pH-Controlled Assembly of Five New Organophosphorus Strandberg-Type Cluster-Based Coordination Polymers for Enhanced Electrochemical Capacitor Performance.

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)1.5[CuI(bipy)(C6H5PO3)2Mo5O15]·H2O (2), H2[CuI2(bipy)2.5(C6H5PO3)2Mo5O15]·2H2O (3), Na2[CuI4CuII(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.