DFT Study on Microhydration of [Ni–Cyclam]2+ Complex with R‐COO− Anions#

Abstract

Nickel–cyclam complex is often used to build metal‐organic frameworks (MOFs) with carboxylate anions as linkers. The stability of the coordinate complex is important for investigating the secondary building unit (SBU) of MOFs. We performed density functional theory study to elucidate the various conformations of the complex, focusing on the metal–ligand coordination. It was found that the most favorable structure is octahedral complex in the triplet state with R‐COO − anions along the axial site. For the hydrated complexes, the extra H2O molecules may make hydrogen bonds with the R‐COO − ligands or act as axial ligands replacing R‐COO − anions. Our calculations suggested that the presence of H2O molecules may result in the weakening of the SBU complex. It was also found that microhydration leads to the shifting of the energy levels of the d orbitals of the complex.