text: Theories of the structure of water involve three-dimensional networks of tetrahedra and chains and rings, linked via hydrogen bonding.
  A polycatenated network, with rings formed from metal-templated hemispheres linked by hydrogen bonds, was reported in 2008.
  In organic chemistry, hydrogen bonding is known to facilitate the formation of chain structures. 4-tricyclanol CHO, for example, shows catenated hydrogen bonding between the hydroxyl groups, leading to the formation of helical chains; crystalline isophthalic acid CHO is built up from molecules connected by hydrogen bonds, forming infinite chains.
  In unusual conditions, a 1-dimensional series of hydrogen molecules confined within a single wall carbon nanotube is expected to become metallic at a relatively low pressure of 163.5 GPa. This is about 40% of the ~400 GPa thought to be required to metallize ordinary hydrogen, a pressure which is difficult to access experimentally.