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[Tomoko Fujino](https://orcid.org/0000-0002-0441-8653), [Mafumi Hishida](https://orcid.org/0000-0003-4511-4039), Masatoshi Ito, [Toshikazu Nakamura](https://orcid.org/0000-0001-8672-0946), [Mizue Asada](https://orcid.org/0000-0003-0837-7753), [Naoya Kurahashi](https://orcid.org/0000-0002-9266-4837), [Hisao Kiuchi](https://orcid.org/0000-0001-9139-8218), Yoshihisa Harada, [Koji Harano](https://orcid.org/0000-0001-6800-8023), [Rie Makiura](https://orcid.org/0000-0003-2589-0698), [Kanokwan Jumtee Takeno](https://orcid.org/0000-0002-4087-7910), [So Yokomori](https://orcid.org/0000-0002-3472-3368), [Hiroshi Oike](https://orcid.org/0000-0001-6866-7774), Hatsumi Mori

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[Macroscopic Structural Transition of Nickel Dithiolate Capsule with Uniaxial Magnetic Anisotropy in Water](https://mdr.nims.go.jp/datasets/f7fab68c-36ad-4dfc-bc97-a6fa7d8b4db6)

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Macroscopic Structural Transition of Nickel Dithiolate Capsule with Uniaxial Magnetic Anisotropy in WaterRESEARCH ARTICLEwww.advancedscience.comMacroscopic Structural Transition of Nickel DithiolateCapsule with Uniaxial Magnetic Anisotropy in WaterTomoko Fujino,* Mafumi Hishida,* Masatoshi Ito, Toshikazu Nakamura, Mizue Asada,Naoya Kurahashi, Hisao Kiuchi, Yoshihisa Harada, Koji Harano, Rie Makiura,Kanokwan Jumtee Takeno, So Yokomori, Hiroshi Oike, and Hatsumi MoriMeeting the Internet of Things (IoT) demand for flexible organic spintronicsrequires dynamically flexible, “soft” organic magnetic materials. Thesematerials should be capable of reordering their macroscopic assemblies inresponse to external stimuli. Unlike conventional rigid, “hard” crystallineorganic paramagnets, that are typically composed of open-shell 𝝅- ord/𝝅-conjugated planar molecules and rely on intermolecular interactions inthe ordered, assembled structures, soft paramagnets necessitate a delicatebalance between long-range structural order (essential for controllingmagnetic properties) and dynamic flexibility a challenge previously unmet foropen-shell planar molecules. In this study, an amphiphilic d/𝝅-conjugatednickel dithiolate radical anion salt is presented that self-assembles intoordered membranes, forming capsule-like macrostructures with exceptionalstability in aqueous environments. This design achieves the desired balance.These assemblies exhibit uniaxial magnetic anisotropy driven by significantspin–spin interactions and undergo temperature-dependent macroscopicstructural transitions representing, to the knowledge, the first observation ofsuch behavior for assemblies of open-shell planar molecules. Thiswell-defined, single-molecular-weight system provides critical structural andmechanism insights for soft matter design and a versatile platform forspintronic applications. The findings advance the development of flexible,tunable molecular soft paramagnets, expanding their potential for innovativeapplications in flexible devices and beyond.T. Fujino, M. Ito, N. Kurahashi, H. Kiuchi, Y. Harada, S. Yokomori, H. MoriThe Institute for Solid State PhysicsThe University of Tokyo5-1-5 Kashiwanoha, Kashiwa, Chiba 277–8581, JapanE-mail: fujino@issp.u-tokyo.ac.jpThe ORCID identification number(s) for the author(s) of this articlecan be found under https://doi.org/10.1002/advs.202504967© 2025 The Author(s). Advanced Science published by Wiley-VCHGmbH. This is an open access article under the terms of the CreativeCommons Attribution License, which permits use, distribution andreproduction in any medium, provided the original work is properly cited.DOI: 10.1002/advs.2025049671. IntroductionOrganic magnetic materials are integralto spintronics research, leveraging tunablespin–spin interactions to advance funda-mental understanding and applications.[1–3]The growing demand for dynamically flex-ible (i.e., “soft”) organic paramagnetic ma-terials, driven by the rapid expansion ofthe Internet of Things (IoT)—particularly inspintronic wearable devices[4,5]—presentsboth opportunities and challenges. Conven-tional rigid (i.e., “hard”) molecular-basedparamagnetic materials in spintronic re-search often consist of 𝜋- or d/𝜋-conjugatedplanar molecules and rely on effective in-termolecular interactions within their as-sembled, stacked forms. In contrast, softorganic paramagnets, capable of adaptingtheir assembled structure in response to ex-ternal stimuli, promise advanced function-alities for a wide range of applications,[6]from magnetically guided drug deliveryto stimuli-responsive devices.