Pulsed Electron Paramagnetic Resonance on two Cu(II)-Cage Compounds With Six, Respectively Eight Copper Ions

Abstract. The copper(II) cages Pd₁₂Cu₆L^DMAP₂₄(Cu6) and Pd₁₂Cu₈L^Pro₂₄ (Cu8), contain six, resp. eight, Cu(II) ions in a complex constituted by palladium ions and organic ligands in a self-assembled nano-meter sphere. Within the sphere, the Cu(II) ions are expected to form polyhedral-like structures. The parent compounds Pd₁₂M₆L^DMAP₂₄ and Pd₁₂M₈L^Pro₂₄ are of interest because of the possibility of introducing a different metal ions for M, such as Cu(II), in a defined arrangement and for catalytic applications, see Bobylev et al. (Chemical Science, 2023, 14, 11840–11849). For structure information, nano-meter distances where measured between the six, respectively eight Cu(II) ions in Cu6 and Cu8. Distances were measured by pulsed double electron electron resonance (DEER) spectroscopy. While DEER is established for measuring distances between pairs of spins, application to multi-spin systems is less common. Since, so far, no reports of DEER with multi-spin interactions between Cu(II) ions were reported, the copper-cages are an ideal model to study them. For Cu6 and Cu8, DEER shows multi-spin interaction, and the method enabled to establish an octahedral arrangement for the Cu-ions in Cu6. For Cu8, two distances were observed that are consistent with two structural models proposed for Cu8, one of which is a cube of Cu-ions.