Evaluation of the Magnetic Interactions in Salts Containing [Ni(dmit)₂]⁻ Radical Anions

Abstract

This paper reports on a theoretical analysis of the electronic structure and magnetic properties of the [Ni(dmit)2] -radical anions in four salt compounds resulting from the combination with supramolecular cation-crown ether assemblies. The selected compounds are representative examples of the diversity of stacking patterns and magnetic behaviors found for systems based on these [Ni(dmit)2] -anions. Difference Dedicated Configuration Interaction calculations have been performed on fragments containing two neighbor [Ni(dmit)2] -units to evaluate the intradimer, interdimer, and interchain magnetic coupling constants and analyze the electronic structure of the [Ni(dmit)2] -ions. The amplitude and sign of these through-space interactions are consistent with the structure and arrangement of the [Ni(dmit)2] monomers in the chain and the overlap and transfer integral between the magnetic orbitals. They accurately simulate the thermal dependence of the magnetic susceptibility but do not agree with the reported J values in two of the systems, both composed by chains of weak dimers. These results highlight the nonunivocal nature of the fitting in complex systems and the difficulties in defining interaction spin models solely based on the quality of the resulting curves. This work shows the limitations of the extended Hückel calculations on the interpretation of the main ingredients of the magnetism and the relevance of reference theoretical calculations as a complementary tool for the understanding of the magnetic behavior of [Ni(dmit)2]-based functional materials.

Light-Induced Control of the Spin Distribution on Cu–Dithiolene Complexes: A Correlated Ab Initio Study

“…This is related to the bonding scheme between the metal and dithiolene ligands in the [M(dithiolene) 2 ] −n complexes, which can be a normal bonding scheme, with the metal orbitals destabilized with respect to the ligand orbitals, or the opposite, called the inverted bonding scheme. In the former case, the highest-occupied molecular orbitals (HOMO) or the single occupied molecular orbitals (SOMO) if the complex is a radical has a dominant metal contribution, while in the case of the inverted bonding scheme, the SOMO is mainly composed by the ligand orbitals [13,35,36]. Different experimental techniques such as XAS, ENDOR/ESEEM, and EPR spectroscopies [35,37,38], as well as quantum chemistry calculations (DFT, CASSCF/PT2) [36,39] on [Ni(dithiolene) 2 ] −n and [Cu(dithiolene) 2 ] −n complexes present evidences of an inverted bonding scheme in most of the Ni complexes, while Cu ones usually have a normal bonding.…”

Theoretical study of the photoconduction and photomagnetism of the BPY[Ni(dmit)2]2 molecular crystal

“…The amplitude of the interaction in S9 dimers is in agreement with that obtained for salts of the [Ni(dmit) 2 ] − radicals with similar packing patterns. 18 In addition to these interactions, there exists the possibility of interactions between the Ni1 and Ni2 units in the crystal through the S-S contacts, but due to their relative orientation and large distances, it is expected that they result in rather weak coupling constants, as illustrated in our previous study of the magnetic behaviour of [Ni(dmit) 2 ] − radicals. 18 The photoinduced charge transfer promotes one electron from an occupied orbital of the Ni(dmit) 2 anion to an unoccupied orbital of the BPY 2+ .…”

“…22 In the case of the isolated radical [Ni(dmit) 2 ] − the doublet ground state is also dominated by a single determinant (Table 2), where the SOMO corresponds to the antibonding combination of the π 1 orbital of the dmit ligands (Table 2), in line with previous theoretical studies on this radical. 18,24 The excited states are distributed in two groups, about 1.0 and 2.4 eV above the ground state. The first excited state at about 1.0 eV results from the single excitation from the (HOMO−1) to the SOMO.…”

“…The energies of the singlet and triplet states on each [Ni(dmit) 2 ] 2 dimer have been evaluated following the same strategy as in our previous work on the salts of the [Ni(dmit) 2 ] − radicals with supramolecular-cations. 18 As starting orbitals, we employed those resulting from a CASSCF(4,4) calculation on the singlet ground state of the neutral dimers. The CAS contains the (π 1 + π 1 ) bonding and (π 1 − π 1 ) antibonding combinations of the dmit ligand orbitals of each Ni(dmit) 2 unit.…”

“…1,3,5,[10][11][12][13][14][15] In this family, the anion radicals of M(dmit) 2 , with M = Ni, Pd, Pt, Cu, Au,… and dmit 2− = 1,3-dithiole-2-thione-4,5-dithiolate, have been distinguished as promising building blocks of magnetic and conducting molecular materials, the [Ni(dmit) 2 ] − radical being one of the most studied radicals. 1 The unpaired electron occupies a π-type orbital of the dmit ligands, [16][17][18] and the interaction of these π electrons with adjacent complexes is responsible for the electronic conduction and the spin-spin interactions. The resulting properties are extremely sensitive to the packing patterns and the nature of the counter cations forming the salt.…”