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[Nattapol Ma](https://orcid.org/0000-0002-6162-1834), Soracha Kosasang, Satoshi Horike, Hiroki Yamada

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[Liquid Coordination Polymers with Anhydrous Proton Conductivity](https://mdr.nims.go.jp/datasets/59aa4ad9-669a-4de8-8901-44908ca0ef7f)

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Liquid Coordination Polymers with Anhydrous Proton ConductivityResearch ArticleHow to cite: Angew. Chem. Int. Ed. 2025, 64, e202504618doi.org/10.1002/anie.202504618Coordination PolymersLiquid Coordination Polymers with Anhydrous Proton ConductivityNattapol Ma,* Soracha Kosasang, Satoshi Horike, and Hiroki YamadaAbstract: Liquid states in coordination polymers (CPs) and metal-organic frameworks (MOFs) are typically consideredtransient intermediates in the crystal-to-glass transformations of organic–inorganic hybrid materials. However, theirpotential as functional materials has remained largely unexplored. Inspired by the unique properties of ionic liquids,organic liquids, and liquid metals, we explore liquid CPs as a platform for novel functionalities distinct from those of theircrystalline and glass counterparts. Here, we present a strategy to achieve functional liquid CPs near ambient conditionsby introducing H3PO4 as a network modifier, shifting compositions away from stoichiometric ratios. This process disruptsextended coordination networks during melting, producing a stable liquid state. By tuning the ratio of network modifiers, weachieve control over liquid properties, including anhydrous proton conductivity up to 27 mS cm−1 at 353 K and viscositiesranging from 18.8 to 105.9 Pa·s at 303 K. These findings demonstrate the transformative potential of liquid CPs, introducingthem as a new platform for designing liquid conductors.IntroductionSolid-to-liquid transition is one of the most fundamentalprocesses in material sciences, yet it is among the mostcomplex phenomena to predict.[1] This process opens upopportunities not only for advanced material processing butalso allows access to their unique properties.[2–4] For example,the discovery of liquid crystals has transformed displaytechnologies by harnessing their anisotropic optical propertiesand stimuli responsiveness in fluid phases.[5] Similarly, ionicliquids have emerged as versatile solvents and electrolytes dueto their low volatility, high thermal stability, and availability ina wide variation of physicochemical properties.[6][*] N. MaInternational Center for Young Scientists (ICYS), National Institutefor Materials Science, 1-1 Namiki, Tsukuba, Ibaraki 305-0044, JapanE-mail: ma.nattapol@nims.go.jpS. Kosasang, S. HorikeDepartment of Chemistry, Graduate School of Science, KyotoUniversity, Kitashirakawa-oiwake-cho, Sakyo-ku, Kyoto 606–8502,JapanS. HorikeDepartment of Materials Science and Engineering, School ofMolecular Science and Engineering, Vidyasirimedhi Institute ofScience and Technology, Rayong 21210, ThailandH. YamadaDiffraction and Scattering Division, Japan Synchrotron RadiationResearch Institute (JASRI) Sayo, Hyogo 679–5198, JapanAdditional supporting information can be found online in theSupporting Information section© 2025 The Author(s). Angewandte Chemie International Editionpublished by Wiley-VCH GmbH. This is an open access article underthe terms of the Creative Commons Attribution-NonCommercialLicense, which permits use, distribution and reproduction in anymedium, provided the original work is properly cited and is not usedfor commercial purposes.Proton and ionic conductivities in liquid systems areoften described by Walden’s rule, which outlines an inverserelationship between conductivity and viscosity.