Sciencemadness Discussion Board - Interesting allotropes, glassifications, and polymorphs.

Interesting allotropes, glassifications, and polymorphs.

BromicAcid - 25-6-2004 at 17:03

Reading though the July 2004 issue of Scientific American I found to my surprise an article on a new carbon allotrope. A nanofoam that posses ferromagnetic properties with an interesting structure:

Quote:

The clusters, which are about six nanometers in diameter seem to be made of graphite layers wrapped by the inclusion of seven-sided heptagons. That configuration gives the layers negative curvature - the "hyperbolic" saddle shape - the converse of what happens in buckyballs...

There is also a list of allotropes of carbon in the issue; Graphite, Diamond, Buckyballs, Nanotubes, Lonsdaleite, Chaoite, Schwarzite, Filamentous Carbon, Carbon Aerogels, Amorphous.

Phosphorus of course has other interesting allotropes and modifications that I could go on about and have in other places already.

I remember reading about an allotrope of antimony called "Exploding Antimony" that detonated from slight agitation, I believe it was deposited by electrolysis on a steel screen cathode from an aqueous solution.

What I would like to see in replies to this would be other interesting allotropes or other modifications of an element, e.g. S2 and also some workable definitions of allotrope, contrasted with polymorphs and glassifications. Or just discussion on different forms of elements in general such as the ones I just mentioned.

Reverend Necroticus Rex - 25-6-2004 at 17:29

I believe promethium has at least six different allotropes, different only by crystalline forms, arsenic and tin both have three different allotropes.

Both sulfur and selenium have several different forms, although I am not sure about tellurium, but I think the record is probably phosphorus having many different allotropes and polymorphs.

Pyrovus - 26-6-2004 at 23:02

Explosive antimony is prepared through electrolysis of SbCl3, and apparently it's explosive properties have something to do with a high presence of unreacted SbCl3.

A new allotrope of oxygen, O4 was discovered a few years back, though it was predicted to exist back in the 1920s.
http://www.nature.com/nsu/011122/011122-3.html

JustMe - 27-6-2004 at 17:22

So, what about Sulfur?

Besides Rhombic and Monoclinic varieties (Both being S8), there's also Plastic Sulfur (long chains). Oh, everybody knows that. But wait, there's more.

My old Textbook of Inorganic Chemistry lists a bunch of allotropes, with other formulas. One variety (these are all identified with greek symbols... don't know how to do that here), is made by heating sulfur to 180° and rapidly cooling, dissolving in Carbon Disulfide and cooling to -80° when another allotrope of sulfur crystallizes out. Hm, it doesn't give the formula for that version. However, if the remaining solution is evaporated in a vacuum, a form of sulfur with the formula S4 remains. In solution in Toluene or CS2 it has a deep yellow color.

Another form is said to be produced "when to concentrated hydrochloric acid at 0° a cold solution of sodium thiosulfate is added and the mixture shaken with Toluene. After a short while orange-yellow rhombohedral crystals separate." This is S6.

Two other forms of sulfur (rhombic plates and hexagonal plates, both nearly colorless, are formed by crystallizing from a solution of sulfur in chloroform containing rubber and a little benzonitrile. The book doesn't list the formula for these allotropes.

Finally, one night when I was bored and did a google search for, oh, I don't remember, something like diatomic sulfur. After sifting through the results I did find a reference to S2, a purple solid... which you mentioned.

I find sulfur fascinating because, like carbon, it has a tendency toward catenation, but also is capable of far more oxidation states.

Reverend Necroticus Rex - 8-7-2004 at 20:59

Manganese has four different allotropes, the alpha form is what is usually seen, silvery white, brittle and very hard, yet the gamma allotrope (reverts to alpha at room temp) is supposed to be soft and pliable, easily cut like the alkali metals.

I don't know about the other two allotropes though and 'tis late so I am not too inclined to do too much searching

Reverend Necroticus Rex - 6-2-2005 at 21:18

I have been reading much about arsenic lately, and found a bit on its allotropy.

Arsenic forms three allotropes, the commonest one being a gray metallic crystalline form, quite brittle, called gamma arsenic, which sublimes when heated and tarnishes somewhat in air.

