The influence of ligand field effects on the magnetic exchange of high-spin Co(ii)-semiquinonate complexes

Abstract

[Co(Me(4)cyclam)(tropolonate)](PF(6)) was synthesised and structurally characterised. Its electronic and W-band EPR spectra have been analysed by means of the angular overlap calculation of the Spin Hamiltonian parameters that provided also a satisfactory reproduction of the temperature dependence of the magnetic susceptibility. The present results can be interpreted assuming a pseudo-octahedral character for the Co(II) center. This prompted us to reconsider the model formerly used for the analysis of the magnetic coupling between hs-Co(II) and the paramagnetic o-semiquinonate ligand in the corresponding derivatives [Co(Me(4)cyclam)(PhenSQ)](PF(6)) and [Co(Me(4)cyclam)(DTBSQ)](PF(6)). These results indicate that the effect of the magnetic coupling is active only below 50 K and that a more refined model of exchange coupling between Co(II) and semiquinonato ligands is needed to quantitatively analyze the magnetic behaviour of this class of systems.

Tuning the Charge Distribution and Photoswitchable Properties of Cobalt–Dioxolene Complexes by Using Molecular Techniques

“…The decrease in the cT values observed on cooling should be attributed to cobalt(II) single ion effects, that is, to the depopulation of the higher multiples that arise from the splitting of the 4 T 1g orbital produced by the combined action of spin-orbit coupling and low-symmetry distortions. [52] These results lead to the conclusions that in the solid state the Co II -SQ species is favoured by increasing the number of methyl substituents on the ancillary ligand, whereas the Co III -Cat species is favoured by low methyl substitution, as could also be inferred by the electrochemical data and electronic spectra of the samples in solution.…”

Single-ion anisotropy and exchange coupling in cobalt(ii)-radical complexes: insights from magnetic and ab initio studies

“…These systems undergo a thermally-induced intramolecular electron transfer between redoxactive metal and redox-active ligand, accompanied by a spin transition at the cobalt center. 26,42,43 The nature of the exchange coupling in the pseudo-octahedral high spin (HS) Co(II)-sq (sq À ¼ semiquinonate) tautomer has been an enduring question in the literature, 44,45 with both ferromagnetic and antiferromagnetic coupling claimed, in tandem with potentially anisotropic exchange interactions. 46,47 In most cases the metal-radical exchange coupling in these systems cannot be determined directly by experiment; however, this can be required to assess the relative amounts of the two redox isomers.…”

Toward an automated analysis of exchange pathways in spin‐coupled systems

“…Electron spin coupling plays an important role in systems such as organic diradicals and transition-metal complexes. For transition-metal complexes, substitutions of the metal centers [1][2][3][4] or modifications in the ligand sphere [5][6][7] affect the spin coupling, and understanding such structure-property relationships is relevant for designing molecules with desired magnetic properties. This also applies to active sites in enzymes, [8][9][10][11] and to spin coupling in magnetic metal organic frameworks.…”