[7,8] Whilethe concept provides a foundational understanding of iontransport in liquids, it also highlights a critical limitation:conductivity in liquid systems is predominantly governedby viscosity. In discrete molecular liquids, such as proticionic liquids, the Walden plot generally classifies theirconductivity as “ionic” or “subionic,” where ion transportprimarily occurs through the migration of low molecular-weight entities (vehicle mechanism).[6,9,10] However, thisprocess is inherently less efficient than the structural dif-fusion (Grotthuss) mechanism observed in “superionic”conductors.[10] Efforts to enhance conductivity efficiencyoften involve reducing the migration of unwanted counterionsvia selective polymerization, observed in polymerized ionicliquids.[11,12] However, this comes at the expense of fluidity.These challenges emphasize the need for new liquid materialplatforms capable of overcoming the viscosity-conductivitytrade-off.Solid-to-liquid-to-glass transformation in some proton-conductive coordination polymers (CPs) and metal-organicframeworks (MOFs) presents an appealing solution for over-coming the limitation of liquid conductors.[13–17] Preservationof coordination networks even above the melting pointhelps restrict the migration of molecular entities, enablingselective proton migration and promoting the probabil-ity of achieving “superionic” behaviors.[18–20] Furthermore,compositional flexibility in these amorphous CPs/MOFsallows for continuous property control by incorporatingdiverse functional components. For instance, doping smallamounts of stimuli-responsive molecules, such as pyranineor tris(bipyrazine)ruthenium(II), allows dynamic control overanhydrous proton conductivity in zinc–phosphate–azole CPglasses.[21,22] The physical properties, including melting andglass transition temperatures, can also be controlled byadjusting the composition of the resulting glass away fromAngew. Chem. Int. Ed. 2025, 64, e202504618 (1 of 8) © 2025 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbHhttps://orcid.org/0000-0002-6162-1834https://orcid.org/0009-0006-5254-2890https://orcid.org/0000-0001-8530-6364https://orcid.org/0000-0003-4960-238Xmailto:ma.nattapol@nims.go.jphttp://creativecommons.org/licenses/by-nc/4.0/http://crossmark.crossref.org/dialog/?doi=10.1002%2Fanie.202504618&domain=pdf&date_stamp=2025-05-26Research ArticleFigure 1. Schematic illustration of the proposed chain scission processin this work induced by the addition of network modifiers.stoichiometric ratios.[23–30] Although functional liquids arecommon in many material families, they remain exotic withinthe context of CPs/MOFs.[31] Since the early observationof melting behavior in CPs/MOFs, liquid states have beenviewed primarily as intermediates for accessing glassy states,mainly because the liquid states are exclusively observedat high temperatures.[32] For examples, zeolite imidazolateframeworks typically melt at 643–863 K,[24,33] while zinc–phosphate–azole CPs, despite having lower melting temper-atures, still require at least ca. 370 K to become liquids.[14]To date, no functional liquid CPs have been reported nearambient conditions.[32,34]This article presents a strategy for synthesizing liquidCPs by adjusting the equivalent amount of H3PO4 as anetwork modifier. Inspired by viscosity modulation in oxideglasses with network modifier additions,[35,36] we proposethat substituting bridging phosphate ligands with terminalphosphate ligands in meltable zinc–phosphate–azole CPssimilarly reduces the viscosity of CP glasses, allowing them tobehave as network-forming liquids near ambient conditions(Figure 1). Here, the “liquid” state is defined based onviscosity-dependent flow properties, beginning at viscositiesbelow the practical melting threshold (η < 10 Pa·s).