UZONITE, As4S5, FROM THE TYPE LOCALITY: SINGLE-CRYSTAL X-RAY STUDY AND EFFECTS OF EXPOSURE TO LIGHT

Abstract

The crystal structure of uzonite from the Uzon caldera, Kamchatka, Russian Federation, has been refined in space group P2 1 /m to a final R index of 2.66%. Unit-cell parameters are: a 7.973(2), b 8.096(2), c 7.148(2) Å, ␤ 101.01(2)°, V 452.9(2) Å 3 , Z = 2. The structural model previously reported for the synthetic analogue is confirmed, although a higher precision was achieved. The structure consists of discrete covalently bonded As 4 S 5 molecules, which are held together by van der Waals forces. Both the intramolecular As-S (2.237-2.261 Å) and As-As (2.527 Å) bond lengths match closely the values commonly observed in the molecule-based structures of other arsenic sulfides. In order to contribute to the understanding of the effects of light exposure on the structure of the arsenic sulfides, we exposed the crystal to filtered polychromatic light. The unit-cell parameters were measured after each exposure. The results obtained seem to indicate that the As 4 S 4 molecules easily undergo such a transformation, whereas the As 4 S 5 molecules do not. SOMMAIRE Nous avons affiné la structure cristalline de l'uzonite provenant de la localité type, la caldeira de Uzon, au Kamchatka, en Russie, dans le groupe spatial P2 1 /m jusqu'à un résidu R de 2.66%. Les paramètres réticulaires sont: a 7.973(2), b 8.096(2), c 7.148(2) Å, ␤ 101.01(2)°, V 452.9(2) Å 3 , Z = 2. Le modèle structural proposé antérieurement pour l'analogue synthétique a été confirmé, tout en atteignant une précision plus élevée. La structure contient des molécules distinctes de As 4 S 5 à liaisons covalentes, retenues par liaisons van der Waals. Les liaisons intramoléculaires As-S (2.237-2.261 Å) et As-As (2.527 Å) correspondent étroitement aux valeurs observées dans la structure d'autres sulfures d'arsenic à base de molécules. Afin de contribuer à une explication des effets sur la structure des sulfures d'arsenic d'une exposition à la lumière, nous avons exposé le cristal à une lumière polychromatique filtrée, et nous avons mesuré les paramètres réticulaires après chaque exposition. Les résultats semblent indiquer que seules les molécules de As 4 S 4 sont facilement transformées, tandis que les molécules de As 4 S 5 ne montrent aucune réaction. (Traduit par la Rédaction)Mots-clés: uzonite, affinement de la structure cristalline, effets d'une exposition à la lumière, sulfure d'arsenic, caldeira de Uzon, Russie. §

Ciriottiite, Cu(Cu,Ag)3Pb19(Sb,As)22(As2)S56, the Cu-Analogue of Sterryite from the Tavagnasco Mining District, Piedmont, Italy

“…In the same arm, the As46 and As47 sites are at short distance along a, i.e., 2.63 Å, forming an As-As pair. Each As atom of this pair is bonded to two S atoms, thus forming an (As2)S4 group, analogous to that occurring in sterryite [8] and similar to those reported in several As sulfides (e.g., alacranite [13], bonazziite [14], realgar [15], uzonite [16], wakabayashilite [17]) and in dervillite [18]. …”

Ab initio quantum chemical investigation of arsenic sulfide molecular diversity from As4S6 and As4

“…Figure 10 Note: Measurements of XRD analysis for dimorphite, realgar, pararealgar, and uzonite are refeared from Bindi et al (2003), Kyono et al (2005), Bonazzi et al (1995), and Whitfield (1973a), respectively. Note: Measurements of XRD analysis for dimorphite, realgar, pararealgar, and uzonite are refeared from Bindi et al (2003), Kyono et al (2005), Bonazzi et al (1995), andWhitfield (1973a), respectively. D = S|d exp -d calc |/n As -As -As As -As -S As -S -As S -As -S …”

Solid-state amorphization of As 45 S 55 alloy induced by high-energy mechanical milling

“…As2S2.5) at higher 200 o C temperatures, but this feature was not more clarified because of DTA measuring restrictions. The first of these compositions limiting phase separation in As-S system near As2S2.7 can be conditionally ascribed to local atomic rearrangement towards uzonitetype molecular structure, since one As2S4/2 bridge and four single AsS3/2 pyramids are needed to form such As4S5 molecule [59][60][61]. The second compositional anomaly observed at As2S2.5 is due to transformation to realgar-type structure, as two single AsS3/2 pyramids and two As2S4/2 bridge are needed to form As4S4 molecule [59,61].…”