New ice outdoes related nets in smallest-ring size

摘要

In a recent Letter, Lobban, Finney and Kuhs reported a remarkable new metastable form of ice (ice Ⅻ) in the field of stability of ice Ⅴ and presented an accurate structure determination. The authors state correctly that the topology of the phase is unlike that of any of the known phases of ice. They also state that it "contains a mixture of five- and seven-membered rings of water molecules" which "is interesting, although not unexpected". This second statement is not completely true; the truth is more interesting and, I believe, unexpected, as is agreed by the authors of ref. 1 (personal communication). The structure contains only seven- and eight-membered rings and is the first example of a 4-connect-ed net of this type.