Hafnium oxide-based thin films, in particular hafnium zirconium oxide (HZO), have potential for applications in nonvolatile memory and energy harvesting. Atomic layer deposition (ALD) is the most widely used method for HZO deposition due to its precise thickness control and ability to provide conformal coverage. Previous studies have shown the effects of different metal precursors, oxidizer precursors, and process temperatures on the ferroelectric properties of HZO. However, no mechanism has been identified to describe the different phase stabilities as the metal precursor purge time varies. This study investigates how varying the metal precursor purge time during plasma-enhanced ALD (PE-ALD) influences the phases and properties of the HZO thin films. Grazing incidence X-ray diffraction, Fourier transform infrared spectroscopy, and scanning transmission electron microscopy are used to study the changes in phase of HZO with variation of the metal precursor purge time during the PE-ALD process. The phases observed are correlated with polarization and relative permittivity responses under an electric field, including wake-up and endurance effects. The resulting phases and properties are linked to changes in composition, as measured using time-of-flight secondary ion mass spectrometry and X-ray photoelectron spectroscopy. It is shown that short metal precursor purge times result in increased carbon and nitrogen impurities and stabilization of the antipolar Pbca phase. Long purge times lead to films comprising predominantly the ferroelectric Pca2₁ phase.

Boron–phosphorus (B–P) frustrated Lewis pairs (FLPs) are an important class of compounds for activating various small molecules. Utilizing the ring expansion reactivity of 9-chloro-9-borafluorene, a borinine-based FLP was synthesized. Various five-membered main-group element heterocycles were obtained via the reaction of the FLP with Me₃NO, S₈, and Se. Subsequent reduction of these species yielded the ring-expanded compounds, each featuring bridging B–E–B (E = O, S, Se) bonds. Similarly, halide abstraction from the FLP with AgNTf₂ led to the formation of a cationic ring-expanded compound with a bridging B–Cl–B motif. This motif constitutes one of the first examples of a boron-stabilized chloronium ion, as verified using in-depth bonding analysis methods. Mechanistic pathways for the reduction- and halide abstraction-mediated ring expansion reactions are proposed with the aid of density functional theory. Electronic structure computations were performed to determine the best representation of bonding interactions in each compound, suggesting phosophorus(V)–chalcogen double bonding and chalcogen–boron(III) dative interactions within the heterocycles.

The bis-acetate complexes (SbQ₃)Pt(OAc)₂ (1) and (SbQ₂Ph)Pt(OAc)₂ (2) (Q = 8-quinolinyl) were used to study C–Cl acetoxylation of 1,2-dichloroethane (DCE) to generate 2-chloroethyl acetate and the complexes (SbQ₃)PtCl₂ (1b) and (SbQ₂Ph)PtCl₂ (2b), respectively. The first acetoxylation step produced the intermediates (SbQ₃)Pt(Cl)(OAc) (1a) and (SbQ₂Ph)Pt(Cl)(OAc) (2a). The reaction was studied using pseudo first order kinetics (excess DCE) in order to compare the rates of reaction of 1 and 2, which revealed that k_obs = 2.44(6) × 10^–4 s^–1 for 1 and 0.51(2) × 10^–4 s^–1 for 2. The intermediate 1a was synthesized independently, and the solid-state structure was determined using single crystal X-ray diffraction. A non-Sb containing control complex, (^tbpy)Pt(OAc)₂ (3) (^tbpy = 4,4′-di-tert-butyl-2,2′bipyridine), was studied for the acetoxylation of DCE to form (^tbpy)Pt(Cl)(OAc) with k_obs = 0.46(1) × 10^–4 s^–1. Density Functional Theory (DFT) calculations were used to examine possible Pt-mediated mechanisms for the reactions of 1, 2, or 3 with DCE. The lowest energy calculated substitution mechanism occurs with nucleophilic attack by the Pt center on the C−Cl bond followed acetate reaction with the Pt−C bond. However, close in energy and potentially also a viable mechanism is a direct substitution mechanism where the coordinated acetate anion directly reacts with the C−Cl bond of DCE. In addition, the rate of acetoxylation for complex 1 in heated dichloromethane-d₂ and chloroform-d was determined (0.43(1) × 10^–4 s^–1 for dichloromethane-d₂ and 0.37(1) × 10^–4 s^–1 for chloroform-d) and compared to the rate of acetoxylation of DCE.

