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Low-Dimensional Metal-Organic Magnets as a Route toward the S = 2 Haldane Phase

Pitcairn, Jem; Iliceto, Andrea; Cañadillas-Delgado, Laura; Fabelo, Oscar; Liu, Cheng; Balz, Christian; Weilhard, Andreas; Argent, Stephen P.; Morris, Andrew J.; Cliffe, Matthew J.

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Jem Pitcairn

Andrea Iliceto

Laura Cañadillas-Delgado

Oscar Fabelo

Cheng Liu

Christian Balz

Andrew J. Morris


Metal-organic magnets (MOMs), modular magnetic materials where metal atoms are connected by organic linkers, are promising candidates for next-generation quantum technologies. MOMs readily form low-dimensional structures and so are ideal systems to realize physical examples of key quantum models, including the Haldane phase, where a topological excitation gap occurs in integer-spin antiferromagnetic (AFM) chains. Thus, far the Haldane phase has only been identified for S = 1, with S ≥ 2 still unrealized because the larger spin imposes more stringent requirements on the magnetic interactions. Here, we report the structure and magnetic properties of CrCl2(pym) (pym = pyrimidine), a new quasi-1D S = 2 AFM MOM. We show, using X-ray and neutron diffraction, bulk property measurements, density-functional theory calculations, and inelastic neutron spectroscopy (INS), that CrCl2(pym) consists of AFM CrCl2 spin chains (J1 = −1.13(4) meV) which are weakly ferromagnetically coupled through bridging pym (J2 = 0.10(2) meV), with easy-axis anisotropy (D = −0.15(3) meV). We find that, although small compared to J1, these additional interactions are sufficient to prevent observation of the Haldane phase in this material. Nevertheless, the proximity to the Haldane phase together with the modularity of MOMs suggests that layered Cr(II) MOMs are a promising family to search for the elusive S = 2 Haldane phase.


Pitcairn, J., Iliceto, A., Cañadillas-Delgado, L., Fabelo, O., Liu, C., Balz, C., …Cliffe, M. J. (2023). Low-Dimensional Metal-Organic Magnets as a Route toward the S = 2 Haldane Phase. Journal of the American Chemical Society, 145(3), 1783-1792.

Journal Article Type Article
Acceptance Date Dec 9, 2022
Online Publication Date Jan 10, 2023
Publication Date Jan 25, 2023
Deposit Date Jan 17, 2023
Publicly Available Date Jan 20, 2023
Journal Journal of the American Chemical Society
Print ISSN 0002-7863
Electronic ISSN 1520-5126
Publisher American Chemical Society (ACS)
Peer Reviewed Peer Reviewed
Volume 145
Issue 3
Pages 1783-1792
Keywords Colloid and Surface Chemistry, Biochemistry, General Chemistry, Catalysis
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