Three new modes of adenine-copper(II) coordination:: interligand interactions controlling the selective N3-, N7- and bridging μ-N3,N7-metal-bonding of adenine to different N-substituted iminodiacetato-copper(II) chelates

The reaction Of Cu2CO3(OH)(2), various N-substituted-iminodiacetic acids [R-N(CH2CO2H)(2))] and adenine (AdeH) in water yields crystalline samples of mixed-ligand copper(H) complexes of formulas [Cu(A)(N7 -AdeH)(H2O)] . H2O (A = N-methyl- or Nethyl-iminodiacetato(2-); compounds 1 and 2, respectively), [Cu(B)(N3-AdeH)(H2O)] . H2O (B = N-benzyl- or N-(p -methylbenzyl)-iminodiacetato(2-); compounds 3 and 4, respectively) as well as [Cu-4(pheida)(4)(mu-N3,N7 -AdeH)(2)(H2O)(4)] . 2H(2)O (pheida = N-phenethyl-iminodiacetato(2-)). Crystal structures of the acid H(2)pheida and compounds 1-5 are reported. H(2)pheida acid exhibits a typical zwitterionic structure. Copper(H) compounds were also studied by TG analysis (with FT-IR study of the evolved gasses), IR, electronic and ESR spectra and magnetic susceptibility data. The N-alkyl- or N-benzyl-like-iminodiacetato(2-) ligands (A or B) give complexes with Cu(II)/(A or B)/AdeH equimolar ratio, whereas pheida yields an unexpected tetranuclear compound with a 2:2:1 Cu(II)/pheida/AdeH molar ratio. In 1 and 2 AdeH binds to the metal by N7, whereas in 3 and 4 the N3 atom is used. An unexpected bridging mu-N3,N7-AdeH-dicopper(II) binding mode is found in the tetra-nuclear compound 5 (without interligand pi,pi-stacking interactions). These AdeH-Cu(II) binding modes have not been referred in the literature before. The difference in AdeH-Cu(II) binding modes in compounds I or 2 and 3 or 4 is rationalised on the basis of the absence or presence of a flexible N-benzyl-like substituent in the iminodiacetato(2-) ligand skeleton, which prevents or permits the interligand pi,pi-stacking interactions. (C) 2002 Elsevier Science B.V. All rights reserved.