Chelate rings bite angle

Complex Ni Ni-L Chelate Bite distances (A) rings Bite angles (deg) Ref. 

O-M-O bond angles required. One can relate bite sizes (distances between the donor atoms) of strain-free chelate rings of different sizes to the dimensions of the chair form of the cyclohexane ring (39), which has the minimum steric strain possible for a cycloalkane. The bite size of strain-free four- and six-membered chelate rings both correspond to... 

Fig. 12. Definition of solid state structural parameters for tris chelate complexes with D3 symmetry 0 is the twist angle and is the projection of the bite angle a onto the plane which is perpendicular to the C3 symmetry axis, 0 is the pitch angle and is the angle subtended by the plane of the chelate ring and the C3 symmetry axis r, d, s and h are the metal ligand distance, bite distance, triangle edge, and the distance between the triangles, respectively. From Ref.82 ...

This effect was attributed to the directionality of the lone pairs of the donor atoms (e. g., primary amines) of unstrained chelate ligands with a constant bite (donor atom - donor atom distance), leading to longer preferred metal-ligand distances for five-membered chelate rings (e.g., 2.5 A for ethane-1,2-diamine (en) vs. 1.6 A for propane-1,3-diamine (tn)). However, the N-M-N valence angles... 

Using a large force constant for the multiple harmonic potential with minima at 90° and 180°. However, this may distort the chromophore in cases where the observed minimum structure is planar but with bite angles involving chelate rings that are smaller (or larger) than 90°. 

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