COORDINATION CHEMISTRY OF ADENINE (HADE) - SYNTHESIS AND CHARACTERIZATION OF [CU-II(TREN)(NUCLEOBASE)]X(2) [TREN=TRIS(2-AMINOETHYL)AMINE, X=CL OR NO3] COMPLEXES AND CRYSTAL-STRUCTURE OF [CU-II(TREN)(ADE)]CL-CENTER-DOT-2H(2)O

The five-co-ordinate complexes [Cu-II(tren)(H2O)]Cl-2 1, [Cu-II(tren)(HAde)]Cl-2 2, [Cu-II(tren)(HAde)]-[NO3](2) 3 and [Cu-II(tren)(Ade)]Cl.2H(2)O 4 [tren = tris(2-aminoethyl)amine and HAde = neutral adenine] have been synthesized and characterized. The geometry and structures of the complexes were studied by electronic and IR spectra and, in addition, the structure of complex 4 has been determined by X-ray crystallography. The physicochemical data for complexes 2 and 3 support the presence of neutral adenine co-ordinated to Cu-II, whereas in complex 4 the adenine molecule is bound in its monoanionic form, as confirmed by the X-ray analysis [monoclinic, space group P2(1)/a, a = 15.001(2), b = 8.422(1), c = 15.039(2) Angstrom, beta = 105.90(6)degrees, Z = 4; R = 0.065 for 2596 unique diffraction data]. The co-ordination polyhedron around the Cu2+ ion is approximately trigonal bipyramidal, with the equatorial sites occupied by the three primary amino nitrogen atoms and the axial positions occupied by the tertiary amino nitrogen and the imidazole N-9 nitrogen from the adenine monoanion. The Cu-N(9) distance is rather short at 1.965(9) Angstrom. Such selective metal bonding in adenine is very probably promoted by the trigonal-bipyramidal geometry around Cu-II and by the relatively low steric hindrance of the Cu-II(tren) moiety.