Experimental and Theoretical Study of Dynamic Structural Transformations between Sensing Copper(II)-Uracil Antiferromagnetic and Metamagnetic Coordination Compounds

摘要

This paper describes the synthesis and characterization of several copper(II)-uracil-l-propionic acid (UPrOH) coordination compounds, including a theoretical and experimental study of their crystalline transformations, from paddlewheel structures ([Cu-2(UPrO)(4)(MeOH)(OH2)]center dot 2H(2)O (1), [Cu-2(UPrO)(4)-(MeOH)(2)]center dot 2MeOH (2), [Cu-2(UPrO)(4)(OH2)(2)]center dot 6H(2)O (3a), [Cu-2(UPrO)(4)(OH2)(2)]center dot 4H(2)O center dot 2MeOH (3b)), to two-dimensional coordination polymer ([KCu2(UPrO)(5)(OH2)(2)](n) (4)), or to dimeric compound ([Cu-2(UPrO)(4)(OH2)(4)]center dot 4H(2)O (5)), due to slight modifications in the water-methanol solvent ratio used in their synthetic processes and thanks to the formation of supramolecular structures by hydrogen bonds. The theoretical study analyzes the thermodynamic stability of the phases, finding that, if we do not consider the supramolecular interactions, paddlewheel structures are more stable than the dimeric one, regardless of the medium in which they exist. However, the cohesive energy calculations can explain the final stabilization of the dimeric structure as a result of the subsequent supramolecular interactions. These transformations also involve color changes, rendering these compounds water and methanol sensors. In addition, the magnetic study confirms the paddlewheel environments with the presence of strong antiferromagnetic Cu-Cu coupling and weak antiferromagnetic intradimer Cu-Cu interactions with metamagnetic behavior in the case of dimeric species.