Oxo-anion binding by metal containing molecular ‘clefts’

A simple but effective route has been developed to produce a series of molecular clefts, [(η6-p-cymene)RuCl(1)2]PF6 (4a), [(dppe)Pd(1)2](BF4)2 (5a), [(dppe)Pd(2)2](BF4)2 (5b), [(dppe)Pt(1)2](BF4)2 (6a) and [(dppe)Pt(2)2](BF4)2 (6b), that contain either a redox active ferrocenyl or a photoactive anthracenyl side arm, attached to a ruthenium(II), palladium(II) or platinum(II) backbone. Compounds 4a, 5a, 5b and 6a act as hosts for oxo-anions. Anion recognition is achieved via convergent hydrogen bond interactions from secondary amine functionality on the side arms. The binding is also enhanced by the positive charge of the metal centres. The X-ray crystal structure of the related [PdCl2(1)2] (7) shows it to possess a trans geometry. The X-ray crystal structures of the monoadducts [(η6-p-cymene)RuCl2(1)] (3a) and [(η6-p-cymene)RuCl2(2)] (3b), which show contrasting behaviour in their hydrogen bonding to coordinated chloride, are also reported.