Analysis of the Magnetic Coupling in a Mn(II)‐U(V)‐Mn(II) Single Molecule Magnet

Abstract

{Mn(TPA)I}{UO2(Mesaldien)}{Mn(TPA)I}]I formula (here TPA = tris(2-pyridylmethyl)amine and Mesaldien = N,N'-(2-aminomethyl)diethylenebis(salicylidene imine)) reported by Mazzanti and coworkers (Chatelain et al. Angew. Chem. Int. Ed. 2014, 53, 13434) is so far the best Single Molecule Magnet (SMM) in the {3d-5f} class of molecules exhibiting barrier height of magnetization reversal as high as 81.0 K. In this work, we have employed a combination of ab initio CAS and DFT methods to fully characterize this compound and to extract the relevant spin Hamiltonian parameters. We show that the signs of the magnetic coupling and of the g-factors of the monomers are interconnected. The central magnetic unit [U V O2] + is described by a Kramers Doublet (KD) with negative g-factors, due to a large orbital contribution. The magnetic coupling for the {Mn(II)-U(V)} pair is modeled by an anisotropic exchange Hamiltonian: all components are ferromagnetic in terms of spin moments, the parallel component JZ twice larger as the perpendicular one J ⊥ . The spin density distribution suggests that spin polarization on the U(V) center favors the ferromagnetic coupling. Further, the JZ /J ⊥ ratio, which is related to the barrier height, was found to correlate to the corresponding spin contribution of the g-factors of the U(V) center. This correlation established for the first time offers a direct way to estimate this important ratio from the corresponding g S -values, which can be obtained using traditional ab initio packages and hence has a wider application to other {3d-5f} magnets. It is finally shown that the magnetization barrier height is tuned by the splitting of the [U V O2] + 5f orbitals.

Exchange Couplings and Magneto‐Structural Correlations of Trinuclear MII‐UIV‐MII (MII=Co, Ni, Cu) Complexes

“…More recently, UO 2 + −M 2+ interactions provide a very convenient route for the controlled assembly of oxo‐bridged 3 d–5 f complexes and promote the cation‐cation interactions between the UO 2 + group and the 3d cations. Indeed, as reported by Mazzanti and co‐workers, [12–15] these hetero‐polymetallic complexes which exhibit a M II −O=U V =O−M II (M II =Mn, Fe, Co, Ni) linear oxo‐core, are of great interest for the design of molecules presenting slow magnetic relaxation of a purely molecular origin and described as single‐molecule magnets (SMMs), and have been put forward as an effect of the 3d spin ion on the magnetic properties [2,12–15] . Indeed, for the trimers in which the 3d metal adopts an octahedral geometry, the value of the energy barrier is directly correlated to the spin ground state, and it decreases along the high spin (Mn>Fe>Ni) series (Mn II : S=5/2; Fe II : S=2; and Ni II : S=1).…”

“…Over the last two decades, an increasing number of heteropolymetallic 3d-4 f and 3d-5f mixed complexes have aroused intense attention, both from experimental and theoretical sides, due to their opening new perspectives in the design of molecular magnets (SMMs), [1][2][3][4][5][6][7][8][9] and their exceptional promising applications such as ultra-high-density data storage, spintronic, and quantum information processing (QIP). [10] Besides its fundamental aspect, the understanding of the nature of metalligand bonding and metal-metal 3 d-4 f/5 f electronic interactions, in the lanthanide and actinide coordination compounds, is crucial in the design of novel magnetic materials.…”

“…Indeed, as reported by Mazzanti and co-workers, [12][13][14][15] these hetero-polymetallic complexes which exhibit a M II À O=U V = OÀ M II (M II = Mn, Fe, Co, Ni) linear oxo-core, are of great interest for the design of molecules presenting slow magnetic relaxation of a purely molecular origin and described as single-molecule magnets (SMMs), and have been put forward as an effect of the 3d spin ion on the magnetic properties. [2,[12][13][14][15] Indeed, for the trimers in which the 3d metal adopts an octahedral geometry, the value of the energy barrier is directly correlated to the spin ground state, and it decreases along the high spin (Mn > Fe > Ni) series (Mn II : S = 5/2; Fe II : S = 2; and Ni II : S = 1). Moreover, the low value of χT observed at ~2 K is due to the strong AF interactions in UO 2…”

The resolution of the weak-exchange limit made rigorous, simple and general in binuclear complexes

“…[58][59][60] In principle, the low-energy ab initio spectrum offers sufficient detail for calculating anisotropy parameters and spin-orbit correction to the exchange interaction if a SOCI is performed, 22,33 as well as EPR parameters and wT profiles provided that the Zeeman interaction is treated. 46,[61][62][63][64] This is the starting point of our work.…”