Hydrogen bonding in perchloric acid hydrates

A bond-valence analysis of five perchloric acid hydrates shows that normal hydrogen bonds account for only about one half of the bonding of the perchlorate ion. Each H atom also forms an average of four additional weak interactions (H ⋯ O acceptor ~ 2.3 to 3.1 Å; O-H ⋯ O ~ 80 to 120°) which account for the rest of the bonding. A distinction can be made between the normal and the very weak hydrogen bonds in the lower hydrates but this …