[37,38] Prop-erties such as anhydrous proton conductivity and viscosityare finely tuned by adjusting the network domain size andlocal structure through specific starting compositions. Despitevariations in their macroscopic properties, pair distributionfunction analysis reveals that the short-to-intermediate rangestructures of all modified samples remain consistent withthose of their parent CPs. This work highlights a versatileapproach for designing liquid CPs with tunable functionalproperties.Results and DiscussionSynthesis and Melting BehaviorA meltable CP, [Zn3(H2PO4)6(H2O)3](1,2,3-benzotriazole)(Figure S1), was chosen as a representative material dueto its low melting temperature among glass-forming CPsand MOFs.[18] This compound, referred to as ZnPBTA’,was synthesized on a gram scale using a mechanochemicalapproach with a Teflon milling set, followed by dehy-dration to remove residual water (see Methods in SI).A series of non-stoichiometric CPs were prepared byreacting 3 mol equivalents of ZnO, 1 mol equivalent of1,2,3-benzotriazole, and varying amounts of H3PO4. TheH3PO4 used were 7.75, 9.5, and 11.25 mol equivalents forZnPBTA’-m1, ZnPBTA’-m2, and ZnPBTA’-m3, respectively,compared to the stoichiometric ratio of 6 mol equivalentsin ZnPBTA (Table S1). Powder X-ray diffraction (PXRD)patterns of the as-synthesized ZnPBTA’-m1, ZnPBTA’-m2,and ZnPBTA’-m3 matched well with the original ZnPBTA’(Figure S2). After dehydration, polycrystalline products wereobtained (Figure S3). The dehydrated forms of ZnPBTA’,ZnPBTA’-m1, ZnPBTA’-m2, and ZnPBTA’-m3 are denotedas ZnPBTA, ZnPBTA-m1, ZnPBTA-m2, and ZnPBTA-m3,respectively (Figure S4). PXRD analysis of the dehydratedsamples suggests a structural change originating from thetransformations around Zn2+ due to the release of watermolecules from the octahedral coordination sphere.[18,39]However, the exact crystal structure of dehydrated ZnPBTAcould not be determined, as the compound lost singlecrystallinity upon dehydration.[39] 31P magic-angle spinningnuclear magnetic resonance (31P MAS NMR, Figure S5)spectra of ZnPBTA-m1, ZnPBTA-m2, and ZnPBTA-m3exhibit peaks exclusively within the orthophosphate range,indicating that no condensation occurs during the dehydrationprocess and that all phosphate remains either anionic orin the form of free orthophosphoric acid.[40,41] Energy-dispersive spectroscopy (EDS) analysis further confirmed theabsence of Teflon contamination in the dehydrated products(Figure S6). Additionally, the actual Zn/P mol fractions,analyzed by inductively coupled plasma optical emissionspectroscopy (ICP-OES) technique, are provided in TableS2. FTIR spectra showed no distinct changes among thesamples (Figure S7). These results suggest that ZnPBTA-m1, ZnPBTA-m2, and ZnPBTA-m3 comprise crystallineZnPBTA domains alongside amorphous H3PO4.[22,27]Heating crystalline ZnPBTA above its melting temper-ature (Tm, peak = 394.6 K) produces a liquid state thatremains stable up to 448 K (Figures S8 and S9). Differ-ential scanning calorimetry (DSC, Figure S8) indicates thatdeviations from the stoichiometric composition result inchanges in melting behavior, attributed to flux melting.[42,43]A similar melting temperature depression is observed insome multicomponent zeolitic imidazolate frameworks.[44,45]Upon heating, ZnPBTA-m1, ZnPBTA-m2, and ZnPBTA-m3Angew. Chem. Int. Ed. 2025, 64, e202504618 (2 of 8) © 2025 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2025, 30, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202504618 by National Institute For, Wiley Online Library on [22/07/2025]. 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 LicenseResearch ArticleFigure 2. a) Melting temperature (Tm), glass transition temperature(Tg), and Tg/Tm as a function of the molar ratio of network modifier tooverall H3PO4. Tm and Tg were determined from melting peaktemperature and the temperature at which viscosity reached 1012 Pa·s,respectively. Optical images of b) ZnPBTA-g, c) ZnPBTA-g-m1, d)ZnPBTA-g-m2, and e) ZnPBTA-g-m3 at 393 K.undergo simultaneous endothermic events corresponding tomelting, dissolution, and depolymerization, with the overallenthalpy changes increasing proportionally