AbstractThe stepwise decomposition of CoBr2py2(s) has been investigated on a thermobalance by the “modified entrainment” method yielding Δ1H=88.6 kJ mol1, Δ1S=156.6 JK−1mol−1and Δ2H=119.0 kJ mol−1, Δ2S=211.8 JK−1mol−1for the dissociation of the first and second pyridine. The evaporation of CoBr2py2(l) and the association of gaseous pyridine to CoBr2py(l) forming CoBr2py2(g) has been studied by vis spectroscopy at 250−420°C. By combining the new results with literature values, a complete thermodynamic cycle for the solid‐liquid‐gas equilibria in the CoBr2‐pyridine system could be established. It shows that in solution the formation of CoBr2py2is not determined by the cobalt‐pyridine bond energy but by the solv