[7–20] How-ever, realizing this potential requires pre-cise control over spin–spin interactionswithin a flexible and dynamic framework, afeat previously unachieved with open-shellM. HishidaDepartment of ChemistryFaculty of ScienceTokyo University of Science1-3 Kagurazaka, Shinjuku, Tokyo 162–8601, JapanE-mail: hishida@rs.tus.ac.jpT.Nakamura,M.AsadaInstitute forMolecular Science38Nishigo-Naka,Myodaiji,Okazaki, Aichi 444–8585, JapanH.Kiuchi, Y.HaradaSynchrotronRadiationCollaborativeResearchOrganizationTheUniversity of TokyoSendai,Miyagi 980–8572, JapanK.HaranoCenter for Basic ResearchonMaterialsNational Institute forMaterials Science (NIMS)1-1Namiki, Tsukuba, Ibaraki 305-0044, JapanAdv. Sci. 2025, 12, 2504967 2504967 (1 of 9) © 2025 The Author(s). Advanced Science published by Wiley-VCH GmbHhttp://www.advancedscience.commailto:fujino@issp.u-tokyo.ac.jphttps://doi.org/10.1002/advs.202504967http://creativecommons.org/licenses/by/4.0/http://creativecommons.org/licenses/by/4.0/mailto:hishida@rs.tus.ac.jphttp://crossmark.crossref.org/dialog/?doi=10.1002%2Fadvs.202504967&domain=pdf&date_stamp=2025-04-23www.advancedsciencenews.com www.advancedscience.comFigure 1. Relationship between degree of disorder and activation energy(ΔG‡) required for dynamics for open-shell planar. This figure illustratesthe general trade-off between the degree of disorder in materials andΔG‡ required for transitions to other states (Adapted from the ref. [7]).Supramolecular materials are an exception to this trend, exhibiting a highdegree of order and dynamic behavior. This unique combination makesthem promising candidates for the development of paramagnetic soft ma-terials, as demonstrated in this study.planar molecules. Reaching this potential necessitates balancingthe long-range structural order (essential for controlled magneticproperties) with the inherent flexibility of soft matter. Increasedstructural order often enhances spin–spin interactions, but it typ-ically compromises the flexibility required for dynamic soft ma-terials. This trade-off reflects an inverse relationship between thestructural order and the activation energy barrier (ΔG‡) associ-ated with the structural state changes (Figure 1).[7] Rigid mate-rials with high ΔG‡ values are typically structurally ordered, asobserved in typical organic paramagnets,[2,3] whereas highly dy-namic soft materials with lowΔG‡ often lack sufficient structuralorder. Overcoming this trade-off necessitates design principlesthat enable open-shell planar molecules to integrate into assem-blies with both dynamic and ordered features to control spin–spin interactions.Current strategies for creating soft magnetic materials—including incorporating magnetic nanoparticles into films,[8–14]encapsulating them within soft assemblies,[15–17] or embeddingK. HaranoResearch Center for Autonomous Systems Materialogy (ASMat)Institute of Integrated ResearchInstitute of Science Tokyo4259 Nagatsuda-cho, Midori-ku, Yokohama, Kanagawa 226–8501, JapanR. Makiura, K. J. TakenoDepartment of Materials ScienceOsaka Metropolitan UniversityGakuen-cho, Naka-ku, Sakai, Osaka 599–8570, JapanH. OikePRESTOJapan Science and Technology Agency (JST)Kawaguchi, Saitama 332-0012, JapanFigure 2. The self-assembly of an open-shell, planar, and amphiphilicnickel Ni(2OMe) anion salt 1 in water, forming dynamically flexible para-magnetic capsule, is demonstrated in this study. The red arrow indicatesa 𝜋-spin delocalized over the anion molecule, including Ni atom.magnetic components into surfactants[18–21]—often face criticallimitations. A key challenge is structural heterogeneity, such asuneven nanoparticle distributions, which impedes precise mag-netic manipulation of spin–spin coupling.[9,13,18] This hetero-geneity also hinders the investigation of structure–property re-lationships and obscures the mechanisms underlying stimuli-responsive behavior. Thus, open-shell single-molecular-weightsystems that balance long-range order with dynamic flexibil-ity are crucial for elucidating these mechanisms, advancingsoft organic paramagnet design, and enabling next-generationspintronic materials. Open-shell planar molecules, in particu-lar, are readily stacked to form highly ordered assemblies withanisotropic intermolecular interactions, exhibiting unique andcontrollable magnetic properties.Amphiphilic assemblies[22–27] offer a promising supramolecu-lar approach[28–32] to reconcile competing requirements of long-range order and flexibility. These systems form dynamically flex-ible membrane structures in water that undergo temperature-,pH-, or additive-induced macrostructural transitions.[22–27] How-ever, integrating spin-active, open-shell components into suchassemblies poses significant challenges due to their chemicalinstability and susceptibility to degradation in aqueous and ox-idative environments. Open-shell planar species, such as rad-ical anions or cations, are particularly sensitive, requiring sta-bilization through strong orbital overlap and intermolecularinteractions.