to the excessH3PO4 content (Table S3). The melting process begins atonset temperatures of approximately 341–344 K, initiated bythe partial dissolution of crystalline domains into the H3PO4flux. This continues until endset temperatures of 390.5, 364.7,and 374.1 K for ZnPBTA-m1, ZnPBTA-m2, and ZnPBTA-m3, respectively. The peak melting temperature (Tm, peak),defined as the temperature at the peak of the DSC curve,decreases to 384.7 K for ZnPBTA-m1 and 359.4 K forZnPBTA-m2 due to increased H3PO4 flux content, whichfacilitates solid-to-liquid transition via dissolution (Figure 2a).However, when the modifier content exceeds the saturationpoint, changes in flux composition lead to a slight increasein Tm, peak to 370.7 K for ZnPBTA-m3.[46] Subsequent DSCheating reveals glass transition temperatures (Tg, DSC) of 282.4and 280.7 K for ZnPBTA and ZnPBTA-m1, respectively. TheTg values for ZnPBTA-m2 and ZnPBTA-m3 fall below themeasurement limit and are discussed in the next section.Thermogravimetric analysis (TGA) results show that allsamples exhibit less than 1% weight loss up to at least423 K, confirming the absence of phosphate condensationduring the melt-quenching process (Figures S9–S13). Addi-tionally, changes in the character of the liquid states wereobserved at 393 K, where they became transparent withincreasing amounts of H3PO4 beyond the stoichiometriclimit (Figure 2b–e). Upon quenching to room temperature,ZnPBTA-g and ZnPBTA-g-m1 solidified into an amorphoussolid, while ZnPBTA-g-m2 and ZnPBTA-g-m3 remained asviscous liquids. Note that -g indicates samples after melting.The PXRD patterns of all melt-quenched samples exhibitedno Bragg peaks, confirming the absence of long-range orders,and are homogeneous without any detectable crystallineH3PO4 (Figure S14).Viscosity and Glass TransitionThe liquid-like behavior at lower temperatures with excessH3PO4 motivated us to quantify changes in viscosity. Theviscosity of all samples follows a MYEGA-like temperaturedependence, with glass transition temperatures (Tg) estimatedby extrapolating viscosity to 1012 Pa·s (Figure 3a, TableS4).[47,48] A clear decreasing trend in Tg was observedwith increasing H3PO4 content, resulting in Tg values of280.4, 276.2, 260.9, and 250.8 K for ZnPBTA-g, ZnPBTA-g-m1, ZnPBTA-g-m2, and ZnPBTA-g-m3, respectively. Theseresults align with the Tg,dsc values obtained from DSCmeasurements for ZnPBTA-g and ZnPBTA-g-m1.At higher temperatures, the viscosity values drop belowthe working point (η = 103 Pa·s) at 312, 299, and 283 K forZnPBTA-g-m1, ZnPBTA-g-m2, and ZnPBTA-g-m3, respec-tively. At this point, the viscosity is comparable to moltensoda-lime glass at above 1373 K.[49] Additionally, prac-tical melting temperatures (η < 10 Pa·s) are achievableat 360, 329, and 308 K for ZnPBTA-g-m1, ZnPBTA-g-m2, and ZnPBTA-g-m3. Below these temperatures, viscosityapproaches the range typical of ionic liquids at theiroperating temperatures.[50] The reduced viscosity valuesfurther support the role of H3PO4 as a network modifier,inducing chain scission in the 1D coordination chains.[20]A similar decreasing trend of viscosity was observedin Zn(HPO4)(H2PO4)2](H2Im)2 upon introducing CsHSO4,where oxyanion exchanging between HSO4− and bridgingphosphate decreases overall viscosity.[27] Analogous behavioris also observed in conventional inorganic glasses, whereincreasing network modifier content continuously decreasesviscosity.[51,52]The liquid characteristics were further evaluated througha fragility diagram (Figure 3b), comparing the melt-quenched samples with references from various materialfamilies.[10,51,53–56] The fragility indexes (m) of the melt-quenched samples ranged from 118 to 146, positioning thembetween ZnCl2, which exhibits intermediate fragility, andfragile H3PO4.