The Klapötke group at Munich are some of the masters of alarming chemical structures, and they basically seem to own the field of chalcogen azides. Perhaps the competition for this class of compounds is not as intense as it might be - the other labs doing this sort of thing are collaborations between USC and various military research wings. But they're still interesting beasts.
A few years ago, both groups reported the synthesis of tellurium azides, with the Munich group sending in their paper a few days before the USC/Air Force team sent in theirs. The parent tetra-azide was explosive, to be sure, but could be kept at room temperature without necessarily blowing up. Klapötke's group and the USC group (led by Karl Christe) then teamed up to tackle the corresponding selenium analogs, which were reported in 2007.
And they're a livelier bunch. The selenium tetra-azide is another yellow solid, like the tellurium compound, but it's rather harder to keep it down on the farm. Taking some selenium tetrafluoride (see below) and condensing it with trimethylsilyl azide at -196 °C did the trick. After warming things up (you'll note the relative use of that term "warming"), they saw that:
"Within minutes, the mixture turned yellow, the color intensified, and a lemon-yellow solid precipitated while the reaction proceeded. Keeping the reaction mixture for about 15 min at -64 °C resulted in a violent explosion that destroyed the sample container and the surrounding stainless-steel Dewar flask."
Did I mention that this prep was performed on less than one millimole? Spirited stuff, that tetra-azide. The experimental section of the paper enjoins the reader to wear a face shield, leather suit, and ear plugs, to work behind all sorts of blast shields, and to use Teflon and stainless steel apparatus so as to minimize shrapnel. Hmm. Ranking my equipment in terms of its shrapneliferousness is not something that's ever occurred to me, I have to say. It's safe to assume that any procedure which involves considering which parts of the apparatus I'd prefer to have flying past me will not get much business in my lab, no matter how dashing I might look in a leather suit.
That procedure deserves a closer look, though. You can't just crack open a can of selenium tetrafluoride whenever you feel the urge, you know. That stuff has to be made fresh, as far as I can see, and the way these hearty sons of toil make it is by reacting selenium dioxide with chlorine trifluoride. Yep, that stuff, the delightful compound that sets sand on fire and eats through asbestos firebrick.
So if you're going to make selenium polyazides, your day starts with chlorine trifluoride and I'm sure that it just rolls along from there. Before you know it, you've gone from viciously reactive halogens, paused to prepare some disgusting selenium fluorides, made some violently unstable azides that explode if you stick your tongue out at them and hey, it's dinnertime already. . .