Bond distances, bispidine ligands

The piperidone precursor of 57 (see Chart 6) is a possible starting material for the synthesis of 2,6-substituted chiral, tetradentate bispidine ligands. The copper(II) complex of 57 is chiral [see Fig. 2(d) for a plot of the experimental structure] and has an interesting set of bond distances. Quite unexpectedly on the basis of the chelate ring sizes, the 2-pyridine substituent of the bispidine backbone is the axial donor (2.25 A), while N3 (2.08 A), N7 (2.05 A), the N7-pendant pyridine (2.01 A) and the chloride (2.28 A) are the in-plane donors (80). 

Build the bispidine complex using Momec and refine the corresponding cobalt(III) and cobalt(II) complexes (note that the force fields are not optimized for tetrahedral chromophores, but our aim here is just to compute relative metal—ligand distances). Note that all these structural optimizations need to be performed with 1,3-non-bonded interactions alone for the angular geometry around the metal ions (i.e., deactivate the multiple harmonic functions for both metal atom types in the force field) compare your results with those in Table 17.16. 

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