COMPLEXATION OF MANGANESE(II) BY CYCLOHEXANO-15-CROWN-5 IN PROPYLENE CARBONATE - CALORIMETRIC AND X-RAY CRYSTALLOGRAPHIC INVESTIGATION

Calorimetric titrimetry reveals that cyclohexano-15-crown-5 (C15C5) fo rms a 1:1 complex with Mn(II) ions (2.5 mM) in propylene carbonate (PC ) solution to which was added levels of water up to 134 mM. The reacti on proceeds with a strong driving force (log K = 4.7-5.0) and is entha lpically driven overall, but the magnitude of the enthalpy change decr eases with increasing water concentration in the case of the Mn(II) ni trate salt. A minor anion effect occurs in which the trifluoromethansu lfonate ion gives slightly more negative values of Delta H and T Delta S than the nitrate ion. Values of log K, however, do not change appre ciably with increasing water concentration, nor are they dependent on the anion. The crystal structure of Mn(C15C5)(CF3SO3)(2) was determine d, showing that the Mn(II) ion is coordinated by a pentagonal bipyrami d of oxygen atoms provided by the equatorial crown ether and apical mo nodentate triflate ions. Crystal data for MnC16H26O11F6S2: monoclinic, C2/c, a = 26.925(3) Angstrom, b = 14.145(1) Angstrom, c = 13.420(1) A ngstrom, beta = 100.31(2)degrees, V = 5028 Angstrom(3), Z = 8, t = 26 degrees C. For 2178 reflections with I > sigma(I), and 325 parameters, R(F) = 0.050 and R(w)(F) = 0.054.