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)(diaqua)nickel(II)]·(cytosinium) hydrate, and [(nta)(diaqua)nickel(II)]·(cytosinium)·(cytosine) hydrate

Abstract

Treatment of Ni(OAc) 2 and nitrilotriacetic acid (H 3nta) with nucleobases, adenine, 9-ethylguanine, cytosine, or uracil, provides a complex, [Ni(nta)(adeninium)(H 2O)] 2·5H 2O ( 1), and two salts, [Ni(nta)(H 2O) 2]·(cytosinium)·2H 2O ( 2) and [Ni(nta)(H 2O) 2]·(cytosinium)·(cytosine)·2H 2O ( 3), crystal structures of which were determined by X-ray diffraction, but no adduct for 9-ethylguanine and uracil. In 1, the adeninium moiety binds to the octahedral Ni 2+ atom, which is capped with a tripodal nta ligand to form the [Ni(nta)(H 2O)] − 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 to the Ni 2+ atom but attaches to the [Ni(nta)(H 2O) 2] − fragment through triple hydrogen bonds. Complex 3 includes neutral and cationic cytosine molecules, neither of which bind to the Ni 2+ atom and to the [Ni(nta)(H 2O) 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 Ni 2+ species, that is, adenine≫9-ethylguanine, cytosine, and uracil, is discussed in terms of interligand interactions.