Doped Semimetal Clusters: Ternary, Intermetalloid Anions [Ln@Sn7Bi7]4– and [Ln@Sn4Bi9]4– (Ln = La, Ce) with Adjustable Magnetic Properties

Two K([2.2.2]­crypt) salts of lanthanide-doped semimetal clusters were prepared, both of which contain at the same time two types of ternary intermetalloid anions, [Ln@Sn7Bi7]4– and [Ln@Sn4Bi9]4–, in 0.70:0.30 (Ln = La) or 0.39:0.61 (Ln = Ce) ratios. The cluster shells represent nondeltahedral, fullerane-type arrangements of 14 or 13 main group metal atoms that embed the Ln3+ cations. The assignment of formal +III oxidation states for the Ln sites was confirmed by means of magnetic measurements that reveal a diamagnetic La­(III) compound and a paramagnetic Ce­(III) analogue. Whereas the cluster anions with a 14-atomic main-group metal cage represent the second examples in addition to a related Eu­(II) cluster published just recently, the 13-atomic cages exhibit a yet unprecedented enneahedral topology. In contrast to the larger cages, which accord to the Zintl–Klemm–Busmann electron number–structure correlation, the smaller clusters require a more profound interpretation of the bonding situation. Quantum chemical investigations served to shed light on these unusual complexes and showed significant narrowing of the HOMO–LUMO gap upon incorporation of Ce3+ within the semimetal cages.