pH-Tuned Modulation of 1D Chain to 3D Metal-Organic Framework: Synthesis, Structure and Their Useful Application in the Heterogeneous Claisen-Schmidt Reaction

Abstract

The role of pH in the formation of metal-organic frameworks (MOFs) has been studied on magnesium-based carboxylate framework systems [Mg(Pdc)(H2O)(3)](n) (1) and [Mg(Pdc)(H2O)](n) (2) (Pdc=pyridine-2,3-dicarboxylate). The investigation reveals the formation of two different compounds of one- or three-dimensions starting from the same reaction mixture that differs only in pH. Isolated compounds have been characterized by IR and elemental analysis; both compounds were also successfully characterized by single-crystal X-ray diffraction. This study shows that the gradual increase in pH helps to construct a higher-dimensional network. Catalytic activity of compounds 1 and 2 was tested for the Claisen-Schmidt reaction. Compound 2 was successfully dehydrated to produce a coordinately unsaturated compound 2a, which shows higher catalytic activity than 1 or 2 in heterogeneous medium.