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 artifical 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.

list of potential structural compounds

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.

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
• beta-C3N4 beta carbon nitride
• N4Si3 silicon nitride
• cubic BN cubic boron nitride
• BP boron phosphide
• SiO2 quartz (& allotropes)
• 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

materials 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

Alkali and earth alkali compounds tend to be rather soluble in binary compounds

• Ca(OH)2 calcium hydroxide aka slaked lime (rather water soluble) [1]
• CaCO3 calcium carbonate (very slightly soluble) [2]
• MgCO3 magnesium carbonate aka magnesite (slightly soluble) [3]

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 complexes
• many many more

dangerous materials 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)