FORMATION OF DIHELICATE AND MONONUCLEAR COMPLEXES FROM ETHANE-BRIDGED DIMERIC BIPYRIDINE OR PHENANTHROLINE LIGANDS WITH COPPER(I), COBALT(II), AND IRON(II) CATIONS

The dimeric ethane-bridged ligands 1,2-bis(6'-methyl-2,2'-bipyridin-6-yl)ethane (1) and 1,2-bis(9-methyl-1,10-phenanthrolin-2-yl)ethane (2) form a double-stranded helicate by complexation with copper(I), yielding the dinuclear complexes [Cu2(1)2](ClO4)2 (1a) and [Cu2(2)2](ClO4)2 (2a). The double-helical structure, in which two ligands are wrapped around two copper(I) cations, has been assigned by H-1 NMR studies and confirmed in the case of the dinuclear complex 1a by X-ray diffraction. This complex C48H44O8Cl2Cu2 crystallizes in the monoclinic space group P2(1)/n with four molecules per unit cell of dimensions a = 19.162 (7) angstrom, b = 11.701 (6) angstrom, c = 20.215 (7) angstrom, beta = 95.25 (2)-degrees, and V = 4513 angstrom 3 at -100-degrees-C. The structure was refined to R = 0.048 (R(w) = 0.076) for 3848 reflection data with I > 3-sigma(I). The copper cations, which are arranged in a distorted tetrahedral fashion, are separated by a distance of 5.926 (1) angstrom. The dinuclear copper complexes with ligands 1 and 2 are oxidized in a single reversible dielectronic wave at potentials somewhat higher than those of the mononuclear analogues. Ligand 2 gives a mononuclear cobalt(II) species of octahedral geometry, which has been fully characterized by X-ray diffraction. This complex C30H22N4O6F6S2Co crystallizes in the monoclinic space group P2(1)/n with four molecules per unit cell of dimensions a = 11.509 (2) angstrom, b = 14.296 (3) angstrom, c = 19.436 (3) angstrom, beta = 106.10 (2)-degrees, and V = 3072 angstrom 3 at room temperature; R = 0.055 (R(w) = 0.075) for 3094 reflections with I > 3-sigma(I). Ligand 3 (1,2-bis(5'-methyl-2,2'-bipyridin-5-yl)ethane) leads to a triply bridged dinuclear iron species.