A family of oxygen coordinated dichlorido-bridged n-X-2-pyridone (1, n = 3, X = Cl; 2, n = 3, X = Br; 3, n = 4, X = Cl; 4, n = 4, X = Br; 5, n = 5, X = Cl; 6, n = 5, X = Br) Cu(II) offset stacked dimer compounds, denoted molecular spin stairs, have been prepared and analyzed by single-crystal X-ray diffraction (1–4), powder X-ray diffraction (1–6), and variable temperature magnetic susceptibility measurements (1–6). Ferromagnetism is dominant in all compounds with a weaker antiferromagnetic exchange present in 1–4. The ferromagnetic exchange correlates to increased twist angles which are defined by the extent of the tetrahedral distortion of the copper coordination sphere and the identity of the halogen on the ring. The compounds were qualitatively fit to a ferromagnetic Heisenberg chain model with a Curie-Weiss interchain correction. The general Hamiltonian used is of the form  H=−J∑S1S2. The ratio of exchange energies denoted α (α=JFM|JAFM|) ranges between 2.6 and 4.7. This family of compounds constitutes possible S = ½ Haldane-like materials.

Fe(II) carboxylates react with dioxygen and carboxylic acid to form Fe₆(μ–OH)₂(μ₃–O)₂(μ–X)₁₂(HX)₂ (X = acetate or pivalate), which is an active oxidant for Rh-catalyzed arene alkenylation. Heating (150–200 °C) the catalyst precursor [(η²–C₂H₄)₂Rh(μ–OAc)]₂ with ethylene, benzene, Fe(II) carboxylate, and dioxygen yields styrene >30-fold faster than the reaction with dioxygen in the absence of the Fe(II) carboxylate additive. It is also demonstrated that Fe₆(μ–OH)₂(μ₃–O)₂(μ–X)₁₂(HX)₂ is an active oxidant under anaerobic conditions, and the reduced material can be reoxidized to Fe₆(μ–OH)₂(μ₃–O)₂(μ–X)₁₂(HX)₂ by dioxygen. At optimized conditions, a turnover frequency of ∼0.2 s^–1 is achieved. Unlike analogous reactions with Cu(II) carboxylate oxidants, which undergo stoichiometric Cu(II)-mediated production of phenyl esters (e.g., phenyl acetate) as side products at temperatures ≥150 °C, no phenyl ester side product is observed when Fe carboxylate additives are used. Kinetic isotope effect experiments using C₆H₆ and C₆D₆ give k_H/k_D = 3.5(3), while the use of protio or monodeutero pivalic acid reveals a small KIE with k_H/k_D = 1.19(2). First-order dependencies on Fe(II) carboxylate and dioxygen concentration are observed in addition to complicated kinetic dependencies on the concentration of carboxylic acid and ethylene, both of which inhibit the reaction rate at a high concentration. Mechanistic studies are consistent with irreversible benzene C–H activation, ethylene insertion into the formed Rh–Ph bond, β–hydride elimination, and reaction of Rh–H with Fe₆(μ–OH)₂(μ₃–O)₂(μ–X)₁₂(HX)₂ to regenerate a Rh-carboxylate complex.

The syntheses and structures of 2-(aminomethyl)aniline (2-AMAn) complexes of CuX₂ and ZnX₂ (X = Cl, Br) are reported: [(2-AMAn)ZnCl₂] (1), [(2-AMAn)ZnBr₂] (2), [(2-AMAn)₂ZnCl₂] (3), [(2-AMAn)₂ZnBr₂] (4), [(2-AMAn)₂CuCl]Cl (5) and [(2-AMAn)₂Cu(H₂O)₂]Br₂ (6). Compounds 1 and 2 are isomorphous and crystallize in the monoclinic space group Ia with two coordinated halide ions and one chelating 2-AMAn ligand. Compounds 3 and 4 are also isomorphous and crystallize in the monoclinic space group P2₁/n with two monodentate 2-AMAn ligands and two coordinated halide ions. All four Zn(II) complexes are slightly distorted tetrahedral in geometry. The Cu(II) complexes are structurally distinct from the Zn(II) complexes. 5 crystallizes in the monoclinic space group P2₁/n and is strongly distorted square pyramidal in geometry with two chelating 2-AMAn ligands, one coordinated chloride ion and one dissociated chloride ion. The bromide compound, 6, crystallizes in the monoclinic space group P2₁/c, also with two chelating 2-AMAn ligands, but with two coordinated water molecules and both bromide ions dissociated in the lattice.

