The structural and electronic properties of oxyanionic crystalline hydrates, LiNO3 center dot 3H(2)O, LiClO4 center dot 3H(2)O, and NaclO(4)center dot H2O, have been studied using density functional theory including van der Waals interactions. It is established that the linear compressibility of lithium perchlorate trihydrate is anisotropic (a < c) and positive, while lithium nitrate trihydrate and sodium perchlorate monohydrate demonstrate negative linear compressibility along the b and c axes, respectively. Deformation of Ow-H center dot center dot center dot O hydrogen bonding motifs is correlated with the negative linear compressibility. The band gaps of lithium nitrate and lithium perchlorate trihydrates decrease with pressure, whereas the band gap of sodium perchlorate monohydrate increases.