Metastability of Ethane Clathrate Hydrate Induced by [Co(NH3)6]3+Complex

Abstract

The metal complex of [Co(NH 3 ) 6 ] 3+ is introduced to C 2 H 6 hydrate to confirm its possible inclusion in hydrogen-bonded water cages and the occurrence of metastable structure. The 13 C NMR spectra of C 2 H 6 +([Co(NH 3 ) 6 ]Cl 3 + 6NaOH in D 2 O) hydrate confirmed a new peak at 6.5 ppm matching with C 2 H 6 in sII-L cages. The retarded appearance of metastable sII phase is due to brine rejection of the cobalt complex occurring during solution freezing. The anions of OH and F were found to be incorporated in the host water cage framework, providing proton-deficient sites. The ionic conductivity of the frozen [Co(NH 3 ) 6 ] 3+ solution increased up to 20-fold after ethane hydrate formation, implying the incorporation of F ― into the host lattice. A notable finding of this work is that the metastability occurs only when the cobalt complex is in the presence of anions such as OH ― and F ― .