The Role of Magnesium(II) Salt Precursor in Controlling the Structure of Coordination Polymers based on Magnesium(II) and benzene 1, 3, 5-tricarboxylic acid

Abstract

Synthesis of coordination polymers based on magnesium(II) and benzene 1, 3, 5-tricarboxylic acid (H3BTC) with two different types of magnesium(II) salts precursors, namely MgCl2·6H2O and Mg(OAc)2·4H2O in ethanol under solvothermal condition was successfully carried out. The synthesized materials were characterized by several methods such as X-Ray Diffraction and FTIR spectroscopy, thermogravimetry and scanning electron microscopy (SEM). The synthesis results showed that the crystallization of the materials was highly influenced by the type of metal ion precursor Mg(II), in this case the anion. XRD analysis revealed that the use of MgCl2·6H2O salt tend to produce a coordination polymer [Mg3(BTC)2 (H2O)12] which called also as National Institute of Chemistry Slovenia-4 (NICS-4, CCDC 768993) with a 1-dimensional structure, while the use of Mg(OAc)2·4H2O salt produced 3-dimensional coordination polymer [Mg3(BTC)2] or well known as National Institute of Chemistry Slovenia-6 (NICS-6, CCDC 768995). NICS-4 and NICS-6 have thermal stability up to 530 ºC and 542 ºC based on the thermogravimetric analysis. A significant shift from absorption peak at 1721 to 1622 dan 1628 cm−1 correspond to the deprotonation of trimesic acid and coordinated to the Mg2+ cation. The coordination of Mg2+ with H2O molecules in NICS-4 is indicated by the presence of broad absorption peak at 3472 cm−1 which was not found in NICS-6. After exposed to the air, the structural dimension of NICS-6 could change due to the coordination with water molecules. SEM image exhibited that NICS-4 has flat-needle-like morphology with an average particle size of 12.42 ± 0.78μm, while NICS-6 has a hollow spherical morphology with an average particle size of 63.21 ± 0.12 μm.