Owing to their favorable thermal characteristics and (relative) non-toxicity, metal acetylacetonates are often employed as precursors for material synthesis in chemical vapor deposition (CVD) and atomic layer deposition (ALD). Iron and manganese acetylacetonates are separately pyrolysed at high temperature in a sealed tube, in inert ambient, giving rise to unique MnO/C and Fe3O4/C composites, respectively. We present a detailed report on the synthesis of such carbon composites, which also comprise a small proportion of the respective metal, a result of the reducing conditions in the tube. In contrast with the conventional low-pressure CVD process, product formation in sealed tube pyrolysis (STP) takes place in a closed system, at high pressure. In the STP-formed composites of the present work, the carbon is obtained both as amorphous powder and as micron-sized solid carbon spheres. As the duration of the STP process was increased, transformation of the initially formed carbon into a CNT-like fiber structure occurs at the high pressure in the STP chamber, although low pressures are typically required for the CVD of CNTs. An attempt is made to understand the STP process and the resultant product morphology based on the thermal characteristics of the precursor metal complex. Electrochemical measurements have been carried out on the carbonaceous powder composite, which reveal its excellent capacitive behavior; but the specific capacitance is limited by the solid-sphere morphology of some of the carbon in the composite.