Microscopic origins of the ferromagnetic exchange coupling in oxoverdazyl-based Cu(II) complex

Abstract

The exchange channels governing the experimentally reported coupling constant ͑J expt =6 cm −1 ͒ value in the verdazyl-ligand based Cu͑II͒ complex ͓Cu͑hfac͒ 2 ͑imvdz͔͒ are inspected using wave function-based difference dedicated configuration interaction calculations. The interaction between the two spin 1/2 holders is summed up in a unique coupling constant J. Nevertheless, by gradually increasing the level of calculation, different mechanisms of interaction are turned on step by step. In the present system, the calculated exchange interaction then appears alternatively ferromagnetic/ antiferromagnetic/ferromagnetic. Our analysis demonstrates the tremendously importance of some specific exchange mechanisms. It is actually shown that both parts of the imvdz ligand simultaneously influence the ferromagnetic behavior which ultimately reaches J calc = 6.3 cm −1 , in very good agreement with the experimental value. In accordance with the alternation of J, it is shown that the nature of the magnetic behavior results from competing channels. First, an antiferromagnetic contribution can be essentially attributed to single excitations involving the network localized on the verdazyl part. In contrast, the ligand-to-metal charge transfer ͑LMCT͒ involving the imidazole moiety affords a ferromagnetic contribution. The distinct nature / of the mechanisms is responsible for the net ferromagnetic behavior. The intuitively innocent part of the verdazyl-based ligands is deeply reconsidered and opens new routes into the rational design of magnetic objects.

Beyond Kahn's Model: Substituent and Heteroatom Influence on Exchange Interaction in a Metal‐Verdazyl Complex

“…It has proven to be fruitful. [9] Moreover, since our recent results underline the importance of the substituent of the verdazyl radical, [7] we also play with this second ingredient. The single-crystal X-ray data obtained on the synthesized complex form a solid basis both for modelling the thermal variation of the magnetic susceptibility and for investigating by wavefunction-based methods the different contributions to the exchange interaction between the metal and the radical.…”

“…We aim to develop a global approach that favours a back-and-forth motion between the synthesis of radicalcontaining coordination architectures [3][4][5] and the theoretical investigation of the intimate mechanisms that govern the exchange interaction between spin bearers with magnetic orbitals of different natures. [6,7] Because the valence-only description that forms the basis of the Kahn's model does not take into account all the mechanisms that contribute to the exchange interaction, wavefunction-based methods appear as central ones to unravel the microscopic origins of this phenomenon in molecule-based magnets. Despite their demanding requirements, they allow to bridge the gap between an incomplete picture of the exchange mechanisms and a comprehensive interpretation with spectroscopic accuracy.…”

From Mononuclear to Dinuclear: Magnetic Properties of Transition Metal Complexes

“…This procedure allows us to split the system following a valence bond-like picture, staying in an orthogonal framework. The method has proven to be extremely e cient not only to reduce in a rational way the number of inactive and virtual MOs in post CASSCF treatments but also to analyse the relevance of chemical regions in energy di↵erences [314]. The procedure is particularly attractive in exchange coupling constants calculations since one can concentrate the numerical e↵orts according the polarizable nature of the di↵erent fragments.…”

“…systems [311][312][313][314]. Thus, dynamic electron correlation contributions were then incorporated using the variational methodology, the CAS+S and the di↵erence dedicated configuration interaction (DDCI) method, implemented in the CASDI code [150,315].…”

Analysis of the Magnetic Exchange Interactions in Yttrium(III) Complexes Containing Nitronyl Nitroxide Radicals

“…83,[104][105][106] In this case, only a set of excitations is included In summary, the subtle mechanism at the origin of the antiferromagnetic through-bond NIT-NIT interaction can be seen as a two-step mechanism involving both the π orbitals of the NIT radicals and the π orbitals of the central hfac − ligand (the one perpendicular to the Figure 1). First, there is a charge transfer from the hfac − to the NIT radical that can relax by interacting with the local excitations on the NIT radical (from occupied to virtual MOs).…”