A molecular modelling study of the effects of pivalate ligand substitutions on the magnetic properties of chromium-wheels host complexes

Abstract

In our recent article, we had a successful experience in applying binuclear chromium (III) model ([Cr2F(tBuCO2)2(H2O)2(OH)4]−1) instead of real chromium-wheel host complex ([Cr8F8(tBuCO2)16]) to calculate the effect of bridged-ligands substitution on the exchange coupling constants (J) values of the complexes. In this work our experienced procedure was used to evaluate the effect of pivalate (tBuCO2) ligands substitution on the J values of the complexes. For this, at first two new groups of complexes were designed based on the replacement of pivalate by X-tBuCO2 and X-iPrCO2 anionic ligands (where X represents F, Cl, Br and I halogens) and then their J values were calculated. Since the existence of two halogen atoms in the structures of complexes leads to form different conformers, at first step a conformational analysis was carried out to identify the stable conformers of each complex. In X-tBuCO2-containing complexes four stable conformers were recognized, while X-iPrCO2-containing complexes had three stable conformers. At next step the J values of each of these conformers were calculated for all complexes. It was found that depending on which conformer was formed, the effect of these substitutions in each complex could be different, leading to a decrease or increase in the antiferromagnetic property of the complex. In both types of complexes, the formation of the least stable conformer, Conf1, led to the strengthening of the antiferromagnetic property of the complex but the impacts of the substitutions in other conformers were diverse. These new designed complexes could be considered as novel synthetic targets with different magnetic properties.