Alpha arsenic is yellow, and not too stable, formed by shock cooling arsenic vapor, UV light converts yellow arsenic back to the metallic gamma type.

Black arsenic is amorphous, and is prepared by subliming arsenic without the presence of air, black arsenic forms the gray allotrope when heated to 360 C.

I would be quite interested to know if any other allotropes or polymorphs have ben prepared, by high pressure, temperature,
or some of the other obscenly hostile conditions that resulted in formation of new phosphorus allotropes.

I thought of obtaining some elemental arsenic, by burning pressure treated wood that has had arsenical preservatives applied to it, leaching the ash with HNO3 to form arsenious acid, then reduction with zinc metal, and thermal decomposition of the evolved arsine.

Does anyone know of a source for such treated timber? as apparently, a 10 meter long 2x6 plank has upwards of 20 grams of elemental arsenic locked within it, that can be quite easily freed and purified :cool:

Magpie - 6-2-2005 at 21:35

Reverend, I would be very careful exposing arsenic to a hot fire. It sublimes at 615 C (alpha form). As2O3 also sublimes. I'd hate to lose the board's only member of the clergy. There must be easier ways to get arsenic. Have you checked rat poison suppliers?

BromicAcid - 6-2-2005 at 21:37

Possibly obtainable from the widely availible herbicides.

Decompose with Fenton's Reagent possibly to get the oxide and reduce with aluminium, the arsenic subliming into the cooler parts of the 'bomb'.

[Edited on 2/7/2005 by BromicAcid]

Reverend Necroticus Rex - 6-2-2005 at 22:44

I think wires were crossed somewhat in my description Magpie, I did not mean that the wood has elemental arsenic physically present, but trapped within it, rather, that the equivalent of 20g of arsenic as the element were present in compound form, my bad

Edit: I am fairly sure arsenic compounds for use as rodenticides went the way of the devil, and probably not that long after phosphorus paste was also disontinued, as it seems, quite a lot of the time they were bought, the rodent in question was to be the unfortunate spouse of the purchaser of the arsenic

[Edited on 7-2-2005 by Reverend Necroticus Rex]

neutrino - 7-2-2005 at 14:16

Tin has two allotropes: normal tin and gray tin. Normal tin is your standard metal: shiny, ductile and malleable. Below 13*C, though, it changes to gray tin, which is a gray, monometallic, amorphous substance which tends to crumble to a powder. For some nice pictures, look at the coins here.

sparkgap - 11-2-2005 at 10:48

CCA wood would be the way to go, then. I'm not sure whether it'd be easy to acquire, but I do know lumber sellers are anxious to get rid of their stock, because, IIRC, it had just been recently banned.

So you'll be pulling As from the wood Marsh-style? Be careful with the arsine!

Otherwise, you might want to try looking for someone selling Fowler's solution.

sparky (^_^)

P.S. @ neutrino: The white to gray tin transition is the phenomenon behind the "tin scourge" in chilly museums. Too bad they can't reassemble those ornaments.

Reverend Necroticus Rex - 14-2-2005 at 17:25

I can't imagine Fowler's solution being sold any more, I have some old household medical books, from the late 1800s, and from the looks of it, fowlers solution was falling into disuse even then, I just find it hard to believe its even made any more.

atombum - 15-2-2005 at 13:04

Not fitting well on this area of the periodic table is nitrogen. I believe there is still only the N2 allotrope.
Some excitement was made about a new "form" of nitrogen in the late 90's when a pentazolium salt of arsenic pentafluoride was formed. It is a five-membered nitrogen pentagon, positively charged, connected to an AsF6- ion (yes six fluorines, hence the negative charge). Those with limited chemistry knowledge who reported it were quickly made aware that an allotrope or "form" of an element cannot contain another atoms.
However the discovery of this salt did make the discovery of nitrogen's new allotrope a remote possiblity - if one could synthesize the azide salt of this pentazole, one would have actually made the N8 allotrope. Only problem is, the arsenic salt is already extremely unstable due to all the N-N bonds, exploding I believe above cryogenic temps. So, even if it exists, this pentazolium azide would therefore be a most hateful compound. :mad:

BromicAcid - 15-2-2005 at 14:18

It's not really a pentagon, the pentanitrogen cation is V-shaped, attempts to isolate the pentagonyl pentazolate ion have all led to the formation of the anion N5- which is incredibly unstable, it's fleeting existence detected only though electrospray ionization in a mass spectrometer.

