Potential Lifshitz transition at optimal substitution in nematic pnictide Ba1-xSrxNi2As2

BaNi2As2 is a structural analog of the pnictide superconductor BaFe2As2, which, like the iron-based superconductors, hosts a variety of ordered phases including charge density waves (CDWs), electronic nematicity, and superconductivity. Upon isovalent Sr substitution on the Ba site, the charge and nematic orders are suppressed, followed by a sixfold enhancement of the superconducting transition temperature (Tc). To understand the mechanisms responsible for enhancement of Tc, we present high-resolution angle-resolved photoemission spectroscopy (ARPES) measurements of the Ba1-xSrxNi2As2 series, which agree well with our density functional theory (DFT) calculations throughout the substitution range. Analysis of our ARPES-validated DFT results indicates a Lifshitz transition and reasonably nested electron and hole Fermi pockets near optimal substitution where Tc is maximum. These nested pockets host Ni dxz/dyz orbital compositions, which we associate with the enhancement of nematic fluctuations, revealing unexpected connections to the iron-pnictide superconductors. This gives credence to a scenario in which nematic fluctuations drive an enhanced Tc.

A cellulose-derived supramolecule for fast ion transport

Supramolecular frameworks have been widely synthesized for ion transport applications. However, conventional approaches of constructing ion transport pathways in supramolecular frameworks typically require complex processes and display poor scalability, high cost, and limited sustainability. Here, we report the scalable and cost-effective synthesis of an ion-conducting (e.g., Na+) cellulose-derived supramolecule (Na-CS) that features a three-dimensional, hierarchical, and crystalline structure composed of massively aligned, one-dimensional, and ångström-scale open channels. Using wood-based Na-CS as a model material, we achieve high ionic conductivities (e.g., 0.23 S/cm in 20 wt% NaOH at 25 °C) even with a highly dense microstructure, in stark contrast to conventional membranes that typically rely on large pores (e.g., submicrometers to a few micrometers) to obtain comparable ionic conductivities. This synthesis approach can be universally applied to a variety of cellulose materials beyond wood, including cotton textiles, fibers, paper, and ink, which suggests excellent potential for a number of applications such as ion-conductive membranes, ionic cables, and ionotronic devices.

Sixfold enhancement of superconductivity in a tunable electronic nematic system

The electronic nematic phase-in which electronic degrees of freedom lower the crystal rotational symmetry-is commonly observed in high-temperature superconductors. However, understanding the role of nematicity and nematic fluctuations in Cooper pairing is often made more complicated by the coexistence of other orders, particularly long-range magnetic order. Here we report the enhancement of superconductivity in a model electronic nematic system that is not magnetic, and show that the enhancement is directly born out of strong nematic fluctuations associated with a quantum phase transition. We present measurements of the resistance as a function of strain in Ba_1-x Sr _x Ni₂As₂ to show that strontium substitution promotes an electronically driven nematic order in this system. In addition, the complete suppression of that order to absolute zero temperature leads to an enhancement of the pairing strength, as evidenced by a sixfold increase in the superconducting transition temperature. The direct relation between enhanced pairing and nematic fluctuations in this model system, as well as the interplay with a unidirectional charge-density-wave order comparable to that found in the cuprates, offers a means to investigate the role of nematicity in strengthening superconductivity.

Synthesis and Characterization of the {Si(NHCH2CH2NH)3[Mo(CO)3]2}2- Complex Comprising the Si(NHCH2CH2NH)32- Octahedron

Reactions of K₁₂Si₁₇ with the low-valent transition-metal complex Mo(CO)₃(C₇H₈) in ethylenediamine/toluene solutions in the presence of 2,2,2-cryptand yield the {Si(NHCH₂CH₂NH)₃[Mo(CO)₃]₂}^2- dianion, which contains an octahedral Si(NHCH₂CH₂NH)₃^2- subunit. The SiN₆ core comprises a rare example of a doubly deprotonated ethylenediame ligand in a coordination complex and is also the first structurally characterized example of a homoleptic Si(N∩N)₃ trischelate. Its structure and spectroscopic properties are described.

