Interligand interactions involved in the molecular recognition between copper(II) complexes and adenine or related purines

Abstract

The available crystal structure information in the CSD database on ternary species prepared by the reaction of diverse copper(II) complexes (CuL) and purine, adenine and guanine or related purine derivatives is considered in order to deepen the intra-molecular interligand interactions affecting the molecular recognition patterns of the ‘metal complex + purine nucleobase’ and closely related systems. The degree of protonation and the possibilities of different tautomeric forms in the purine-like moieties are taken into account. The main conclusion is a general trend to form a Cusingle bondN(purine-like) coordination bond which can be reinforced by an intra-molecular interligand H-bonding interaction. Nsingle bondH(purines)cdots, three dots, centeredA (O or Cl acceptor) or Nsingle bondH(amino ligand L)cdots, three dots, centeredO6(oxo-purines) are commonly observed. In addition, selected examples revealed that the presence of a variety of non-coordinating groups in L or in the purine-like nucleobases can significantly influence the structurally observed molecular recognition pattern. Moreover, examples are known where binuclear cores of the types CuII2(μ2-N3,N9-adeninate)4(aqua)2 or CuI2(μ2-N3,N9-adeninate)2(aqua)2 recognise CuL chelates by means of the expectable pattern (Cusingle bondN7 coordination bond + N6single bondHcdots, three dots, centeredO(L) interaction).