Influence of the Reaction Sequence on the Complexation of an NS4-Macrocycle with Cd-II and Cu-I Salts Leading to the Formation of Supramolecular Isomers and an Endo/Exocyclic Cu-I Complex

Abstract

In the construction of metallosupramolecules, the reaction sequence in a three-reactant system (one ligand plus two metal ions) could be one of the controlling factors influencing the outcome of the reaction. In this work, the formation of supramolecular isomers (1 and 2) and an endo/exocyclic Cu+ complex (4) of the NS4-macrocycle (L) via different sequential metal addition protocols (routes I-III) is reported. In one-pot reactions of L with Cu(CH3CN)4PF6 in the absence (route I) and presence (route II) of CdI2, a cyclic dimer CuI complex, [Cu-2(L)(2)](PF6) 2 (1), and a one-dimensional coordination polymer, [Cu2(L)2] n center dot n[CdI4] (2), were obtained, respectively. Interestingly, the complex cations in 1 and 2 are supramolecular isomers formed via cyclization and polymerization upon complexation, respectively, probably due to different geometric and electronic complementarities, via the C-H center dot center dot center dot X- hydrogen bonds, between L and the counterion. In the two-step reaction (route III), an endocyclic Cd2+ complex, [Cd(L)I-2] (3), obtained in the first step was utilized in the following reaction with Cu((CHCN)-C-3)(PF6)-P-4, giving rise to an endo/exocyclic tetranuclear Cu+ complex, [Cu-4(L)(2)(CH3CN)(6)](PF6)(4) (4), via Cd2+ -> 2Cu+ substitution, which is not accessible by conventional procedures. Solution studies by comparative NMR and electrospray ionization mass spectroscopy also support metal substitution by showing the stronger binding affinity of Cu+ over Cd2+. These results demonstrate that the metal substitution protocol could be useful for reaching novel metallosupramolecules difficult to obtain by other methods.