We report the synthesis and characterization of a series of BNP-incorporated borafluorenate heterocycles formed via thermolysis reactions of pyridylphosphine and bis(phosphine)-coordinated borafluorene azides. The use of diphenyl-2-pyridylphosphine (PyPh₂P), trans-1,2-bis(diphenylphosphino)ethylene (Ph₂P(H)C═C(H)PPh₂), and bis(diphenylphosphino)methane (Ph₂PC(H₂)PPh₂) as stabilizing ligands resulted in Staudinger reactions to form complex heterocycles with four- (BN₂P, BNPC, P₂N₂) and five-membered (BNP₂C and BN₂PC) rings, which were successfully isolated and fully characterized by multinuclear NMR and X-ray crystallography. However, when bis(diphenylphosphino)benzene (Ph₂P-Ph-PPh₂) was used as the ligand in a reaction with 9-bromo-9-borafluorene (BF-Br), due to the close proximity of the donor P atoms, the diphosphine-stabilized borafluoronium ion with an unusual borafluorene dibromide anion was formed. Reaction of the borafluoronium ion with trimethylsilyl azide left the cation intact, and the dibromide anion was substituted by a diazide. Density functional theory calculations were used to provide mechanistic insight into the formation of these new boracyclic compounds. This work highlights a new method in which donor phosphine ligands may be used to promote dimerization, cyclization, and ring contraction reactions to produce boracycles via Staudinger reactions.

Four new copper compounds of 2-amino-5-nitropyridine/pyridinium (5NAP/5NAPH) have been prepared and characterized: (5NAPH)₂[CuBr₄], 2; (d₂-5NAPD)₂[CuBr₄], 2a; (5NAP)₂CuCl₂, 3; (5NAP)₂CuBr₂, 4. Compounds 2 and 2a are isomorphous and crystallize in the triclinic space group P-1. Packing is stabilized by hydrogen/deuterium bonds. Short Br…Br contacts provide potential magnetic superexchange pathways, but only very weak antiferromagnetic exchange is observed (J/k_B∼-2 K). Compounds 3 and 4 are also isomorphous and crystallize in the monoclinic space group P2₁/c. The molecules are linked into chains by bihalide bridges, and the chains linked into rectangular/square layers by short X…X. contacts. Variable temperature magnetic data were best fit by the S = ½ antiferromagnetic rectangular model for 3 (C = 0.429(1) emu-K/mol-Oe, J/k_B = −9.38(6) K, J’/k_B = −5.91(4) K). Variable temperature magnetic susceptibility data for 4 were best fit by the two-dimensional antiferromagnetic square lattice model (C = 0.43(1) emu-K/mol-Oe, J/k_B = −36.5(2) K).

Using the Cambridge Structural Database along with the analysis and visualization programs provided by the Cambridge Crystallographic Data Centre, we identified three organic small molecules with good diffraction data but poorly refined (R₁ > 40%) structures. These structures were used as teaching examples in an introductory chemical crystallography course for an activity in which students were asked to identify the errors in the original structure solution or refinement processes. The structures were redetermined, yielding R₁ values between 4.04 and 7.04%. In two cases, two chemically equivalent but crystallographically distinct molecules were found in the asymmetric unit, only one of which had been refined in each of the originally published CIFs. In the third case, a false solution found by SHELXS direct methods was corrected and the structure was refined as a hydrated tautomer of what had been originally reported. The identification of this tautomer was supported by theoretical calculations.

