Assembling of Dimeric Entities of Cd(II) with 6-Mercaptopurine to Afford One-Dimensional Coordination Polymers:  Synthesis and Scanning Probe Microscopy Characterization

The direct reaction between 6-mercaptopurine (6-MP) and Cd^II under different conditions yields either [Cd₂(6-MP)₄(NO₃)₂](NO₃)₂ (1) or [Cd(6-MP^-)₂·2H₂O]_n (4). Compound 1 behaves as the building block of the polymer [Cd(6-MP^2-)₂]_n[Ca(H₂O)₆]_n (3), by deprotonation of 6-MP ligand. In the reaction of 1 to give 3, the dinuclear compound [Cd₂(6-MP)₄(H₂O)₂](NO₃)₄·2H₂O (2) can be isolated as an intermediate. Polymers 3 and 4 convert into each other in water via deprotonation−protonation reactions. The structures of compounds 1−3 have been determined by X-ray diffraction. Given the small differences in the arrangement shown in the crystal structures of the polymer 4 and the polyanion of 3, the stabilities and energetics of the two arrangements have been examined by DFT calculations to determine the possibility of identifying new conformations of both polymers. In addition, the two polymers have been characterized on surfaces by means of AFM. The direct reaction between 6-MP and Cd^II and the deprotonation of the polymer 4 have proven to be useful routes for the isolation of one-dimensional systems on surfaces. The development of new strategies to characterize these types of polymers on surfaces opens the possibility to perform nanoscale studies on their properties and their potential use as nanomaterials.