[48] The high fragility is attributed to therelatively low viscosity near Tm, estimated at 0.5–5.5 Pa·sfor the modified samples and 102.7 Pa·s for ZnPBTA. Incontrast, the strong ZIF-62 glass exhibits a much lowerfragility index (m = 23) and an exceptionally high viscosityof 105.5 Pa·s at Tm.[55] Another key parameter to describethe liquid behavior is the Tg/Tm ratio, which indicates thetendency of a liquid to form glass upon cooling rather thancrystallizing.[38,57] ZnPBTA exhibits a Tg/Tm of 0.71. Withincreasing H3PO4 fractions, Tg/Tm initially increases, reachingAngew. Chem. Int. Ed. 2025, 64, e202504618 (3 of 8) © 2025 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2025, 30, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202504618 by National Institute For, Wiley Online Library on [22/07/2025]. 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 LicenseResearch ArticleFigure 3. Viscosity of melt-quenched samples. a) Temperature-dependent viscosity of ZnPBTA-g, ZnPBTA-g-m1, ZnPBTA-g-m2, and ZnPBTA-g-m3with MYEGA (Mauro-Yue-Ellison-Gupta-Allan)[47] fit. Fitting parameters are listed in Table S4. b) Fragility plot of melt-quenched samples incomparison with reference compounds. Data of reference compounds are taken from ref. [10, 51, 53–56]a maximum of 0.73 for ZnPBTA-m2, before decreasing to 0.67for ZnPBTA-m3 due to its higher Tm.Short-to-intermediate Range OrderHaving observed alterations in viscosity and thermal behav-iors, we further focused on examining the role of the networkmodifier (H3PO4) in inducing changes to the local structure ofthe modified samples compared to the pristine ZnPBTA. Weprobed the short-to-intermediate range order in all samplesbefore and after melt-quenching using pair-distribution func-tion (PDF) analyses, which provide the probability of findingatomic pair distances presented as weighted histograms(Figure 4).[58] Despite slight intensity differences below 5 Å,the peak features of the crystalline derivatives remainedlargely identical to the pristine ZnPBTA, highlighting theretention of short-range order within crystalline domains(Figure 4c). Pair correlations from Zn2+ to its first and secondnearest-neighbor Zn2+ appeared at ca. 3.3 Å (Zn�Zn1st)and 5.2–5.5 Å (Zn�Zn2nd), respectively (Table S5). Thesemeasured distances align well with the predicted values of3.19 and 5.37 Å from the crystal structure of ZnPBTA’ at100 K.[18] The peak splitting observed in the Zn�Zn2nd regionof ZnPBTA, compared to the simulated PDF pattern ofZnPBTA’ (Figure S16), was attributed to the deformation ofthe Zn2+ octahedral coordination sphere upon dehydration.With increasing H3PO4 content from ZnPBTA to ZnPBTA-m3, a gradual increase in peak intensity corresponding tothe intramolecular P–O correlation at 1.5 Å was observed.A peak at ca. 3.9 Å and a recombined peak correspondingto the Zn�Zn2nd correlation at 5.2–5.3 Å emerged withexcess H3PO4, plausibly due to Zn2+ coordination withphosphate, which completes the octahedral coordination. Asimilar transformation occurred at ca. 7.5 Å (Zn�Zn3nd)when comparing ZnPBTA to ZnPBTA-m1. However, inZnPBTA-m2 and ZnPBTA-m3, this Zn�Zn3nd correlationwas hindered, plausibly due to strong contributions fromZn�P, Zn�O, P�O, and O�O correlations from excessH3PO4 or increased structural disorder. A slight reduction inamplitude at ca. 2.1, 3.3, and 4.4 Å, corresponding to Zn–O,Zn�Zn/P, and O�Zn/P correlations, respectively, indicates ahigher degree of disorder within the 1D chains. These peakassignments are supported by calculated partial PDFs derivedfrom the crystal structure of ZnPBTA’ (Figure 4e).[18,59]After melt-quenching, the distinct peak features below5 Å are preserved, although some positions and intensitiesshift compared to those of the parent crystals (Figures 4d,S17–S24). The shift in Zn–O correlations from 2.1 Å to below2.0 Å suggests a transformation in the coordination envi-ronment of Zn2+, from octahedral to tetrahedral geometry.This transformation is further supported by the diminishedcontributions from Zn�Zn1st and Zn�Zn2nd, along with ashift in the Zn–P contribution from ca. 3.3 Å in the crystallinestate to ca. 3.2 Å after melt-quenching. Additionally, a newpeak emerges at ca. 5.8–5.9 Å (Table S6), representinga Zn�Zn1st correlation unique to Zn-phosphate-azole CPswith tetrahedral geometry (Figure 4a–d).