[2,3]In this study, we extend a supramolecular approach to assem-blies of open-shell planarmolecules by designing an amphiphilicd/𝜋-conjugated planar nickel dithiolate. The nickel dithiolateradical anion acts as a counter anion to the hydrophobic alkylchains, forming a tail structure[33] (Figure 2). The anion saltsself-assemble into membranes that balance long-range orderand dynamic flexibility, exhibiting exceptional stability in aque-ous environments. Unlike previous amphiphilic nickel dithio-late salts, which were partially incorporated into vesicular filmsAdv. Sci. 2025, 12, 2504967 2504967 (2 of 9) © 2025 The Author(s). Advanced Science published by Wiley-VCH GmbH 21983844, 2025, 29, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202504967, Wiley Online Library on [07/08/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.advancedscience.comwww.advancedsciencenews.com www.advancedscience.comScheme 1. Synthesis of Ni(2OMe) anion salts 4 and 1, and the assembly of 1 in water (1a).and lacked the effective intermolecular interactions necessary forefficient spin–spin coupling,[34] our designed open-shell planarbuilding blocks readily stack and self-assemble into membranesthat exhibit uniaxial magnetic anisotropy via significant inter-molecular spin–spin interactions. The assemblies form capsule-likemacroscopic structures and undergo temperature-dependentstructural transitions—representing, to our knowledge, the firstobservation of such behavior for assemblies of open-shell planarmolecules. Our findings provide valuable insights for the devel-opment of advanced paramagnetic materials with tunable prop-erties, broadening their potential applications in nanomedicineand beyond.2. Results and Discussion2.1. Molecular Design and Synthesis of Amphiphilic SaltInitially, we designed and synthesized an amphiphilic salt bycombining a bis(4-methoxybenzene-1,2-dithiolato)nickelate(III)anion and an ammonium cation containing long hydropho-bic alkyl chains derived from ligand precursor 2.[35] Thiswas achieved through decyaoethylation of 2 under basicconditions, followed by coupling with nickel(II) diacetatetetrahydrate[36] in the presence of didodecyldimethylammo-nium (DDA)[37] chloride, yielding DDA·Ni(2OMe) (compound 1,Scheme 1). To prepare a reference compound, a reaction withtetraphenylphosphonium bromide followed by transmetallationproduced Ph4P·Ni(2OMe) (compound 4). These synthetic pro-cedures are scalable, enabling the production of hundreds ofmilligrams in a single sequence. The structural integrity of theNi(2OMe) anion is confirmed by analyzing its single-crystal struc-ture of 4 (Figure S1; Table S1, Supporting Information).[38] Thesingle crystal consisted of a 1:1 ratio of cations to anions, confirm-ing themonoanionic nature of theNi(2OMe) anionwith a square-planar Ni center. The space group of 4 was identified as P–1,confirming two crystallographically half-molecule-independentanions in the unit cell: one ordered and the other orientation-ally disordered in a 63:37 ratio. The bulky cations in the single-crystal structure likely hinder effective intermolecular interac-tions between the anions, resulting in the electronic structureresembling that of the isolated anion. The two ligands in theFigure 3. Structure of theNi(2OMe) anion in trans configuration. a) Chem-ical structure. b) Singly occupied molecular orbital (SOMO) calculated us-ing Gaussian software (UB3LYP/6-311G++(d,p), SDD for Ni). The orbitaldelocalized over the anion, including Ni atom. (Top) The top view. (Bot-tom) The side view. c) Single-crystal structure of anion salt 4 with differentbond lengths. Hydrogen atoms are omitted for clarity. Atoms are coloredas follows. Nickel: green, carbon: gray, sulfur: yellow, oxygen: red, hydro-gen: white.Ni(2OMe) anion adopt a trans configuration (Figure 3; FigureS1, Supporting Information). Bond-length analysis of the ligand(Figure 3c; Figure S1b, Supporting Information) reveals two dis-tinct Ni–C bond lengths in the ordered anion (2.1606 and 2.149Å; Figure 3c), indicating intramolecular polarization caused bythe electron-donating 4-methoxy group in the ligand. The elec-tronic asymmetry of the ligand is further supported by the dis-torted shape of the singly occupied molecular orbital (SOMO)Adv. Sci. 2025, 12, 2504967 2504967 (3 of 9) © 2025 The Author(s). Advanced Science published by Wiley-VCH GmbH 21983844, 2025, 29, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202504967, Wiley Online Library on [07/08/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.advancedscience.comwww.advancedsciencenews.com www.advancedscience.comalong the short-axis of the molecule, as revealed by the densityfunctional theory (DFT)-optimized structure using the Gaussiansoftware (UB3LYP/6-311G++(d,p), SDD for nickel; Figure 3b;Table S3, Supporting Information). The planar structure, devoidof bulky