A binuclear silver(I) perchlorate macrocycle based on 2,5-bis[(E)-(3-pyridyl)methylene]cyclopentanone: Crystal structure and solution behavior

The homobinuclear complex [Ag(MeC N)(OClO3)(μ-L)]2 (L = 2,5-bis[(E)-(3-pyridyl)methylene]cyclopentanone) (3) has been prepared by the diffusion-controlled reaction of [AgClO4] (1) dissolved in acetonitrile with equimolar amounts of L (2) in chloroform. The coordination complex 3 was characterized by single-crystal X-ray diffraction studies, showing that in the solid state a 26-membered disilver macrocycle is formed. The four coordination sites at the silver metal center are occupied by two nitrogen donor atoms of neighboring ligands, one nitrogen donor atom of an acetonitrile solvent molecule and an oxygen donor atom from a weakly-coordinated OClO3 counter-anion. During a 6 months period compound 3 in the solid state does not undergo any visible changes upon action of ambient light (NMR check), whilst dimethylsulfoxide (DMSO) solutions of 3 on exposure to sunlight undergo a rapid (ca. 1 day) photochemical transformation, namely trans/cis-isomerization and [2+2] cycloaddition reactions. This phenomenon is explained by the dissociation of 3 to the starting components 1 and 2 in DMSO and acetonitrile solutions, as has been demonstrated by 1H NMR spectroscopy and ESI-TOF mass-spectrometry.