Reduced rare-earth iodides without and with carbon

Abstract

The rare-earth diiodides RI 2 may be divided into two classes. At ambient conditions, the rare-earth cation R 2+ may have the electronic configuration [Xe]6s 0 5d 0 4f n (R = Nd, Sm, Eu, Dy, Tm, Yb). The respective diiodides, also classified as (R 2+ )(I − ) 2 , are structurally reminiscent of alkaline-earth iodides. Diiodides with R = La, Ce, Pr, and Gd have one excess electron according to [Xe]6s 0 5d 1 4f n −1 , chemically: (R 3+ )(e − )(I − ) 2 , and exhibit mostly CuTi 2 or MoS 2 type structures. The configuration crossover 5d 0 4f n ⇔ 5d 1 4f n −1 is observed with praseodymium (and neodymium) and is dependent upon the conditions (temperature, pressure) and the crystal structure adopted. “ScI 2 ” is a special case as it stabilizes its electronic structure through an under-occupation of the scandium sites. Further stabilization of “reduced iodides” is possible by encapsulation of mono- or di-carbon units in tetrahedral or octahedral clusters. Examples are Pr{Pr 6 C}I 12 , Cs 2 {Pr 6 (C 2 )}I 12 and Sc 24 C 10 I 30 .