X-ray studies of terpenoid derivatives. Part II. Crystal and molecular structure of the 1 :1 adduct of germacratriene with silver nitrate

Abstract

Crystals of the 1 : 1 adduct of silver nitrate with the novel sesquiterpene germacratriene, C₁₅H₂₄AgNO₃, are monoclinic, space group P2₁/c, with a= 7·530, b= 10·010, c= 20·905 Å, β= 102·1°, and Z= 4. The crystal structure has been elucidated by a three-dimensional X-ray study, based on 1198 independent reflection intensities visually estimated from Weissenberg photographs, with the silver ion as the phase-determining heavy-atom. Positional and isotropic thermal parameters have been refined by full-matrix least-squares methods to a final R of 0·097. The all-trans stereochemistry has been confirmed for germacratriene. Each silver ion complexes to two double bonds in different molecules forming chains parallel to a, and these are cross-linked by chains of Ag⁺ and NO₃^–ions parallel to b. The differences in reactivity of the ethylenic bonds are explicable in terms of their torsional strain. The interaction between germacratriene and the ionic layers, and the co-ordination of the Ag⁺ ion, are also discussed.