be used as molecular building blocks for self-assembly of molecular crystals. Adamantane analogues Many molecules and ions adopt adamantane-like cage structures. Those include phosphorus trioxide P4O6, arsenic trioxide As4O6, phosphorus pentoxide P4O10 = (PO)4O6, phosphorus pentasulfide P4S10 = (PS)4S6, and hexamethylenetetramine C6N4H12 = N4(CH2)6. Particularly notorious is tetramethylenedisulfotetramine, often shortened to "tetramine", a rodenticide banned in most countries for extreme toxicity to humans. The silicon analogue of adamantane, sila-adamantane, was synthesized in 2005. Arsenicin A is a naturally occurring organoarsenic analogue isolated from the New Caledonian marine sponge Echinochalina bargibanti and is the first known polyarsenic organic compound. Conjoining adamantane cages produces higher diamondoids, such as diamantane (C14H20 – two fused adamantane cages), triamantane (C18H24), tetramantane (C22H28), pentamantane (C26H32), hexamantane (C26H30), etc. Their synthesis is similar to that of adamantane and like adamantane, they can also be extracted from petroleum, though at even much smaller yields. See also twistane Urotropin References