Metal complexes (already in extensive use today by nature and human) can give some inspiration how metal atoms could be integrated in future atomically precise structures.
Metal complexes have usually strong covalent character avoiding the problems of metallic bonds.
- Coordination complexes with their ligands not mutually linked together can show optimal coordination geometries.
- Chelate complexes can be seen as examples of bond networks that are suitable to weakly restrain the various fingers to a configuration space matching the metal to be chelated.
The bonds are not holding the fingers in (fully) place since single sigma binds can rotate and long chains of double bonds can flex.
The weak restraint can be seen as a increase in "effective concentration".
Geometries from these examples both metal-to-ligand from the simple complexes and ligand-to-ligand bonds from the chelates can be used for the design of foldamer structures or diamondoid structures that match these geometries. Those though can have much higher stiffness while still being simple (compact and highly symmetry) unlike many natural proteins.
Periodic lattices of compact complexes can be seen as a transition to gemstone like compounds.
Metal complexes often have strong colors (pigments) so one possible reason to include them could be to give products color.
Complexes containing very common elements like e.g. iron can be used as structural building material.
Some examples (complexes and/or chelates)
- Twofold coordination (nitrogen lone pairs): Ethylendiamine  – e.g. copper (Cu)
- Fourfold coordination (nitrogen lone pairs): Dimethylglyoxime  – two molecules can form a complex with nickel (Ni) – (color red)
- Sixfold coordination (two nitrogen and four oxygen): EDTA can chelate calcium (Ca) and iron (Fe)
- Sixfold coordination: Hexol – Cobalt (Co)
- Eightfold coordination(?): Citric acid  when chelating Calcium (Ca) – Calcium_citrate (occurs as mineral Earlandite)