${\mathrm{CrI}}_2$ is a van der Waals layered material that exhibits helimagnetism that propagates along ribbon chains. This is determined from neutron time-of-flight diffraction measurements. Below $T_N=17$ K in the orthorhombic structure, a screwlike helimagnetic order develops with an incommensurate wave vector of $q\approx (0.2492,0,0)$ at 8 K. Using density functional theory ($\mathrm{DFT})+U$ calculations, the $J_1\text{−}{J}_2$ model is leveraged to describe the helimagnetism, where $J_1(>0)$ and $J_2(<0)$ correspond, respectively, to a ferromagnetic nearest-neighbor and antiferromagnetic next-nearest-neighbor intrachain interaction. The $\mathrm{DFT}+U$ calculations suggest that orthorhombic ${\mathrm{CrI}}_2$ satisfies conditions that favor formation of helimagnetic order.

The Dirac magnon system ${\mathrm{CrI}}_3$ with a honeycomb lattice is a potential host of topological edge magnons. It ideally orders ferromagnetically (FM) $(T_c=61K)$ on cooling from a monoclinic (M) to a rhombohedral (R) phase, but antiferromagnetic (AFM) order has been detected in nanometer thin flakes, attributed to M-type layer stacking. There remains confusion, however, as to the extent to which such behavior is present in bulk samples. Using a powder sample in which the sliding transition to the R phase was largely inhibited (2:1 M:R ratio), clear evidence for M-type AFM order $(T_N\sim 50K)$ coexisting with R-type FM order is observed in the bulk. From inelastic neutron scattering, a lower magnon energy is observed compared to the R phase, consistent with smaller interlayer interactions expected in the M phase. While a gap at the Dirac points has been reported in the R phase, the gap is clearly observed even when the majority is M type, as in our sample, suggesting that the same nontrivial magnon topology of the R phase is present in the M phase as well.

For nearly a century, chemists have explored how transition-metal complexes can affect the physical and chemical properties of linear conjugated polyenes and heteropolyenes. While much has been written about higher hapticity complexes (η⁴–η⁶), less is known about the chemistry of their η² analogues. Herein, we describe a general method for synthesizing 5,6-η²-(1-azatriene) tungsten complexes via a 6π-azaelectrocyclic dihydropyridine ring-opening that is promoted by the π-basic nature of {WTp(NO)(PMe₃)}. This study includes detailed spectroscopic and crystallographic data for the η²-dihydropyridine and η²-1-azatriene complexes, both of which were prepared as single regio- and stereoisomers.

Carbon fiber (CF) is a versatile material renowned for its excellent mechanical, thermal, and electrical properties. Polyacrylonitrile (PAN)-based CFs dominate the market due to their high tensile strength, rendering them suitable for structural applications in a wide variety of applications ranging from sporting goods to aerospace. Over five decades of commercial development of PAN-based CF has resulted in a range of varieties with different tensile moduli and tensile strengths. The microstructures, nanostructures, and crystal structures of PAN-based CF play pivotal roles in the macroscale properties of this material. In particular, the crystal structure and crystallite orientation in CF is closely related to the mechanical properties. The crystal structure of PAN-based CF generally consists of turbostratic carbon, which is a disordered form of graphite, the characteristics of which can be effectively characterized in a bulk format through wide-angle x-ray diffraction (WAXD). In this work, we employed a three-part approach to the analysis of WAXD patterns collected from four intermediate modulus PAN-based CFs. The approach incorporates a Scherrer analysis, a Debye analysis, and an orientational analysis to provide precise estimates of crystallite sizes, crystallite distributions, and crystallite orientations with the fiber axis. The results presented here suggest that intermediate modulus PAN-based CF mostly consists of small turbostratic crystallites (<4 nm), with larger crystallites having increased orientation with the fiber axis. The results here imply the presence of curvature and/or wrinkling of the turbostratic layers within the CF structure.