Characterization studies of adenine complexes with 3d metal perchlorates

Abstract

A series of adenine (LH) complexes with 3d metal perchlorates were prepared by refluxing solutions of the metal salts in ethanol-triethyl orthoformate with the ligand for 2–5 days. Our studies indicate that, depending on the ligand to metal molar ratio employed and the duration of the refluxing step, complexes with either neutral LH or anionic L − can be obtained. Among the new complexes, Cu(LH) 2(ClO 4) 2·C 2H 5OH appears to be of the familiar dimeric type with quadruple bridges of N(3), N(9)-bonded LH, one terminal -OClO 3 ligand per Cu 2+ ion and lattice ethanol ( μ eff = 1.66 μB at 298K.). The Fe 3+ complex ( μ eff = 2.39 μB) seems to be also a dimer of the [(O 2ClO 2)(LH) 2FeL 2Fe(LH) 2(O 2ClO 2)] type, with N(9)-bonded terminal and N( y), N(9)-bonded ( y = 1, 3 or 7) bridging adenine. A similar type of bridging (N( y), N(9)-bonded) adenine is also present in the probably double-bridged dimeric FeL(ClO 4)·C 2H 5OH·2H 2O complex ( μ eff = 4.86 μB), and a number of presumably linear, single-bridged polymers of the M(LH) 2(ClO 4) 2·χC 2H 5OH ( x=2 for M = Mn; x=3 for M = Co) and ZnL(ClO 4)·C 2H 5OH·3H 2O types. However, the two remaining complexes of the ML(ClO 4)·C 2H 5OH·2H 2O (M = Co, Ni) type, involve adenine apparently coordinated through the NH 2 nitrogen. For these compounds, linear polymeric single-bridged structures with N(6), N( z)-bonded ( z is most probably 9) bridging L, were considered as likely. The ambient temperature magnetic moments of the complexes considered as linear polymers range from slightly below normal to normal, but it is anticipated that studies at 300-80K. will reveal magnetic exchange interactions in general, in view of the established spin-spin coupling in the corresponding purine complexes.