[14] To verify thesepeak assignments, we performed experimental and calcu-lated partial PDF analyses of [Zn(HPO4)(H2PO4)2](ImH2)2(H2Im = imidazolium) in both crystalline (ZnPIm) and glassy(ZnPIm-g) states, which also feature tetrahedral coordinationaround Zn2+ (Figures S26 and S27).[13,14] Note that thecalculated Zn�Zn1st distance from the crystal structure ofZnPIm at 243 K is ca. 5.7 Å.[13]Despite a significant change in viscosity, the short-to-intermediate-range features of the modified samples remainlargely consistent with those of unmodified ZnPBTA-g(Figure 4d). The correlation at ca. 5.8 Å, correspondingto the Zn�Zn1st pair, suggests that some degree of metal-ligand-metal connectivity is retained in all samples, even inZnPBTA-g-m3 with the highest modifier content. However,the peak is relatively weak, indicating that the 1D coordi-nation chains may undergo substantial scission, potentiallyfragmenting into much smaller species, including trimers,dimers, or even monomers, depending on the amount ofZn2+ in the coordination network.[20,60] Furthermore, theobserved decrease in viscosity with increasing H3PO4 contentsupports extensive chain fragmentation, likely driven byAngew. Chem. Int. Ed. 2025, 64, e202504618 (4 of 8) © 2025 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2025, 30, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202504618 by National Institute For, Wiley Online Library on [22/07/2025]. 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 LicenseResearch ArticleFigure 4. Local structure of modified samples. Local arrangements around Zn2+ in a) octahedral coordination[18] and b) tetrahedral coordination.[13]Zn, P, and O atoms are represented by light blue, orange, and red, respectively. Pair distribution function (PDF) of c) ZnPBTA, ZnPBTA-m1,ZnPBTA-m2, and ZnPBTA-m3 and d) ZnPBTA-g, ZnPBTA-g-m1, ZnPBTA-g-m2, and ZnPBTA-g-m3. Zn�Zn1st and Zn�Zn2nd represent pair correlationfrom Zn2+ to the first and second nearest neighbor Zn2+, respectively. e) Simulated PDF and partial PDF of ZnPBTA. Additional S(Q) data andextended PDF data up to 30 Å are provided in Figures S16–S25 of the Supporting Information. Note that ZnPBTA-g shows partial recrystallization dueto its fast crystallization under ambient conditions.[14]anion exchange between bridging and terminal phosphateligands.[27] At higher r distances, the melt-quenched samplesexhibit peak broadening, reflecting a loss of periodicity.Anhydrous Proton ConductivityWe measured the proton conductivity of melt-quenched sam-ples using alternative current (AC) impedance spectroscopyunder a dry Ar atmosphere. Samples in their molten statewere loaded into a conductivity cell with fixed dimensions.For each measurement, the samples were heated to specifictemperatures for at least 3 h and allowed to equilibrate untilthe conductivity values stabilized.ZnPBTA exhibits Arrhenius-type behavior, with protonconductivity values of 3.3 × 10−4 mS cm−1 at 303 K and5.7 × 10−3 mS cm−1 at 323 K.[18] An abrupt increase inproton conductivity was observed above 50 °C, reaching9.0 × 10−2 mS cm−1 at 333 K and 1.2 mS cm−1 at373 K. Below 60 °C, conductivity is primarily governedby the mobility of phosphate moieties along the 1D zinc-phosphate chains. Above this temperature, the randomrotation of BTA molecules provides an additional contribu-tion to proton conductivity, alongside enhanced phosphatedynamics, leading to a change in activation energy.[18]A similar abrupt change in proton conductivity uponheating has also been observed in other zinc-phosphate-azole CPs, such as [Zn3(H2PO4)6(H2O)3](benzimidazole)[39]and Zn(HPO4)(H2PO4)2](H2Im)2.