substituents observed in the single-crystal and DFT-optimized structures, suggests the potential for efficient stackingassemblies with favorable intermolecular spin–spin interactions.Furthermore, the SOMO is primarily delocalized over the anionmolecule, including the Ni atom, which may contribute to theenhanced aqueous stability of the open-shell species.2.2. Assembly of Amphiphilic Nickel Dithiolate Salt in WaterThe amphiphilic nickel dithiolate salt 1 was next dispersed inwater using ultrasonication. A mixture of 1 and water was sub-jected to ultrasonic irradiation at 90 °C, followed by slow coolingover 12 h, resulting in a whitish-green suspension 1a (≈1 μm;Scheme 1). The green color is a characteristic feature of nickelbisdithiolenes and is mainly attributed to the SOMO-to-LUMO(lowest unoccupied molecular orbital) transition (Table S2, Sup-porting Information). The transition arises from hybridized or-bitals formed between nickel ions and the ligands. The whitishappearance indicates its dispersed state in water. The dispersionwas then analyzed by small-angle X-ray scattering (SAXS) withthe scattering vector q range, revealing the absence of diffractionpeaks. This data indicates the absence of a multilamellar struc-ture, whose structure may be affected by the low concentration.The scattering intensity was dominated by the bilayer form factor.The primary peak at the lowest q corresponds to the characteristicfirst hump of the bilayer form factor, with subsequent oscillatoryscattering patterns (Figure 4a). A dip location in the scatteringintensity ≈ 0.1 Å−1 is consistent with the thickness of a bilayermembrane, as previously reported.[37]The bilayer thickness was quantified by analyzing the electrondensity (ED) value[39] obtained from the SAXSprofiles (Figure S2,Supporting Information), assuming a vesicle model with the hy-drophobic alkyl chains oriented parallel to the bilayer planes. Theanalyses revealed amembrane structure with an inner hydropho-bic layer thickness of 27 Å, comprising the alkyl chains. Thisthickness exceeds the individual alkyl chain lengths (16 Å)[40] butis shorter than twice the chain length, indicating the bilayer isformed by an amphiphilic salt 1 with alkyl chains inclined out-of-plane (Figure 5, top). Conversely, the outer hydrophilic headregion of themembrane, comprising theNi(2OMe) anion, exhib-ited a thickness of 3 Å. Considering the short-axis length of theanion of ≈5 Å,[41] this shorter thickness (3 Å) suggests that theanions are stacked while inclining along the long-axis and shift-ing along the short-axis of the molecule (Figure 5, top). Wide-angle X-ray scattering (WAXS) profiles of 1a showed compara-tively broad diffraction peak, seemingly reflecting intermolecu-lar interactions. This suggest that the structure forms a highlyordered phase (likely a gel phase), although not a periodic crys-talline phase. The peaks at q of 1.5 and 1.6 Å−1 (Figure S5, Sup-porting Information) correspond to stacking distances of 4.2 and3.9 Å, respectively. This observation suggests the in-plane order-ing of the DDA alkyl chain[26] and stacking of the nickel dithi-olate anions. Compared to the 𝜋–𝜋 stacking distance of ≈3.5 Åobserved in the single-crystal nickel dithiolene complex,[36] theFigure 4. Temperature-dependent small-angle X-ray scattering data of 1aduring the heating (a) and cooling (b) processes. Assembly forms changefrom 1a to 1b during the heating process and from 1b to 1c during thecooling process in a hysteretic manner.slightly increased intracolumnar stacking distance (3.9 Å) indi-cates that either a shift of anion molecules along the short-axis orthe interference from the long alkyl chains of the counter cationshinder the efficient 𝜋–𝜋 stacking. Notably, themembranes exhib-ited exceptional stability in water for several months. This stabil-ity is primarily attributed to their stacking structure to promoteintermolecular spin–spin interactions (vide infra) or the delocal-ization of the SOMO over the anion molecule.2.3. Structural Transition of Nickel Dithiolate MembraneThe bilayer membranes exhibited unique temperature-dependent structural transitions. When heated above 65 °C,Adv. Sci. 2025, 12, 2504967 2504967 (4 of 9) © 2025 The Author(s). Advanced Science published by Wiley-VCH GmbH 21983844, 2025, 29, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202504967, Wiley Online Library on [07/08/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.advancedscience.comwww.advancedsciencenews.com www.advancedscience.comFigure 5. Possible temperature-dependent structural changes: bilayermembrane 1a, dissociated form 1b, and interdigitated membrane 1c.the SAXS profiles showed substantial changes with the dis-appearance of significant form factors (Figure 4a), indicatingmembrane dissociation (1b in Figure 5, middle). Such a dynamicstructural