Gemstone-like compound

Diamondoid materials encompass all materials that:

• do not diffuse at room temperature
• are stiff enough to keep their shape under thermal movement
• have dense three dimensional networks of covalent bonds - (short bond loops => no polymeres)
• (not necessarily but desirable) do not react or dissolve in water

The main reason why diamondoid materials are the material of choice for diamondoid molecular elements DMEs (the constituents of artificial advanced AP systems) is that they do not jitter and wobble or even diffuse away while they are built robotically (a blind process) and that products out of those systems can be made so that they only have one to a few tightly controlled degrees of freedome. This way one can test one action at a time which enables engineering with fast progress. The necessity for scientific entangling of convoluted relationships is only inherent in natural biological nanosystems.

Wikipedia has its own page about diamondoid materials. See here: [1]

By now (2014) carbon is the only building material for which extensive studies about tooltip chemistry have been undertaken.
Note that it's likely that just by structuring carbon (and adding a bit hydrogen as passivation agent) many material properties will be archivable.

Diamondoid compounds

list of potential structural compounds

Compounds that are synthesizable under solution are of interest for technology level II to bridge the gap between technology level I and III.

binary compounds that do not react or dissolve in water

• carbon in diamond lonsdaleite or intermediate forms
• silicon carbide (also cubic or hexagonal)
• silicon (also cubic or hexagonal)
• B₄C boron carbide
• SiB₄; SiB₆ ?
• four allotropes of elementar boron
• AlB₁₂
• β-C₃N₄ beta carbon nitride
• N₄Si₃ silicon nitride
• cubic BN cubic boron nitride
• BP boron phosphide
• SiO₂ quartz & allotropes (it's actually slightly water soluble)
• Tectosilicates: [2] [3]
• Al₂O₃ aluminum oxide - aka sapphire
• Fe₃C iron carbide aka cementite
• iron silicides & iron borides ? - unknown properties
• FeS₂ FeS iron sulfides - pyrite marcasite ...
• Fe₂O₃ Fe₃O₄ hämatite magnetite
• Cu₃P CuS (copper is not too abundant)

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

Surisingly titanium forms chemically rather stable compounds with many nonmetals.

• TiC titanium carbide
• TiSi₂ ?(unknown properties)
• TiB₂ titanium diboride
• TiN titanium nitride
• TiP Titanium Phoshide (too metallic?)
• TiS titanium sulphide
• TiO₂ Ti₂O₃ titanium oxides

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.

• Al₄C₃
• AlN (oxidizes on air)
• the three natural allotropes of elementar phosphorus
• S₂N₂ S₄N₄ (SN)_X - diamondoid?
• allotropes of elementar sulfur

simplest most water stable compounds of abundant alkaline eart metals

• MgB₂ magnesium diboride (high temperature superconductor)
• MgO magnesium oxide aka magnesia
• CaB₂ calcium diboride
• CaS calcium sulfite

most water stable solid fluorides

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

ternary and higher compounds

Look out for rock forming minarals here.
Alkali and earth alkali compounds tend to be rather soluble in binary compounds.

• Ca(OH)₂ calcium hydroxide aka slaked lime (rather water soluble) [4]
• CaCO₃ calcium carbonate (very slightly soluble) [5]
• MgCO₃ magnesium carbonate aka magnesite (slightly soluble) [6]
• ... many more

other nommetallic or ceramic compounds ...

compounds which contain relatively scarce elements

Those may be useful in the lower technology levels or special tooltip chemistry where only very small amounts are needed (e.g. germaium containing tips).

• molybdenium oxide structures
• germanium compounds
• ... many more

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.

Sources for elements

Carbon is planned to be drawn from [ethyne] more commonly known as the welding gas acetylene. It has the advantage of a triple bond that when partly split up provides four unpassivated bonds and it's carrying around a minimal amount of hydrogen. Since DMEs are compact and crystal like they have a lot less surface than the source molecules and thus require a lot less hydrogen passivation. Ethyne cant be delivered in highly compressed gasseous form since it explosively decomposes. It is hardly soluble in water but well soluble in acetone ethanol or dimethylformamide. Ethyne can be manufactured by the partial combustion of methane and thus potentially be gained from renewable resources.

If one looks at the most common or most easily accessible elements and their simplest compounds one finds a list of potential structural building materials:
Link to a graphic of the most common elements in the earths crust from Wikimedia Commons.

Most easily accessible are nitrogen oxygen and argon since they can direcly be drawn from the atmosphere.
To investigate:

• Means for filtering/capturing N₂ and O₂ each selectively from the atmosphere.
• Mechanosynthetic tooltips and manipulations to gain reactive moieties out captured N₂ and O₂.

Chlorine could be drawn from common salt leaving behind sodium. To get this residual into a nonreactive environmentally acceptable form that could be used as structural material rather than just constituting waste one could chose from sodium minerals. To prefer are compounds with no crystal water and simple formulas with only elements of high importance for APM (that is which we are likely to gain control of soon after reaching technology level III) like e.g. jadeite and further ones to find.