Soncini Research Group

The use of an amino-pyridyl substituted $\beta$-diketone, N-(2-pyridyl)-ketoacetamide (paaH), has allowed for the isolation of two new families of isostructural mononuclear lanthanide complexes with general formulae: [Ln(paaH*)$_2$(H$_2$O)$_4$][Cl]$_3$$\cdot$H$_2$O (Ln = Gd (1), Tb (2), Dy (3), Ho (4), Er (5) and Y (6)) and [Ln(paaH*)$_2$(NO$_3$)$_2$(MeOH)][NO$_3$] (Ln = Tb (7), Dy (8), Ho (9) and Er (10)). The dysprosium members of each family (3 and 8) show interesting slow magnetic relaxation features. Compound 3 displays Single Molecule Magnet (SMM) behaviour in zero DC field with an energy barrier to thermal relaxation of $E_a = 177(4)$ K (123(2) cm$^{-1}$) with $\tau_0 = 2.5(8) \times 10^{-7}$ s, while compound 8 shows slow relaxation of the magnetization under an optimum DC field of 0.2 T with an energy barrier to thermal relaxation of $E_a = 64$ K (44 cm-1) with $\tau_0= 6.2 \times 10^{-7}$ s. Ab initio multiconfigurational calculations of the Complete Active Space type have been employed to elucidate the electronic and magnetic structure of the low-lying energy levels of compounds 2-5 and 8. The orientation of the anisotropic magnetic moments for compounds 2-5 are rationalized using a clear and succinct, chemically intuitive method based on the electrostatic repulsion of the aspherical electron density distributions of the lanthanides.