Co-ordination chemistry of adenine (HAde): synthesis and characterization of [CuII(tren)(nucleobase)]X2[tren = tris-(2-aminoethyl)amine, X = Cl or NO3] complexes and crystal structure of [CuII(tren)(Ade)]Cl·2H2O

Abstract

The five-co-ordinate complexes [CuII(tren)(H2O)]Cl21, [CuII(tren)(HAde)]Cl22, [CuII(tren)(HAde)]-[NO3]23 and [CuII(tren)(Ade)]Cl·2H2O 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 CuII, whereas in complex 4 the adenine molecule is bound in its monoanionic form, as confirmed by the X-ray analysis [monoclinic, space group P21/a, a= 15.001(2), b= 8.422(1), c= 15.039(2)Å, β= 105.90(6)°, 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 N9 nitrogen from the adenine monoanion. The Cu–N(9) distance is rather short at 1.965(9)Å. Such selective metal bonding in adenine is very probably promoted by the trigonal-bipyramidal geometry around CuII and by the relatively low steric hindrance of the CuII(tren) moiety.