Hydrogen bonding and structural complexity of the Cu3(AsO4)(OH)3 polymorphs (clinoclase, gilmarite): a theoretical study

Density functional theory (DFT) is used to determine positions of H atoms and to investigate hydrogen bonding in the crystal structures of two polymorphs of Cu-3(AsO4)(OH)(3) : clinoclase and gilmarite. Hydrogen bonds in clinoclase involve interactions between hydroxyl groups and O atoms of arsenate tetrahedra, whereas the crystal structure of gilmarite features OH. OH bonding, which is rather uncommon in copper hydroxy-oxysalts. Information-based parameters of structural complexity for clinoclase and gilmarite show that the former is more complex (I-G,I-total = 213.212 bits/cell) than the latter (I-G,I-total = 53.303 bits/cell), which indirectly points out that gilmarite is metastable. This suggestion is supported by the lower density of gilmarite (4.264 g/cm(3)) compared to that of clinoclase (4.397 g/cm(3)). The hypothesis of metastable character of gilmarite is in agreement with the Goldsmith's simplexity principle and the Ostwald-Volmer rule.