Low Temperature Thermodynamic Study of C₅H₅Mn(CO)₃ and C₄H₄NMn(CO)₃

Abstract

The heat capacities of the complexes C₅H₅Mn(CO)₃ and C₄H₄NMn(CO)₃ were measured from 10 to 300 K by an adiabatic calorimeter and the thermodynamic functions reported. For C₅H₅Mn(CO)₃ the heat capacity appears to be to some degree “abnormally” high in the temperature range 75-135 K. This small anomaly is discussed in connection with our vibrational results. For C₄H₄NMn(CO)₃, there is no anomaly of the Cp curve between 10 and 300 K, however a phase transition is detected by DTA at 315.5 K, (about 10 K below the melting point) associated with an enthalpy variation ΔH = 1910 ± 40 J mol⁻¹. An attempt is made to calculate the “normal” Cp curves from spectroscopic data and to estimate the compressibility for both compounds. Finally, we compare the thermal behaviour of these compounds with those of other arene metal carbonyls in terms of disorder and lattice energy.