[Al(Al3R3)2]: Prototype of a Metalloid Al Cluster or a Sandwich-Stabilized Al Atom?

摘要

Some years ago we established the developing area of metalloid Al clusters with the cluster ion [Al7R6]- (1, R=N(SiMe3)2).[1]-[4] The topology of the seven Al atoms in the form of two vertex-sharing tetrahedral {Al4} moieties is unique for metal atom clusters and has raised the still unanswered question: Can the central "naked" Al atom with its six directly bound neighbors be regarded as a section of the face-centered cubic (fcc) structure of solid aluminum, that is, the basic form of metalloid clusters, or is it better understood as an Al3+ ion stabilized by two aromatic {Al3R3}2- moieties in a sandwich-type arrangement as in the aluminocenium cation [AlCp*2]+, prepared by us for the first time (Cp*=C5Me5)?[5] In the meantime, we could demonstrate for further substituted [Al7R6]- clusters (R=N(SiMe2R'), R'=hexyl, Bu, iPr)[6] that these {Al7} clusters are evidently energetically favored in their monoanion form.