Why Some fluorido-gold complexes are known to undergo F/Cl exchange in di-chloro methane solution after several days. Rationalize this behavior?

Why Some fluorido-gold complexes are known to undergo F/Cl exchange in di-chloro methane solution after several days. Rationalize this behavior? 

The observation that some fluorido-gold complexes undergo F/Cl exchange in dichloromethane solution after several days can be rationalized based on the relative stability and reactivity of gold-fluoride (Au-F) and gold-chloride (Au-Cl) bonds, as well as the chemical properties of fluorine and chlorine.

Fluorine is a highly electronegative element, and its smaller size allows for strong electrostatic interactions with the gold atom in the complex. However, despite the strong initial bond between gold and fluorine, the Au-F bond is generally weaker compared to the Au-Cl bond due to the smaller size and higher electronegativity of fluorine.

The weaker bond strength of Au-F can make the fluorido-gold complex more prone to ligand exchange reactions. In dichloromethane solution, where both chloride ions (Cl-) and fluoride ions (F-) are present, the exchange reaction between Au-F and Cl- can occur. This exchange reaction is driven by the stronger bonding affinity of chloride towards gold compared to fluoride.

The larger size and lower electronegativity of chlorine compared to fluorine make the Au-Cl bond more stable. As a result, the chloride ligand can more effectively displace the fluoride ligand, leading to F/Cl exchange in the complex:

[Au-F] + Cl- → [Au-Cl] + F-

The exchange reaction is favored by the higher stability of the resulting Au-Cl bond. The larger size of the chloride ligand may also provide steric factors that facilitate the ligand exchange process.

The rate at which F/Cl exchange occurs in dichloromethane solution can depend on various factors, including temperature, concentration, and the specific nature of the gold complex. These factors can influence the kinetic stability of the gold-fluoride complex and the availability of chloride ions for the exchange reaction.

It's important to note that the specific mechanisms and rates of F/Cl exchange in fluorido-gold complexes in dichloromethane solution can vary depending on the exact nature of the complex and the specific reaction conditions. Experimental studies and detailed investigations in the literature would provide more specific information on the behavior of these complexes.