The Elusive Tetrasamarium‐oxide‐hexabromide, Sm₄OBr₆

Abstract

Black single crystals of tetrasamarium(II)-oxide-hexabromide, Sm 4 OBr 6 , were obtained from a reaction of SmBr 3 , Sm 2 O 3 and Na in a sealed tantalum container at 750°C. Sm 4 OBr 6 crystallizes in the hexagonal space group P6 3 mc (Z ϭ 2, a ϭ 985.89(9), c ϭ 753.50(6) pm, R ϭ 0.035 for all data) as do all M 4 OX 6 type oxide halides with M ϭ Ca,Sr,Ba,Eu,Sm,Yb and X ϭ Cl,Br,I, as far as they have been obtained. The crystal structure is also the Oxide-halides of the formula type M 4 OX 6 have been obtained for the alkaline-earth elements calcium, strontium, and barium and for the lanthanides samarium, europium, and ytterbium in their divalent state. Only the elements of the triad chlorine, bromine and iodine have been observed as X elements. Of the 18 possible combinations, all chlorides, four out of six iodides and, hitherto, only one bromide, Eu 4 OBr 6 , were obtained as single crystals, in many cases not deliberately, rather as by-products. Table 1 gives an overview.

Anion-Centered Tetrahedra in Inorganic Compounds

“…The most simple unit is an isolated (XLn 4 ) tetrahedron found in a number of Ln oxyhalogenides and oxychalcogenides known as promising storage phosphors . Figure shows the surrounding of the (OSm 4 ) tetrahedron by 18 Br – anions in the structure of Sm 4 OBr 6 . The Br – ions are classified with relation to their structural role respective to the oxocentered tetrahedron into μ 1 -, μ 2 -, and μ 3 -types so that the unit shown in Figure should be described as {[OSm 4 ]­(μ 3 -Br) 3 (μ 2 -Br) 6 (μ 1 -Br) 9 } 12– .…”

“…Isolated [OSm 4 ] 6+ tetrahedron surrounded by 18 Br – anions in the crystal structure of Sm 4 OBr 6 . Reprinted with permission from ref . Copyright 2006 Wiley-VCH Verlag GmbH & Co KGaA.…”

“…369 Figure 66 shows the surrounding of the (OSm 4 ) tetrahedron by 18 Br − anions in the structure of Sm 4 OBr 6 . 350 The Br − ions are classified with relation to their structural role respective to the oxocentered tetrahedron into μ 1 -, μ 2 -, and μ 3types so that the unit shown in Figure 66 the structure of Nd 4 NS 3 Cl 3 , 354 the (NNd 4 ) tetrahedron is surrounded by anions in the same fashion with the same symmetry, but with different bridging role of anions (Figure 67).…”

Lanthanides: Divalent Solid Halides

“…The oxide chlorides {OR 4 }Cl 6 are now all known with Ae, R = Ca, Sr, Ba, Sm, Eu, Yb, for {OR 4 }Br 6 (R = Sm, Eu) as well as for {OR 4 }I 6 (Ae, R = Sr, Ba, Sm, Eu). 36 Isostructural compounds with neodymium, dysprosium, and thulium are elusive. This cannot be a size effect.…”