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Metal complexes of iminodiacetamide (imda) ligands and metal ions Zn(II), Cu(II), Ni(II) and Co(II) were prepared, using eight imda ligands (L1-L8) substituted with groups of different steric and electronic properties on the central amine nitrogen atom (hydrogen atom, methyl, isopropyl, benzyl) and the para-position of phenyl rings (nitro, dimethylamino). The effect of these substituents on the stoichiometry (ML, ML2), geometry and stereochemistry (mer, transfac, cis-fac) of the complexes was studied in solid state, in solution and by DFT calculations. X-Ray single crystal and powder diffraction, thermogravimetry, and IR spectroscopy showed that in the solid state imda ligands preferentially form transfac ML2 complexes, with the exception of the cis-fac complex 7Zn. NMR spectroscopy of diamagnetic Zn(II) and paramagnetic Co(II) complexes revealed the formation of both ML and ML2 complexes in solution. Variable temperature NMR was used to study the effect of the substituent on the central amine nitrogen on the Zn─N bond strength and nitrogen inversion. Relative stabilities of isomers were rationalized by computations and the optimized structures used for the geometry analysis.

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