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pH-Controlled Assembly of Five New Organophosphorus Strandberg-Type Cluster-Based Coordination Polymers for Enhanced Electrochemical Capacitor Performance
151
Citations
62
References
2020
Year
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, (H<sub>2</sub>bipy)<sub>2</sub>[(C<sub>6</sub>H<sub>5</sub>PO<sub>3</sub>)<sub>2</sub>Mo<sub>5</sub>O<sub>15</sub>]·2H<sub>2</sub>O (<b>1</b>), (H<sub>2</sub>bipy)<sub>1.5</sub>[Cu<sup>I</sup>(bipy)(C<sub>6</sub>H<sub>5</sub>PO<sub>3</sub>)<sub>2</sub>Mo<sub>5</sub>O<sub>15</sub>]·H<sub>2</sub>O (<b>2</b>), H<sub>2</sub>[Cu<sup>I</sup><sub>2</sub>(bipy)<sub>2.5</sub>(C<sub>6</sub>H<sub>5</sub>PO<sub>3</sub>)<sub>2</sub>Mo<sub>5</sub>O<sub>15</sub>]·2H<sub>2</sub>O (<b>3</b>), Na<sub>2</sub>[Cu<sup>I</sup><sub>4</sub>Cu<sup>II</sup>(bipy)<sub>4</sub>(C<sub>6</sub>H<sub>5</sub>PO<sub>3</sub>)<sub>2</sub>(Mo<sub>5</sub>O<sub>15</sub>)<sub>2</sub>]·15H<sub>2</sub>O (<b>4</b>), [Cu<sup>II</sup><sub>2</sub>(bipy)(H<sub>2</sub>O)<sub>4</sub>(C<sub>6</sub>H<sub>5</sub>PO<sub>3</sub>)<sub>2</sub>Mo<sub>5</sub>O<sub>15</sub>] (<b>5</b>) (bipy = 4,4'-bipyridine). Compound <b>1</b> 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 <b>2</b> represents a unique one-dimensional (1D) channel chain structure linked by intermolecular hydrogen bonding and π-π interaction. Compounds <b>3</b> and <b>4</b> exhibit the first example of an interdigitated architecture based on organophosphorus Strandberg-type clusters [1D + 1D → two-dimensional (2D) for <b>3</b> and 2D + 2D → three-dimensional (3D) for <b>4</b>]. Compound <b>5</b> displays a novel (3,4)-connected 3D microporous framework with (8<sup>1</sup>·6<sup>2</sup>) (8<sup>3</sup>·6<sup>3</sup>) topology. Notably, the more complicated structures of compounds <b>1-5</b> 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 <b>5</b> shows the highest specific capacitance, 160.9 F g<sup>-1</sup>, at a current density of 2 A g<sup>-1</sup>, and for favorable cycling stability, after 1000 cycles, the retention rate of the capacitance is 95.6% at 10 A g<sup>-1</sup>.
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