How does increasing oxidation number affect the bonding in transition-metal halides?

In the chemistry of transition metals, the bonding character of halides is significantly influenced by the oxidation number of the metal atom. As the oxidation number increases, the metal-halide bonds become increasingly covalent in nature and more susceptible to hydrolysis.1

This trend reflects a shift in the nature of the chemical interaction between the metal and the halogen. While lower oxidation states often exhibit more ionic character, higher oxidation states involve a greater degree of electron sharing, which is characteristic of covalent bonding. Additionally, for the heavier transition metals, higher oxidation states are generally more stable than they are for the elements in the first transition series, allowing for the formation of higher halides (such as tungsten chloride, ${\text{WCl}}_6$, or platinum fluoride, ${\text{PtF}}_6$) that have no direct analogues among the lighter first-row elements.123