Keggin-type polyoxometalate based coordination polymers of 3,5-bis(1′,2′,4′-triazol-1′-yl)pyridine: Synthesis, structures and electrochemical properties

Abstract

Four Keggin-type polyoxometalate-templated coordination polymers (POMCPs), [M${}^{\text{II}}$₂(btap)₄(HPMo${}^{\text{V}}$₂Mo${}^{\text{VI}}$₁₀O₄₀)(H₂O)₄] (M = Ni, Co and Cd, Ni/Co/Cd-POMCP) and [Zn${}^{\text{II}}$(btap)₂(HPW${}^{\text{VI}}$₁₂O₄₀)(H₂O)₂]⋅5H₂O (Zn-POMCP) (btap = 3,5-bis(1′,2′,4′-triazol-1′-yl)pyridine), were synthesized under the hydrothermal condition. Crystal structure analysis of Ni-POMCP and Zn-POMCP revealed that polyoxoanions fitted snugly into the cavities of the frameworks with hydrogen bond and electrostatic interactions. Ni-POMCP displayed a two-fold interpenetrating 4-connected 3D framework with a point symbol of (12⁶)(12)2 topology. By optimizing the pyrolysis temperature, the overpotentials of the hydrogen evolution reaction for the thermal derivatives of Ni/Co/Cd-POMCP in 0.5 M H₂SO₄ solution were significantly reduced. Among them, the overpotentials of Ni-POMCP-700, Co-POMCP-700 and Cd-POMCP -800 at a current density of 10 mA cm⁻² reached 69, 64 and 96 mV dec⁻¹, respectively, and good stability was maintained during the long-term electrocatalytic process, further confirming their potential for practical applications.