[13] After melt-quenching,ZnPBTA-g exhibits significantly enhanced conductivity, withvalues of 0.33 mS cm−1 at 303 K and 8.0 mS cm−1 at 393 K.[18]By tuning the ratio of network modifiers, we achievedcontrol over anhydrous proton conductivity (Figures 5a,S28–S34, and Table S7). The maximum proton conductivitiesof 13.8 mS cm−1 at 393 K, 17.2 mS cm−1 at 373 K, and27 mS cm−1 at 353 K were achieved for ZnPBTA-g-m1, ZnPBTA-g-m2, and ZnPBTA-g-m3, respectively, allexceeding the 8.0 mS cm−1 measured for ZnPBTA-g at 393 K.Note that proton conductivity measurements for ZnPBTA-g-m2 and ZnPBTA-g-m3 could not be conducted above 373 and353 K, respectively, as the samples began leaking in our setupdue to their low viscosity. The temperature-dependent protonconductivity of the sample with stoichiometric compositiontransitions from Arrhenius-type behavior in crystallineZnPBTA to Vogel–Fulcher–Tammann (VFT)-type behaviorafter melt-quenching.[61–63] The Arrhenius behavior, linked toactivated local ion hopping in crystalline conductors, contrastswith the VFT behavior, which reflects ion migration coupledwith structural dynamics and assisted by structural relaxationin amorphous glasses or polymers.[48] The obtained fittingparameters are summarized in Table S8. The VFT behavior isretained in ZnPBTA-g-m1 and ZnPBTA-g-m2, accompaniedby an increase in proton conductivity. In these cases,additional network modifiers enhance structural dynamics, asAngew. Chem. Int. Ed. 2025, 64, e202504618 (5 of 8) © 2025 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2025, 30, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202504618 by National Institute For, Wiley Online Library on [22/07/2025]. 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 LicenseResearch ArticleFigure 5. Anhydrous proton conductivity of melt-quenched ZnPBTA-g,ZnPBTA-g-m1, ZnPBTA-g-m2, and ZnPBTA-g-m3. a) Variabletemperature proton conductivity under dry Ar atmosphere incomparison with crystalline ZnPBTA. Data of ZnPBTA and ZnPBTA-g aretaken from ref. [18] Nyquist plots are available in Figures S28–S32 in thesupporting information. b) Walden plots in comparison with 85%, 95%H3PO4, and protic ionic liquids. Reference data of H3PO4, protic ionicliquids, and calibrated ideal KCl line are taken from ref. [8, 10]reflected in the decreased Tg values. We observed a decreasingtrend in activation factors (B) and a smaller differencebetween the VFT-fitted ideal transition temperature (T0)and Tg with increasing network modifier content. The formersuggests weaker temperature dependence and lower barriersfor proton conduction, while the latter indicates a reduceddecoupling effect.[48,64–66] Further increases in networkmodifiers in ZnPBTA-g-m3 result in a transition back toArrhenius-type behavior with a relatively high activationenergy of 1.20 eV. This shift is likely driven by the dominantcontributions of free H3PO4 and highly fragmented CP chains,as evidenced by a decrease in the measured density (TableS9). The observed activation energy aligns closely with thoseof crystalline ZnPBTA (1.22 eV) and [Zn3(H2PO4)6](1,3-benzimidazole) (1.5 eV), measured at temperatures belowthe threshold where azole molecules begin to rotate andcontribute to proton conduction.[18,39]The Walden plot was utilized to examine the relation-ship between viscosity (η), equivalent conductivity (�m),and the proton-conductivity mechanisms.[6,67] In this study(Figure 5b), all samples deviate from Walden’s ideal line,occupying the superionic region. Equivalent conductivitiesexceeding those predicted by Walden’s rule indicate adecoupling of charge carriers from the overall structuralnetworks that govern viscosity. This suggests that protonmigration predominantly occurs via the Grotthuss mecha-nism. The weak dependence of conductivity on viscosityallows for the adjustment of viscosity without compromisinghigh proton conductivity. As the content of the networkmodifier increases, the trend shifts closer to the ideal line ofionic conduction in a fluid-diluted solution.