Hydrohalogenation of Unactivated Alkenes Using a Methanesulfonic Acid/Halide Salt Combination

The hydrochlorination, hydrobromination, and hydroiodination of unactivated alkenes using methanesulfonic acid and inorganic halide salts (CaCl2, LiBr, LiI) in acetic acid are reported. This approach uses readily available and inexpensive reagents to provide the alkyl halides in up to 99% yield. An example of deuteriochlorination using deuterated acetic acid as the solvent is also demonstrated.

Hexa-μ-acetato-chlorido(μ-N,2-dioxodobenzene-1-carboximidato)-μ3-oxido-tetrairon(III)–water (1/1) and hexa-μ-acetato-(μ-N,2-dioxodobenzene-1-carboximidato)fluorido-μ3-oxido-tripyridinetetrairon(III)–pyridine–water (1/1/0.24)

The title compounds, [Fe4(C2H3O2)6(C7H4O3)FO(C5H5N)3]·C5H5N·0.24H2O (1-F) and [Fe4(C2H3O2)6(C7H4O3)ClO(C5H5N)3]·H2O (1-Cl) were synthesized using a self-assembly reaction in methanol and pyridine with stoichiometric addition of salicylhydroxamic acid (H3shi), acetic acid (HOAc), and the appropriate ferric halide salt. The compounds crystallize as solvates, where 1-F has one pyridine molecule that is disordered about a twofold axis and one water molecule with an occupancy of 0.24 (2); and 1-Cl has one water molecule that is disordered over two sites with occupancies of 0.71 (1) and 0.29 (1). The space groups for each analog differ as 1-F crystallizes in Fdd2 while 1-Cl crystallizes in P21. The difference in packing is due to changes in the intermolecular interactions involving the different halides. The two molecules are mostly isostructural, differing only by the torsion of the pyrine ligands and slight orientation changes in the acetate ligands. All of the iron(III) ions are in six-coordinate octahedral ligand field geometries but each one exhibits a unique coordination environment with various numbers of O (four to six) and N (nought to two) atom donors. Bond-valence sums confirm each iron is trivalent. The hydroximate ligand is bound to three iron(III) ions using a fused chelate motif similar to those in metallacrown compounds.

Seed Mediated Synthesis of Colloidal Halide Perovskite Nanoplatelets

<p><b>Two-dimensional lead halide perovskite nanoplatelets (2D LHP NPLs) have been emerging as one of the most promising semiconductor nanomaterials due to their narrow absorption and emission line widths, tunable bandgaps, high exciton binding energies, high defect tolerance as well as highly localized energy states. Colloidal synthesis of 2D LHP NPLs is generally performed using hot-injection or ligand assisted precipitation techniques (LARP). In the LARP method, perovskites are synthesized in polar solvents, which decrease the stability of the 2D LHP NPLs due to their weakly bonded nature. In fact, the presence of residual polar solvent in the LHP NPL colloid can cause deterioration of thickness uniformity, degradation of NPLs to parent precursors, and undesired phase transformations. Herein, for the first time, we report facile seed-mediated synthesis route of monolayer, 2-monolayers, and thicker lead halide perovskite nanoplatelets without using A site cation halide salt (AX</b><b>;</b><b> A = Cesium, methylammonium, formamidinium and, X = Cl, Br, I) and long chain alkylammonium halide salts (LX; L = oleylammonium, octylammonium, butylammonium and, X = Cl, Br, I). The seed solution has been synthesized by reacting lead (II) halide salt and coordinating ligands (oleylamine or octylamine and oleic acid) in nonpolar high boiling solvent (1-octadecene). The seed mediated synthesis has been carried out in hexane by reacting seed solution with A-site cation precursors (Cs-oleate, FA-oleate, or diluted MA solution in hexane) under ambient conditions. More importantly, the seed mediated growth of NPLs has been tracked for the first time by performing in-situ optical measurements. Furthermore, the optical properties and morphologies of the seeds have been extensively studied. We find that our facile synthesis route provides highly stable, monodisperse NPLs with narrow absorption, and photoluminescence line widths (68-201 meV), and high PLQY (37.6-1.66% for 2ML NPLs). Furthermore, anion exchange reactions have been performed by mixing pre-synthesized LHP NPLs with counter halide seeds. The optical properties of NPLs have been affectively tuned by postsynthetic chemical reactions without changing the thickness of the NPLs. We anticipate that our new synthetic route provides further understanding of growth dynamics of LHP NPLs.</b></p>

Seed Mediated Synthesis of Colloidal Halide Perovskite Nanoplatelets

<p><b>Two-dimensional lead halide perovskite nanoplatelets (2D LHP NPLs) have been emerging as one of the most promising semiconductor nanomaterials due to their narrow absorption and emission line widths, tunable bandgaps, high exciton binding energies, high defect tolerance as well as highly localized energy states. Colloidal synthesis of 2D LHP NPLs is generally performed using hot-injection or ligand assisted precipitation techniques (LARP). In the LARP method, perovskites are synthesized in polar solvents, which decrease the stability of the 2D LHP NPLs due to their weakly bonded nature. In fact, the presence of residual polar solvent in the LHP NPL colloid can cause deterioration of thickness uniformity, degradation of NPLs to parent precursors, and undesired phase transformations. Herein, for the first time, we report facile seed-mediated synthesis route of monolayer, 2-monolayers, and thicker lead halide perovskite nanoplatelets without using A site cation halide salt (AX</b><b>;</b><b> A = Cesium, methylammonium, formamidinium and, X = Cl, Br, I) and long chain alkylammonium halide salts (LX; L = oleylammonium, octylammonium, butylammonium and, X = Cl, Br, I). The seed solution has been synthesized by reacting lead (II) halide salt and coordinating ligands (oleylamine or octylamine and oleic acid) in nonpolar high boiling solvent (1-octadecene). The seed mediated synthesis has been carried out in hexane by reacting seed solution with A-site cation precursors (Cs-oleate, FA-oleate, or diluted MA solution in hexane) under ambient conditions. More importantly, the seed mediated growth of NPLs has been tracked for the first time by performing in-situ optical measurements. Furthermore, the optical properties and morphologies of the seeds have been extensively studied. We find that our facile synthesis route provides highly stable, monodisperse NPLs with narrow absorption, and photoluminescence line widths (68-201 meV), and high PLQY (37.6-1.66% for 2ML NPLs). Furthermore, anion exchange reactions have been performed by mixing pre-synthesized LHP NPLs with counter halide seeds. The optical properties of NPLs have been affectively tuned by postsynthetic chemical reactions without changing the thickness of the NPLs. We anticipate that our new synthetic route provides further understanding of growth dynamics of LHP NPLs.</b></p>

Synergistic improvements in the performance and stability of inverted planar MAPbI3-based perovskite solar cells incorporating benzylammonium halide salt additives

Three different benzylammonium halide (Cl, Br, and I) salts were investigated to elucidate their effects as additives on MAPbI3 perovskite surface morphology, crystal structure, optical properties, and solar cell performance and stability.