POLYATOMIC-MOLECULES WITHOUT ELECTRON-PAIR BONDS - HIGH-SPIN TRIGONAL, TETRAHEDRAL, AND OCTAHEDRAL LITHIUM CLUSTERS

Bound polyatomic molecules without any spin-paired valence electrons a re exemplified by lithium clusters in high-spin states. Three unpaired valence electrons are able to bind the ((4)A(1)) quartet states of Li -3 and of Li-4(+) in trigonal (D-3h) geometries. The tetrahedral Li-4 and Li-5(+) ((5)A(1)) quintet state structures illustrate bound molecu les with four unpaired valence electrons. Five, six, and seven spin-un coupled valence electrons bind the square pyramidal Li-5 (B-6(1)) stru cture, the Li-6 ((7)A(2u)) distorted octahedral structure, and the Li- 6(-)((8)A(1g)) octahedral (O-h) octuplet, respectively. However, these high-multiplicity structures are only local minima; forms with lower spin states are more favorable energetically. Other high symmetry, hig h multiplicity clusters, e.g., triangular Be-3(+)((6)A(1)'), also have positive atomization energies. The results demonstrate that chemical bonding in multiatom species does not require spin-coupling.