Tuning of the dimensional linkage from the complex to the framework by thermal conversion in the system Fe/Cl/piperazine

Abstract

An attempt to control the three structural features linkage, structural dimensionality and coordination mode is presented for the combination of Fe^II and Fe^III chlorides together with the ditopic ligand piperazine (pipz). Thermal conversion of small units like complexes into highly aggregated structures such as coordination polymers is demonstrated for the framework formation of ³_∞[Fe^IICl₂(pipz)] starting from both FeCl₂ and FeCl₃. Depending on the oxidation state of iron, different reaction paths and metastable products are observed. Iron(II)chloride reacts with piperazine to form the previously unknown 2-dimensional network, ²_∞[Fe^II₂Cl₄(pipz)₃]·pipz, which can be thermally converted into the 3-dimensional framework at elevated temperatures by release of piperazine. The use of iron(III)chloride starts with an internal redox reaction giving the divalent complex [Fe^IICl₃(Hpipz)(pipz)] in the first step, followed by thermal conversion yielding the framework ³_∞[Fe^IICl₂(pipz)] and the salt [Fe^IICl₃(Hpipz)(pipz)](Hpipz)Cl₂. Both thermal conversion mechanisms were further investigated by in situ IR-spectroscopy, differential thermal analysis and thermogravimetry.