change was previously unachieved in open-shell pla-nar molecule-based paramagnets. Considering the q dependenceat the low region at high temperatures, the dissociated form1b likely disassembles into smaller assemblies, resulting in amixture of coexisting structures such as membranes, micelles,and monomers. Notably, this structural transition was reversiblebut exhibited hysteresis; the dissociated form 1b persisted untilthe temperature dropped to 30 °C. Upon further cooling below30 °C, a SAXS profile corresponding to 1c appeared (Figure 4b).Intriguingly, after aging the solution at room temperature formore than 3 h, the SAXS profile corresponding to 1a is recovered(Figure S4, Supporting Information). This phenomenon sug-gests that 1c is a metastable state under kinetic control,[42] wherethe dynamic transition depends on the cooling rates.[2] Theseresults demonstrated that the assembly of 1 in water uniquelyexhibited reversible but hysteretic dynamic changes in themembrane structures, exhibiting transitions among the threestates: from the thermodynamically stable bilayer membrane1a, through dissociated form 1b, to the metastable membrane1c. This hysteretic dynamic change is a rare feature amongtypical aggregates constituting amphiphilic molecules.[26,37] Theobserved metastable state (1c) may be induced by spin–spin in-termolecular interactions between planar molecules (vide infra)or kinetically favored antiparallel orientation of alkyl chains,contributing to the stabilization of 1c during the transitionprocess.The radial ED distribution analysis[39] revealed that the hy-drophobic alkyl chain moiety in 1c was 17 Å thick, shorter thanthat in state 1a. This thickness was nearly equivalent to that ofa single alkyl chain (16 Å),[40] suggesting an interdigitated mem-brane structure (Figure 5, bottom).[26] In contrast, the thicknessof the hydrophilicNi(2OMe) anionmoiety increased to 5Å,whichwas comparable to the short-axis molecular length (≈5 Å).[36,41]This observation indicates intracolumnar stacking without sig-nificant shifts along the short-axis of the molecule. The WAXSprofiles exhibited scattering exclusively at q = 1.5 Å−1 (i.e., 4.2 Å;Figure S5, Supporting Information), likely attributed to the in-plane alkyl chain ordering, with no significant scattering at 1.6Å−1. These results suggest that the elongation of the anion–aniondistances in interdigitated membrane 1cmay weaken the anion-stacking interaction.2.4. Macroscopic Structural Transition in the MembraneThe structural details of molecular assembly of 1 within mem-branes provided insights into the macroscopic structures andtheir temperature-dependent transitions. Transmission electronmicroscopy (TEM) observation of bilayer membrane 1a revealedcircular capsule structures with diameters ranging from 50 to100 nm (Figure 6a; Figure S6a, Supporting Information), con-sistent with the dynamic light scattering (DLS) analysis, whichestimates the average size of 1a to be approximately 55 nm(Figure S7a, Supporting Information). These TEM images closelyresemble the bilayer vesicles formed in water that collapsedunder the vacuum conditions of TEM observation.[43] The bi-layer membrane structure indicated by the ED analyses of 1a(Figure S2, Supporting Information) further supports the forma-tion of spherical bilayer vesicle-like capsules in water. Notably,the macroscopic structures were observed without staining theTEM sample with metallic reagents, confirming the presence ofnickel atoms in the assemblies. In contrast, the TEM image of 1cexhibited a flat, elliptical shape (Figure 6b; Figure S6b, Support-ing Information), with sizes ranging from 50 to 100 nm, similarto 1a, suggesting the formation of an ellipsoidal vesicular struc-ture in water. Despite the difference in macroscopic shapes, theaverage size of 1c is also estimated to be approximately 55 nmby the DLS analysis (Figure S7b, Supporting Information), con-Adv. Sci. 2025, 12, 2504967 2504967 (5 of 9) © 2025 The Author(s). Advanced Science published by Wiley-VCH GmbH 21983844, 2025, 29, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202504967, Wiley Online Library on [07/08/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.advancedscience.comwww.advancedsciencenews.com www.advancedscience.comFigure 6. Transmission electron microscopy (TEM) images of dried samples of 1a (a) and 1c (b) on films supported by a TEM microgrid. Other imagesare shown in Figure S6 (Supporting Information). Illustrations of the assembly forms are shown in the images.sistent with 1a. The membrane structural changes from the bi-layer membrane (1a) to interdigitated membrane (1c) may resultin the macroscopic structural changes observed in TEM images.Notably, the DLS data at high temperatures indicates the averagesize of 1b is estimated to be 25 nm. This supports the