Octahedron = three bidentate chelates. Each κ² chelate fills two of the six coordination sites, so a homoleptic or heteroleptic octahedron is any multiset of three chelates drawn from two donor families:
Charge rule. Complex charge = metal oxidation state + Σ(ligand charge). Metals are the canonical robust low-spin d⁶ centres Ir(III) +3, Os(II) +2, Ru(II) +2. Only neutral or cationic complexes are kept (charge ≥ 0), so e.g. an M(II) tris-amidate (−1) is excluded while Ir(III) tris-amidate is a neutral [Ir(N^N⁻)₃].
Stereoisomers & chirality. Every distinct diastereomer (the unsymmetric amidate gives fac/mer- and cis/trans-type isomers) is enumerated with the T-REX library; each chiral one is emitted as an enantiomer pair. Handedness is Δ/Λ (helical, from the propeller twist) or @/@@ (point-central, when the six donor environments make the centre point-chiral) — computed by trex.chirality on the actual 3D geometry. The T-REX string below each structure encodes metal, oxidation state, ligand SMILES, the trans-pair topology (MAP), geometry (G:O) and chirality (X:).
3D. Structures are assembled on an octahedral template (trans-pairs pinned to the three axes → exact diastereomer) and relaxed with GFN-FF/GFN2-xTB (metal frozen); the mirror image gives the partner enantiomer. Geometries are illustrative; the T-REX record is the authoritative chemistry.