Transition Metal Chelates of 1,2-Diimines

For transition metal chelate rings of type 23 of Fig. 2, which contain 1,2-di-imine ligands, the three known structurally different types of complexes, A, B, and C, have to be treated separately in a 7r-electron model  

Type A contains only one chelate ring and is formed in molybdenum (O)-carbonyl chelates 121 41 or in copper(I) chelates 122 42, both synthesized and studied experimentally and theoretically by Bock and tom Dieck 121,123) 

Type B, containing two chelate rings in planar quadratic arrangement, may be observed in 1,2-diimine chelates 124 l2s 43. But an X-ray structure determination of nickel glyoxime, 26) showed that it does not possess ideal D2h symmetry in the crystal because of contacts to atoms of neighbouring molecules. 

Type C, with three chelate rings in an octahedral arrangement, is observed in Krumholz s 6S iron(II) complex 23 

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