Synthesis, characterization and unusual crystal structures of two cytosine cadmium(II) chloride compounds

Abstract

Two cytosine (Cyt) cadmium(II) chloride compounds have been prepared and their crystal structures determined: [Cd(Cyt)₃Cl][Cd(Cyt)Cl₃]·H₂O 1 and [{CdCl₂(H₂O)₂·2Cyt}_n]2. Compound 1 is triclinic, space group P, Z= 2, a= 7.243(2), b= 13.860(3), c= 14.113(3)Å, α= 95.07(2), β= 90.79(2), γ= 104.52(2)°, R= 0.027; compound 2 is monoclinic, space group C2/c, Z= 4, a= 22.355(6), b= 3.853(1), c= 18.645(5)Å, β= 115.43(2)°, R= 0.038. Both crystal structures are rather unusual. Compound 1 consists of two different ionic moieties, in both of which the cytosine molecules co-ordinate through N(3) and more weakly through O(2). Thus, taking into account only the stronger N(3) interaction, the cadmium(II) ions have a distorted-tetrahedral arrangement. When also the weaker interactions with the carbonyl oxygens are considered, in the first moiety the metal ion is seven- and in the second it is five-co-ordinated. Compound 2 is not a cytosine complex, as the Cyt molecules are not linked to the Cd^II; the metal atoms form a one-dimensional chain through bridging chlorine atoms along the b axis. The arrangement around the cadmium atoms is octahedral and each metal is linked to four equatorial Cl atoms and to two axial water molecules. The cytosine bases are hydrogen bonded to these water molecules in an arrangement allowing both inter-base stacking interactions and base pairing via hydrogen bonds. The structures are compared with that of [CdCl₂(mcyt)₂]3(mcyt = 1-methylcytosine).