The cyclo-Sb6 ring in the [Sb6(RuCp*)2]2− ion

The [Sb₆(RuCp*)₂]²⁻ anion represents the first example of a Zintl cluster with a boat-like cyclo-Sb₆ subunit and the first ruthenium polyantimonide complex. The anion is dynamic in solution and fragments in the gas phase. Structural parameters and DFT calculations suggest the possibility of SbSb double bond character.

Facile and template-free solvothermal synthesis of mesoporous/macroporous metal–organic framework nanosheets

A facile and template-free solvothermal method was developed as a bottom-up approach to synthesize mesoporous/macroporous MOF nanosheets in a simple and scalable way. It was found that starting coordination complexes of different copper(ii)-ligand compounds mediated the controlled growth and morphology of MOF crystals. By controlling the size and shape of the MOF crystals, the possibility to adjust and tailor the structure and performances of the assemblies was demonstrated. This work provides a bottom-up approach to synthesize MOF films and nanosheets in a simple and scalable way, which may have potential in energy and biomedical applications.

A facile and template-free solvothermal method was developed as a bottom-up approach to synthesize mesoporous/macroporous MOF nanosheets in a simple and scalable way.

Sb@Ni12@Sb20-/+ and Sb@Pd12@Sb20n Cluster Anions, Where n = +1, -1, -3, -4: Multi-Oxidation-State Clusters of Interpenetrating Platonic Solids

K₅Sb₄ and K₃Sb₇ Zintl ion precursors react with Pd(PPh₃)₄ in ethylenediamine/toluene/PBu₄⁺ solutions to give crystals of Sb@Pd₁₂@Sb₂₀^n-/PBu₄⁺ salts, where n = 3, 4. The clusters are structurally identical in the two charge states, with nearly perfect I_h point symmetry, and can be viewed as an Sb@Pd₁₂ icosahedron centered inside of an Sb₂₀ dodecahedron. The metric parameters suggest very weak Sb-Sb and Pd-Pd interactions with strong radial Sb-Pd bonds between the Sb₂₀ and Pd₁₂ shells. All-electron DFT analysis shows the 3- ion to be diamagnetic with I_h symmetry and a 1.33 eV HOMO-LUMO gap, whereas the 4- ion undergoes a Jahn-Teller distortion to an S = 1/2 D_3d structure with a small 0.1 eV gap. The distortion is predicted to be small and is not discernible by crystallography. Laser desorption-ionization time-of-flight mass spectrometry (LDI-TOF MS) studies of the crystalline samples show intense parent Sb@Pd₁₂@Sb₂₀^- ions (negative ion mode) and Sb@Pd₁₂@Sb₂₀⁺ (positive ion mode) along with series of Sb@Pd_12-y@Sb_20-x^-/+ ions. Ni(cyclooctadiene)₂ reacts with K₃Sb₇ in en/tol/Bu₄PBr solvent mixtures to give black precipitates of Sb@Ni₁₂@Sb₂₀^n- salts that give similar Sb@Ni₁₂@Sb₂₀^-/+ parent ions and Sb@Ni_12-y@Sb_20-x^-/+ degradation series in the respective LDI-TOF MS studies. The solid-state and gas-phase studies of the icosahedral Sb@M₁₂@Sb₂₀^n-/n+ ions show that the clusters can exist in the -4, -3, -1, +1 (M = Pd) and +1, -1 (M = Ni) oxidation states. These multiple-charge-state clusters are reminiscent of redox-active fullerenes (e.g., C₆₀ⁿ, where n = +1, 0, -1, -2, -3, -4, -5, -6).

[(ZnSb6)2]4−: a new structure type for coupled norbornadiene-like subunits

The coupled norbornadiene-like dimer [(ZnSb₆)₂]⁴⁻ contains planar ZnSb₃ triangles and a new structure type for 14-atom clusters.

