Magnetism in a homometallic square-planar Cu(II)4Cu(II) metallacrown
Abstract
The well-established homometallic metallacrown Cu(II)[12-MCCu(II)N(Shi)-4]2−, comprising four square-planarly arranged Cu(II) ions surrounding a slightly off-plane central Cu(II) ion, provides an excellent platform for investigating magnetism in exchange-coupled Cu(II) clusters both by experimental and ab initio numerical methods. In the present work, sterically bulky substituents are introduced into the salicylhydroxamate ligand to obtain a modified derivative, Cu(II)[12-MCCu({\mathrm{II})}N(L)-4]2− (Cu4Cu), thereby effectively suppressing intermolecular magnetic interactions and enabling a detailed investigation of its intrinsic ground-state spin structure and exchange interactions. Static magnetization reveals competing antiferromagnetic exchange interactions of J1=−8.1(2) THz (−33.5(8) meV) between the central and the peripheral sites and J2=−4.40(12) THz (−18.2(5) meV) between neighboring sites on the ring of the metallacrown, which are corroborated by ab initio broken symmetry-based density functional theory (DFT). These couplings yield an S=1/2 ground state for Cu4Cu at low temperatures, for which X-band and high-frequency/high-field electron paramagnetic resonance (EPR) precisely determine the g-factors gx = 2.028, gy = 2.056, and gz = 2.222 close to axial anisotropy and in agreement with our DFT results. The ground-state spin-configuration is characterized by dxy-character of the unoccupied states. Furthermore, our magnetization data evidence thermal transitions across a doublet-to-quartet gap of Δ1/2→3/2 = 4.8(4) THz which is also indicated by the emergence of an excited-state EPR signal.
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BibTeX
@misc{bischof2026magnetism,
title = {{Magnetism in a homometallic square-planar Cu$(\mathrmII)$$_4$Cu$(\mathrmII)$ metallacrown}},
author = {Luca Bischof and Ariyan Tavakoli and Sascha Pietruska and Lena Spillecke and Ina Heckelmann and Changhyun Koo and Luca M. Carrella and Eva Rentschler and Hans Christian Schneider and Rüdiger Klingeler},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.38989},
eprint = {2610.38989},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.38989},
note = {CC BY-NC-ND 4.0},
}
RIS
TY - UNPB
TI - Magnetism in a homometallic square-planar Cu(II)_4Cu(II) metallacrown
AU - Luca Bischof
AU - Ariyan Tavakoli
AU - Sascha Pietruska
AU - Lena Spillecke
AU - Ina Heckelmann
AU - Changhyun Koo
AU - Luca M. Carrella
AU - Eva Rentschler
AU - Hans Christian Schneider
AU - Rüdiger Klingeler
PY - 2026
DA - 2026/10/28
PB - arXiv
DO - 10.48550/arxiv.2610.38989
UR - https://arxiv.org/abs/2610.38989
AB - The well-established homometallic metallacrown Cu(II)[12-MC_Cu(II)N(Shi)-4]^2−, comprising four square-planarly arranged Cu(II) ions surrounding a slightly off-plane central Cu(II) ion, provides an excellent platform for investigating magnetism in exchange-coupled Cu(II) clusters both by experimental and ab initio numerical methods. In the present work, sterically bulky substituents are introduced into the salicylhydroxamate ligand to obtain a modified derivative, Cu(II)[12-MC_Cu({\mathrm{II})}N(L)-4]^2− (Cu_4Cu), thereby effectively suppressing intermolecular magnetic interactions and enabling a detailed investigation of its intrinsic ground-state spin structure and exchange interactions. Static magnetization reveals competing antiferromagnetic exchange interactions of J_1=−8.1(2) THz (−33.5(8) meV) between the central and the peripheral sites and J_2=−4.40(12) THz (−18.2(5) meV) between neighboring sites on the ring of the metallacrown, which are corroborated by ab initio broken symmetry-based density functional theory (DFT). These couplings yield an S=1/2 ground state for Cu_4Cu at low temperatures, for which X-band and high-frequency/high-field electron paramagnetic resonance (EPR) precisely determine the g-factors g_x = 2.028, g_y = 2.056, and g_z = 2.222 close to axial anisotropy and in agreement with our DFT results. The ground-state spin-configuration is characterized by d_xy-character of the unoccupied states. Furthermore, our magnetization data evidence thermal transitions across a doublet-to-quartet gap of Δ_1/2→3/2 = 4.8(4) THz which is also indicated by the emergence of an excited-state EPR signal.
ER -