Chemical and Electrochemical Alkali Cations Intercalation/Release in an Ionic Hydrogen Bonded Network

The chemical oxidation of a hydrogen bonded network, formed upon combination of a hydrogen bond donor dication (1²⁺, a dicationic bis-amidinium organic moiety bearing four propyl chains) with [Fe^III/II(CN)₆]^3–/4– anions has been studied using vibrational spectroscopies. The postsynthetic oxidation of the microcrystalline powder of X₂1₃-[Fe^II(CN)₆]₂ (X = Na, K, and Cs) by S₂O₈^2– into 1₃-[Fe^III(CN)₆]₂ appeared to be partial for X = K⁺ and Cs⁺ and total for Na₂1₃-[Fe^II(CN)₆]₂. It corresponds to a two-step process involving a second order reaction. The reaction time appears to be dependent on the nature of the alkali cation and is faster for X = Na⁺. The integrity of the hydrogen bonded network, after oxidation, was also confirmed by powder X-ray diffraction. The flexible nature of the hydrogen bonded network allows alkali cation motions within the network during the oxidation process. In addition, the investigation of the electrochemical behavior evidenced an amorphous deposition on a gold electrode immersed into a solution containing (1²⁺ and [Fe^III(CN)₆]^3–) after 100 cycles. This is the first evidence of an electrochemical ion intercalation for a molecular hydrogen bonded network.