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A spatiotemporal experimental route is reported for the antisolvent vapor diffusion crystal growth of metal halide perovskitoids. A computational analysis combining automated image capture and diffusion modeling enables the determination of the critical concentrations required for nucleation and crystal growth from a single experiment. Five different solvent systems and ten distinct organic ammonium iodide salts were investigated with lead iodide, from which nine previously unreported compounds were discovered. Automated image capture of the mother liquor and antisolvent vials was used to determine changes in solution meniscus positions and detect the nucleation event location. Matching the observations to a numerical solution of Fick's second law diffusion model enables the calculation of reactant, solvent, and antisolvent concentrations at both the time and position of the first stable nucleation and crystal growth. A machine learning model was trained on the resulting data, and it reveals solvent- and amine-specific crystallization tendencies. Solvent systems that interact more weakly with dissolved lead species promote crystallization, while those with stronger interactions can prevent crystallization through increased solubilities. Organic amines that interact more strongly with inorganic components and exhibit greater rigidity are more likely to be incorporated into crystalline products.

Metal halide perovskite (MHP) derivatives, a promising class of optoelectronic materials, have been synthesized with a range of dimensionalities that govern their optoelectronic properties and determine their applications. We demonstrate a data-driven approach combining active learning and high-throughput experimentation to discover, control, and understand the formation of phases with different dimensionalities in the morpholinium (morph) lead iodide system. Using a robot-assisted workflow, we synthesized and characterized two novel MHP derivatives that have distinct optical properties: a one-dimensional (1D) morphPbI3 phase ([C4H10NO][PbI3]) and a two-dimensional (2D) (morph)2PbI4 phase ([C4H10NO]2[PbI4]). To efficiently acquire the data needed to construct a machine learning (ML) model of the reaction conditions where the 1D and 2D phases are formed, data acquisition was guided by a diverse-mini-batch-sampling active learning algorithm, using prediction confidence as a stopping criterion. Querying the ML model uncovered the reaction parameters that have the most significant effects on dimensionality control. Based on these insights, we discuss possible reaction schemes that may selectively promote the formation of morph-Pb-I phases with different dimensionalities. The data-driven approach presented here, including the use of additives to manipulate dimensionality, will be valuable for controlling the crystallization of a range of materials over large reaction-composition spaces.

C-Nitroso compounds (RNO, R = alkyl and aryl) are byproducts of drug metabolism and bind to heme proteins, and their heme-RNO adducts are isoelectronic to ferrous nitroxyl (NO−/HNO) complexes. Importantly, heme-HNO compounds are key intermediates in the reduction of NO to N2O and nitrite to ammonium in the nitrogen cycle. Ferrous heme-RNO complexes act as stable analogs of these species, potentially allowing for the investigation of the vibrational and electronic properties of unstable heme-HNO intermediates. In this paper, a series of six-coordinate ferrous heme-RNO complexes (where R = iPr and Ph) were prepared using the TPP2− and 3,5-Me-BAFP2− co-ligands, and tetrahydrofuran, pyridine, and 1-methylimidazole as the axial ligands (bound trans to RNO). These complexes were characterized using different spectroscopic methods and X-ray crystallography. The complex [Fe(TPP)(THF)(iPrNO)] was further utilized for nuclear resonance vibrational spectroscopy (NRVS), allowing for the detailed assignment of the Fe–N(R)O vibrations of a heme-RNO complex for the first time. The vibrational properties of these species were then correlated with those of their HNO analogs, using DFT calculations. Our studies support previous findings that RNO ligands in ferrous heme complexes do not elicit a significant trans effect. In addition, the complexes are air-stable, and do not show any reactivity of their RNO ligands towards NO. So although ferrous heme-RNO complexes are suitable structural and electronic models for their HNO analogs, they are unsuitable to model the reactivity of heme-HNO complexes. We further investigated the reaction of our heme-RNO complexes with different Lewis acids. Here, [Fe(TPP)(THF)(iPrNO)] was found to be unreactive towards Lewis acids. In contrast, [Fe(3,5-Me-BAFP)(iPrNO)2] is reactive towards all of the Lewis acids investigated here, but in most cases the iron center is simply oxidized, resulting in the loss of the iPrNO ligand. In the case of the Lewis acid B2(pin)2, the reduced product [Fe(3,5-Me-BAFP)(iPrNH2)(iPrNO)] was identified by X-ray crystallography. [ABSTRACT FROM AUTHOR]

