9-Anthracenyl-substituted pyridyl enones revisited: photoisomerism in ligands and silver(I) complexes.

In solution, (E) to (Z)-isomerism is facile both in 3-(9-anthracenyl)-1-(pyridin-4-yl)propenone, 2, and in its silver(I) complex [Ag(2)(2)](+). The crystal structures of (E)-2, (Z)-2 and [Ag{(E)-2}(2)][SbF(6)] are presented, and the roles of edge-to-face and face-to-face π-interactions in the lattice are discussed. Solution NMR spectroscopic data suggest that the driving force for (E) to (Z) isomerization is intramolecular π-stacking of the pyridine and anthracene domains. The reversed enone 3-(9-anthracenyl)-1-(pyridin-4-yl)propen-3-one, (E)-3, and the silver(I) complex [Ag{(E)-3}(2)][SbF(6)] have been prepared and characterized, including a single crystal X-ray determination of the latter. Surprisingly, no π-stacking between anthracene or pyridine domains is observed in the solid state, and the crystal packing is dominated by Ag···F, CH(anthracene)···π-pyridine and CH···F interactions. In contrast to (E)-2 and [Ag{(E)-2}(2)](+), neither (E)-3 nor [Ag{(E)-3}(2)](+) undergoes photoisomerization in solution.