Akin, S.T.; Zamudio-Bayer, V.; Duanmu, K.; Leistner, G.; Hirsch, K.; Bülow, C.; Lawicki, A.; Terasaki, A.; von Issendorff, B.; Truhlar, D.G.; Lau, J.T.; Duncan, M.A.: Size-Dependent Ligand Quenching of Ferromagnetism in Co3(benzene)n+ Clusters Studied with X-ray Magnetic Circular Dichroism Spectroscopy. Journal of Physical Chemistry Letters 7 (2016), p. 4568-4575

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.