Based on differential vapour pressure measurements, excess free energies, excess enthalpies and excess entropies of the solvent of n-Bu(4)N-butyrate aqueous solutions have been determined over wide temperature and molality ranges (20-80 degrees C, 0.5-6.0 rn). The minima observed with the excess entropies Delta S-1(ex)/m and enthalpies Delta H-1(ex)/m at 1.7m correspond to the solid clathrate composition of the n-Bu(4)N(+), i.e. to 1:33 solute/solvent ratio. This suggest that in the solution at around 1.7m concentration, a clathrate-hydrate-like arrangement dominates in time average, and this structure results from solute-solute interaction ("structural hydrational interaction") and not from solute-solvent interaction (hydrophobic hydration). Similar minima of Delta S-1(ex)/m and Delta H-1(ex)/m were observed previously with n-Bu(4)NBr solution. However, here the structuring effect was only half of that with the butyrate system. This shows that the Br- ion significantly disturbs the hydrophobic hydration structure, while the butyrate anion fits into this structure.