Polyoxometalate-Incorporated Metallapillararene/Metallacalixarene Metal-Organic Frameworks as Anode Materials for Lithium Ion Batteries

A series of remarkable crystalline compounds containing metallapillararene/metallacalixarene metal-organic frameworks (MOFs), [Ag₅(pyttz)₃·Cl·(H₂O)]­[H₃SiMo₁₂O₄₀]·3H₂O (1), [Ag₅(trz)₆]­[H₅SiMo₁₂O₄₀] (2), [Ag₅(trz)₆]­[H₅GeMo₁₂O₄₀] (3), and [Ag₅(trz)₆]­[H₄PW₁₂O₄₀] (4) (pyttz = 3-(pyrid-4-yl)-5-(1H-1,2,4-triazol-3-yl)-1,2,4-triazolyl, trz = 1,2,4-triazole), have been obtained by using a simple one-step hydrothermal reaction of silver nitrate, pyttz for 1 and trz for 2–4, and Keggin type polyoxometalates (POMs). Crystal analysis reveals that Keggin POMs have been successfully incorporated in the windows of the metallapillararene/metallacalixarene MOFs in compounds 1–4. In addition, the Keggin silicomolybdenate-based hybrid compounds 1 and 2 were used as anode materials in lithium ion batteries (LIBs), which exhibited promising electrochemical performance with the first discharge capacities of 1344 mAh g^–1 for 1 and 1452 mAh g^–1 for 2, and this stabilized at 520 mAh g^–1 for 1 and 570 mAh g^–1 for 2 after 100 cycles at a current density of 100 mA g^–1. The performances are better than that of (NBu₄)₄[SiMo₁₂O₄₀] matrix and commercial graphite anodes.