Development of Metal-Organic Framework for Gaseous Plant Hormone Encapsulation To Manage Ripening of Climacteric Produce

Controlled ripening of climacteric fruits, such as bananas and avocados, is a critical step to provide consumers with high-quality products while reducing postharvest losses. Prior to ripening, these fruits can be stored for an extended period of time but are usually not suitable for consumption. However, once ripening is initiated, they undergo irreversible changes that lead to rapid quality loss and decay if not consumed within a short window of time. Therefore, technologies to slow the ripening process after its onset or to stimulate ripening immediately before consumption are in high demand. In this study, we developed a solid porous metal-organic framework (MOF) to encapsulate gaseous ethylene for subsequent release. We evaluated the feasibility of this technology for on-demand stimulated ripening of bananas and avocados. Copper terephthalate (CuTPA) MOF was synthesized via a solvothermal method and loaded with ethylene gas. Its crystalline structure and chemical composition were characterized by X-ray diffraction crystallography, porosity by N2 and ethylene isotherms, and morphology by electron microscopy. The MOF loaded with ethylene (MOF-ethylene) was placed inside sealed containers with preclimacteric bananas and avocados and stored at 16 °C. The headspace gas composition and fruit color and texture were monitored periodically. Results showed that this CuTPA MOF is highly porous, with a total pore volume of 0.39 cm(3)/g. A 50 mg portion of MOF-ethylene can absorb and release up to 654 μL/L of ethylene in a 4 L container. MOF-ethylene significantly accelerated the ripening-related color and firmness changes of treated bananas and avocados. This result suggests that MOF-ethylene technology could be used for postharvest application to stimulate ripening just before the point of consumption.

Synthesis, Structure, and Properties of Al((R)bpy)3 Complexes (R = t-Bu, Me): Homoleptic Main-Group Tris-bipyridyl Compounds

The neutral homoleptic tris-bpy aluminum complexes Al((R)bpy)3, where R = tBu (1) or Me (2), have been synthesized from reactions between AlX precursors (X = Cl, Br) and neutral (R)bpy ligands through an aluminum disproportion process. The crystalline compounds have been characterized by single-crystal X-ray diffraction, electrochemical experiments, EPR, magnetic susceptibility, and density functional theory (DFT) studies. The collective data show that 1 and 2 contain Al(3+) metal centers coordinated by three bipyridine (bpy(•))(1-) monoanion radicals. Electrochemical studies show that six redox states are accessible from the neutral complexes, three oxidative and three reductive, that involve oxidation or reduction of the coordinated bpy ligands to give neutral (R)bpy or (R)bpy(2-) dianions, respectively. Magnetic susceptibility measurements (4-300 K) coupled with DFT studies show strong antiferromagnetic coupling of the three unpaired electrons located on the (R)bpy ligands to give S = (1)/2 ground states with low lying S = (3)/2 excited states that are populated above 110 K (1) and 80 K (2) in the solid-state. Complex 2 shows weak 3D magnetic interactions at 19 K, which is not observed in 1 or the related [Al(bpy)3] complex.

Elucidation of the Fe(III) Gallate Structure in Historical Iron Gall Ink

Synthetic, structural, spectroscopic and aging studies conclusively show that the main colorant of historical iron gall ink (IGI) is an amorphous form of Fe(III) gallate·xH2O (x = ∼1.5-3.2). Comparisons between experimental samples and historical documents, including an 18th century hand-written manuscript by George Washington, by IR and Raman spectroscopy, XRD, X-ray photoelectron spectroscopy, and Mössbauer spectroscopy confirm the relationship between the model and authentic samples. These studies settle controversy in the cultural heritage field, where an alternative structure for Fe(III) gallate has been commonly cited.

Synthesis, structure, and properties of a dialumane supported by pyrazolate ligands

The dialumane [Al2][Na(Ph2pz)3]2 () has been prepared by the reaction of Na(Ph2pz) with a metastable solution of AlCl. The structure of contains two hydrotris(pyrazolyl)borate-like Na(Ph2pz)3(2-) moieties that are coordinated to each Al atom of the dialumane in a κ(2),κ(1)-N,N,N fashion and several π-stacking interactions are present between the pyrazolate and phenyl rings. In solution the pyrazolate ligands in are in dynamic exchange, even at -80 °C, which shows the lability of these ligands to the low-valent aluminum centers.

