Inhaltsübersicht. PrCl(BO 2 ) 2 entsteht kristallin bei der Reaktion von Praseodym, Pr 6 O 11 und PrCl 3 mit einem geringen Überschuß an B 2 O 3 in evakuierten Quarzglasampullen nach sieben Tagen bei 850 °C. Verwendet man zusätzlich NaCl als Flußmittel, so resultiert hauptsächlich Pr(BO 2 ) 3 in Form von Einkristallen. Beide Praseodym(III)-meta-Borate sind gegenüber Luft und Wasser stabil. PrCl(BO 2 ) 2 fällt in langen, dünnen, hellgrünen Nadeln an, die aufgrund ihres faserigen Habitus stark zur Wachstumsverzwillingung neigen. Die Kristallstruktur (triklin, P1 ¯; a ϭ 420,56(4), b ϭ 655,42(7), c ϭ 808,34(8) pm, Ͱ ϭ 82,361(8), β ϭ 89,173(9), γ ϭ 71,980(7)°; Z ϭ 2) weist parallel [100] verlaufende Zickzack-Ketten
Pr(BO 2 ) 3 and PrCl(BO 2 ) 2 : Two Praseodymium meta-Borates in Comparison Abstract. Single-crystalline PrCl(BO 2 ) 2 can be obtained by the reaction of praseodymium, Pr 6 O 11 and PrCl 3 with a small excess of B 2 O 3 in evacuated silica tubes after seven days at 850 °C. If NaCl is additionally used as flux, single crystals of Pr(BO 2 ) 3 dominate the main product. Both praseodymium(III) meta-borates are air and water stable. The crystals of PrCl(BO 2 ) 2 emerge as long, thin, pale green needles which tend to severe twinning due to their fibrous habit. The crystal structure (triclinic, P1 ¯; a ϭ 420.56(4), b ϭ 655.42(7), c ϭ 808.34(8) pm, Ͱ ϭ 82.361(8), β ϭ 89.173(9), γ ϭ 71.980(7)°, Z ϭ 2) exhibits zigzag chains 1
triangles with syndiotactic orientation of the terminal oxygen atoms which are running parallel to the [100] direction. The Pr 3ϩ cations are surrounded by three Cl Ϫ and seven O 2Ϫ anions with the shape of a