Octahedral non-helical bis(bipyridyl) metallomacrocycles

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Abstract
The crystal structure of bis{2,6-bis[3-(6′-methyl-2,2′-bipyridin-6-yl)-2-oxapropyl]naphthalene}dinickel tetrakis (hexafluorophosphate)[Ni2L1 2][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).

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