Crystal structure refinement of MnTe₂, MnSe₂, and MnS₂: cation-anion and anion–anion bonding distances in pyrite-type structures

Abstract

The stability of hauerite (MnS2) as compared to that of pyrite (FeS2) can be explained by the long Mn–S distance and departure from the typical pyrite-type structures. The structural differences of MnX2 compounds (X=S, Se, and Te) are the result of spin configurations that are different than those of other MX2 compounds; however, the arrangement of d-electrons and the size of the ions in MnX2 compounds do not clearly explain why Mn2+ in MnX2 does not exist as a low spin state. To investigate the structural differences of MnX2 compounds, we synthesized single-crystal MnTe2 and MnSe2 and performed single-crsytal X-ray diffraction experiments. The single-crystal X-ray diffraction experiments were conducted on MnTe2 [a=6.9513(1) Å, u-parameter=0.38554(2), space group Pa3̅, Z=4], MnSe2 [a=6.4275(2) Å, u-parameter=0.39358(2)], MnS2 [hauerite; a=6.1013(1) Å, u-parameter=0.40105(4), obtained from Osorezan, Aomori, Japan], and FeS2 [pyrite; a=5.4190(1) Å, u-parameter 0.38484(5), obtained from Kawarakoba, Nagasaki, Japan]. The X-ray intensity datasets of these compounds do not show any evidence of symmetry reduction. In MnS2, the S–S distance is 2.0915(8) Å, which is significantly shorter than that of FeS2 (2.1618(9) Å), and the mean square displacement of S (U11=0.00915(9) Å2) is smaller than that of Mn (U11=0.01137(9) Å2). The thermal vibration characteristics of MnX2 compounds are significantly different than those of FeS2. Based on structural refinement data, we discuss the low spin state of MnX2 compounds and the structural stability of pyrite-type structures.

Crystal structure, XANES and charge distribution investigation of krennerite and sylvanite: analysis of Au—Te and Te—Te bonds in Au1–x Ag x Te2 group minerals

“…Those for Au sites occupied by 100% Au in krennerite (126 K) and sylvanite (125 K) are significantly lower than the corresponding D value of 178 K for the pure gold metals. The Debye temperature for the site with the highest value in the crystal corresponds to the bulk Debye temperature of the compound (Tokuda et al, 2019;. The Debye temperatures of Te atoms are responsible for bulk D in these minerals.…”

“…Group V and VI elements (As, Sb, Bi, Se, Te), especially Te, form many minerals and compounds with gold, and are also frequently contained in gold minerals as subcomponents. Gold and platinum group compounds such as AuSb 2 , PtAs 2 and PdSe 2 have pyrite-type MX 2 structures characterized by an X 2 unit with X-X covalent bond in the structure (Ewald & Friedrich, 1914;Tokuda et al, 2019;Yoshiasa et al, 2021). On the other hand, Te-Te covalent bonds do not systematically occur in tellurides; for instance, they are absent in petzite.…”

Crystal structure refinements of stoichiometric Ni3Se2 and NiSe

“…The (Tokuda et al, 2019). Characteristically, the effective potentials of both atoms in MnSe 2 and NiSe are very soft compared to those of other transition-metal chalcogenides.…”

“…The D correlates with the melting temperature and physical properties, such as the hardness of crystals. The D for each atom can be estimated using the dynamic component in the Debye-Waller factor based on the Debye approximation (Willis & Pryor, 1975;Wood et al, 2002;Christensen et al, 2006;Nakatsuka et al, 2011Nakatsuka et al, , 2015Yoshiasa et al, 2016;Tokuda et al, 2019;Hongu et al, 2019). We estimated D for each atom using the values of U eq (Table 3) under the assumption that there are no static disorder components of atoms.…”

“…A phase diagram has been proposed (Røst & Vestersjø, 1968;Lee & Nash, 1992;Tesfaye & Taskinen, 2012) and the stable phases of NiSe 2 , Ni 1-x Se (x = 1.00-0.85) and Ni 3 Se 2 are known under ambient conditions. NiSe 2 , in which Se forms the Se 2 molecule, is a stoichiometric perselenide with a pyrite-type structure (Tokuda et al, 2019). Ni 3 Se 2 has the same structure type as that of Ni 3 S 2 (mineral name heazlewoodite) (Agarwala & Sinha, 1957;Hulliger, 1968;Parise, 1980).…”