Aluminium(III) amidinates formed from reactions of `AlCl' with lithium amidinates

The disproportionation of AlCl(THF)n (THF is tetrahydrofuran) in the presence of lithium amidinate species gives aluminium(III) amidinate complexes with partial or full chloride substitution. Three aluminium amidinate complexes formed during the reaction between aluminium monochloride and lithium amidinates are presented. The homoleptic complex tris(N,N'-diisopropylbenzimidamido)aluminium(III), [Al(C13H19N2)3] or Al{PhC[N(i-Pr)]2}3, (I), crystallizes from the same solution as the heteroleptic complex chloridobis(N,N'-diisopropylbenzimidamido)aluminium(III), [Al(C13H19N2)2Cl] or Al{PhC[N(i-Pr)]2}2Cl, (II). Both have two crystallographically independent molecules per asymmetric unit (Z' = 2) and (I) shows disorder in four of its N(i-Pr) groups. Changing the ligand substituent to the bulkier cyclohexyl allows the isolation of the partial THF solvate chloridobis(N,N'-dicyclohexylbenzimidamido)aluminium(III) tetrahydrofuran 0.675-solvate, [Al(C19H27N2)2Cl]·0.675C4H8O or Al[PhC(NCy)2]2Cl·0.675THF, (III). Despite having a twofold rotation axis running through its Al and Cl atoms, (III) has a similar molecular structure to that of (II).

Morphotropic phase boundaries in ferromagnets: Tb(1-x)Dy(x)Fe2 alloys

The structure and properties of the ferromagnet Tb(1-x)Dy(x)Fe(2) are explored through the morphotropic phase boundary (MPB) separating ferroic phases of differing symmetry. Our synchrotron data support a first order structural transition, with a broadening MPB width at higher temperatures. The optimal point for magnetomechanical applications is not centered on the MPB but lies on the rhombohedral side, where the high striction of the rhombohedral majority phase combines with the softened anisotropy of the MPB. We compare our findings with single ion crystal field theory and with ferroelectric MPBs, where the controlling energies are different.

Tetra-bromidobis(dicyclo-hexyl-phosphane-κP)digallium(Ga-Ga)

The title compound, a Ga^II dimer, [Ga₂Br₄(C₁₂H₂₃P)₂], was synthesized by reaction of GaBr(THF)_n (THF is tetra­hydro­furan) with dicyclo­hexyl­phosphine in toluene. At 150 K the crystallographically centrosymmetric molecule exhibits disorder in which one of the two independent cyclo­hexyl groups is modelled over two sites in a 62 (1):38 (1) ratio. In d₆-benzene solution, the compound exhibits virtual C_2h symmetry as determined by ¹H NMR. The coordination environment of the Ga^II atom is distorted tetrahedral.

Hydrothermal Synthesis of Vanadium Oxides

The pH of the reaction media is a critical factor in the formation of new vanadium oxides with the tetramethylammonium (TMA) ion via the conventional hydrothermal method. New vanadium oxides; TMAV3O7, Li0.6V2−δO4−δ·H2O and Li0.6V2−δO4−δ, TMAV4O10, and two more new vanadium phases with d spacings of 11.5Å and 19.1Å are formed as the pH is varied with acetic acid. The synthesis and characterization of TMAV3O7, a new vanadium oxide with tetramethylammonium ions residing between its layers is discussed. The intercalation of alkylamines, DMSO, and water into Li0.6V2−δO4−δ·H2O is described. Microwave hydrothermal synthesis is a new and alternate soft chemistry technique used to accelerate the synthesis of TMAV4O10. This method also aided in the formation of a new cluster compound, [Li(H2O)4]2TMA(V10O28)·4H2O.

