DEPENDENCE OF THE THERMODYNAMIC CHARACTERISTICS OF MOLYBDENUM HALOGENIDES ON THE NATURE OF HALOGENS AND THE DEGREE OF OXIDATION OF MOLYBDENUM

Thermodynamic characteristics – enthalpy of formation and entropy of crystalline and gaseous molybdenum halides in all oxidation states – were determined and/or refined using semi-empirical calculation methods. Molybdenum fluorides have the highest thermodynamic stability. The obtained complete information allowed us to conduct a system analysis and establish patterns of change in the thermodynamic characteristics of halides depending on the nature of halogens and the oxidation state of molybdenum. It was found that in the series MoFn → MoCln → MoBrn → MoIn, in general, with an increase in the ordinal number of halogens, the enthalpy of formation decreases and the entropy of halogens increases. The thermodynamic properties of fluorides differ from other molybdenum halides. Measurement of Cl-, Br- and I- ions keeps the enthalpy of formation of halides equal at the same degree of Mo oxidation and increases with increasing oxidation state of metals. Based on the difference in changes in thermodynamic characteristics, a method has been developed to quantify the influence of the nature of halogens and the degree of oxidation of molybdenum on the thermodynamic properties of molybdenum halides.