Yb M5 -edge XMCD of molecular complexes: Can spin and orbital moments be resolved for YbPc2 ?

Resolving spin and orbital contributions to the magnetism of ytterbium in molecular coordination environments remains a significant challenge.Here, bis(phthalocyaninato)ytterbium (YbPc2) has been investigated by Yb M5 edge X-ray magnetic circular dichroism (XMCD) at two synchrotron facilities (WERA at the KIT Light Source (KLS) and Beamline 6.3.1 at the Advanced Light Source (ALS)), complemented by superconducting quantum interference device (SQUID) magnetometry, exchange coupling modeling, and ab initio Complete Active Space Configuration Interaction (CAS-CI@CHYF) calculations.Quantitative M4,5 edge analyses of TbPc2 and ErPc2 served as benchmarks.The Yb M4,5 -edge X-ray absorption spectroscopy (XAS) spectrum is dominated by a single M5 band, with the M4 edge largely absent, consistent with calculations.Simulations revealed sensitivity of the XMCD response to the molecular charge state, including signal inversion and an approximately tenfold intensity change upon reduction to [YbPc2] -.SQUID magnetometry confirmed paramagnetic behavior from a Yb 3+ ion in a 2 F7/2 ground state weakly coupled to a ligand-centered radical.Sum rule analyses were applied to extract spin and orbital contributions to the Yb magnetic moment.While reliable for the Tb and Er benchmarks, Yb-derived susceptibility values were up to an order of magnitude lower than SQUID values, highlighting the need for refined correction schemes for molecular Yb systems.