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Research Article | Open Access

Supramolecular assembly of covalently modified Anderson-type polyoxometalates and crown ethers towards pseudo-rotaxane structures

Yi-An Yin1,§Wu-Ji Chen1,§Chun-Yan Liu1Meng-Meng Zhang1Chang-Gen Lin1 ( )Haralampos N. Miras2Yu-Fei Song1 ( )
State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China
School of Chemistry, The University of Glasgow, Glasgow G12 8QQ, UK

§ Yi-An Yin and Wu-Ji Chen contributed equally to this work.

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Abstract

The supramolecular assembly of a series of covalently modified Anderson-type polyoxometalates (POMs) and 18-crown-6 ethers was investigated for the first time. Seven new POM–crown ether complexes were prepared by varying the countercations and the modification mode of the Anderson clusters, and they were fully characterized by single-crystal X-ray diffraction, electrospray ionization time-of-flight mass spectrometry (ESI–TOF–MS), 1H nuclear magnetic resonance (NMR), etc. Alkali metal cations within the cavities of the crown ethers served as supercations to bind to the POM hybrids, thereby forming supramolecular assemblies with different architectures and compositions. More interestingly, five of the seven POM–crown ether complexes possessed novel pseudo-rotaxane structures, which were obtained by changing the modification mode of the Anderson clusters from symmetric to asymmetric. These pseudo-rotaxanes have not been reported previously and are considered important intermediates in the construction of POM-based supramolecular architectures with complementary structural and chemical properties.

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References

[1]

Wang, S. S.; Yang, G. Y. Recent advances in polyoxometalate-catalyzed reactions. Chem. Rev. 2015, 115, 4893–4962.

[2]

Anyushin, A. V.; Kondinski, A.; Parac-Vogt, T. N. Hybrid polyoxometalates as post-functionalization platforms: From fundamentals to emerging applications. Chem. Soc. Rev. 2020, 49, 382–432.

[3]

Wu, Z. K.; Zhai, Y. Y.; Zhao, W. S.; Wei, Z. Y.; Yu, H.; Han, S.; Wei, Y. G. An efficient way for the N-formylation of amines by inorganic-ligand supported iron catalysis. Green Chem. 2020, 22, 737–741.

[4]

Li, H. F.; Yang, M. N.; Yuan, Z. L.; Sun, Y. H.; Ma, P. T.; Niu, J. Y.; Wang, J. P. Construction of one Ru2W12-cluster and six lacunary keggin tungstoarsenate leading to the larger Ru-containing polyoxometalate photocatalyst. Chin. Chem. Lett. 2022, 33, 4664–4668.

[5]

Zhang, Y.; Wang, X.; Wang, Y.; Xu, N.; Wang, X. L. Anderson-type polyoxometalate-based sandwich complexes bearing a new “V”-like bis-imidazole-bis-amide ligand as electrochemical sensors and catalysts for sulfide oxidation. Polyoxometalates 2022, 1, 9140004.

[6]

Gu, Q. X.; Zhao, X. L.; Meng, M.; Shao, Z. Y.; Zheng, Q.; Xuan, W. M. Crystalline porous ionic salts assembled from polyoxometalates and cationic capsule for the selective photocatalytic aerobic oxidation of aromatic alcohols to aldehydes. Chin. Chem. Lett. 2023, 34, 107444.

[7]

Dong, Y. Y.; Feng, Y. Q.; Li, Z.; Zhou, H.; Lv, H. J.; Yang, G. Y. CsPbBr3/polyoxometalate composites for selective photocatalytic oxidation of benzyl alcohol. ACS Catal. 2023, 13, 14346–14355.

[8]

Liu, G.; Chen, Y. F.; Chen, Y. L.; Shi, Y. Q.; Zhang, M. Y.; Shen, G. D.; Qi, P. F.; Li, J. K.; Ma, D. L.; Yu, F. et al. Indirect electrocatalysis S–N/S–S bond construction by robust polyoxometalate based foams. Adv. Mater. 2023, 35, 2304716.

