The standard molar enthalpy of sublimation of η5-bis-pentamethylcyclopentadienyl iron measured with an electrically calibrated vacuum-drop sublimation microcalorimetric apparatus

A heat-flow Calvet microcalorimeter was adapted for the measurement of sublimation enthalpies by the vacuum-drop method, with samples of masses in the range 1 mg to 5 mg. The electrically calibrated apparatus was tested by determining the enthalpies of sublimation of benzoic acid and ferrocene, at T = 298.15 K. The obtained results, Delta H-g(cr)m(o)(C7H6O2) = (88.3 +/- 0.5) kJ.mol(-1) and Delta H-g(cr)m(o)(C10H10Fe) = (73.3 +/- 0.1) kJ.mol(-1), are in excellent agreement with the corresponding values recommended in the literature. Subsequent application of the apparatus to the determination of the enthalpy of sublimation of eta (5)-bis-pentamethylcyclopentadyenyl iron, at T = 298.15 K, led to Delta H-g(cr)m(o)(C20H30Fe) = (96.8 +/- 0.6) kJ.mol(-1). (C) 2001 Academic Press.