Oddball compound

Unusual transition element oxides

Transparent volatile liquids that are highly toxic:

• http://en.wikipedia.org/wiki/Osmium_tetroxide
• http://en.wikipedia.org/wiki/Ruthenium_tetroxide
• http://en.wikipedia.org/wiki/Rhenium(VII)_oxide

Rather inert compounds with fluorine

• Sulfur hexafluoride
• Nitrogen trifluoride

Other compounds with unusual properties

• Carbon disulfide
• Trimethylphosphine (leave to Wikipedia - please come back again)
• Carbon suboxide (leave to Wikipedia - please come back again)

Carbon suboxide has a low energy state in earth’s oxidative environment and can be polymerized to a solid that could easily be stored by today’s means. When chemomechanical converters will become available there most likely will be better storage methods for depleted energy available though. So its just a curiosity. Note: Somewhat unintuitively the compound C₂O₂ (ethylene dione) is very unstable. It has a short lifetime even at low temperatures. This is one of the more subtel instances where one can see that the "periodic table as construction kit" metaphor must often be taken with a grain of salt.

Compounds dominantly containing nitrogen

• http://en.wikipedia.org/wiki/Nitrous_oxide
• http://en.wikipedia.org/wiki/Ammonium_azide
• http://en.wikipedia.org/wiki/Tetrazene
• http://en.wikipedia.org/wiki/Ammonium_nitrate
• http://en.wikipedia.org/wiki/Ammonium_nitrite