Magnetic Isolation of the Linear Trinuclear Anion in [Cu(Him)6] {Cu(Him)4[Cu(μ-EDTA)(Him)]2}·6H2O (1) as the Novel Imidazolium(+) Salt (H2im)2[Cu(Him)4{(µ-EDTA)Cu(Him)}2]·2H2O (2)—A Comparative Look to Their Crystal Structures, Thermal, Spectral and

Inspired by the reported crystal structure of compound <b>1</b>, we aimed to synthesize and determine the structure of compound <b>2</b>, where two imidazolium (H₂im⁺) ions serve as diamagnetic countercations. Here, we report the thermal stabilities, FT-IR, visible, and RSE spectra, as well as the magnetic properties of both compounds. In these structures, µ-EDTA acts as a pentadentate chelator for both terminal Cu centers within the centrosymmetric linear trinuclear anion. The Cu(µ-EDTA) chelates bind to the central Cu(Him)₄ unit in subtly different ways: in compound <b>1</b>, µ-EDTA has a free acetate arm and binds the central Cu(II) center through a syn,anti-carboxylate group. In contrast, in compound <b>2</b>, the non-chelating acetate arm serves as a monodentate O-donor to the central Cu(II) atom, increasing the Cu(terminal)···Cu(central) distance from 6.08 Å in <b>1</b> to 6.80 Å in <b>2</b>. Additionally, pairs of H₂im⁺ ions in compound <b>2</b> display antiparallel π-stacking interactions. We conclude that the H₂im⁺ counterions in compound <b>2</b> enable the magnetic isolation of the nearly identical trinuclear anion present in both compounds. DFT calculations further support the role of different interactions in stabilizing each crystal structure. In compound <b>2</b>, dominant contributions from N-H···O hydrogen bonds and π-stacking interactions are accompanied by other, less conventional interactions, such as multiple C-H···O contacts and an O···CO(π-hole) interaction within the trinuclear anion.