A high-pressure synchrotron X-ray powder diffraction study of K₂SnBr₆

Abstract

Using synchrotron energy-dispersive x-ray pcwder diffraction (EDXRPD) we have shown that K,SnBr, transforms at pressuresot 14 kbar and above from the parent monoclinic cell to a cubic structure of symmetry Fm3m. which is stable to 120 kbar. A different phase appean toexist above 120 kbar.

Alkali Tin Halides: Exploring the Local Structure of A2SnX6 (A = K, Rb; X = Cl, Br, I) Compounds Using Solid-State NMR and DFT Computations

“…The nonspinning NMR spectrum for K 2 SnBr 6 was acquired using a solid echo experiment [(π/2) x − τ 1 − (π/2) y − τ 2 − ACQ] with 5.0 μs π/2 pulses and a 10 s recycle delay. The number of scans for 39 K NMR experiments ranged from 4 to 512, and all spectra were referenced with a 1 M KCl (aq) solution at δ( 39 K) = 0.00 ppm.…”

“…In such spectra, it is difficult to differentiate the central transition from the SSBs or to identify the effects of other interactions (e.g., CSA) without analysis at higher magnetic fields. 84−88 The 39 K NMR parameters are shown in Table 3, while the MAS and nonspinning 39 K NMR spectra for K 2 SnCl 6 and K 2 SnBr 6 are shown in Figure 5. In the cubic K 2 SnCl 6 compound, K + resides in a symmetric cuboctahedron formed by 12 neighboring halogen anions, resulting in a single sharp resonance at δ iso = −16 ppm.…”

“…is a quadrupolar nucleus that can be difficult to study due to the frequent presence of large quadrupole coupling constants. 86,90 However, 87 Rb is more sensitive than 39 K due to its more favorable gyromagnetic ratio (∼1/3rd that of 1 H), which has enabled the successful study of this nucleus in many materials at moderate magnetic field strengths in the past. 86,87,90−92 The 87 Rb NMR spectra under both MAS and nonspinning conditions are shown in Figure 6 and fitted NMR parameters are shown in Table 3.…”

“…57 Only recently has NMR spectroscopy been used to investigate Cs 2 SnX 6 , revealing important information about octahedral lattice dynamics, 33 which is a property known to influence the optoelectronic properties of these materials. 58,59 Herein, multinuclear magnetic resonance spectroscopy is exploited to probe the atomic-level structure of A 2 SnX 6 by examining the A-and B-site cationic environments ( 119 Sn, 39 K, and 87 Rb) across the halide series. Quantum chemical computations are further used to expose how the paramagnetic, diamagnetic, and spin−orbit (SO) shielding contributions to the 119 Sn chemical shift are affected by halogen substitutions.…”

“…The A-site was also investigated using high and ultrahigh-field 39 K and 87 Rb NMR spectroscopy. The quadrupolar and CSA parameters are successfully resolved for 39 K in K 2 SnBr 6 , but the presence of octahedral dynamics in Rb 2 SnI 6 makes it impossible to identify these parameters for 87 Rb. The experimental and theoretical analysis of the local structure was also complemented by diffuse reflectance experiments to determine the optical band gaps, which follow the typical trend of a decreasing band gap as the size of the halide is increased.…”