Syntheses, structures, and magnetic properties of the europium(II) selenido pnictogenates(III), Eu PnSe 3 ( Pn=Sb, Bi)

Abstract

Eu PnSe 3 ( Pn=Sb, Bi) have been synthesized through the reaction of Eu with Pn 2Se 3 ( Pn=Sb, Bi) and Se at 850–900 °C. These compounds are isotypic with Sr PnSe 3 ( Pn=Sb, Bi) and consist of square pyramidal PnSe 5 units and distorted PnSe 6 octahedra that form hollow columns that extend along the c-axis. These columns are separated by Eu 2+ cations that occur as nine-coordinate tricapped trigonal prisms. There are also additional V-shaped triselenide Se 3 2− anions between the columns that bind the Eu 2+ cations. The Se⋯Se contacts (in EuSbSe 3) in these units are 2.4584(11) and 2.4359(11) Å, which are consistent with Se–Se single bonds. The overall structure is chiral. Bond-valence sum calculations indicate that these compounds contain Eu 2+. Magnetic susceptibility measurements provide values of 7.66 μ B/Eu for EuSbSe 3 and 7.64 μ B/Eu for EuBiSe 3, which are close to the expected free-ion moment for Eu 2+. These compounds follow essentially Curie behavior from 300 to 5 K, and undergo an apparently antiferromagnetic transition below 5 K. Crystallographic data: EuSbSe 3, orthorhombic, space group P2 12 12 1, a = 32.936 ( 2 ) Å , b = 15.406 ( 1 ) Å , c = 4.2622 ( 3 ) Å , V = 2162.7 ( 2 ) Å 3 , Z = 16 , R ( F ) = 2.63 % for 183 parameters and 5095 reflections with I > 2 σ ( I ) ; EuBiSe 3, orthorhombic, space group P2 12 12 1, a = 33.307 ( 2 ) Å , b = 15.5804 ( 9 ) Å , c = 4.2274 ( 2 ) Å , V = 2193.7 ( 2 ) Å 3 , Z = 16 , R ( F ) = 2.68 % for 183 parameters and 4895 reflections with I > 2 σ ( I ) .