The stabilization of layered Manganese Oxides for use in Rechargeable Lithium Batteries

The layered structure LixTiS2 and LixCoO2 are excellent reversible cathodes for lithium batteries. However, layered lithium manganese oxides are metastable relative to the spinel form on cycling in lithium batteries. They may be stabilized in the layer form by insertion of larger ions such as potassium in the interlayer region, which minimizes the diffusion of the manganese ions from the MnO2 blocks. Their low conductivity is an impediment to their use in high rate batteries. Cobalt can be doped into the layered alkali manganese dioxides, MxMn1-yCoyO2 for M = K or Na, during the hydrothermal synthesis from the alkali permanganates. A single phase is obtained up to about 5% mole cobalt. The cobalt doping is found to enhance the conductivity by two orders of magnitude relative to pure KxMnO2.

Anode Hosts for Lithium Batteries: Revisiting Tin and Aluminum

Pure tin reacts readily with four lithium atoms, and so is a prime candidate as the host for the anode of lithium batteries. Tin foil and an expanded tin grid (microporous tin) have a capacity of >600 mAh/g over more than 10 deep reaction cycles, indicating the inherent reversibility of tin anode. The microporous tin showed superior chemical capacity retention. Different phases are observed during the intercalation of lithium. Capacity loss was observed after 10 cycles though, consistent with the significant increase of the cell impedance. For comparison aluminum expanded grids were also examined as hosts, where LiAl is formed. Capacities approaching 1 Ah/g were obtained. LiBOB (lithium bis(oxalato)borate) was also studied as the electrolyte salt for comparison with the reactive and high cost LiPF6 salt.

Pericyclic reaction of a zwitterionic salt of an enedione-diazoester. A novel strategy for the synthesis of highly functionalized resorcinols

Enedione-diazoesters formed from 3-TBSO-2-diazo-3-butenoates undergo base-catalyzed pericyclization that with dinitrogen extrusion and methyl migration provide a novel and efficient route to 2-carboalkoxyresorcinols. Intercepting the intermediate enolate anion with methyl vinyl ketone leads to the corresponding 4-substituted 2-carboalkoxyresorcinol and suggests generalization of this methodology.

Structural and architectural evaluation of bimetallic nanoparticles: a case study of Pt-Ru core-shell and alloy nanoparticles

A comprehensive structural/architectural evaluation of the PtRu (1:1) alloy and Ru@Pt core-shell nanoparticles (NPs) provides spatially resolved structural information on sub-5 nm NPs. A combination of extended X-ray absorption fine structure (EXAFS), X-ray absorption near edge structure (XANES), pair distribution function (PDF) analyses, Debye function simulations of X-ray diffraction (XRD), and field emission transmission electron microscopy/energy dispersive spectroscopy (FE-TEM/EDS) analyses provides complementary information used to construct a detailed picture of the core/shell and alloy nanostructures. The 4.4 nm PtRu (1:1) alloys are crystalline homogeneous random alloys with little twinning in a typical face-centered cubic (fcc) cell. The Pt atoms are predominantly metallic, whereas the Ru atoms are partially oxidized and are presumably located on the NP surface. The 4.0 nm Ru@Pt NPs have highly distorted hcp Ru cores that are primarily in the metallic state but show little order beyond 8 A. In contrast, the 1-2 monolayer thick Pt shells are relatively crystalline but are slightly distorted (compressed) relative to bulk fcc Pt. The homo- and heterometallic coordination numbers and bond lengths are equal to those predicted by the model cluster structure, showing that the Ru and Pt metals remain phase-separated in the core and shell components and that the interface between the core and shell is quite normal.

Conformational isomers of extraordinary stability: carboxamidate-bridged dimetalloorganic compounds

Unprecedented non-interconvertable conformational isomers derived from cyclic amide ligands in a paddlewheel dimetallic framework are reported.

