New supramolecular complexes of manganese(II) and cobalt(II) with nucleic bases. Crystal structures of [M(H2O)(6)(1-Mecyt)(6)][ClO4](2)center dot H2O, [Co(1-Mecyt)(4)][ClO4](2) and [M(H2O)(4)(cyt)(2)][ClO4](2)center dot 2cytcenter dot 2H(2)O [M = Co-II or Mn-II; cyt = cytosine; 1-Mecyt=1-methylcytosine]

The reactivity of cytosine [cyt] and 1-methylcytosine [1-Mecyt] towards tra nsition metal ions Mn2+ and Co2+ has been tested through the analysis of th eir complexes. Two new compounds have been obtained from 1-Mecyt in aqueous medium, [M(H2O)(6)(1-Mecyt)(6)][ClO4](2). H2O [M=Mn-II 1 or Co-II 2], and consist of hexaaqua ions linked to six 1-Mecyt molecules in such a way as t o constitute a supramolecular cationic entity. Crystallization water molecu les join the supramolecular assemblies by means of hydrogen bonds. Perchlor ate anions, which are held in the crystal by electrostatic interactions wit h the cationic assemblies, insure the electroneutrality of the compounds. C ompound 2 (pale pink crystals), when not filtered, over time disappears and gives rise to dark pink crystals of formula [Co(1-Mecyt)(4)][ClO4](2) 3. C ompound 3 contains four 1-Mecyt molecules directly linked through N(3) atom s to Co2+ ions in a tetrahedral arrangement. No water molecule is present. The [Co(1-Mecyt)(4)](2+) cationic units are joined together through hydroge n bonds and form a chain. Perchlorate anions hold these cationic chains tog ether by means of electrostatic forces. The reaction of cyt with Mn2+ and C o2+ ions leads to compounds of formulae [M(H2O)(4)(cyt)(2)][ClO4](2). 2cyt . 2H(2)O [M=Mn2+ 4 or Co2+ 5] in which base pairs are formed between the tw o unco-ordinated cytosine molecules and those co-ordinated to the metal ion through the O(2) atom. Each metal ion is six-co-ordinated, being linked al so to four water molecules. Perchlorate anions and crystallization water mo lecules interact with the base pairs and the metal ion through hydrogen bon ds to form five-membered rings. The cobalt(II) compound constitutes the fir st example of cytosine-cobalt(II) co-ordination via O(2).