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Cluster-based coordination polymers (CCPs) have shown promise as capacitors. To investigate the relativity between capacitor performance and crystal structure, herein, five new CCPs based on organophosphorus Strandberg-type clusters were synthesized via in situ hydrothermal reactions at different pH’s, namely, (H2bipy)2(C6H5PO3)2Mo5O15·2H2O (1), (H2bipy)1.5CuI(bipy)(C6H5PO3)2Mo5O15·H2O (2), H2CuI2(bipy)2.5(C6H5PO3)2Mo5O15·2H2O (3), Na2CuI4CuII(bipy)4(C6H5PO3)2(Mo5O15)2·15H2O (4), CuII2(bipy)(H2O)4(C6H5PO3)2Mo5O15 (5) (bipy = 4,4′-bipyridine). Compound 1 is a zero-dimensional monomer, in which the protonated bipy ligands as countercations combine Strandberg-type clusters by hydrogen bonding and π–π interaction forming a supramolecular layer. Compound 2 represents a unique one-dimensional (1D) channel chain structure linked by intermolecular hydrogen bonding and π–π interaction. Compounds 3 and 4 exhibit the first example of an interdigitated architecture based on organophosphorus Strandberg-type clusters 1D + 1D → two-dimensional (2D) for 3 and 2D + 2D → three-dimensional (3D) for 4. Compound 5 displays a novel (3,4)-connected 3D microporous framework with (81·62) (83·63) topology. Notably, the more complicated structures of compounds 1–5 were obtained with an increase in pH. The isolation of five compounds is beneficial for our systematic understanding of the effect of pH on the assembly of CCPs. Organophosphorus Strandberg-type polyoxometalate clusters were explored as supercapacitor electrode materials for the first time. Compared with other CCPs in this work, compound 5 shows the highest specific capacitance, 160.9 F g–1, at a current density of 2 A g–1, and for favorable cycling stability, after 1000 cycles, the retention rate of the capacitance is 95.6% at 10 A g–1.
Lu et al. (Wed,) studied this question.