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

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 Cu-N(purine-like) coordination bond which can be reinforced by an intra-molecular interligand H-bonding interaction. N-H(purines)center dot center dot center dot A(O orCl acceptor) or N-H(amino ligand L)center dot center dot center dot O6(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 Cu(II)2(mu(2)-N3,N9-adeninate)(4)(aqua)(2) or Cu-2(I)(mu(2)-N3,N9-adeninate)(2)(aqua)(2) recognise CuL chelates by means of the expectable pattern (Cu-N7 coordination bond + N6-H center dot center dot center dot O(L) interaction). (C) 2007 Elsevier B.V. All rights reserved.