Double-helix molecules are frequently encountered in biological and synthetic organic systems, where they typically provide improved strength and better electrical properties relative to materials containing linear chains or single helices. DNA is the defining example. A purely inorganic double helix has been hard to come by.
Chemists have been seeking out inorganic double helices for decades. Researchers have reported X-ray crystal structures of bulk LiP and LiAs containing spiral and coaxial chains, but it remained unclear as to whether they should be called double-helix structures. More recently, researchers have attempted making metal or metal salt double-helix materials using nanotubes or DNA as templates. But a nontemplated, carbon-free example with a fully characterized double-helix structure had remained elusive.
A team of some 20 researchers led by Tom Nilges of the Technical University of Munich has prepared the first completely inorganic substance, SnIP, featuring a well-defined double-helix structure. This semiconducting material consists of a twisted tin iodide (SnI+) chain intertwined with a twisted phosphide (P–) chain. The team prepared gram amounts of SnIP by heating tin, red phosphorus, and tin tetraiodide together.
https://cen.acs.org/articles/94/i39/Chemists-prepare-inorganic-double-helix.html
Study: http://onlinelibrary.wiley.com/doi/...ionid=D84384E8F126E6CA1917474C9C15AA77.f02t02
Chemists have been seeking out inorganic double helices for decades. Researchers have reported X-ray crystal structures of bulk LiP and LiAs containing spiral and coaxial chains, but it remained unclear as to whether they should be called double-helix structures. More recently, researchers have attempted making metal or metal salt double-helix materials using nanotubes or DNA as templates. But a nontemplated, carbon-free example with a fully characterized double-helix structure had remained elusive.
A team of some 20 researchers led by Tom Nilges of the Technical University of Munich has prepared the first completely inorganic substance, SnIP, featuring a well-defined double-helix structure. This semiconducting material consists of a twisted tin iodide (SnI+) chain intertwined with a twisted phosphide (P–) chain. The team prepared gram amounts of SnIP by heating tin, red phosphorus, and tin tetraiodide together.

https://cen.acs.org/articles/94/i39/Chemists-prepare-inorganic-double-helix.html
Study: http://onlinelibrary.wiley.com/doi/...ionid=D84384E8F126E6CA1917474C9C15AA77.f02t02