Binary gem-like compound

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Binary diamondoid compounds are diamondoid compounds that are constituted out of just two chemical elements.

Possible motivations for preferring them over single element compounds (allotropes)

  • desired biodegradability
  • making use of abundant reactive elements like e.g. calcium beside just carbon silicon and maybe boron
  • better accessibility of these materials in earlier productive nanosystems
  • access of properties that are not emulatable by bond topology and bond strain alone (that is by metamaterial structure) most prominently electronic properties

An exhaustive list of the binary compounds of interest is possible

There aren't that many elements in the periodic table that are available in vast abundance. Systematically combining them to pairs does leas to a manageable amount of possibilities. A pretty exhaustive list can be given. After checking for the stability and suitability of these compounds the list of the ones that turn out to seem suitable as structural building materials become even shorter.

Many ternary compounds can be derived from binary ones by suitable substitution of atoms. For orientation something like pseudo phase diagrams can be used.

Classification by resistance against water

binary compounds that do not react or dissolve in water

Theres is a big stable group of B-C-N compounds, a few aluminum (Al2O3,AlB) and few silicon (SiC,SiO2,N4Si3) compounds.

There seem to be no binary iron minerals that have hardness above mohs 6.5

Titanium forms chemically and mechanically rather stable compounds with many nonmetals.

binary compounds which very slowly dissolve in water and are thought to be rather nontoxic

Solubility is good for an envirounmental viewpoint (decay time of abandoned scrap material) but bad for engineering materials. Especially in nanosystems the slightes bit of dissolvation completely destroys the outermost layer of nanomachinery. This makes sealing of products and high system reduncancy even more necessary than it is when more stable materials are used.

simplest most water stable compounds of abundant alkaline eart metals

most water stable solid fluorides from abundant metals

  • TiF3 titanium fluoride
  • MgF2 magnesium fluoride aka sellaide
  • CaF2 calcium fluoride aka fluorite

dangerous compounds to stay away from

  • solid nitrogen (except you want to make highly potent explosives)
  • AlP extremely toxic
  • Al2S3 toxic - H2S generation
  • sulphur phosphorus compounds - highly toxic
  • Fe3P highly toxic
  • BF3 BCl3 PCl3 all highly toxic (but gasseous anyway)

reactive but useful compounds

Many other highly reactive compounds may be useful when encapsulated and serving a non structural like electronic or other function.

III - V compounds

Note that nitrogen and phosphor forms four covalent bonds here instead the usual three. This can be pictured as their lone pair of electrons sticking into the electron deficient orbitals of boron or aluminum. The character of this bond is distributed over all four bonds such that perfectly tetrahedral symmetry is reached.

  • BN cubic boron nitride - highly stable and similar to diamond
  • BP boron phosphide - rather stable thus maybe low toxicity (?)
  • AlN aluminium nitride - slowly attacked by water - low toxicity
  • AlP aluminium phosphide - highly toxic - releases phosphine when in contact with water

The elements Ga,In,Th & As,Sb,Bi that are also in group III and V respectively are rather scarce and thus not considered here.

Table of III - V compounds: (wikipedia)

Silicon dioxide and related compounds

All compounds reached by full substitution of silicon or oxygen by their groupmembers carbon or sulfur respectively are rather unstable. Partial substitutions should work though. See: pseudo phase diagrams.

  • allotropes SiO2 (e.g. quartz,...)
  • structurally equivalent solid CO2 - probably explosive (similar to room-temperature solid nitrogen) since normally the well known low energy gas
  • structurally equivalent solid CS2 - normally a molecular liquid
  • structurally equivalent SiS2 - normally a soft solid made from polymeric chains

Passivation layer minerals of today's industrial metals

We do have daily skin contact with these minerals without even realizing it.
Often these minerals are naturally present as ores from which the metals are extracted.

wikipedia: passivation in general

Passivation of passivation layer minerals

Here an interesting problem occurs. To prevent two atomically precisely flat blocks from fusing seamlessly together on contact their surfaces must look differently than their insides. Specifically it is often a good idea to cover the whole surface with lone pairs of electrons. But further oxidation of an already oxidized material will probably not work or be rather unstable [to investigate for every specific situation]. What should be doable almost always is hydrogen passivation. (Such passivation may cause higher friction due to high lateral spacing between the small hydrogen atoms sitting atop larger atoms and the low lateral stiffness of the single bonded hydrogen atoms) It may be necessary to find a special solution for each indivitual material - nitrogen phosphorus and sulfur may often be useful for plugging surfaces closed.

Some interesting oddballs (not necessarily diamondoid)

  • CS2, SO3, Osmium oxide, ...
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