High coordination number fluoride species

Inorganic main-group fluorides or oxofluorides offer a unique opportunity to study unusually high coordination numbers and problems associated widi them, such as the steric activity of free valence electron pairs, steric crowding of the ligands, and fluxionality. Of particular interest are heptacoordinated species which could exist either... 

Acidity and acid-base reactions are related and important features of the chemistry of molecular fluorides. In addition to the archetypal Brpnsted acid anhydrous hydrogen fluoride (I), molecules in which an hydroxyl group is bonded to a high oxidation state centre (II), for example also behave as strong Brpnsted acids. The coordination numbers found most commonly in high oxidation state binary fluorides are four and six, hence important molecular Lewis acids are (III), (IV) and (V), where X can be B, Si or Sb for example, which in many situations behave as coordinatively unsaturated species. 

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