Reaction of copper(II) bromide with 3,5-di­chloro­pyridine (3,5-Cl₂py) or 3,5-di­methyl­pyridine (3,5-Me₂py) led to the isolation of the coordination polymers catena-poly[[bis­(3,5-di­chloro­pyridine)­copper(II)]-di-μ-bromido], [CuBr₂(C₅H₃Cl₂N)₂]_n or [CuBr₂(3,5-Cl₂py)₂]_n (1), and catena-poly[[bis­(3,5-di­methyl­pyridine)­copper(II)]-di-μ-bromido], [CuBr₂(C₇H₉N)₂]_n or [CuBr₂(3,5-Me₂py)₂]_n (2), respectively. The structures are characterized by bibromide-bridged chains [d(av.)_Cu⋯Cu = 3.93 (9) Å]. In 1, the chains are linked perpendicular to the a axis by non-classical hydrogen bonds and halogen bonds, while in 2, only non-classical hydrogen bonds are observed.

The reaction of CAAC-CS₂ betaine (1; CAAC = cyclic(alkyl)(amino)carbene) and alkali metal reductants under ambient conditions yields carbene-stabilized carbon disulfide radical anions as crystalline alkali metal salts. The radicals 3–5 form multinuclear clusters featuring diverse metal sulfide and disulfide interactions, which promote unusual reductive coupling and cyclization of adjacent CS₂ units to C₂S₃ heterocycles (6). The addition of crown ethers to 3–5 sequesters the alkali cations and facilitates disulfide cleavage to yield stable [CAAC-CS₂]^·– monomers (7 and 8). Calculated natural atomic spin populations suggest that the spin densities in the clustered and monomeric species are comparable and evenly distributed between the CAAC and CS₂ subunits. Subsequent reductions afford [CAAC-CS₂]^2– dianions (9–12), which can be reoxidized to radicals by comproportionation reactions with 1. The radicals are, in turn, oxidized to betaine 1 through salt elimination reactions with transition metals. Cyclic voltammograms of 1 feature reversible 1/1^·–/1^2– couples with a small separation between the events (ΔΔG = 11.1 kcal mol^–1). All isolated compounds were characterized by a combination of electron paramagnetic resonance spectroscopy, heteronuclear NMR spectroscopy, infrared spectroscopy, and single-crystal X-ray diffraction. Insights into their electronic structure are supported by density functional theory calculations.

Two-dimensional hybrid organic–inorganic perovskites (HOIPs) have emerged as promising materials for light-emitting diode applications. In this study, by using time-of-flight neutron spectroscopy we identified and quantitatively separated the lattice vibrational and molecular rotational dynamics of two perovskites, butylammonium lead iodide (BA)₂PbI₄ and phenethyl-ammonium lead iodide (PEA)₂PbI₄. By examining the corresponding temperature dependence, we found that the lattice vibrations, as evidenced by neutron spectra, are consistent with the lattice dynamics obtained from Raman scattering. We revealed that the rotational dynamics of organic molecules in these materials tend to suppress their photoluminescence quantum yield (PLQY) while the vibrational dynamics did not show predominant correlations with the same. Additionally, we observed photoluminescence emission peak splitting for both systems, which becomes prominent above certain critical temperatures where the suppression of PLQY begins. This study suggests that the rotational motions of polarized molecules may lead to a reduction in exciton binding energy or the breaking of degeneracy in exciton binding energy levels, enhancing non-radiative recombination rates, and consequently reducing photoluminescence yield. These findings offer a deeper understanding of fundamental interactions in 2D HOIPs and could guide the design of more efficient light-emitting materials for advanced technological applications.

Two copper(II) complexes of 2,3,5,6-tetramethylpyrazine (tmpz) are reported, [Cu(tmpz)Cl₂]n (1), and [Cu(tmpz)Br₂]n (2). The compounds crystallize in the monoclinic space group C2/m as pyrazine-bridged linear chains (parallel to the b-axis). The pyrazine rings are oriented nearly perpendicular to the CuN₂X₂ coordination planes. Adjacent chains parallel to the a-axis are offset by ½ unit cell translation parallel to the b-axis rendering the closest interchain X…X contact distance to be 4.83(2) Å (1) or 4.59(1) Å (2). Parallel to the c-axis, the chains are further separated by the methyl groups. Magnetic interactions for 2 are well fit by the uniform Heisenberg chain model with a Curie-Weiss correction for interchain interactions giving: J/k_B = −19.2(1) K, Curie constant (CC) = 0.451(1) emu-K/mol-Oe and θ = −0.18(1) K.

