Halogenide der Seltenerdmetalle Ln 4 X 5 Z. Teil 2: Eine orthorhombische Verknüpfungsvariante o ‐Ln 4 X 5 Z

Rare Earth Halides Ln 4 X 5 Z. Part 2: An Orthorhombic Variant of Ln 4 X 5 Z The compounds Ln 4 Cl 5 C 2 (Ln = La, Pr) and the isotypic bromides of lanthanum and cerium are prepared by reaction of LnX 3 , Ln metal and carbon in sealed Ta‐ampoules at temperature 900 °C < T < 950 °C. They crystallize in the orthorhombic space group Immm : La 4 Cl 5 C 2 : a = 3.9208(8) Å, b = 7.9446(16) Å, c = 17.2967(35) Å, Pr 4 Cl 5 C 2 : a = 3.8475(8) Å, b = 7.7590(16) Å, c = 17.0105(34) Å, La 4 Br 5 C 2 : a = 3.9950(8) Å, b = 8.2770(17) Å, c = 18.1010(36) Å and Ce 4 Br 5 C 2 : a = 3.9835(8) Å, b = 8.1865(16) Å, c = 18.0171(36) Å. In the crystal structure the metal atoms are connected to Ln 6 octahedra centered by C 2 units. The Ln 6 C octahedra are condensed via opposite egdes to chains and connected via X atoms. The special interconnection of the M 6 X 12 C 2 chains by the halogen atoms, Ln 2 n +2 X i−i 2/2 X i−i (2 n −2)/2 X i−a 4/2 X a−i 4/2 ( n = 1), results in an orthorhombic crystal structure in contrast to the monoclinic variant described in part 1. The C 2 groups together with the halogen atoms form ccp anionic substructure, and 4/5 of the octahedral voids is occupied by the Ln atoms. The C‐C distances vary between 1.41 und 1.44Å corresponding to a shortened C–C single bond and a lengthened C=C double bond. For metal‐metal bonds are 1 < e − < 3 electrons available suggesting an ionic formulation (Ln 3+ ) 4 (X − ) 5 C 2 m− e − with C 2 6− or C 2 4− ions (4 < m < 6).