Strong Magnetic Interactions through Weak Bonding Interactions in Organometallic Radicals: Combined Experimental and Theoretical Study

Abstract

The magnetic properties of a series of three neutral radical organometallic complexes of general formula [CpNi(dithiolene)]. have been investigated by a combination of X-ray crystal structure analysis and magnetic susceptibility measurements, while the assignment of the exchange coupling constants to the possible exchange pathways has been accomplished with the help of calculations based on density functional theory (DFT). The syntheses and X-ray structures of [CpNi(adt)] (adt=acrylonitrile-2,3-dithiolate) and [CpNi(tfd)] (tfd=1,2-bis(trifluoromethyl)ethene-1,2-dithiolate) complexes are described, while [CpNi(mnt)] (mnt=maleonitriledithiolate) was reported earlier. In the three complexes, we observed strong antiferromagnetic coupling that could not be explained solely by short SS intermolecular contacts. Our calculations indicated that spin density in these complexes is strongly delocalized on the NiS2 moiety, with up to 20% on the Cp ring. As a consequence, CpCp and Cpdithiolene overlap interactions have been identified as responsible for antiferromagnetic couplings. The [CpNi(adt)] complex thus has a value J=-369.5 cm(-1) for an exchange interaction through a pi stacking due to the CpCp overlap.

Radical CpNi(dithiolene) and CpNi(diselenolene) complexes: Synthetic routes and molecular properties

“…This large delocalisation on the Cp ring has been shown to be at the origin of strong antiferromagnetic coupling interactions in the solid state, when two radical complexes crystallize in a Cp· · ·Cp face-to-face motif [26,34], as indeed experimentally observed in [CpNi(adt)], [CpNi(bdt)] and [CpNi(bds)].…”

“…(15) 1.710 (5) 1.691 (6) 1.320 (7) 93.246 (62) 88.9 (2) [34] dmit 2.138 (2) 2.133 (2) 1.706 (8) (16) 1.738 (5) 1.739 (6) 1.337 (7) 92.34 (6) 88.87 [44] F2pddt 2.1195 (9) 2.1314 (9) 1.724 (3) (16) 1.739 (6) (10) 89.5 (4) [26] a The molecule is located on a mirror plane incorporating the nickel atom and one carbon atom of the Cp ring. b One of the four crystallographically independent molecules.…”

“…A standard unrestricted DFT procedure within the Gaussian03 program [53] was initially employed to obtain the fully relaxed ground state. The same computational details, B3LYP hybrid functional [54] and triple-basis set with polarisation functions [55], were used as in our previous calculations on similar [CpNi(dt)] compounds [21,34]. The molecular spinorbital diagram of [CpNi(pddt)] is reported in Fig.…”

[CpNi(diselenolene)] Neutral Radical Complexes: Electron Paramagnetic Resonance and Density Functional Theory Investigations

“…4 A similar behavior was also recently observed in the CpNi(adt) complex where the faceto-face Cp‚‚‚Cp interaction of two CpNi(adt) complexes (Chart 1) was held for responsible for the large antiferromagnetic interaction measured in this complex. 8 Calculation of the spin densities on the Cp ring indicated indeed that up to 20% spin density was indeed delocalized on the Cp ring, in CpNi(bdt) 4 as well as in CpNi(adt). 8 However, confirmation of this hypothesis of a strong antiferromagnetic interaction through an intermolecular Cp‚‚‚Cp interaction requires to experimentally accessing the exact spin delocalization in the isolated complex.…”

Combined DFT and BS study on the exchange coupling of dinuclear sandwich-type POM: comparison of different functionals and reliability of structure modeling

“…BS technique, developed by Noodleman et al [16], has been proven to be the most commonly used method [20] to solve this difficulty. It has been successfully applied in TM systems [44][45][46][47][48][49], organic diradicals [50][51][52] and hybrid systems consisting of both TM ions and organic radicals [53][54][55]. BS state is monodeterminantally constructed to have opposite spins essentially localized on different magnetic centers and thus it breaks the spatial symmetry from the view of spin distribution.…”