[9]

Huang, X. Q.; Liu, S.; Liu, G.; Tao, Y. W.; Wang, C. R.; Zhang, Y. L.; Li, Z.; Wang, H. W.; Zhou, Z.; Shen, G. D. et al. An unprecedented 2-fold interpenetrated lvt open framework built from Zn6 ring seamed trivacant polyoxotungstates used for photocatalytic synthesis of pyridine derivatives. Appl. Catal. B: Envion. 2023, 323, 122134.

[10]

Liu, Y.; Liu, G. P.; Zeng, B. X.; Li, Y. Z.; Chen, L. J.; Zhao, J. W. 2,5-Thiophenedicarboxylic acid bridging hexameric CeIII-substituted selenotungstate and its application for detecting Mucin 1. Inorg. Chem. 2024, 63, 7858–7868.

[11]

Hu, Q. L.; Liu, Y. F.; Lin, X. L.; Lin, Z. F.; Cao, J. W.; Yang, G. P. Two different three-dimensional uranium-containing polymolybdates based on Zn(II) for the heterogeneous catalytic construction of C–N bond. Inorg. Chem. 2024, 63, 8919–8924.

[12]

Long, D. L.; Tsunashima, R.; Cronin, L. Polyoxometalates: Building blocks for functional nanoscale systems. Angew. Chem., Int. Ed. 2010, 49, 1736–1758.

[13]

Miras, H. N.; Vilà-nadal, L.; Cronin, L. Polyoxometalate based open-frameworks (POM–OFs). Chem. Soc. Rev. 2014, 43, 5679–5699.

[14]

Li, X. X.; Zhao, D.; Zheng, S. T. Recent advances in POM-organic frameworks and POM-organic polyhedra. Coord. Chem. Rev. 2019, 397, 220–240.

[15]

Zhang, J. W.; Huang, Y. C.; Li, G.; Wei, Y. G. Recent advances in alkoxylation chemistry of polyoxometalates: From synthetic strategies, structural overviews to functional applications. Coord. Chem. Rev. 2019, 378, 395–414.

[16]

Wu, P. F.; Wang, Y.; Huang, B.; Xiao, Z. C. Anderson-type polyoxometalates: From structures to functions. Nanoscale 2021, 13, 7119–7133.

[17]

Zhuang, Q. H.; Sun, Z. Q.; Lin, C. G.; Qi, B.; Song, Y. F. Latest progress in asymmetrically functionalized Anderson-type polyoxometalates. Inorg. Chem. Front. 2023, 10, 1695–1711.

[18]

Blazevic, A.; Rompel, A. The Anderson-Evans polyoxometalate: From inorganic building blocks via hybrid organic-inorganic structures to tomorrows “Bio-POM”. Coord. Chem. Rev. 2016, 307, 42–64.

[19]

Ying, J.; Zhang, B. Y.; Tian, A. X.; Wang, X. L. A series of A- and B-type Anderson compounds with Al, Te and Cr as centers by tuning different ligands: Syntheses, electrochemical, photocatalytic and CO2RR properties. CrystEngComm 2021, 23, 2572–2581.

[20]

Marcoux, P. R.; Hasenknopf, B.; Vaissermann, J.; Gouzerh, P. Developing remote metal binding sites in heteropolymolybdates. Eur. J. Inorg. Chem. 2003, 2003, 2406–2412.

[21]

Song, Y. F.; Long, D. L.; Cronin, L. Noncovalently connected frameworks with nanoscale channels assembled from a tethered polyoxometalate-pyrene hybrid. Angew. Chem., Int. Ed. 2007, 46, 3900–3904.

[22]

Song, Y. F.; Long, D. L.; Kelly, S. E.; Cronin, L. Sorting the assemblies of unsymmetrically covalently functionalized Mn-Anderson polyoxometalate clusters with mass spectrometry. Inorg. Chem. 2008, 47, 9137–9139.

[23]

Thiel, J.; Yang, D. M.; Rosnes, M. H.; Liu, X. L.; Yvon, C.; Kelly, S. E.; Song, Y. F.; Long, D. L.; Cronin, L. Observing the hierarchical self-assembly and architectural bistability of hybrid molecular metal oxides using ion-mobility mass spectrometry. Angew. Chem., Int. Ed. 2011, 50, 8871–8875.

