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

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) angstrom, u-parameter= 0.38554(2), space group Pa (3) over bar, Z=4], MnSe2 [a= 6.4275(2) angstrom, u-parameter = 0.39358(2)], MnS2 [hauerite; a = 6.1013(1) angstrom, u-parameter =0.40105(4), obtained from Osorezan, Aomori, Japan], and FeS2 [pyrite; a =5.4190(1) angstrom, 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) angstrom, which is significantly shorter than that of FeS2 (2.1618(9) angstrom), and the mean square displacement of S (U-11 = 0.00915(9) angstrom(2)) is smaller than that of Mn (U-11 = 0.01137(9) angstrom(2)). 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.