Synthesis and Topological Trapping of Cyclic Poly(alkylene phosphates)

The zwitterionic ring-opening polymerization of 2-isopropoxy-2-oxo-1,3,2-dioxaphospholane (iPP) with <i>N</i>-heterocyclic carbenes (NHC) generates poly­(alkylene phosphate)­s with molecular weights of <i>M</i>_n = 55000–202000 Da. MALDI-TOF mass spectrometry provided clear evidence for cyclic poly­(alkylene phosphate)­s (poly­(iPP)) for lower molecular weight fractions (<i>m</i>/<i>z</i> ≤ 3000). The cyclic topology of the higher molecular weight fractions was inferred by trapping of poly­(iPP) in cross-linked 2-hydroxyethyl methacrylate (HEMA) hydrogels. Cross-linked HEMA hydrogels were generated in the presence of a high molecular weight (<i>M</i>_n = 202000 Da) poly­(iPP) generated from the zwitterionic ring-opening polymerization of iPP with the NHC 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene <b>2</b>. Extraction of the resulting gel with methanol for 11 days revealed that 36% of the poly­(iPP) was retained in the gel, whereas a linear poly­(iPP) was completely extracted under similar conditions. The retention of the poly­(iPP)­s in the gels is attributed to topological trapping of the cyclic poly­(iPP) in the cross-linked network

Synthesis and Topological Trapping of Cyclic Poly(alkylene phosphates)

The zwitterionic ring-opening polymerization of 2-isopropoxy-2-oxo-1,3,2-dioxaphospholane (iPP) with <i>N</i>-heterocyclic carbenes (NHC) generates poly­(alkylene phosphate)­s with molecular weights of <i>M</i>_n = 55000–202000 Da. MALDI-TOF mass spectrometry provided clear evidence for cyclic poly­(alkylene phosphate)­s (poly­(iPP)) for lower molecular weight fractions (<i>m</i>/<i>z</i> ≤ 3000). The cyclic topology of the higher molecular weight fractions was inferred by trapping of poly­(iPP) in cross-linked 2-hydroxyethyl methacrylate (HEMA) hydrogels. Cross-linked HEMA hydrogels were generated in the presence of a high molecular weight (<i>M</i>_n = 202000 Da) poly­(iPP) generated from the zwitterionic ring-opening polymerization of iPP with the NHC 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene <b>2</b>. Extraction of the resulting gel with methanol for 11 days revealed that 36% of the poly­(iPP) was retained in the gel, whereas a linear poly­(iPP) was completely extracted under similar conditions. The retention of the poly­(iPP)­s in the gels is attributed to topological trapping of the cyclic poly­(iPP) in the cross-linked network

A Direct Bandgap Copper–Antimony Halide Perovskite

Since the establishment of perovskite solar cells (PSCs), there has been an intense search for alternative materials to replace lead and improve their stability toward moisture and light. As single-metal perovskite structures have yielded unsatisfactory performances, an alternative is the use of double perovskites that incorporate a combination of metals. To this day, only a handful of these compounds have been synthesized, but most of them have indirect bandgaps and/or do not have bandgaps energies well-suited for photovoltaic applications. Here we report the synthesis and characterization of a unique mixed metal ⟨111⟩-oriented layered perovskite, Cs₄CuSb₂Cl₁₂ (<b>1</b>), that incorporates Cu²⁺ and Sb³⁺ into layers that are three octahedra thick (<i>n</i> = 3). In addition to being made of abundant and nontoxic elements, we show that this material behaves as a semiconductor with a direct bandgap of 1.0 eV and its conductivity is 1 order of magnitude greater than that of MAPbI₃ (MA = methylammonium). Furthermore, <b>1</b> has high photo- and thermal-stability and is tolerant to humidity. We conclude that <b>1</b> is a promising material for photovoltaic applications and represents a new type of layered perovskite structure that incorporates metals in 2+ and 3+ oxidation states, thus significantly widening the possible combinations of metals to replace lead in PSCs

Heterometallic Alumo- and Gallodisilicates with M(O–Si–O)₂M′ and [M(O–Si–O)₂]₂M′ Cores (M = Al, Ga; M′ = Ti, Zr, Hf)

The synthesis and stabilization of alumo- and gallodisilicates [HC­{C­(Me)­N­(2,6-<i>i</i>Pr₂C₆H₃)}₂]­M­[(μ-O)­Si­(OH)­(O<i>t</i>Bu)₂]₂ [M = Al (<b>1</b>), Ga (<b>2</b>)] containing two silicate subunits have been achieved through reactions between 2 equiv of the silanediol (<i>t</i>BuO)₂Si­(OH)₂ and the aluminum hydride [HC­{C­(Me)­N­(2,6-<i>i</i>Pr₂C₆H₃)}₂]­AlH₂ or the gallium amide [HC­{C­(Me)­N­(2,6-<i>i</i>Pr₂C₆H₃)}₂]­Ga­(NHEt)₂, respectively. Compounds <b>1</b> and <b>2</b> exhibit M­(O–SiO₂–OH)₂ moiety and represent the first molecular metallosilicate-based analogues of neighboring silanol groups found in silicate surfaces. The substitution of both SiOH groups led to the formation of bimetallic compounds with 4R topologies, which are regularly found in zeolitic materials. Thus, reactions between group 4 metal amides M′(NEt₂)₄ (M′ = Ti, Zr, Hf) and <b>1</b> and <b>2</b> resulted in the formation of nine heterometallic silicates (<b>3</b>–<b>11</b>) containing inorganic M­(O–Si–O)₂M′ and [M­(O–Si–O)₂]₂M′ cores with 4R and spiro-4R topologies, respectively. The latter have M···M distances of 0.81 nm. NMR studies of the heterometallic derivatives showed a fluxional behavior at room temperature due to a high flexibility of the eight-membered ring

Optical, Electronic, and Magnetic Engineering of ⟨111⟩ Layered Halide Perovskites

Antimony and bismuth ⟨111⟩ layered perovskites have recently attracted significant attention as possible, nontoxic alternatives to lead halide perovskites. Unlike lead halide perovskites, however, ⟨111⟩ halide perovskites have shown  limited ability to tune their optical and electronic properties. Herein, we report on the metal alloying of manganese and copper into the family of materials with formula Cs₄Mn_1–<i>x</i>Cu_<i>x</i>Sb₂Cl₁₂ (<i>x</i> = 0–1). By changing the concentration of manganese and copper, we show the ability to modulate the bandgap of this family of compounds over the span of  2 electron volts, from 3.0 to 1.0 eV. Furthermore, we show that in doing so, we can also adjust other relevant properties such as their magnetic behavior and their electronic structure