Metal ion interactions with nucleobases in the tripodal tris(2-aminoethyl)amine (tren) ligand-system. Crystal structures of [Cu(tren)(adeninato)]·ClO4, [Ni(tren)(9-ethylguanine–0.5H)(H2O)]2·(ClO4)2.5·(ClO3)0.5 and [{Cu(tren)}2(hypoxanthinato)]·(ClO4)3

Reaction of tris(2-aminoethyl)amine (tren) and Cu(ClO4)2 or Ni(ClO4)2 with nucleobases (adenine, 9-methyladenine, 9-ethylguanine, hypoxanthine, cytosine, or uracil) has yielded ternary metal complexes of adenine (complex 1 for Cu2+), 9-ethylguanine (2 for Cu2+ and 3 for Ni2+), and hypoxanthine (4 for Cu2+ and 5 for Ni2+) but no adduct for 9-methyladenine, cytosine, and uracil. Crystal structures of [Cu(tren)(adeninato)]·ClO4 (1), [Ni(tren)(9-ethylguanine–0.5H)(H2O)]2·(ClO4)2.5·(ClO3)0.5 (3), and [{Cu(tren)}2(hypoxanthinato)]·(ClO4)3 (4) were determined by X-ray diffraction. In 1, the trigonal-bipyramidal Cu2+ ion capped with a tripodal tetradentate tren ligand, [Cu(tren)]2+, binds to an adeninate anion through N(9) with the formation of an intramolecular hydrogen bond between the amino group of tren and N(3) of the base. The complex 3 involves two crystallographically independent but chemically equivalent [Ni(tren)(9-ethylguanine–0.5H)(H2O)]1.5+ structural units, in each of which the tren-capped octahedral Ni2+ ion, [Ni(tren)(H2O)]2+, binds to the guanine moiety, its N(1) site being hemideprotonated, through N(7) with the formation of two intramolecular hydrogen bonds involving the keto substituent O(6) of the base, one with the amino group of tren and the other with the water ligand. In 4, a hypoxanthinate anion is bound to two [Cu(tren)]2+ fragments, one through N(7) with the formation of an intramolecular hydrogen bond between O(6) of the base and the amino group of tren and the other through N9 with the formation of an intramolecular hydrogen bond between the ring nitrogen N(3) of the base and the amino group of tren. The observed guanine-specific binding property of the tren-capped 5-coordinated Cu2+ or 6-coordinated Ni2+ species, that is, 9-ethylguanine≫9-methyladenine, cytosine, and uracil, is rationalized by interligand interactions.