Cs_1–<i>x</i>Rb_<i>x</i>PbCl₃ and Cs_1–<i>x</i>Rb_<i>x</i>PbBr₃ Solid Solutions: Understanding Octahedral Tilting in Lead Halide Perovskites

The structures of the lead halide perovskites CsPbCl₃ and CsPbBr₃ have been determined from X-ray powder diffraction data to be orthorhombic with <i>Pnma</i> space group symmetry. Their structures are distorted from the cubic structure of their hybrid analogs, CH₃NH₃PbX₃ (X = Cl, Br), by tilts of the octahedra (Glazer tilt system <i>a</i>^–<i>b</i>⁺<i>a</i>^–). Substitution of the smaller Rb⁺ for Cs⁺ increases the octahedral tilting distortion and eventually destabilizes the perovskite structure altogether. To understand this behavior, bond valence parameters appropriate for use in chloride and bromide perovskites have been determined for Cs⁺, Rb⁺, and Pb²⁺. As the tolerance factor decreases, the band gap increases, by 0.15 eV in Cs_1–<i>x</i>Rb_<i>x</i>PbCl₃ and 0.20 eV in Cs_1–<i>x</i>Rb_<i>x</i>PbBr₃, upon going from <i>x</i> = 0 to <i>x</i> = 0.6. The band gap shows a linear dependence on tolerance factor, particularly for the Cs_1–<i>x</i>Rb_<i>x</i>PbBr₃ system. Comparison with the cubic perovskites CH₃NH₃PbCl₃ and CH₃NH₃PbBr₃ shows that the band gaps of the methylammonium perovskites are anomalously large for APbX₃ perovskites with a cubic structure. This comparison suggests that the local symmetry of CH₃NH₃PbCl₃ and CH₃NH₃PbBr₃ deviate significantly from the cubic symmetry of the average structure

Rearrangement of Benzylic Trichloro­acetimidates to Benzylic Trichloroacetamides

The rearrangement of allylic trichloro­acetimidates is a well-known transformation, but the corresponding rearrangement of benzylic trichloro­acetimidates has not been explored as a method for the synthesis of benzylic amines. Conditions that provide the trichloroacetamide product from a benzylic trichloro­acetimidate in high yield have been developed. Methods were also investigated to transform the trichloroacetamide product directly into the corresponding amine, carbamate, and urea. A cationic mechanism for the rearrangement is implicated by the available data

Hodgkin lymphoma patients have an increased incidence of idiopathic acquired aplastic anemia.

Idiopathic acquired aplastic anemia (AA) is a rare lymphocyte-mediated bone marrow aplasia. No specific mechanisms or triggers of AA have been identified. We recently observed several patients who developed AA after Hodgkin lymphoma (HL). We hypothesized that the co-occurrence of HL and AA is not random and may be etiologically significant. To test this hypothesis, we determined the incidence of AA in HL patients at our institution. We identified four patients with co-occurring HL and AA, with the incidence of AA in HL patients >20-fold higher compared to the general population. We identified 12 additional patients with AA and HL through a systematic literature review. Of the 16 total patients,15 (93.8%) developed AA after or concurrent with a HL diagnosis. None of the patients had marrow involvement by HL. Five of 15 patients were in complete remission from HL at the time of AA diagnosis, and six had a concurrent presentation with no prior cytotoxic therapy, with diagnostic timeframe information unavailable for four patients. The median interval between HL diagnosis and AA onset was 16 months, ranging from concurrent to 14 years after a HL diagnosis. The median survival after AA diagnosis was 14 months (range: 1 month to 20 years). Our results show that patients with HL have a higher incidence of AA compared to the general population and suggest that HL-related immune dysregulation may be a risk factor for AA. Better recognition and management of AA in HL patients is needed to improve outcomes in this population