Super Strand of Eight Water Icosahedra

A super strand of eight water icosahedra, showing the tessellation ability. Eight complete but overlapping icosahedral clusters form this strand-like structure containing 1750 water molecules. For clarity, only the oxygen atoms are shown (for interactive structures see Chime, 43 KB). This is shown as an indicative example of the type of structure expected as water is (super)cooled, so encouraging the expanded icosahedra (ES) structures to increase their degree of structuring. These structures are far less strained than more-symmetric supercluster structuring and are as expected in the related low-energy minimal polytetrahedral Dzugutov clusters where they are stabilized by the presence of high barriers between potential energy minimal structures, of particular importance at low temperatures [295]. Actual icosahedral strands are unlikely to be complete (as pictured), but to contain partial additions or deletions and be of a variety of lengths and shapes. The presence of such clusters, in principle, is in agreement with computer simulation studies [216] and may explain the properties of deeply-supercooled water as it is in agreement with such water being a good solvent for inert gas (Xenon) atoms, which fit well into the dodecahedral clathrate sites, but a very poor solven for salt (LiCl) [1120 ], which would have to disrupt the hydrogen bonding.

Other liquids have been found to solidify on heating. An aqueous solution of α-cyclodextrin and 4-methylpyridine is liquid below 45°C then (reversibly) freezes (before 75°C) to melt again at above 100°C [1026 ]. The rationale is that the liquid contains mainly intramolecular hydrogen bonds but the solid contains inter molecular hydrogen bonds; a similar underlying principle to the proposal above.