Metal-nucleobase interactions: Synthesis and crystal structure of trichlorobis(N-6-benzyl adeninium)copper(II) chloride dihydrate

The crystal structure of trichlorobis(N-6-benzyl adeninium)copper(II) chloride dihydrate has been investigated to explore the relation among site of protonation, mode/site of coordination, and conformation of the substituent in the adenine system, which is one of the major bases of nucleic acids. Space group: P2(1)/c, a = 10.713(9), b = 21.214(12), c = 13.560(10) Angstrom, beta = 110.52(6)degrees, R = 0.0512. Three chloride ions and two benzyl adeninium cations [coordinating through (N9)] complete the trigonal bipyramidal coordination sphere around copper. There are two water molecules of crystallization and a chloride ion, which are not coordinated to the metal, but held in the lattice by the network of hydrogen bonding. The N-6 substituent is distal to the imidazole nitrogen as reported for N-6 substituted adenines; Both of the adenine moieties are protonated at N(3) in addition to N(7), which is rather unusual and very interesting, whereas under normal situations in adenine, N(1) is the preferred site of protonation. The dihedral angles between the adenine and benzene groups in the ligands are 100.2(2)degrees and 92.7(2)degrees, which is close to 90 degrees, as expected for active cytokinins.