Structural studies of copper(I) complexes with ethylene. Crystal structures of [Cu(2,2′-bipyridine)(ethylene)]ClO4 and [Cu(1,10-phenanthroline)(ethylene)]ClO4

The crystal structures of the complexes [Cu(2,2′-bipyridine)(ethylene)]ClO4 (I) and [Cu(1,10-phenanthroline)(ethylene)]ClO4 (II) have been determined from X-ray diffraction studies. Complex I crystallizes in the triclinic space group, P 1 , with four molecules in a unit cell of dimensions a 10.657(1), b 6.998(1), c 18.251(2) A, α 91.05(1), β 93.35(1), and γ 84.97(1)°. Complex II crystallizes in the monoclinic space group, P21/a, with four molecules in a unit cell of dimensions a 19.981(5), b 10.904(2), c 6.955(1) A, and β 103.90(2)°. Both structures were solved by heavy-atom methods, and refined by block-diagonal least-squares methods. The final R-values for I and II were 0.044 for 2225 observed reflections for I and 0.066 for 2005 observed reflections for II. In both crystals, the CuI ion is coordinated to two nitrogen atoms of 2,2′-bipyridine or 1,10-phenanthroline, and two carbon atoms of ethylene in an approximately planar form. The CC bond distances of the coordinated ethylene molecules, 1.360(13) and 1.346(18) A for I and 1.361(22) A for II, do not show marked lengthening compared with that for free ethylene, and may be explained by dπ(Cu) → dπ (ethylene) back-bonding between the Cu 3dπ orbital and the Rydberg 3dπ orbital of the ethylene molecule.