Electronic properties of boron octahedral cluster. Interim report

A series of lithium-boron alloys have been developed in recent years at the Naval Surface Weapons Center. Principally through x-ray and NMR analysis, in the composition range, Li/B /sup +/ 80/20 approx. 30/70 atomic %, two cubic phases, LI/sub 2/B/sub 3/ and LiB/sub 2/ have been tentatively identified. In these compounds, boron essentially exists as a six-atoms octahedral cluster much similar to the boron cluster in recently found LiB/sub 6/ as well as in other MB/sub 6/ metal-boride compounds. However, the principal difference between Li/sub 2/B/sub 3/, LiB/sub 2/ (Hereafter to be referred to as the alloy phases) and LiB/sub 6/ is that the boron cluster are directly linked to one another in LiB/sub 6/ whereas the boron clusters are insulated from one another by lithium or non-clustered boron atom in the alloys. Physically, the alloy phases are also dramatically different from LiB/sub 6/; LiB6 is brittle and stable in air whereas the alloy phases are ductile and react with air. The picture of the electronic properties of the B/sub 6/ octahedron that emerges from the present study is in reasonable agreement with much of the earlier work using simplified LCAO formalisms. It has been possible to classify the B/submore » 6/ boron cluster orbitals within the cluster as whether internal or external in nature and to further divide these classes into bonding and anti-bonding combinations. That fourteen electrons are required to fill the internal bonding orbitals of the B/sub 6/ octahedron is confirmed and in agreement with the conventional picture. The response of the B/sub 6/ cluster orbitals to different local lattice structures has also been investigated. (GRA)« less