Antiferromagnetic Coupling Supported by Metallophilic Interactions: Theoretical View

Abstract

The antiferromagnetic coupling supported by metallophilic interactions has been studied in the framework of the broken symmetry approach (BS) and multiconfigurational calculations (CASSCF). A series of heterobimetallic complexes of the form [PtCo(X) 4 (Y)] 2 (X = tba thiobenzoate, SAc thioacetate, and Y = H 2 O, NO 2 py, py), previously reported, have been used as model systems. Magnetic coupling constants were found in good agreement with the experimental reports, and it could be concluded that axial ligands with a pure σ-donor character have a marked effect on the J value strengthening the antiferromagnetic coupling, as shown for [PtCo-(SAc) 4 (H 2 O)] 2 and [PtNi(SAc) 4 (H 2 O)] 2 . The latter complex, included for comparative purposes, also made it possible to evidence that the interaction between magnetic orbitals and low-level excitation in the Pt•••Pt region is also relevant favoring the stronger antiferromagnetic coupling found in this case. A careful analysis of the energetic components involved in Pt•••Pt interaction suggests that the stabilization arises from a combination of favorable orbital contributions, which allows a weak covalent Pt•••Pt σ(dz 2 ...dz 2 ) bond. Theoretical tools evidence that the weak σ-bond found between monomeric units is responsible for a spin polarization mechanism resulting in the observed antiferromagnetic interaction. Multiconfigurational calculations finally allowed us to establish that the spin polarization mechanism involves not only the d z 2 orbitals in the M-Pt•••Pt-M bond direction but also the empty 6p z orbitals of Pt atoms. The inclusion of these orbitals favors a correlation-induced delocalization of magnetic orbitals and therefore a better balance among direct and kinetic exchange. The results shown in this work are relevant in the molecular design of systems supported by metallophilic interactions not only between platinum atoms but also could be extended to other cases with similar interactions.

Experimental assignment of long-range magnetic communication through Pd & Pt metallophilic contacts

“…30 The axial zero-field splitting (D = −8 cm −1 ) is significantly reduced relative to {NiPt} (D = −12 cm −1 ). The difference in coordination strength of pyNO 2 (dimer axial ligand) and py (monomer axial ligand) is not great enough to cause such a drastic decrease in D. It is therefore believed that the decrease partially results from the delocalization of electrons from the filled Pt 2+ d z 2 orbital into bonding (metallophillic) molecular orbitals 42 , thereby reducing its coordination strength towards Ni 2+ .…”

“…We chose a similar level of theory and methodology as that employed in a recent study of the exchange coupling in related dinuclear platinum systems. 42 DFT calculations were performed for both { NiPt } 2 and { NiPd } 2 . Geometry scans of the Pt⋯Pt and Pd⋯Pd distances were done on geometry optimized rigid structures for the remaining internal coordinates using the ORCA software and including dispersion correction to account for the soft M′⋯M′ interaction.…”

Voltage-induced modulation of the magnetic exchange in binuclear Fe(iii) complex deposited on Au(111) surface

“…To address this challenge, we performed a rigorous computational study focused on the deposition of a binuclear magnetic complex over a metallic surface. Although isolated polynuclear magnetic molecules have been extensively studied through sophisticated wave function based methods (WFT), [36][37][38][39][40] this is no longer possible once they are deposited on a substrate due to the extensive size of the systems. In this sense, we employed Density Functional Theory (DFT) based methods, widely used to determine the magnetic properties of metallic complexes interacting with different substrates, [41][42][43][44][45][46] and even their transport properties in single molecule junctions architectures.…”