Synthon Robustness and Structural Modularity of Copper(II) Two-Dimensional Coordination Polymers with Isomeric Amino Acids and 4,4 '-Bipyridine

摘要

Reactions of copper(II) nitrate trihydrate with 4,4'-bipyridine (bipy) and isomeric amino acids (aa) L-leucine or L-isoleucine were investigated under different solution-based and mechanochemical synthetic procedures. Four different, but isoreticular two-dimensional coordination polymers of the general formula [Cu-2(aa)(2)(NO3)(2)(bipy)(H2O)(2)](n), with solvent molecules within voids in thus formed crystal structures were isolated. Electron spin resonance spectroscopy confirmed that the subtle differences in the coordination spheres, imposed by ligand branchiness, are reflected in the local magnetic structure of copper(II) ions. Solvent molecules can be readily removed by heating, which affects the crystal structure, but it also influences the coordination sphere and the electron spin properties of the copper(II) nodes. The main structural motif remains conserved even upon water and solvent loss, leading to the swift formation of the target coordination polymers upon short exposure to the solvent-vapors atmosphere.