Investigating the Structural Factors Influencing the Magnetic Interaction between Individual Copper Spins in the CuCu4 Metallacrown Complex, from Its Bulk Form to Its Adsorption on Au(111)

ABSTRACT Metal‐organic complexes with multiple metal ions and unsaturated spin structures are intriguing for their potential to tune magnetic properties. We focus on the Cu(II)[12‐MCCu(II)N(Shi)‐4] metallacrown complex (CuCu4) to show how phase‐dependent geometric transformations influence magnetic coupling between copper spins and shape molecular magnetic behavior. To uncover these effects, we investigated the valence band structure of CuCu4 in bulk form and as a monolayer on Au(111). Using ultraviolet photoemission spectroscopy (UPS) and ab‐initio calculations, we analyzed the experimental UPS spectra of the bulk state and the CuCu4/Au(111) interface with the total density of states (tDOS) obtained via density functional theory (DFT) approaches. While adsorption causes subtle changes in the tDOS, the exchange coupling constants between copper ion‐related spins shift significantly. This leads to a transformation in molecular spin configuration from a low‐spin state (S = 1/2) in bulk to a higher‐spin state (S = 3/2) upon adsorption on Au(111). Analysis of the spin‐resolved tDOS reveals partial spin polarization in the adsorbed state, absent in bulk, while bridging earlier experimental data on bulk and surface‐bound CuCu4. This behavior suggests the CuCu4/Au(111) interface as a promising candidate for molecular spintronics, where control over spin states is key.