conclusionthat the dissociated state 1b comprises a mixture of coexistingstructures, such as membranes, micelles, and monomers. Thisis also supported by SAXS data in the low q range (Figure 4; mid-dle in Figure 5) and suggests that 1b is not the completely solu-ble in water. The dissociated state 1b in water may enhance thechemical stability of the open-shell molecule 1 by maintainingthe effective intermolecular interactions.2.5. Intermolecular Spin–Spin Interaction in Bilayer CapsulesThe bilayer capsules 1a and 1c exhibited unique magnetic prop-erties in water, distinct from those in their isolated states.Their electronic spin resonance (ESR) spectra demonstratedunique paramagnetic behavior with uniaxial anisotropy (Figure7a; Figure S8, Supporting Information), which significantly dif-fered from those observed in the solution and powder forms. Indichloromethane, a single Lorentzian curve was observed (repre-senting the isolated state) due to Brownian motion. In contrast,the powders (polycrystals) displayed a typical triaxial anisotropyspectrum, consistent with a monoanionic square-planar Ni(III)dithiolate anion possessing a rhombic g tensor.[44]The magnetic anisotropy, observed for 1a and 1c, has pre-viously been observed only in highly long-range ordered (crys-talline) conductive polymer films[45] and a limited number of sin-gle crystals with strong spin–spin interactions.[46–48] This obser-vation supports the presence of long-range order in 1a and 1c.Remarkably, this observation of paramagnetic behavior with uni-axial anisotropy, driven by strong intracolumnar spin–spin in-teractions, is unprecedented among soft organic magnetic ma-terials. This behavior is likely due to the planar structure of theNi(2OMe) anions and their specific orientation within themacro-Figure 7. a) Electronic spin resonance spectra (ESR) of theNi(2OMe) an-ion salt in dichloromethane, powder, 1a, and 1c, with water as a back-ground. b) Possible stacking in a head-to-tail manner. c) Possible orienta-tion of Ni(2OMe) anions in the bilayer membrane (1a) and interdigitatedmembrane (1c).scopic assemblies (Figure 5). The 4-methoxy groups in the lig-ands appear to induce a head-to-tail stacking arrangement of theNi(2OMe) anions, minimizing steric hindrance from the steric4-methoxy substituents. This stacking configuration facilitatesAdv. Sci. 2025, 12, 2504967 2504967 (6 of 9) © 2025 The Author(s). Advanced Science published by Wiley-VCH GmbH 21983844, 2025, 29, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202504967, Wiley Online Library on [07/08/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.advancedscience.comwww.advancedsciencenews.com www.advancedscience.comFigure 8. Ni X-ray absorption spectroscopy (XAS) for Ni atoms of the Ni(2OMe) anion salt in capsule 1a. a) Spectra of the Ni L3 region during theheating and cooling processes. b) Spectra in the broad ranges covering Ni L3 and L2 during the heating and cooling processes, with satellite signalsindicated by arrows.molecular fluctuations via rotation along the stacking direction(Figure 7b,c). This fluctuation may impede the formation of aperiodic crystalline phase, potentially leading to a highly orderedphase (likely a gel phase), as indicated by WAXS data. Addition-ally, the SOMO of theNi(2OMe) anion, characterized by its nodalstructure along the molecular long-axis (Figure 3b), supports in-tracolumnar orbital overlap in the head-to-tail arrangement, evenwith slight uniaxial rotating fluctuations.[49]The uniaxially anisotropic electronic structure observed inboth 1a and 1c highlights significant intracolumnar spin–spininteractions shared by these capsules. The potential uniformcolumnar stacking of the planar Ni(2OMe) anions in 1a and1c likely generates a consistent electronic environment of d/𝜋-spins, resulting in identical uniaxial magnetism in both forms.Although the WAXS data (Figure S5, Supporting Information)suggests that the intracolumnar stacking distance in 1c may belonger than that in 1a, the uniform stacking appears to mitigatethe impact of this difference (Figure 7c), thereby maintaining ro-bust magnetic properties. Moreover, the strong intracolumnarspin–spin interactions likely contribute to the exceptional sta-bility of the capsules in water, which is sustained over severalmonths. Magnetic anisotropy in soft organic materials heavily re-lies on spin–spin interactions, especially in systems composed oflight elements. The strong anisotropic spin–spin interactions ob-served in this study suggest a promising design strategy for creat-ing soft organic paramagnets with stable and tunable properties.Their absorption spectra further confirmed the comparableelectronic structures of capsules 1a and 1c. At 20 °C, the UVspectra of both forms exhibit similar absorption peaks at 902and 800 nm (Figure S9, Supporting