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

Abstract

The metal complex of [Co(NH3)(6)](3+) is introduced to C2H6 hydrate to confirm its possible inclusion in hydrogen-bonded water cages and the occurrence of metastable structure. The C-13 NMR spectra of C2H6 + ([Co(NH3)(6)]Cl-3 + 6NaOH in D2O) hydrate confirmed a new peak at 6.5 ppm matching with C2H6 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(NH3)(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-.