Corinna Sieke

Pr(BO2)3 und PrCl(BO2)2: Zwei meta-Borate des Praseodyms im Vergleich

PrCl(BO2)2 entsteht kristallin bei der Reaktion von Praseodym, Pr6O11 und PrCl3 mit einem geringen Uberschus an B2O3 in evakuierten Quarzglasampullen nach sieben Tagen bei 850 °C. Verwendet man zusatzlich NaCl als Flusmittel, so resultiert hauptsachlich Pr(BO2)3 in Form von Einkristallen. Beide Praseodym(III)-meta-Borate sind gegenuber Luft und Wasser stabil. PrCl(BO2)2 fullt in langen, dunnen, hellgrunen Nadeln an, die aufgrund ihres faserigen Habitus stark zur Wachstumsverzwillingung neigen. Die Kristallstruktur (triklin, P1¯ a = 420, 56(4), b = 655, 42(7), c = 808, 34(8) pm, α = 82, 361(8), β = 89, 173(9), γ = 71, 980(7)° Z = 2) weist parallel [100] verlaufende Zickzack-Ketten {[(B1)ot1/1Oe2/2(B2)Ot1/1Oe2/2]2−} (≡ {[BO2]−}) aus eckenverknupften [BO3]3−-Dreiecken mit syndiotaktischer Ausrichtung der terminalen Sauerstoffatome auf. Die Pr3+-Kationen sind von drei Cl−- und sieben O2−-Anionen in Form von vierfach uberkappten trigonalen Prismen koordiniert. Die grunen, transparenten Kristalle von Pr(BO2)3 (monoklin, C2/c; a= 984, 98(9), b = 809, 57(8), c = 641, 02(6) pm, β = 126, 783(9)°; Z = 4) treten lattenformig oder mit eher spharischem Habitus in Erscheinung. In der Kristallstruktur liegen die B3+-Kationen sowohl trigonal-planar als auch tetraedrisch von Sauerstoffatomen koordiniert vor. Dabei werden die beiden unterschiedlichen Boratpolyeder ([BO3]3− und [BO4]5−) parallel [101] uber Ecken zu Ketten der Zusammensetzung {[(B2)-Ot1/1Oe2/2(B1)Oe4/2(B2)Ot1/1Oe2/2]3−} (≡ {[BO2]−}) verknupft. Die Umgebung der Pr3+-Kationen besteht aus zehn Oxid-Anionen, die ein doppelt uberkapptes quadratisches Antiprisma bilden. Pr(BO2)3 and PrCl(BO2)2: Two Praseodymium meta-Borates in Comparison Single-crystalline PrCl(BO2)2 can be obtained by the reaction of praseodymium, Pr6O11 and PrCl3 with a small excess of B2O3 in evacuated silica tubes after seven days at 850 °C. If NaCl is additionally used as flux, single crystals of Pr(BO2)3 dominate the main product. Both praseodymium(III) meta-borates are air and water stable. The crystals of PrCl(BO2)2 emerge as long, thin, pale green needles which tend to severe twinning due to their fibrous habit. The crystal structure (triclinic, P1¯; a = 420.56(4), b = 655.42(7), c = 808.34(8) pm, α = 82.361(8), β = 89.173(9), γ = 71.980(7)°, Z = 2) exhibits zigzag chains {[(B1)ot1/1Oe2/2(B2)Ot1/1Oe2/2]2−} (≡ {[BO2]−}) of corner-linked [BO3]3− triangles with syndiotactic orientation of the terminal oxygen atoms which are running parallel to the [100] direction. The Pr3+ cations are surrounded by three Cl− and seven O2− anions with the shape of a tetracapped trigonal prism. The green, transparent crystals of Pr(BO2)3 (monoclinic, C2/c; a= 984.98(9), b = 809.57(8), c = 641.02(6) pm, β = 126.783(9)°, Z = 4) appear either lath-shaped or rather spherical. In the crystal structure the B3+ cations reside both in trigonal planar as well as in tetrahedral coordination of oxygen atoms. Both types of borate polyhedra ([BO3]3− and [BO4]5−) are linked via corners to form chains of the composition {[(B2)-Ot1/1Oe2/2(B1)Oe4/2(B2)Ot1/1Oe2/2]3−} (≡ {[BO2]−}) which run parallel [101]. The coordination sphere of the Pr3+ cations consists of ten oxide anions which build up a bicapped square antiprism.

Sulfidisch derivatisierte Oxodisilicate der schweren Lanthanide vom Formeltyp M4S3[Si2O7] (M = Gd - Tm) / Sulfide Derivatized Oxodisilicates of the Heavy Lanthanides with the Formula M4S3[Si2O7] (M = Gd - Tm)

The sulfide derivatized oxodisilicates M4S3[Si2O7] of the heavy lanthanides (M = Gd - Tm) have been synthesized by reaction of M, M2O3, S, and SiO2 using MCl3 as flux in evacuated silica tubes at 850 °C for 7 d. The title compounds crystallize tetragonally in the space group I41/amd with 8 formula units per unit cell. Their crystal structure contains isolated [Si2O7]6− pyroanions of two vertex-sharing [SiO4] tetrahedra in eclipsed conformation with Si-O-Si bridging angles of about 130°. The two crystallographically independent lanthanide cations (M3+) both reside in tricapped trigonal prismatic environments of chalcogen ligands. In the case of M1 five S2− and three plus one O2− anions (CN = 8+1), for M2 three S2− and six O2− anions (CN = 9) fill the coordination spheres. Two of the three different sulfide anions are surrounded by four M3+ cations forming a seesaw (S2) and a square (S3), respectively. The third one (S1) is coordinated by six lanthanide cations in the form of a distorted octahedron. The whole structure is basically built up of cationic lanthanide silicate layers which are threaded by sulfide anions.