Information), possibly cor-responding to SOMO-to-LUMO and HOMO–n-to-LUMO transi-tions, respectively. These transitions were simulated by TDDFTcalculations (Gaussian software, UB3LYP/6-311G++ (d,p), SDDforNi; Table S2, Supporting Information). Upon heating the sam-ple above 65 °C, the dispersed form 1 was generated, accompa-nied by the appearance of a new absorption band at 960 nm,which was absent in the spectra at low temperatures. This obser-vation suggests the emergence of a unique electronic structure athigh temperatures inwater, likely attributed to the intramolecularcharge transfer between the metal and ligands. The intramolec-ular charge transfer may be facilitated by hydrogen bonding withthe surrounding water molecules,[35] as supported by TDDFTsimulations (Figures S10 and S11; Tables S4–S7, Supporting In-formation). The energy level shifting may be induced by theHOMO−n to LUMO transition in the presence of a hydrogen-bonded water molecule (Table S2, Supporting Information).2.6. Electronic Structure in Nickel Atom within the CapsulesInsights into the unique dynamic electronic structures of the bi-layer capsules 1a and 1c and their temperature-dependent behav-ior in water were obtained throughX-ray absorption spectroscopy(XAS).[50,51] The Ni L-edge XAS spectrum of 1a at 14 °C exhibitstwo major peaks at 853.2 and 853.7 eV (Figure 8), correspond-ing to the L3 absorption region edge of nickel atoms. The broadspectral features likely reflect band dispersion arising from inter-molecular interactions between the Ni(2OMe) anions in water.Adv. Sci. 2025, 12, 2504967 2504967 (7 of 9) © 2025 The Author(s). Advanced Science published by Wiley-VCH GmbH 21983844, 2025, 29, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202504967, Wiley Online Library on [07/08/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.advancedscience.comwww.advancedsciencenews.com www.advancedscience.comThese finding supports the spin–spin interactions, as suggestedby the ESR spectra results (Figure 7; Figure S8, Supporting In-formation), with the SOMO delocalized over the anion moleculeand including Ni atom. The spectral shapes remained consis-tent within the ranges of 14–60 °C, aligning with the SAXS pro-files (Figure 4a). However, at 80 °C, the membrane structure 1adisassembled to smaller assemblies in the dissociated form 1b,and the absorption transformed into a sharper peak centered at853.7 eV, indicating a change in the electronic structure of theNi atom within the Ni(2OMe) anion. This change was likely at-tributed to the disruption of intermolecular Ni–Ni interactions ofthe Ni(2OMe) anions that were present at 60 °C and below.Notably, the XAS spectrum at higher energy ranges revealedthe emergence of charge-transfer satellite peaks at 80 °C, ap-pearing on the long-wavelength side of the L3 and L2 absorp-tion edges (Figure 8b). These observations underscore signif-icant alterations in the electronic structures of the Ni atom,driven by temperature-induced structural transition in the cap-sule. The satellite peaks likely arise from changes in charge trans-fer between the Ni atom and ligands,[52] influenced by the sur-rounding water molecules and possibly facilitated by the hy-drogen bonding between ligands and water molecules.[35] Thisunique phenomenon is supported by the observed changes inthe absorption spectrum (Figure S9, Supporting Information)and corresponding simulations (Figures S10 and S11; TableS2, Supporting Information). The temperature-dependent dy-namic structural change enables alterations in the electronicstructure of the Ni(2OMe) anion through both intermolecularand intramolecular interactions, involving the surrounding wa-ter molecules. These findings highlight the unique properties ofthe d/𝜋-conjugated planar molecule-based soft paramagnet cap-sule in water. The dynamic microscopic and macroscopic geo-metric and electronic structural changes, potentially involvinghydrogen-bonding with surrounded water molecules, suggestthe potential for advanced applications in soft magnetic materi-als.3. ConclusionWe addressed the trade-off between achieving long-range struc-tural order and preserving the inherent dynamic flexibility insoft materials composed of open-shell planar molecules a com-mon challenge in molecular paramagnets by developing an am-phiphilic assembly of the hydrophilic d/𝜋-conjugated Ni(2OMe)anion. The resulting bilayer membrane structure in water ex-hibited a unique arrangement, with anions stacking and shift-ing along the short-axis of the molecules to form spherical cap-sules. The assembly exhibited temperature-dependent hysteretictransformations, transitioning from the bilayer membrane (1a)to a dissociated form (1b) and subsequently to an interdigitatedmembrane (1c), which likely adopted ellipsoidal structures. Ef-fective intermolecular spin–spin