Size-Dependent Ligand Quenching of Ferromagnetism in Co₃(benzene) _n ⁺ Clusters Studied with X-ray Magnetic Circular Dichroism Spectroscopy

Abstract

Cobalt-benzene cluster ions of the form Co(bz) (n = 0-3) were produced in the gas phase, mass-selected, and cooled in a cryogenic ion trap held at 3-4 K. To explore ligand effects on cluster magnetic moments, these species were investigated with X-ray absorption spectroscopy (XAS) and X-ray magnetic circular dichroism (XMCD) spectroscopy. XMCD spectra yield both the spin and orbital angular momenta of these clusters. Co has a spin magnetic moment of μ = 6 μ and an orbital magnetic moment of μ = 3 μ. Co(bz) and Co(bz) complexes were found to have spin and orbital magnetic moments identical to the values for ligand-free Co. However, coordination of the third benzene to form Co(bz) completely quenches the high spin state of the system. Density functional theory calculations elucidate the spin states of the Co(bz) species as a function of the number of attached benzene ligands, explaining the transition from septet to singlet for n = 0 → 3.

Complex magnetic orders in small cobalt–benzene molecules

“…46,47 During the preparation of this manuscript S.T. Akin et al 22 reported XMCD measurements for Co 3 Bz + 3 cluster with null spin-magnetic moment. The null signal could be understood as a consequence of the predicted noncollinear character of the local magnetic moments.…”

“…By using collinear DFT calculations they tried to explain the origin of the quenched magnetic moment, but the results were highly sensible to the exchange correlation functionals used. 22 Henceforth, the magnetic properties of Co-Bz clusters and their response to magnetic fields require further research.…”

Experimental and theoretical 2p core-level spectra of size-selected gas-phase aluminum and silicon cluster cations: chemical shifts, geometric structure, and coordination-dependent screening

“…80 It might be particular useful to elucidate the degree of valence electron delocalization, which should have a pronounced effect on electron binding energies and core-level excitation energies via charge screening, 43,81 but also on the quenching of local magnetic moments. 80,[82][83][84][85]…”

Large orbital magnetic moments of small, free cobalt cluster ions Co${_n^+}$ with n ${ \leqslant 9}$

“…Experimcntatly determined orbital-to-spin magnetic moment ratio as a function of cluster size. For comparison the values for Co;t clusters with n = 2, 3, 10 -15 [18,19,10] and t he value of 0.07 for bulk cobalt [3] are also shown. Note t hat the ratio for the cobalt cation in its [Ar]3d 8 3 F ground state is 1.5 and for the cobalt atom with [Ar]3d 7 4s 2 4 F ground state is 1, both of which ru·e outside the scale that is shown here.…”