Stereochemistry of Hexacoordinated Zn(II), Cu(II), Ni(II), and Co(II) Complexes with Iminodiacetamide Ligands

Abstract

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.

Structural Variety of Isopropyl-bis(2-picolyl)amine Complexes with Zinc(II) and Copper(II)

“…However, in these conditions the tetrafluoroborate ion undergoes a decomposition reaction, BF 4 – ⇄ BF 3 + F – , forming fluoride ions. Fluorinated counterions like BF 4 – are known to be potential sources of fluoride ions. ,, The counterion decomposition could be accelerated by the basicity of the i Pr-bpa ligand and/or by the metal, oxygen, and water. , The free fluoride ion, being a small ion of localized charge, can easily bind to the metal center. The crystal structure of 2 Zn shows a complex of M 2 L 2 stoichiometry, with two bridging fluoride anions.…”

“…The hexa-coordinated complex 3 Zn forms a [ZnN 6 ] distorted octahedron of cis-fac geometry [angle N–Zn–N (amine) 102.9(2)°]. Our interest is to study effects that govern the formation of different geometrical isomers in ML 2 complexes; , therefore, we described the relative stability of cis-fac , mer , and trans-fac isomers using DFT calculations. Our approach relied on optimizing molecular geometries with the M05-2 X /6-31+G­(d)/LanL2DZ + ECP model both in gas phase and acetonitrile, the latter modeled through the implicit solvation model based on density (SMD) solvation, being in line with our earlier reports. , The quality of this methodology was evaluated by performing a series of single-point electronic energy calculations using a range of DFT functionals.…”

“…Recently, we reported on metal complexes of bpa and iminodiacetamide ( imda ) ligands. , Both bpa and imda ligands are tridentate with a central amine nitrogen atom substituted with two methylene pyridine ( bpa ) or methylene acetamide ( imda ) moieties. Interestingly, despite their similarity in structure, the two ligand systems differ significantly in their stereochemical preference for formation of ML 2 complexes.…”

Self‐Assembly of Cobalt(II) Coordination Polymers with Differently Halosubstituted Nicotinate Ligands and 4,4’‐Bipyridine – The Effect of the Halosubstituent Positions on Polymer Types

“…Also, during geometry optimization we included the implicit SMD solvation with all parameters for pure water, in line with our earlier reports that used the same approach to interpret solid-state features of a variety of metal complexes. [49][50][51][52] Atomic charges were obtained through the natural bond orbital (NBO) analysis [53] by the same model. All calculations were performed using the Gaussian 16 software.…”

Novel Bis- and Mono-Pyrrolo[2,3-d]pyrimidine and Purine Derivatives: Synthesis, Computational Analysis and Antiproliferative Evaluation

“…Thermal corrections were extracted from the matching frequency calculations, so that all presented results correspond to differences in the Gibbs free energies at room temperature and normal pressure. The choice of such computational setup was prompted by its success in reproducing various features of different organic [65][66][67], organometallic [68,69] and biological systems [70,71], being particularly accurate for relative trends among similar reactants, which is the focus here. All transition state structures were located using the scan procedure, employing both 1D and 2D scans, the latter specifically utilized to probe the possibility for concerted mechanisms.…”