2,2′ : 6′,2″ : 6″,2‴-Quaterpyridine (qtpy): a versatile ligand in metallosupramolecular chemistry; crystal and molecular structures of [Ni(qtpy)(OH ₂ ) ₂ ][BF ₄ ] ₂ , [Pd(qtpy)][PF ₆ ] ₂ , [Cu ₂ (qtpy) ₂ ][Pf ₆ ] ₂ and [Ag ₂ (qtpy) ₂ ][BF ₄ ] ₂

The co-ordination behaviour of 2,2′ : 6′,2″ : 6″,2‴-quaterpyridine (qtpy) has been systematically studied. Double-helical dinuclear complexes were only obtained with ions bearing a low charge or a low charge-to-radius ratio and which have no electronically imposed preference for geometries in which the ligand can present a planar donor set. The double-helical complexes [Cu2(qtpy)2][PF6]2 and [Ag2(qtpy)2][BF4]2 have been structurally characterised, as have the mononuclear species [Ni(qtpy)(OH2)2][BF4]2 and [Pd(qtpy)][PF6]2. Complexes with zinc(II) and cadmium(II) are mononuclear but it is suggested that a double-helical dinuclear complex is formed with mercury(II).