}(n) (2), and {[Cu(bpee)Cl].2H(2)O}(n) (3) with different anions have been synthesized and structurally characterized. The framework topology and dimensionality depends upon the anions. This is a one step synthesis of Cu(I) coordination frameworks with 1 : 2 stoichiometry in relation to dhfa and Cu(II). By controlling the concentration of dhfa, a mixed-valent porous Cu(I)/Cu(II) framework, [Cu(II)Cu(I)(2)(2,4-pyrdc)(2)(pyz)(3)].2H(2)O}(n) (4) has been synthesized and characterized by XPS and magnetic studies. Dehydrated frameworks of 3 and 4 exhibit interesting sorption properties with different solvent molecules. In a similar reaction CuCl(2) and pyz without dhfa produced the corresponding Cu(II)-compound, {Cu(pyz)Cl(2)}(n) (5), suggesting the reducing role of dhfa. Therefore by this simple reaction, it is possible to control the oxidation state as well as the coordination number and geometry of Cu ions. This is a novel synthetic methodology for the stabilization of the Cu +1 state in aqueous solution and open atmosphere.