Size-Dependent Ligand Quenching of Ferromagnetism in Co₃(benzene)_<i>n</i> ⁺ Clusters Studied with X‑ray Magnetic Circular Dichroism Spectroscopy

Abstract

Cobalt–benzene cluster ions of the form Co3(bz)n + (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. Co3 + has a spin magnetic moment of μS = 6 μB and an orbital magnetic moment of μL = 3 μB. Co3(bz)+ and Co3(bz)2 + complexes were found to have spin and orbital magnetic moments identical to the values for ligand-free Co3 +. However, coordination of the third benzene to form Co3(bz)3 + completely quenches the high spin state of the system. Density functional theory calculations elucidate the spin states of the Co3(bz)n + species as a function of the number of attached benzene ligands, explaining the transition from septet to singlet for n = 0 → 3