Thermodynamically unstable binary fluorides

From the above it can be seen that the hydrolytic behavior of N2F2 is quite different from those of the other binary nitrogen fluorides discussed earlier. Difluorodiazine is strongly endothermic (12) and thermodynamically unstable (11) this makes it necessary to consider not only direct chemical attack by water but also the thermal decomposition to the elements. The reactivity of d -N2F2 toward glass (2) presents an additional question of possible competing reactions with the container walls. 

Zemva, Bartlett and colleagues reported a general approach to synthesis from HF of polymeric binary fluorides [67] which has a major advantage over many of the synthetic routes used to date. Some of these fluorides are thermodynamically unstable or marginally stable at ambient temperature. Earlier attempts to prepare some of these compounds at elevated temperatures had proved unsuccessful or had led to contaminated products. Some reported synthetic procedures for transition metal tetrafluorides, for example, involving reduction by the metal of the stable pentafluoride at elevated temperature have resulted in products contaminated to greater or lesser extent with the trifluoride or with the metal. 

Difluorine combines directly with all elements except O2, N2 and the lighter noble gases reactions tend to be very violent. Combustion in compressed F2 (fluorine bomb calorimetry) is a suitable method for determining values of Af77° for many binary metal fluorides. However, many metals are passivated by the formation of a layer of nonvolatile metal fluoride. Silica is thermodynamically unstable with respect to reaction 16.5, but, unless the Si02 is powdered, the reaction is slow provided that HF is absent the latter sets up the chain reaction 16.6. 

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