Asymmetric and Symmetric Dicopper(II) Paddle-Wheel Units with Modified Nucleobases

New copper­(II) paddle-wheel complexes with different modified nucleobases and simple molecules in the axial positions have been prepared by direct reactions between copper­(II) salts and the corresponding uracil- or thymine-1-acetic acids under inert atmosphere to produce the two homoleptic complexes, [Cu2(μ-OOCCH2-T)4(G)2] and [Cu2(μ-OOCCH2-U)4(G)2], and the heteroleptic one [Cu2(μ-OOCCH2-T)2(μ-OOCCH2-U)2(G)2] (where OOCCH2-T = thymine-1-acetate, OOCCH2-U = uracil-1-acetate, and G = dimethylformamide, water, dimethylacetamide, or dimethyl sulfoxide). Interestingly, the crystal structures of this family of closely related molecules present significant differences in their supramolecular arrangements affecting the crystal networks mainly due to the interactions defined between the different apical ligands and the coordinated modified nucleobases. Thus, depending upon the dimetallic complex several H-bonding interactions have been found in these series: (i) base pairing through Watson–Crick faces of adjacent dimetallic units, (ii) between a coordinated nucleobase and an oxygen atom from a carboxylic group of a neighboring molecule, and (iii) between a nucleobase and a solvent molecule. All these together with weaker π–π staking interactions define different 1D and 2D supramolecular assemblies. Interestingly, the magnetic studies show strong antiferromagnetic Cu···Cu interactions in agreement with the presence of four μ-κO:κO′ carboxylates bridging the metallic centers in each dinuclear complex. Finally, the crystal-to-crystal exchange reaction involving the ligands coordinated in the axial positions of the dimetallic [Cu2(OOCCH2-T)4(DMF)2]3[Cu2(OOCCH2-T)4(DMF)­(H2O)]2 to the related 1D coordination polymer [Cu­(OOCCH2-T)2(H2O)2]n has been confirmed in the presence of water vapor. This transformation implies a chemical stimuli magnetic response going from strong antiferromagnetic to almost paramagnetic, respectively.