[24]

Zhang, B.; Yue, L.; Wang, Y.; Yang, Y.; Wu, L. X. A novel single-side azobenzene-grafted Anderson-type polyoxometalate for recognition-induced chiral migration. Chem. Commun. 2014, 50, 10823–10826.

[25]

Saad, A.; Oms, O.; Dolbecq, A.; Menet, C.; Dessapt, R.; Serier-Brault, H.; Allard, E.; Baczko, K.; Mialane, P. A high fatigue resistant, photoswitchable fluorescent spiropyran-polyoxometalate-BODIPY single-molecule. Chem. Commun. 2015, 51, 16088–16091.

[26]

Li, X. X.; Wang, Y. X.; Wang, R. H.; Cui, C. Y.; Tian, C. B.; Yang, G. Y. Designed assembly of heterometallic cluster organic frameworks based on Anderson-type polyoxometalate clusters. Angew. Chem., Int. Ed. 2016, 55, 6462–6466.

[27]

Lin, C. G.; Fura, G. D.; Long, Y.; Xuan, W. M.; Song, Y. F. Polyoxometalate-based supramolecular hydrogels constructed through host-guest interactions. Inorg. Chem. Front. 2017, 4, 789–794.

[28]

Xu, W. T.; Pei, X. K.; Diercks, C. S.; Lyu, H.; Ji, Z.; Yaghi, O. M. A metal-organic framework of organic vertices and polyoxometalate linkers as a solid-state electrolyte. J. Am. Chem. Soc. 2019, 141, 17522–17526.

[29]

Xia, Z. Q.; Lin, C. G.; Yang, Y.; Wang, Y. K.; Wu, Z. P.; Song, Y. F.; Russell, T. P.; Shi, S. W. Polyoxometalate-surfactant assemblies: Responsiveness to orthogonal stimuli. Angew. Chem., Int. Ed. 2022, 61, e202203741.

[30]

Song, Y. F.; Tsunashima, R. Recent advances on polyoxometalate-based molecular and composite materials. Chem. Soc. Rev. 2012, 41, 7384–7402.

[31]

Zhang, J. W.; Huang, Y. C.; Zhang, J.; She, S.; Hao, J.; Wei, Y. G. A direct anchoring of Anderson-type polyoxometalates in aqueous media with tripodal ligands especially containing the carboxyl group. Dalton Trans. 2014, 43, 2722–2725.

[32]

Zhang, J. W.; Liu, Z. H.; Huang, Y. C.; Zhang, J.; Hao, J.; Wei, Y. G. Unprecedented χ isomers of single-side triol-functionalized Anderson polyoxometalates and their proton-controlled isomer transformation. Chem. Commun. 2015, 51, 9097–9100.

[33]

Li, X. X.; Ma, X.; Zheng, W. X.; Qi, Y. J.; Zheng, S. T.; Yang, G. Y. Composite hybrid cluster built from the integration of polyoxometalate and a metal halide cluster: Synthetic strategy, structure, and properties. Inorg. Chem. 2016, 55, 8257–8259.

[34]

Zhang, J. W.; Huang, Y. C.; Hao, J.; Wei, Y. G. β-{Cr[RC(CH2O)3]2Mo6O18}3−: The first organically-functionalized β isomer of Anderson-type polyoxometalates. Inorg. Chem. Front. 2017, 4, 1215–1218.

[35]

Li, X. X.; Deng, C. C.; Zhao, D.; Yu, H.; Zeng, Q. X.; Zheng, S. T. Composite cluster-organic frameworks based on polyoxometalates and copper/cobalt-oxygen clusters. Dalton Trans. 2018, 47, 16408–16412.

[36]

Zhang, Y. S.; Jia, H. L.; Li, Q.; Huang, Y. C.; Wei, Y. G. Synthesis and characterization of an unprecedented water-soluble tris-functionalized Anderson-type polyoxometalate. J. Mol. Struct. 2020, 1219, 128555.

[37]

Dai, G. Y.; Li, Q.; Zang, D. J.; Wei, Y. G. A bifunctional molecular catalyst built up of L-proline grafted polyoxometalate for one-pot three-component green synthesis of heterocycles. Green Chem. 2023, 25, 6263–6269.

