High Pressure Investigation of the S–N₂System up to the Megabar Range: Synthesis and Characterization of the SN₂Solid

Abstract

Sulfur and nitrogen represent one of the most studied inorganic binary systems at ambient pressure on account of their large wealth of metastable exotic ring-like compounds. Under high pressure conditions however, their behavior is unknown. Here, sulfur and nitrogen were compressed in a diamond anvil cell up to about 120 GPa and laser-heated at regular pressure intervals in an attempt to stabilize novel sulfur-nitrogen compounds. Above 64 GPa, an orthorhombic (space group Pnnm) SN2 compound was synthesized and characterized by single-crystal and powder X-ray diffraction as well as Raman spectroscopy. It is shown to adopt a CaCl2-type structure-hence is isostructural, isomassic and isoelectronic to CaCl2-type SiO2-comprised of SN6 octahedra. Complementary theoretical calculations were performed to provide further insight into the physico-chemical properties of SN2, notably its equation of state, the bonding type between its constitutive elements and its electronic density of states. This new solid is shown to be metastable down to about 20 GPa, after which it spontaneously decomposes into S and N2. This investigation shows that despite the many metastable S-N compounds existing at ambient conditions, none of them are formed by pressure.

Neutral binary chalcogen–nitrogen and ternary S,N,P molecules: new structures, bonding insights and potential applications

“…These authors found that the reaction of elemental sulfur and N 2 gas in a diamond anvil cell at pressures above 60 GPa with laser heating produces an orthorhombic (P nnm ) SN 2 compound. 40 The lattice parameters of this material obtained from powder diffraction data match closely the theoretically pre-dicted crystalline structure of SN 2 . 37 Single crystal X-ray diffraction analysis revealed a CaCl 2 -type structure composed of edge-sharing SN 6 octahedra with N atoms that are triply coordinated by S atoms (Fig.…”

“…8). 40 The SN 2 solid was found to be metastable down to ca. 20 GPa, at which point it dissociates into its elements.…”

“…Klapötke 41 Furthermore, no spectroscopic evidence for the formation of SN 4 was garnered from the recent study of the S-N 2 system at high pressures, which led to the characterisation of metastable SN 2 (section 4.1). 40 The main focus of early theoretical investigations of SN 4 was an estimate of the aromaticity of the cyclic isomer, which is a 6π-electron five-membered ring formally related to thiophene by the replacement of four CH units by four nitrogen atoms. Schleyer and co-workers calculated NICS (nucleus independent chemical shift) and NICS(1) values of −18.40 and −17.48 for cyclo-SN 4 ; the large negative values are indicative of substantial aromatic character in the ring.…”

Novel sulfur hydrides synthesized at extreme conditions

“…The samples were mainly characterized by single-crystal (sc-XRDp) and powder x-ray diffraction (XRDp) measurements. The subscript "p" in sc-XRDp emphasizes the very small, just a few microns size of the single crystals, for which a special approach to the high-pressure XRD data acquisition and analysis was recently developed in high-pressure crystallography [28], and its reliability demonstrated numerous times [35][36][37]. The x-ray diffraction data were acquired at the P02.2 and 13-IDD beamlines of PETRA III and the APS, respectively.…”

Synthesis, crystal structure and structure–property relations of strontium orthocarbonate, Sr2CO4

“…The analysis procedure includes the peak search, the removal of the diamond anvil's parasitic reflections and saturated pixels of the detector, finding reflections belonging to a unique single crystal, the unit-cell determination and the data integration. The crystal structures were then solved with the SHELXT (Sheldrick, 2008) analysis was previously demonstrated and successfully employed (Bykova, 2015;Laniel et al, 2019;Laniel, Winkler, Bykova et al, 2020;.…”