Interligand interactions affecting specific metal bonding to nucleic acid bases:: the tripodal nitrilotriacetato (nta) ligand-system.: Crystal structures of [(nta)(adeninium)(aqua)nickel(II)] hydrate, [(nta)(diagua)nickel(II)]•(cytosinium) hydrate, and [(nta)(diaqua)nickel(II)]•(cytosinium)•(cytosine)•hydrate

Treatment of Ni(OAc)(2) and nitrilotriacetic acid (H(3)nta) with nucleobases, adenine, 9-ethylguanine, cytosine, or uracil, provides a complex, [Ni(nta)(adeninium)(H2O)](2).5H(2)O (1), and two salts, [Ni(nta)(H2O)(2)].(cytosinium).2H(2)O (2) and [Ni(nta)(H2O)(2)].(cytosinium).(cytosine).2H(2)O (3), crystal structures of which were determined by X-ray diffraction, but no adduct for 9-ethylguanine and uracil. In i, the adeninium moiety binds to the octahedral Ni2+ atom, which is capped with a tripodal nta ligand to form the [Ni(nta)(H2O)](-) fragment, at the axial position through the N(7) atom with the formation of an interligand hydrogen bond or hydrogen bonds between the amino substituent N(6) of the base and a carboxylato oxygen or carboxylato oxygens of nta. In 2, the cytosinium molecule does not bind directly fo the Ni2+ atom but attaches to the [Ni(nta)(H2O)(2)]-fragment through triple hydrogen bonds. Complex 3 includes neutral and cationic cytosine molecules, neither of which bind to the Ni2+ atom and to the [Ni(nta)(H2O)(2)](-) fragment either, and, instead, there forms a cytosinium-cytosine complementary base-pair through triple hydrogen bonds. The observed base-specific binding property of the nta-capped octahedral Ni2+ species, that is, adenine much greater than 9-ethylguanine, cytosine, and uracil, is discussed in terms of interligand interactions. (C) 2000 Elsevier Science B.V. All rights reserved.