Synthesis and structure of cytosine dichloride cuprate: direct binding of copper to cytosine.

Dichlorobis(cytosine)copper(II), [CuCl2-(C4H5N3O)2], Mr = 356.65, monoclinic, P2(1)/n, a = 8.399 (2), b = 13.773 (2), c = 10.775 (2) A, beta = 90.8 (2) degrees, V = 1246.3 (9) A3, Z = 4, Dx = 1.901 Mg m-3, lambda (Mo K alpha) = 0.7107 A, mu = 2.195 mm-1, F(000) = 716, T = 298 K, R = 0.032, wR = 0.037 for 2313 reflections greater than 2 sigma(F). The crystal structure of the title compound consists of two crystallographically independent cytosine molecules attached together through the direct bonding of a Cu2+ ion with two N atoms of the pyrimidine rings. In addition to the N atoms, the Cu ions are coordinated to two Cl atoms forming approximately a square-planar environment. The bond distances of Cu to Cl(1), Cl(2), N(3) and N(3') atoms are 2.299 (1), 2.267 (1), 1.985 (4) and 1.996 (3) A, respectively. Packing of the Cyt(I)-CuCl2-Cyt(II) complex in the crystal is ensured by an extensive extramolecular N--H...Cl and N--H...O network. Hydrogen bonds involving Cl, O and H atoms of the neighboring Cyt(I) and Cyt(II) induce a slight distortion in Cu--Cl, C = O distances but do not significantly affect intramolecular bond lengths and angles in the cytosine rings and their flatness.