Copper(II) complexes of hexadentate ethylenediaminetetracarboxylic acid type ligands H(4)eda3p and H(4)eddadp (H(4)eda3p = ethylenediamine-N-acetic-N,N',N'-tri-3-propionic acid; H(4)eddadp = ethylenediamine-N,N'-diacetic-N,N'-di-3-propionic acid) have been prepared. An octahedral trans(O(6)) geometry (two propionate ligands coordinated in axial positions) has been established crystallographically for the Ba[Cu(eda3p)]·8H(2)O compound, while Ba[Cu(eddadp)]·8H(2)O is proposed to adopt a trans(O(5)) geometry (two axial acetates) on the basis of density functional theory calculations and comparisons of IR and UV-vis spectral data. Experimental and computed structural data correlating similar copper(II) chelate complexes have been used to better understand the isomerism and departure from regular octahedral geometry within the series. The in-plane O-Cu-N chelate angles show the smallest deviation from the ideal octahedral value of 90°, and hence the lowest strain, for the eddadp complex with two equatorial β-propionate rings. A linear dependence between tetragonality and the number of five-membered rings has been established. A natural bonding orbital analysis of the series of complexes is also presented.

No abstract

A ligand field molecular mechanics (LFMM) force field (FF) has been developed for d(9) copper(II) complexes of aminopolycarboxylate ligands. Training data were derived from density functional theory (DFT) geometry optimizations of 14 complexes comprising potentially hexadentate N2O4, tetrasubstituted ethylenediamine (ed), and propylenediamine cores with various combinations of acetate and propionate side arms. The FF was validated against 13 experimental structures from X-ray crystallography including hexadentate N2O4 donors where the nitrogens donors are forced to be cis and bis-tridentate ONO ligands which generate complexes with trans nitrogen donors. Stochastic conformational searches for [Cu{ed(acetate)n(propionate)(4-n)}](2-), n = 0-4, were carried out and the lowest conformers for each system reoptimized with DFT. In each case, both DFT and LFMM predict the same lowest-energy conformer and the structures and energies of the higher-energy conformers are also in satisfactory agreement. The relative interaction energies for n = 0, 2, and 4 computed by molecular mechanics correlate with the experimental log β binding affinities. Adding in the predicted log β values for n = 1 and 3 suggest for this set of complexes a monotonic decrease in log β as the number of propionate arms increases.

The P-APC ligands (EDTA-like aminopolycarboxylate ligands comprising 1,3-propanediamine backbone) H 4 pdta, H 4 pd3ap, H 4 pddadp and H 4 pdtp (H 4 pdta = 1,3-propanediamine-N,N,N 0 ,N 0 -tetraacetatic acid; H 4 pd3ap = 1,3-propanediamine-N,N,N 0 -triacetic-N 0 -3-propionic acid; H 4 pddadp = 1,3-propanediamine-N,N 0 -diacetatic-N,N 0 -di-3-propionic acid; H 4 pdtp = 1,3-propanediaminetetra-3-propionic acid) were investigated. The chelating ligands coordinate to copper(II) via five or six donor atoms affording distorted trigonal-bipyramid and octahedral structures that were verified by X-ray analysis for Ba[Cu(pd3ap)]Á 6H 2 O (1) and trans(O 6 )-Ba[Cu(pddadp)]Á8H 2 O (2) complexes respectively. The impact of counter-ions on the P-APC complexes is shown in detail together with the analysis of another strain parameters. EPR spectral results confirm the penta-coordination of 1 and hexa-coordination of 2 in aqueous solution, even if several Cu(II) species with different protonation degree exist as a function of pH, and indicate that a hexa-coordinated structure is favored when the two axial COO À donors close five-membered chelate rings. We also present here the results of molecular mechanics (LFMM) calculations based on our previously-developed force field along with results of DFT (Density Functional Theory). On the basis of extensive DFT and TD-DFT calculations the B1LYP/6-311++G(d,p) level has been seen as an accurate theory for calculating and predicting the UV-Vis spectra in case of copper-P-APC compounds.

No abstract