Ice Pentamers on Copper (110)

Figure: A novel one dimensional ice structure built from pentagons has been discovered.

Ice, ice, maybe... Heterogeneous ice nucleation plays a key role in fields as diverse as atmospheric chemistry and biology. Ice nucleation on metal surfaces affords an opportunity to watch this process unfold at the molecular-scale on a well-defined, planar interface. A common feature of structural models for such films is that they are built from hexagonal arrangements of molecules. Here we show, through a combination of scanning tunneling microscopy, infra-red spectroscopy, and density-functional theory, that ca. one nanometer wide ice chains that nucleate on Cu(110) are not built from hexagons, but instead are built from a face sharing arrangement of water pentagons. The pentagon structure is favored over others because it maximizes the water-metal bonding whilst at the same time maintaining a strong hydrogen bonding network. It reveals an unanticipated structural adaptability of water-ice films, demonstrating that the presence of the substrate can be sufficient to favor non-hexagonal structural units.

References:

[1] J. Carrasco et. al., Nature Mater. 8, 427 (2009) [pdf]