This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Magnetic properties in molecular materials depend not only on the molecular components themselves but also on their solid-state organization. In charged π-electronic systems, electrostatic and dispersion forces can organize molecules into distinct ion-pairing structures.
Oppositely charged species may form charge-by-charge assemblies, whereas like-charged π-electronic units can, under favorable intermolecular interactions, overcome electrostatic repulsion and form stacked dimers. Because intermolecular spin–spin interactions are sensitive to the proximity and relative orientation of paramagnetic units, controlling the assembly pattern provides a route to modulating magnetic behavior. Yet solid-state intermolecular spin–spin interactions in CuII complexes of π-electronic macrocycles have been reported only in limited cases.
A research team led by professor Hiromitsu Maeda at Ritsumeikan University investigated whether counteranions could be used to control the assembly and magnetic behavior of thiaporphyrin CuII complexes. Their findings were published online in the journal Chemical Science on Aug. 24, 2026. Thiaporphyrins contain a thiophene unit within the porphyrin macrocycle and can act as monoanionic ligands.
Complexation with divalent metals produces positively charged π-electronic complexes through partial charge compensation. Incorporating CuII introduces electron spin as well as charge, making these complexes useful building blocks for studying how ion-pairing structure influences magnetism. "In this study, the CuII complexation of thiaporphyrins was investigated to afford paramagnetic π-electronic cations that modulate ion-pairing assembly modes in combination with coexisting anions," said Maeda.
The researchers synthesized two thiaporphyrin CuII complex cations and first obtained them as chloride ion pairs. The chloride ions were then exchanged for several counteranions, including BF4−, PF6−, B(C6F5)4− (FABA−) and pentacyanocyclopentadienide (PCCp−). The resulting ion pairs were characterized by single-crystal X-ray analysis, solid-state electron spin resonance (ESR), magnetic susceptibility measurements, UV/visible spectroscopy and theoretical calculations to examine their solid-state structures and magnetic properties.
Computational approaches were also used to evaluate interaction energies and spin-density distributions, enabling the team to connect molecular packing directly with magnetic behavior. A clear structural contrast emerged. With the π-electronic PCCp− counteranion, one CuII complex formed a charge-by-charge assembly based on π-stacked ion pairs.
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