Conversion of kinetically stable metal-organic product to thermodynamically stable one approved by thermal treatment and sonochemical reaction

Abstract

A new nickel-based metal-organic compound [Ni(3-Clb)2.4H2O]n (1), (3-HClb = 3-chlorobenzoic acid), has been synthesized and structurally characterized by single crystal X-ray crystallography. One type of Ni(II) ion is present in 1 and two oxygen atoms from two 3-Clb‾ ligand and four oxygen atoms of four water molecules coordinate to each Ni(II) ion. Secondary hydrogen bonding interactions between primary structural building unit results in formation of two-dimensional supramolecular network. After thermal treatment of 1 at 130 °C, the coordinated water molecules were removed from 1 and compound [Ni(3-Clb)2]n (2) was formed. Irreversible desorption of water in this nickel coordination polymer were studied by IR spectroscopy, thermogravimetric and differential thermal analyses (TG-DTA), X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). On the other hand, the sonochemical reactions between 3-HClb and Ni(NO3)2·6H2O in the presence of water resulted in formation of 2. Compound 1 is the kinetically stable product and compound 2 is the thermodynamically stable product. In addition to thermal treatment, ultrasonic irradiation also can provide the necessary activation energy for formation of thermodynamically stable product.