The interaction of the tetracyanoethylene (TCNE) π-acceptor with oxo- and fluoro-anions (BF4−, PF6−, ClO4−, NO3−) led to the formation of anion–π complexes in which these polyatomic anions were located over the face of alkenes, with multiple contacts being shorter than the van der Waals separations. The anion–π associations of TCNE with halides were delimited by the electron-donor strengths and nucleophilicity of the anions. Specifically, while bromides formed persistent anion–π associations with TCNE in the solid state and in solutions, only transient anion–π complexes with iodides and chlorides were observed. In the case of iodide (strong 1e reducing agent), the formation of anion–π complexes was followed by the reduction of the π-acceptor to the TCNE−˙ anion-radical. The interaction of TCNE with Cl− (and F−) anions (which are better nucleophiles in the aprotic solvents) led to the formation of 1,1,2,3,3-pentacyanoprop-2-en-1-ide anions. Thermodynamics, UV-Vis spectra, and structures, as well as contributions of electrostatics, orbital interactions, and dispersion to the interaction energies in the complexes of TCNE with various anions were closely related to the characteristics of the corresponding associations with the aromatic and p-benzoquinone acceptors. This points out the general equivalence of the interactions in the anion–π complexes with different π-acceptors and the critical role of the nature of the anions in these bindings. [ABSTRACT FROM AUTHOR]

Nominally, meso-hydroxyoxochlorins, like known 5-hydroxy-7-oxo-octaethylchlorin (9), its nickel complex [5-hydroxy-7-oxo-octaethylchlorinato]nickel(II) (9Ni), or the novel 5-hydroxy-7,17-dioxo-octaethylbacteriochlorin (10), incorporate an acetylacetonate (acac)-moiety in the enol form in their chromophore structures. X-Ray diffraction studies of the compounds show the presence of a strong H-bond between the enol and flanking β-ketone. Like acac, the functionality can be deprotonated. However, unlike regular acac-like moieties, we did not find any indication that this functionality is competent in chelating any of the 3d or 4d transition metal ions tested. Evidently, the conjugation that contributes to the stability of acac as a ligand cannot be expressed in the meso-hydroxyoxochlorins since it would perturb the aromaticity of the porphyrinic chromophores; in other words, the metal binding energies do not offset the loss in aromaticity. The halochromic properties of the molecules provide some more insight into the location of the protonation/deprotonation sites. The interpretation of the findings is supported by computations. [ABSTRACT FROM AUTHOR]

Macrocyclisation of the upper-rim distal disubstituted bromomethylene calix[4]arene derivative proceeds spontaneously on a silica gel due to the spatial proximity of two reaction centers, affording the formation of a bridged calixarene derivative. Due to the short span of the bridge, the product represents an extreme example of calix[4]arenes fixed in the pinched cone conformation with two aromatic rings steeply inclined into the center of the calixarene cavity. Dynamic NMR spectroscopy was used to investigate the temperature-dependent rocking motion of the bridgehead and thermochemical parameters of this motion were determined experimentally, as well as estimated using computational methods. Mass spectrometry was employed to study the upper rim macrocyclization reaction in the gas phase. [ABSTRACT FROM AUTHOR]

