Syntheses, crystallographic characterization, and structural relations of Rb[SCN]

Abstract

Colorless rubidium thiocyanate was synthesized by three different approaches. DCS-TGA measurements allowed for extraction of phase transition, melting, and decomposition temperatures. Single-crystal X-ray diffraction showed Rb[SCN] to crystallize in the low-temperature LT-K[SCN] crystal structure type (Pbcm, oP16). Above its phase-transition temperature (432.1 K) the title compound crystallizes with the high-temperature HT-K[SCN] crystal structure type (I4/mcm, tI28) with head-to-tail disordered thiocyanate anions. Both modifications are related to one another and to the LT/HT-Cs[SCN] structure types, and the relation has been studied in detail employing the Bärnighausen formalism. Phase purity and bulk phase transition were confirmed by temperature-dependent PXRD.

Synthesis and Stability of Ammonium Selenocyanate [NH4][SeCN] and Its Reactivity toward Ag[SeCN]

“…Nuclear Magnetic Resonance Spectroscopy. 1 H-, 13 C-, and 77 Se-NMR spectra were acquired on a Bruker AV III (500 MHz) spectrometer at 300 K if not stated otherwise. 1 H-and 13 C-NMR spectra were referenced to the most downfield solvent resonance.…”

“…1 H-NMR (500 MHz, THF-d 8 ): δ = 7.12 (s, 4H, NH 4 ) ppm. 13 [SeCN] (93 mg, 0.76 mmol, 1.0 equiv) and Ag[SeCN] (161 mg, 0.76 mmol, 1.0 equiv) were heated in 9 mL of dry THF to 85 °C. After the mixture reached boiling temperature, the reactants dissolved and subsequently a gray powder precipitated.…”

“…Upon heating, it undergoes phase transitions: first, from its monoclinic ( P 2 1 / c , own prototype) to its orthorhombic ( Pbcm , low-temperature K­[SCN]-type) polymorph at 86 °C, and second to its tetragonal ( I 4/ mcm , high-temperature K­[SCN]-type) polymorph at 118 °C, which in turn is stable until its melting point at 149 °C . The latter phase transitions are also found in Rb­[SCN], and the structural relations have recently been developed on the basis of the Bärnighausen formalism . Only if held at high temperatures for longer times, ammonium thiocyanate rearranges akin to its lighter congener and yields thiourea.…”

“…12 The latter phase transitions are also found in Rb [SCN], and the structural relations have recently been developed on the basis of the Barnighausen formalism. 13 Only if held at high temperatures for longer times, ammonium thiocyanate rearranges akin to its lighter congener and yields thiourea. The reaction is reversible, very slow below 110 °C, and the equilibrium at 160 °C still contains ca.…”

Inorganic Metal Thiocyanates

“…As metal pseudohalides, they adopt structures similar to the NaCl (Na, Li) 74,75 and CsCl structures (K, Rb, Tl, Cs) . [80][81][82][83] The ionic bonding means that order-disorder transitions are a common feature of these compounds, like other metal pseudohalides, with phase transitions to plastic phases reported for K(NCS), Rb(NCS), Tl(NCS) and Cs(NCS). [76][77][78][79][80] Sodium and lithium thiocyanate both adopt rocksalt-like structures with space group Pmcn, in which both the N and S termini are bonded to three metal ions, and each metal ion is coordinated [76][77][78][79] (c) Cs(NCS) has a different CsCl derived structure which transforms into a cubic phase shortly before melting.…”