[38]

Proust, A.; Matt, B.; Villanneau, R.; Guillemot, G.; Gouzerh, P.; Izzet, G. Functionalization and post-functionalization: A step towards polyoxometalate-based materials. Chem. Soc. Rev. 2012, 41, 7605–7622.

[39]

She, S.; Bian, S. T.; Hao, J.; Zhang, J. W.; Zhang, J.; Wei, Y. G. Aliphatic organoimido derivatives of polyoxometalates containing a bioactive ligand. Chem.—Eur. J. 2014, 20, 16987–16994.

[40]

Chen, K.; Dai, G. Y.; Liu, S. Q.; Wei, Y. G. Reducing obesity and inflammation in mice with organically-derivatized polyoxovanadate clusters. Chin. Chem. Lett. 2023, 34, 107638.

[41]

Wu, Z. K.; Dai, G. Y.; Li, Q.; Wei, Z. Y.; Ru, S.; Li, J. D.; Jia, H. L.; Zang, D. J.; Čolović, M.; Wei, Y. G. POV-based molecular catalysts for highly efficient esterification of alcohols with aldehydes as acylating agents. Chin. Chem. Lett. 2024, 35, 109061.

[42]

Yin, P. C.; Li, D.; Liu, T. B. Solution behaviors and self-assembly of polyoxometalates as models of macroions and amphiphilic polyoxometalate-organic hybrids as novel surfactants. Chem. Soc. Rev. 2012, 41, 7368–7383.

[43]

Zhu, Y. L.; Wang, L. S.; Hao, J.; Yin, P. C.; Zhang, J.; Li, Q.; Zhu, L.; Wei, Y. G. Palladium-catalyzed Heck reaction of polyoxometalate-functionalised aryl iodides and bromides with olefins. Chem.—Eur. J. 2009, 15, 3076–3080.

[44]

Bayaguud, A.; Zhang, J.; Khan, R. N. N.; Hao, J.; Wei, Y. G. A redox active triad nanorod constructed from covalently interlinked organo-hexametalates. Chem. Commun. 2014, 50, 13150–13152.

[45]

Li, X. X.; Zhang, L. J.; Cui, C. Y.; Wang, R. H.; Yang, G. Y. Designed construction of cluster organic frameworks from Lindqvist-type polyoxovanadate cluster. Inorg. Chem. 2018, 57, 10323–10330.

[46]

Luo, J. C.; Chen, K.; Yin, P. C.; Li, T.; Wan, G.; Zhang, J.; Ye, S. T.; Bi, X. M.; Pang, Y.; Wei, Y. G. et al. Effect of cation-π interaction on macroionic self-assembly. Angew. Chem., Int. Ed. 2018, 57, 4067–4072.

[47]

Wang, P.; Wang, Z. T.; Wang, P. S.; Chishti, A. N.; Zhang, H. X.; Shi, J. H.; Ni, L. B.; Jamil, S.; Wei, Y. G. Supramolecular self-assembly of polyoxometalates and cyclodextrin: Progress and perspectives. Polyoxometalates 2024, 3, 9140047.

[48]

Guan, W. M.; Wang, G. X.; Li, B.; Wu, L. X. Organic macrocycle-polyoxometalate hybrids. Coord. Chem. Rev. 2023, 481, 215039.

[49]

Moussawi, M. A.; Leclerc-Laronze, N.; Floquet, S.; Abramov, P. A.; Sokolov, M. N.; Cordier, S.; Ponchel, A.; Monflier, E.; Bricout, H.; Landy, D. et al. Polyoxometalate, cationic cluster, and γ-cyclodextrin: From primary interactions to supramolecular hybrid materials. J. Am. Chem. Soc. 2017, 139, 12793–12803.

[50]

Khlifi, S.; Marrot, J.; Haouas, M.; Shepard, W. E.; Falaise, C.; Cadot, E. Chaotropic effect as an assembly motif to construct supramolecular cyclodextrin-polyoxometalate-based frameworks. J. Am. Chem. Soc. 2022, 144, 4469–4477.