Five new copper(II) complexes of substituted quinoxaline ligands have been prepared and characterized via single crystal X-ray diffraction, including [Cu(5-Mequinox)₂(NO₃)₂] (2), [Cu(5-Mequinox)(NO₃)(H₂O)(μ-1,3-NO₃)]_n (3), the chloride salt (5-MequinoxH)₂[Cu₃Cl₈] (4), the complex [Cu(6-Mequinox)₂(NO₃)₂] (5) and [(2-carboxylato-3-methylquinox)(2-hydroxymethyl-3-methylquinox)nitratocopper(II)]. CH₃CN (6) [quinox = quinoxaline; 5-Mequinox = 5-methylquinoxaline; 6-Mequinox = 6-methylquinoxaline]. None of the complexes produced diazine bridged chain structures (as seen in [(quinox)Cu(NO₃)₂]_n (1)), although 3 forms chains via a bridging nitrate ion. Crystal packing is controlled primarily through hydrogen bonding and π-stacking of nitrate ions. The temperature dependent magnetic susceptibility data of the parent compound [(quinox)Cu(NO₃)₂]_n are also reported and discussed.

Main-group element-mediated C–H activation remains experimentally challenging, and the development of clear concepts and design principles have been limited by the increased reactivity of relevant complexes, especially for the heavier elements. Herein, we report that the stibenium ion [(pyCDC)Sb][NTf2]3 (1) (pyCDC = bis-pyridyl carbodicarbene; NTf2 = bis(trifluoromethanesulfonyl)imide) reacts with acetonitrile in the presence of the base 2,6-di-tert­-butylpyridine to enable C(sp3)–H bond breaking to generate the stiba-methylene nitrile complex [(pyCDC)Sb(CH2CN)][NTf2]2 (2). Kinetic analyses were performed to elucidate the rate dependence for all the substrates involved in the reaction. Computational studies suggest that C–H activation proceeds via a mechanism in which acetonitrile first coordinates to the Sb center through the nitrogen atom in a κ1 fashion, thereby weakening the C–H bond which can then be deprotonated by base in solution. Further, we show that 1 reacts with terminal alkynes in the presence of 2,6-di-tert­-butylpyridine to enable C(sp)–H bond breaking to form stiba-alkynyl adducts of the type [(pyCDC)Sb(CCR)][NTf2]2 (3a-f). Compound 1 shows excellent specificity for the activation of the terminal C(sp)–H bond even across alkynes with diverse functionality. The resulting stiba-methylene nitrile and stiba-alkynyl adducts react with elemental iodine (I2) to produce iodoacetonitrile and iodoalkynes, while regenerating an Sb trication.

Five synthetically tunable Co(II) salts with the general formula (2-amino-5-iodopyridinium)₂[Co(II)Cl_4-xBr_x] have been prepared: (1, (2-amino-5-iodopyridinium)₂[CoCl₄]·H₂O 2, (2-amino-5-iodopyridinium)₂[CoCl_4-xBr_x]·H₂O (x = 0.542) 3, (2-amino-5-iodopyridinium)₂[CoCl_4-xBr_x]·H₂O (x = 2.34) 4, (2-amino-5-iodopyridinium)₂[CoCl_4-xBr_x]·H₂O (x = 3.47) 5, and (2-amino-5-iodopyridinium)₂[CoBr₄]·H₂O). All compounds crystallize in the space group P2₁/c. Controlling the amount of each halide ion introduced into the reaction mixture can control the relative amounts of chloride and bromide in the products; variable temperature magnetic susceptibility data indicate the presence of single-ion anisotropy in all compounds. In addition, increasing amounts of bromide ion in the samples lead to measurable antiferromagnetic interactions. Additionally, we find that changing the relative amounts of chloride ion and bromide ion changes the anisotropy of the compound.