[8] Along this line,molar conductivity is directly proportional to the fluidity ofthe medium, indicating that ion migration is fully coupledwith the structural dynamics.[48] The shift is attributed toreduced viscosity and an increased contribution from thevehicle mechanism, facilitated by free phosphoric acid andthe formation of smaller coordination network fragments withhigher H3PO4 content. These observations are consistent withthe reduced decoupling effect identified in the VFT fittinganalysis as the network modifier content increases. However,even with the highest modifier content (ZnPBTA-m3), thesample remains above phosphoric acid on the Walden plot(Figure 5b). This suggests that ZnPBTA-m3 still relies heavilyon the Grotthuss mechanism for proton conductivity, similarto phosphoric acid (∼97% Grotthuss contribution).[48,68,69]ConclusionThis study presents a strategy for preparing liquid CPsnear ambient conditions by shifting their composition awayfrom stoichiometric ratios. Excess phosphate ligands act asnetwork modifiers, enabling control over thermal behavior,proton conductivity, and viscosity. By varying the amountof network modifiers, we achieved tunable CP properties,including anhydrous proton conductivity ranging from 2.6to 27 mS cm−1 at 353 K and viscosities from 18.8 to105.9 Pa·s at 303 K. Synchrotron X-ray total scatteringand PDF analysis revealed a structural transformation inthe coordination environment around Zn2+, shifting fromoctahedral to tetrahedral geometry upon melt-quenching,with evidence of substantial chain fragmentation. This workthus establishes a foundation for designing next-generationfunctional liquid materials with tailored properties, offeringan exciting platform for applications that demand flexibility,dynamic mixing capabilities, and intrinsic proton conductivity.Supporting InformationThe authors have cited additional references within theSupporting Information.[13,14,18,20,22,27,59,70–91]AcknowledgementsN.M. acknowledges the support from ICYS for a researchfellowship, from the Japan Society of the Promotion ofScience (JSPS) for a Grant-in-Aid for Research ActivityAngew. Chem. Int. Ed. 2025, 64, e202504618 (6 of 8) © 2025 The Author(s). Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2025, 30, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202504618 by National Institute For, Wiley Online Library on [22/07/2025]. 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 LicenseResearch ArticleStart-up (JP24K23109) and Grant-in-Aid for Early-Career Scientists (JP25K18055), and from the SumitomoFoundation basic science grant number 2402150. Theauthors acknowledge BL04B2 beamlines at SPring-8 forthe synchrotron X-ray total scattering experiments with theapproval of JASRI (Proposal No. 2024B1167). They thankDr. Takashi Nakanishi (NIMS) and Dr. Renzhi Ma (NIMS)for access to equipment. They thank Dr. Daiki Umeyamafor discussions. They thank Nao Horike for 31P MAS NMRmeasurements. 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Angewandte Chemie International Edition published by Wiley-VCH GmbH 15213773, 2025, 30, Downloaded from https://onlinelibrary.wiley.com/doi/10.1002/anie.202504618 by National Institute For, Wiley Online Library on [22/07/2025]. 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 Licensehttps://doi.org/10.26434/chemrxiv-2025-3m7vvhttps://doi.org/10.26434/chemrxiv-2025-3m7vv Liquid Coordination Polymers with Anhydrous Proton Conductivity  Introduction  Results and Discussion  Synthesis and Melting Behavior  Viscosity and Glass Transition  Short-to-intermediate Range Order  Anhydrous Proton Conductivity  Conclusion  Supporting Information  Acknowledgements  Conflict of Interests  Data Availability Statement