[51]

Wei, Z. Y.; Wu, Z. K.; Ru, S.; Ni, L. B.; Wei. Y. G. Research progress of polyoxometalates-cyclodextrin supramolecular system. Chem. J. Chin. Univ. 2022, 43, 20210665.

[52]

Nie, S. Q.; Yuan, Y. Y.; Zeng, H. M.; Jiang, Z. G.; Zhan, C. H. Homohelical self-assembly of trimer of α-cyclodextrin and octamolybdate. Inorg. Chem. 2023, 62, 19153–19158.

[53]

Ni, L. B.; Gu, J.; Jiang, X. Y.; Xu, H. J.; Wu, Z.; Wu, Y. C.; Liu, Y.; Xie, J.; Wei, Y. G.; Diao, G. W. Polyoxometalate-cyclodextrin-based cluster-organic supramolecular framework for polysulfide conversion and guest-host recognition in lithium-sulfur batteries. Angew. Chem., Int. Ed. 2023, 62, e202306528.

[54]

Ding, X. X.; Yuan, Y. Y.; Zhang, Y. G.; Jiang, Z. G.; Zhan, C. H. Chiral polyoxometalate-cyclodextrin frameworks via Mn-mediated assembly: Enhanced stability and catalytic activity. Polyoxometalates 2024, 3, 9140046.

[55]

Liu, X. H.; Zhang, J. L.; Lan, Y. X.; Zheng, Q.; Xuan, W. M. Infinite building blocks for directed self-assembly of a supramolecular polyoxometalate-cyclodextrin framework for multifunctional oxidative catalysis. Inorg. Chem. Front. 2022, 9, 6534–6543.

[56]

Yang, P.; Zhao, W. L.; Shkurenko, A.; Belmabkhout, Y.; Eddaoudi, M.; Dong, X. C.; Alshareef, H. N.; Khashab, N. M. Polyoxometalate-cyclodextrin metal-organic frameworks: From tunable structure to customized storage functionality. J. Am. Chem. Soc. 2019, 141, 1847–1851.

[57]

Gokel, G. W.; Leevy, W. M.; Weber, M. E. Crown ethers: Sensors for ions and molecular scaffolds for materials and biological models. Chem. Rev. 2004, 104, 2723–2750.

[58]

Shi, J. H.; Zhang, H. X.; Wang, P. S.; Wang, P.; Zha, J. J.; Liu, Y.; Gautam, J.; Zhang, L. N.; Wang, Y.; Xie, J. et al. Inorganic-organic hybrid supramolecular architectures based on keggin polyoxometalates and crown ether: Synthesis, crystal structure and electrochemical properties. CrystEngComm 2021, 23, 8482–8489.

[59]

Wang, P.; Zhang, H. X.; Wang, P. S.; Zha, J.; Gautam, J.; Zhang, H. Z.; Li, R.; Zhang, L. N.; Diao, G. W.; Ni, L. B. A crown ether supramolecular host-guest complex with keggin polyoxometalate: Synthesis, crystal structure and electrocatalytic performance for hydrogen evolution reaction. Catal. Commun. 2022, 165, 106446.

[60]

Yang, G.; Wu, Y. C.; Lv, Z. X.; Jiang, X. Y.; Shi, J. H.; Zhang, Y. Z.; Chen, M.; Ni, L. B.; Diao, G. W.; Wei, Y. G. Keggin-type polyoxometalate-based crown ether complex for lithium-sulfur batteries. Chem. Commun. 2023, 59, 788–791.

[61]

You, W. S.; Wang, E. B.; Xu, L.; Zhu, Z. M.; Gu, Y. P. A molecule based on polyoxometalate acid and crown ether: Synthesis and characterization of [(H3O)(C20H24O6)]2[HPMo12O40]·C20H24O6·3MeCN·H2O (C20H24O6 = dibenzo-18-crown-6). J. Mol. Struct. 2002, 605, 41–49.

[62]

You, W. S.; Wang, E. B.; Xu, Y.; Li, Y. G.; Xu, L.; Hu, C. W. An alkali metal-crown ether complex supported by a Keggin anion through the three terminal oxygen atoms in a single M3O13 triplet: Synthesis and characterization of [{Na(dibenzo-18-crown-6)(MeCN)}3{PMo12O40}]. Inorg. Chem. 2001, 40, 5468–5471.

