Solubility of β-Diketonate Complexes of Copper(II) and Cobalt(II) in Supercritical Carbon Dioxide

Abstract

The solubilities of the divalent β-diketonate metal complexes, copper(II) and cobalt(II) acetylacetonates (Cu(acac)2 and Co(acac)2), and 2,2,6,6-tetramethyl-3,5-heptanedionates (Cu(thd)2 and Co(thd)2) in supercritical carbon dioxide (scCO2) were measured using a circulation-type apparatus with in situ UV−vis spectrometry at temperatures ranging from (313 to 343) K to accumulate new solubility data on the precursors of conducting and magnetic materials. The solubilities of Cu(thd)2 were about 50- to 65-fold higher than those of Cu(acac)2 at approximately 20 MPa for each temperature level. As for the cobalt complexes, the solubilities of Co(acac)2 were greater than those of Co(acac)3 at 313 K. On the other hand, the solubilities of Co(thd)2 were higher than those of Co(thd)3 in the low CO2 density region and lower than those of Co(thd)3 in the high CO2 density region. Moreover, the solubilities of the cobalt complexes were higher than those of the copper complexes for both the metal(acac)2 and metal(thd)2.