Supplementary material for:
Stoichiometric assembly of [Sb(PCy) 3]2Li6•6HNMe2•2C6H5Me; a highly fluxional antimony(III) phosphinidine complex containing Me 2NH ligation of lithium M. A. Beswick, J. M. Goodman, C. N. Harmer, A. D. Hopkins, M. A. Paver, P. R. Raithby, A. E. H. Wheatley, D. S. Wright. Chem. Comm. 1997, 1879-1880.
[Sb(PCy)3]2Li6.6HNMe2.2C6H5CH3 was modelled in the simplified form [Sb(PH)3]2Li6.6H3N using a PM3 Hamiltonian (J. J. P. Stewart J. Comp. Chem. 1989, 10, 209), as implemented in VAMP, version 5.6, kindly donated by Oxford Molecular.

Minimisation of the crystal structure geometry using PM3 did not significantly alter the geometry. This gave us confidence that PM3 might produce qualitatively reasonable results for this system. Two different pathways for lithium interconversion were investigated:
(i) Movement around the ring of six lithium atoms: Li-Li-Li-Li-Li-Li-
(ii) Movement around the ring of two antimony atoms and four lithium atoms: Sb-Li-Li-Sb-Li-Li-

The first pathway was found to have a lower energy barrier than the second. Illustrations of pathway (i) and pathway (ii) are available.

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