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Variable temperature N M R studies have established equilibrium constants and/or activation parameters for the exoz -exo3 equilibrium in the series M(o-tolyl), ( M = P, As), X M (o-tolyl), ( M = P, X = 0, S, Se; M = As, X = 0, S) and [MeM(o-tolyl),]"+ ( n = 0, M = Si; n = 1, M = P, As). The crystal structure of OAs(o-tolyl),H,O is reported. Molecular mechanics studies of P(o-tolyl), reproduce correctly the ground state ~X O , conformation and provide an analysis of the lowest energy two-ring flip exchange mechanism.t If a regular pyramid is constructed from the lp, 0, S, Se or Me as the apex and the three puru ring carbons as the base, a proximal (exo) substituent will point away from the base, while a distal (endo) substituent will point towards the base.

The molecular structures of 1,1′-di-tert-butylferrocene (1) and isopropylferrocene (2) have been examined by solid-state X-ray crystallography, gas-phase electron diffraction, and DFT and molecular mechanics calculations. Whereas the solid-state structure of 1 has crystallographically imposed staggered C 2h symmetry, electron diffraction and calculations support a mixture of C 2 eclipsed isomers. The eclipsed ring-ring and the ring-isopropyl conformations found for 2 are essentially identical in the solid and gas phase and are supported by calculations. The molecular mechanics analysis may be extended to other alkylferrocene derivatives.

Reaction of a di-copper(i1) complex of a macrocyclic ligand with acetonitrile in the presence of O2 and H20 affords a pentanuclear complex containing two-co-ordinate and three-co-ordinate copper(1) atoms linked via triply bridging 3,5-dimethyl-I ,2,4-triazolate groups.

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