interactions between the open-shell d/𝜋-conjugated Ni(2OMe) anion molecules contributed tothe formation of a band-like structure, enabling dynamic elec-tronic functionalities. These interactions were modulated by therotational fluctuation of the anions along the stacking direction,influenced by the molecular design features such as the hy-drophilic 4-methoxy group. This fluctuation imparted uniaxialmagnetic anisotropy to both 1a and 1c. At elevated temperaturesabove 65 °C, the assembly dissociated, disrupting significant Ni–Ni interactions, as evidenced by the narrowing Ni XAS signals.The emergence of satellite features in the L3 and L2 bands ofthe Ni XAS spectrum and long-wavelength UV absorption sug-gested that intramolecular charge transfer between the metaland ligands[52] might occur, likely facilitated by hydrogen bond-ing with surrounding water molecules.[35] These macroscopicdynamic structural and electronic changes were previously un-achieved in open-shell planar molecule-based paramagnets. Thestructural homogeneity, based on single-molecular-weight mate-rials, enabled us to address structural insights and mechanismsvia a combination of structural and theoretical investigations.The designability of d/𝜋-conjugated molecularcomplexes,[53,54] enabled by tunable ligand and metalcombinations[33,34,40] and hydrophobic alkyl chains[26,33,37] offerssignificant potential for engineering tailored intermolecularinteractions in both aqueous and organic environments. Theself-assembly approach demonstrated in this study establishesa versatile platform for creating stable paramagnetic molecularassemblies with tunable magnetic properties and responsive-ness to external stimuli. This paves the way for innovativeapplications in advanced materials, including nanomedicineand stimuli-responsive systems. This molecular design strategyexpands possibilities for diversifying electronic functionalitiesin soft conductors, integrating magnetic, electrical, thermal, andoptical properties, and represents a significant advancement inthe field of soft material sciences.Supporting InformationSupporting Information is available from the Wiley Online Library or fromthe author.AcknowledgementsThe authors thank Prof. Eiichi Nakamura for the use of DLS measure-ments and Dr. Aiko Sakamoto for elemental analysis. This work bene-fited from the use of the SasView application, originally developed un-der NSF award DMR-0520547. SasView contains code developed withfunding from the European Union’s Horizon 2020 research and innova-tion program under the SINE2020 project, grant agreement No. 654000.The XAS measurements at BL07LSU of SPring-8 were performed by thejoint research in SRRO and ISSP, the University of Tokyo (Proposal No.2022A7448). This work was partially supported by the JSPS Grants-in-Aid for Scientific Research (No. JP20H05206, JP21K05018, JP22H04523to T.F., JP19H05717 to M.H. and Y.H., JP23H04874 to K.H., JP19H05715,JP23K17865, JP23KK0255, JP24K01301 to R.M., JP23K22435, JP23H04861to H.O., JP22H00106 to H.M.), JST PRESTO (JPMJPR22Q8 to T.F., JP-MJPR21Q2 to H.O.), Core-to-Core Program “Emergent Quantum Elec-tronics in Molecular Layer” (JPJSCCA20240001 to T.F., H.O., and H.M.),and a research grant from the Iketani Sci. and Technol. Foundation, theNaito Foundation, and the Kao Foundation for Arts and Science to T.F.Part of this work was conducted at the Institute for Molecular Science,supported by the Advanced Research Infrastructure forMaterials andNan-otechnology (JPMXP1224MS1096) of the Ministry of Education, Culture,Sports, Science and Technology (MEXT), Japan.Conflict of InterestThe authors declare no conflict of interest.Adv. Sci. 2025, 12, 2504967 2504967 (8 of 9) © 2025 The Author(s). 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Advanced Science published by Wiley-VCH GmbH 21983844, 2025, 29, Downloaded from https://advanced.onlinelibrary.wiley.com/doi/10.1002/advs.202504967, Wiley Online Library on [07/08/2025]. See the Terms and Conditions (https://onlinelibrary.wiley.com/terms-and-conditions) on Wiley Online Library for rules of use; OA articles are governed by the applicable Creative Commons Licensehttp://www.advancedsciencenews.comhttp://www.advancedscience.com Macroscopic Structural Transition of Nickel Dithiolate Capsule with Uniaxial Magnetic Anisotropy in Water 1. Introduction 2. Results and Discussion 2.1. Molecular Design and Synthesis of Amphiphilic Salt 2.2. Assembly of Amphiphilic Nickel Dithiolate Salt in Water 2.3. Structural Transition of Nickel Dithiolate Membrane 2.4. Macroscopic Structural Transition in the Membrane 2.5. Intermolecular Spin9040�Spin Interaction in Bilayer Capsules 2.6. Electronic Structure in Nickel Atom within the Capsules 3. Conclusion Supporting Information Acknowledgements Conflict of Interest Data Availability Statement Keywords