[63]

Li, Y. G.; Hao, N.; Wang, E. B.; Yuan, M.; Hu, C. W.; Hu, N. H.; Jia, H. Q. New high-dimensional networks based on polyoxometalate and crown ether building blocks. Inorg. Chem. 2003, 42, 2729–2735.

[64]

Akutagawa, T.; Endo, D.; Kudo, F.; Noro, S. I.; Takeda, S.; Cronin, L.; Nakamura, T. A solid-state supramolecular rotator assembled from a Cs-crown ether polyoxometalate hybrid: (Cs+)3([18]crown-6)3(H+)2[PMo12O40]. Cryst. Growth Des. 2008, 8, 812–816.

[65]

Chatterjee, T.; Sarma, M.; Das, S. K. Supramolecular architectures from ammonium-crown ether inclusion complexes in polyoxometalate association: Synthesis, structure, and spectroscopy. Cryst. Growth Des. 2010, 10, 3149–3163.

[66]

Akutagawa, T.; Endo, D.; Imai, H.; Noro, S. I.; Cronin, L.; Nakamura, T. Formation of p-phenylenediamine-crown ether-[PMo12O40]4− salts. Inorg. Chem. 2006, 45, 8628–8637.

[67]

Akutagawa, T.; Endo, D.; Noro, S. I.; Cronin, L.; Nakamura, T. Directing organic-inorganic hybrid molecular-assemblies of polyoxometalate crown-ether complexes with supramolecular cations. Coord. Chem. Rev. 2007, 251, 2547–2561.

[68]

Xiong, J.; Kubo, K.; Noro, S. I.; Akutagawa, T.; Nakamura, T. Self-assembled structure of inorganic-organic hybrid crystals based on keggin polyoxometallates [SMo12O402-] and supramolecular cations. Cryst. Growth Des. 2016, 16, 800–807.

[69]

Xiong, J.; Kubo, K.; Lü, S. F.; Li, M.; Nakamura, T. Supramolecular self-assembly for designing non-centrosymmetric crystals based on keggin polyoxometallates and crown ether. Dalton Trans. 2018, 47, 14001–14007.

[70]

Xiong, J.; Luo, T.; Zhang, J.; Li, X. X.; Lv, S. F.; Peng, J. J.; Li, M.; Li, W.; Nakamura, T. Two supramolecular Inorganic-organic hybrid crystals based on keggin polyoxometalates and crown ethers. Crystals 2018, 8, 17.

[71]

Xiao, F. P.; Meng, X. G.; Wang, L. S.; Hao, J.; Lv, C. L.; Wei, Y. G. Polyoxometalatocrown ether: A new type of metallacrown ether based on polyoxometalate. Polyoxometalates 2024, 3, 9140055.

[72]

Yin, Y. A.; Chen, W. J.; Liu, C. Y.; Zhang, M. M.; Lin, C. G.; Tsunashima, R.; Miras, H. N.; Song, Y. F. Manipulating the supramolecular assembly of γ-cyclodextrin and Anderson polyoxometalate hybrids through variations in remote functionality. Cell Rep. Phys. Sci. 2024, 5, 102061.

[73]

Zhang, M. M.; Yin, Y. A.; Chen, W. J.; Lin, C. G.; Wei, Y. G.; Song, Y. F. Asymmetric modification of Anderson-type polyoxometalates towards organic-inorganic homo- and hetero-cluster oligomers. Inorg. Chem. Front. 2023, 10, 1712–1720.

Polyoxometalates
Article number: 9140081
Cite this article:
Yin Y-A, Chen W-J, Liu C-Y, et al. Supramolecular assembly of covalently modified Anderson-type polyoxometalates and crown ethers towards pseudo-rotaxane structures. Polyoxometalates, 2025, 4(1): 9140081. https://doi.org/10.26599/POM.2024.9140081

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Received: 27 June 2024
Revised: 01 August 2024
Accepted: 16 August 2024
Published: 13 September 2024
© The Author(s) 2025. Published by Tsinghua University Press.

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