Solution dynamics and gas-phase chemistry of Pd2@Sn18 4-

Sn9(4-) reacts with Pd(PPh3)4 in ethylenediamine/toluene solvent mixtures in the presence of 2,2,2-cryptand to give the Pd2@Sn18(4-) cluster as the K(2,2,2,-crypt)+ salt. The cluster is isostructural with Pd2@Ge18(4-) and has a nuclearity different from that of the Pt and Ni analogues, Ni2@Sn17(4-) and Pt2@Sn17(4-). The Pd2@Sn18(4-) ion has a deltahedral capsulelike structure with 40 cluster bonding electrons and is the largest free-standing polystannide characterized to date. Like Pt2@Sn17(4-), the Pd2@Sn18(4-) complex is highly dynamic in solution, showing a single (119)Sn NMR resonance indicative of an intramolecular liquidlike dynamic exchange. LDI-MS studies of the crystalline sample show extensive fragmentation and the formation of five gas-phase cluster series: Sn(x)- (1 < x < 12), PdSn(x-1) - (4 < x < 18), Pd 2Sn(x-2) - (6 < x < 21), Pd3Sn(x-3) - (8 < x < 21), and Pd 4Sn(x-4) - (13 < x < 21). The most abundant ion in the gas phase is the PdSn(10) - cluster, which presumably has an Sn(10) bicapped-square-antiprismatic structure with an endohedral Pd (e.g., Ni@Pb(10)(2-)).

Cluster Growth and Fragmentation in the Highly Fluxional Platinum Derivatives of Sn94-: Synthesis, Characterization, and Solution Dynamics of Pt2@Sn174- and Pt@Sn9H3-

Sn94- reacts with Pt(PPh3)4 in ethylenediamine/toluene solvent mixtures in the presence of 2,2,2-cryptand to give four different complexes: "Rudolph's complex" of proposed formula [Sn9Pt(PPh3)x]4- (2), the previously reported [Pt@Sn9Pt(PPh3)]2- ion (3), and the title complexes Pt2@Sn174- (4) and Pt@Sn9H3- (5). The use of Pt(norbornene)3 instead of Pt(PPh3)4 gives complex 4 exclusively. The structure of 4 contains two Pt atoms centered in a capsule-shaped Sn17 cage. The complex is highly dynamic in solution showing single, mutually coupled 119Sn and 195Pt NMR resonances indicative of an intramolecular liquidlike dynamic exchange process. Complex 5 has been characterized by selectively decoupled 1H, 119Sn, and 195Pt NMR experiments and shows similar liquidlike fluxionality. In addition, the H atom scrambles across the cage showing small couplings to both Sn and Pt atoms. Neither 3 nor 4 obeys Wades rules; they adopt structures more akin to the subunits in alloys such as PtSn4. The structural and chemical relevance to supported PtSn4 heterogeneous catalysts is discussed.

Reversible Cation/Anion Extraction from K2La2Ti3O10: Formation of New Layered Titanates, KLa2Ti3O9.5 and La2Ti3O9

A new soft-chemical transformation of layered perovskite oxides is described wherein K2O is sequentially extracted from the Ruddlesden-Popper (R-P) phase, K2La2Ti3O10 (I), yielding novel anion-deficient KLa2Ti3O(9.5) (II) and La2Ti3O9 (III). The transformation occurs in topochemical reactions of the R-P phase I with PPh4Br and PBu4Br (Ph = phenyl; Bu = n-butyl). The mechanism involves the elimination of KBr accompanied by decomposition of PR4+ (R = phenyl or n-butyl) that extracts oxygen from the titanate. Analysis of the organic products of decomposition reveals formation of Ph3PO, Ph3P, and Ph-Ph for R = phenyl, and Bu3PO, Bu3P along with butane, butene, and octane for R = butyl. The inorganic oxides II and III crystallize in tetragonal structures (II: P4/mmm, a = 3.8335(1) A, c = 14.334(1) A; III: I4/mmm, a = 3.8565(2) A, c = 24.645(2) A) that are related to the parent R-P phase. II is isotypic with the Dion-Jacobson phase, RbSr2Nb3O10, while III is a unique layered oxide consisting of charge-neutral La2Ti3O9 anion-deficient perovskite sheets stacked one over the other without interlayer cations. Interestingly, both II and III convert back to the parent R-P phase in a reaction with KNO3. While transformations of the R-P phases to other related layered/three-dimensional perovskite oxides in ion-exchange/metathesis/dehydration/reduction reactions are known, the simultaneous and reversible extraction of both cations and anions in the conversions K2La2Ti3O10 right harpoon over left harpoon KLa2Ti3O9.5 right harpoon over left harpoon La2Ti3O9 is reported here for the first time.