4-Nitroquinoline-N-oxide (NQO) and 4-nitropyridine-N-oxide (NPO) are important precursors for the synthesis of substituted heterocycles while NQO is a popular model mutagen and carcinogen broadly used in cancer research; intermolecular interactions are critical for their reactions or functioning in vivo. Herein, the effects of the coordination of N-oxide's oxygen atom to Lewis acids on multicenter donor–acceptor bonding were explored via a combination of experimental and computational studies of the complexes of NQO and NPO with a typical π-electron donor, pyrene. Coordination with ZnCl2 increased the positive electrostatic potentials on the surfaces of these π-acceptors and lowered the energy of their LUMO. Analogous effects were observed upon the protonation of the N-oxides' oxygen or bonding with boron trifluoride. The interaction of ZnCl2, NPO, or NQO and pyrene resulted in the formation of dark co-crystals comprising π-stacked Zn-coordinated N-oxides and pyrene similar to that found with protonated or (reported earlier) BF3-bonded N-oxides. Computational studies indicated that the coordination of N-oxides to zinc(II), BF3, or protonation led to the strengthening of the multicenter bonding of the nitro-heterocycle with pyrene, and this effect was related both to the increased electrostatic attraction and molecular–orbital interactions in their complexes. [ABSTRACT FROM AUTHOR]

An NMR-guided procedure for refining crystal structures has recently been introduced and shown to produce unusually high resolution structures. Herein, this procedure, is modified to include 15N shift tensors instead of the 13C values employed previously. This refinement involves six benchmark structures and 45 15N tensors. All refined structures show a statistically significant improvement in NMR fit over energy based refinements. Metrics other than NMR agreement indicate that NMR refinement does not introduce errors with no significant changes observed in atom positions or diffraction patterns. However, refinement does change bond lengths by more than experimental uncertainty with most bond types become shorter than diffraction values. Although this decrease is small (1–4 pm), it significantly alters computed 15N tensors. The NMR refinement was further evaluated by refining two tripeptides. These structures rapidly converged and achieved an NMR agreement equivalent to benchmark values. To ensure accurate comparisons, a complete atomic structure of the tripeptide AGG was determined by single crystal neutron diffraction at 0.58 Å resolution, allowing unambiguous determination of all hydrogen positions. To verify that all NMR refinements represent genuine improvements rather than artifacts of DFT methods, an independent approach was included to evaluate the final NMR refined coordinates. This analysis employs cluster methods and the PBE0 functional. The unusually small 15N NMR root-mean-square error of the final refined structures (3.6 ppm) supports the conclusion that the changes made represent improvements over both diffraction coordinates and lattice-including DFT energy refined coordinates. [ABSTRACT FROM AUTHOR]

This laboratory experiment demonstrates the important utility of transition-metal complexes as catalysts in the addition reaction of carbon tetrabromide (CBr ) to select alkenes. This application offers students the opportunity to understand why transition-metal complexes are worth synthesizing. The experiment builds on fundamental theories presented during first-year general chemistry courses and integrates concepts taught in organic chemistry, inorganic chemistry, organometallics, and instrumental analysis. It incorporates some advanced laboratory practices for students to assimilate with, such as literature searches and interpretation; organometallic compound analysis; catalysis experiment design; reaction mechanisms; NMR spectroscopy with comprehensive spectra interpretation; and X-ray crystallography.

Np(IV) Lewis base adducts were prepared by ligand substitution of NpCl4(DME)2. Using acetonitrile and pyridine, NpCl4(MeCN)4 (1) and NpCl4(pyr)4 (2) were isolated, respectively. Addition of t-butylbipyridine and triphenylphosphine oxide generated the respective Lewis base adducts, NpCl4( tBuBipy)2 (3) and NpCl4(OPPh3)2 (4). All species were fully characterized using spectroscopic and structural analyses. [ABSTRACT FROM AUTHOR]

1,2,4‐triazolo‐[4,3‐a]pyrazine was prepared via a two‐step electrochemical, photochemical process. First, a 5‐substituted tetrazole is electrochemically coupled to 2,6‐dimethoxypyrazine to yield 1,5‐ and 2,5‐ disubstituted tetrazoles. Subsequent photochemical excitation of the 2,5‐disubstituted tetrazole species using an ultraviolet lamp releases nitrogen gas and produces a short‐lived nitrilimine intermediate. Subsequent cyclization of the nitrilimine intermediate yields a 1,2,4‐triazolo‐[4,3‐a]pyrazine backbone. The scope of this reaction was explored using various tetrazoles and pyrazines. Materials produced were identified using chemical analytical techniques and computationally studied for potential application as an insensitive energetic material. [ABSTRACT FROM AUTHOR]