Octahedral non-helical bis(bipyridyl) metallomacrocycles

Abstract

The crystal structure of bis{2,6-bis[3-(6′-methyl-2,2′-bipyridin-6-yl)-2-oxapropyl]naphthalene}dinickel tetrakis (hexafluorophosphate)[Ni₂L¹₂][PF₆]₄ was determined by X-ray diffraction methods and refined to a residual of 0.078 for 2765 independent observed reflections: triclinic, space group P, a= 13.555(3), b= 17.801(5), c= 10.305(7)Å, α= 100.2(4), β= 99.74(3), γ= 101.83(2)°. The two nickel(II) ions are bound to four nitrogens from two bipyridyl groups and two oxygen atoms from the ether linkers in a grossly distorted octahedral geometry. The complex has a non-helical configuration and the two naphthalene rings are parallel and offset by 4.11 Å. The torsional flexibility of the ether linkers facilitates this orientation and allows the aromatic rings to stack in the complex. In solution L¹, which contains a 2,6-disubstituted naphthalene spacer, forms non-helical and helical [2 + 2] tridentate metallomacrocycles with zinc(II)(7 : 3) and cadmium(II)(45 : 55), and forms a labile complex(es) with mercury(II). No complexation with iron(II) or ruthenium(II) was observed. The effect of the substitution pattern of the naphthalene spacer was examined by comparison of the zinc(II) complexes obtained with L¹, a 2,7-disubstituted naphthalene (L²) and a 1,5-disubstituted naphthalene (L³). While L¹ and L² both formed mixtures of [2 + 2] complexes, L³ formed a [1 + 1] complex. Ligands L¹ and L⁵(containing a p-CH₂C₆H₄CH₂ spacer) exhibited poor ligand self–self recognition properties when treated with zinc(II).