Of course things change so this information is accurate as of Jan 1999 (pentanitrogen cation) and Aug 2002 (pentazolate anion) Chemical and Engineering news.

As for the azide salt of the pentanitrogen cation, attempts to make it have met 'with nothing but explosions'.

atombum - 18-2-2005 at 09:54

Bromic Acid wrote:
It's not really a pentagon, the pentanitrogen cation is V-shaped, attempts to isolate the pentagonyl pentazolate ion have all led to the formation of the anion N5- which is incredibly unstable, it's fleeting existence detected only though electrospray ionization in a mass spectrometer.

Oh yeah, you're right, it isn't cyclic. It has been a few years since I first heard of the discovery.

In regards to all the explosions in the pentazene azide (nomenclature?) synthesis, I wonder if any of the researchers did form N8 for a fleeting second, just too quick and too violent to be detected. It could be possible, it would just be that the driving force to convert N8 into 4 N2 would be so incredibly strong that no low temperature or other variation in conditions (I doubt low-pressure would help, it would likely increase the ease of N2 formation, would it not?), can keep the equilibrium to the left for a long enough period of time.

Kanem - 19-2-2005 at 03:04

I read an article about a new nitrogen-modification some time ago:
Using high pressure and temperatures, they managed to bring it into some kind of 3-dimensional "Diamond-structure".
It is supposed to be the strongest chemical explosive possible, if it could be obtained at standard-conditions.

Kanem

sparkgap - 19-2-2005 at 03:11

Reverend, it is to my knowledge that homeopaths still make use of Fowler's solution. It is their belief that poisons, sufficiently diluted, are curative. Yeah right.

I mean that you can try asking any in your area as to where they acquire their arsenicals. Otherwise, it's CCA wood or cacodylate-based herbicides just like what Bromic suggested.

N can form an adamantine structure? How would they be joined, then?

(edited for clarity)

sparky (^_^)

[Edited on 19-2-2005 by sparkgap]

JohnWW - 19-2-2005 at 14:29

There is a tertiary amine with a structure like that of the hydrocarbon adamantane, in which the 4 apical C atoms are replaced with N atoms each with 3 Cs attached, with the formula (NCH2)4. The common name of it has slipped my mind for the present, but its systematic name would probably be tetracyclo-[1,1,1,1]-methyleneamine.

However, a 3-dimensional diamond-like structure for solid nitrogen under great pressure is simply not possible, because each N would have to be bonded covalently to 4 other Ns. This can only happen if the N atoms lose an electron (as in ammonium salts), thereby becoming pentavalent. A 3-dimensional covalent lattice of N atoms, each bearing a charge, would immediately fly apart due to the lack of electrical neutrality.

However, a 2-dimensional lattice of N atoms, arranged in fused hexagonal rings, in which each N is bonded to 3 others, is theoretically feasible; also a one-dimensional infinite chain of N atoms bonded by alternate single and double bonds (which would be electrically conducting). But, even so, they would require very high pressure to make and stabilize, and would be no more stable than pentazole.

[Edited on 19-2-2005 by JohnWW]

sparkgap - 19-2-2005 at 23:03

I used the adjective "adamantine" in the sense of "diamond-like networked structure". Sorry if I confused you, John. I am most certainly aware of adamantane look-alikes like methenamine (hexamine, urotropine, hexamethylenetetramine) and TETS (tetramethylenedisulfotetramine). Methenamine was the compound you had in mind. You may remember it as an RDX precursor.

The question in my previous post was meant to be rhetorical. As you have said, trivalent nitrogen will not be able to form a 3D network much like that of diamond, and that the catenated and hexagonal forms are not very likely to form. IIRC, N's catenation limit is 5.

edit: Methenamine's systematic name would be 1,3,5,7-tetraazatricyclo[3.3.1.1<sup>3,7</sup>]decane

sparky (^_^)

[Edited on 20-2-2005 by sparkgap]

Kanem - 20-2-2005 at 06:29

Well, I referred to:
this
and that

JustMe - 20-2-2005 at 18:39

Amazing!