[M@Sn14-xSbx]q- (M = La, Ce, or U; x = 6-8; q = 3, 4): Interaction of 4f or 5f Metal Ions with 5p Metal Atoms in Intermetalloid Clusters.

The impact of 4f metal ions Ln3+ (Ln = La or Ce) versus 5f metal ions Un+ (n = 3 or 4) on the compositions and distribution of 5p metal atoms in the cluster shells of endohedral species [M@Sn14-xSbx]q- (M = La, Ce, or U; x = 6-8; q = 3, 4) was studied by means of combined experimental and quantum chemical investigations. While all known f-block metal ion-centered endohedral clusters possessed combinations of larger main group metal atoms so far (Sn/Bi or Pb/Bi), resulting in mixtures of 13- and 14-atom cages, the 14-atom cages reported herein comprise exclusively Sn and Sb atoms and therefore are challenged in accommodating the large 4f and 5f ions. We show that the clusters form in reactions of (Sn2Sb2)2- anions with [Ln(C5Me4H)3] or [U(C5Me4H)3Cl], and that salts of [La@Sn6Sb8]3-, [La@Sn7Sb7]4-, [U@Sn8Sb6]4-, and [U@Sn7Sb7]3- can be isolated from them. The assignment of Sn versus Sb in the encapsulating cage follows a simple rule. Different central atoms cause only slight differences in this regard and with respect to distortions of the cluster shells. The reactions also yielded the salt of the new binary anion (Sn4Sb4)2- that was recently predicted by quantum chemical studies.