Rings In Metal Chelates Research Articles

DFT Quantum-Chemical Calculations of Molecular Structures for Heteroligand M(III) Complexes of 3d Elements with Porphyrazine and Fluoride Ion

The molecular structures of heteroligand (6666)macrotetracyclic chelates of M(III) (M = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, or Cu) with porphyrazine (an (NNNN)-donating ligand) and F– ion are calculated by the DFT OPBE/TZVP method. The key bond lengths, bond angles, and nonbonded angles in these complexes are reported. The standard enthalpies, entropies, and Gibbs free energies of formation are calculated for the complexes. All complexes have a slightly distorted tetragonal-pyramidal geometry, where the complex former M(III) is to some degree raised above the pyramid base made up of the donor nitrogen atoms. Characteristically, all 6-membered metal chelate rings in these metal chelates are identical to one another both in terms of the sum of bond angles and in their varieties.

Towards understanding π-stacking interactions between non-aromatic rings.

The first systematic study of π interactions between non-aromatic rings, based on the authors' own results from an experimental X-ray charge-density analysis assisted by quantum chemical calculations, is presented. The landmark (non-aromatic) examples include quinoid rings, planar radicals and metal-chelate rings. The results can be summarized as: (i) non-aromatic planar polyenic rings can be stacked, (ii) interactions are more pronounced between systems or rings with little or no π-electron delocalization (e.g. quinones) than those involving delocalized systems (e.g. aromatics), and (iii) the main component of the interaction is electrostatic/multipolar between closed-shell rings, whereas (iv) interactions between radicals involve a significant covalent contribution (multicentric bonding). Thus, stacking covers a wide range of interactions and energies, ranging from weak dispersion to unlocalized two-electron multicentric covalent bonding ('pancake bonding'), allowing a face-to-face stacking arrangement in some chemical species (quinone anions). The predominant interaction in a particular stacked system modulates the physical properties and defines a strategy for crystal engineering of functional materials.

Ligand mediated structural diversity and role of different weak interactions in molecular self-assembly of a series of copper(II)–sodium(I) Schiff-base heterometallic complexes

We report three new Cu–Na heterometallic complexes namely [Cu(L12−)Na(NO3)(CH3OH)] (1), [Cu(L22−)Na(NO3) (CH3OH)] (2) and [Cu Na (L33−)]n (3) where the topology of the synthon is directly governed by the π–π interaction involving the Cu-Schiff base chelate rings. The crystal structure analysis also reveals how the systematic variation in the ligand framework influences the supramolecular assembly and the mutual cooperation of different π-forces and the hydrogen bonding forces in the supramolecular assembly. The π-forces are more important than the hydrogen bonding forces in such compounds is evident from the supramolecular assembly of compound 3. Most interesting revelation of the studies are the presence of relatively uncommon π-forces such as chelate ring⋯chelate ring and metal–π interactions in the supramolecular architecture of the complexes. The analysis of the supramolecular assembly of the complexes 1–3 reveals that metal-chelate rings play prominent role in the organization of the molecular complexes and should seriously consider along with other π-stacking forces.

Synthesis and structure of aqua-2′,‴-(2,6-pyridindiyldiethylidene) dioxamohydrazide-copper(II) hydrate

In a template synthesis from copper(II) acetate, 2,6-diacetylpyridine, and semioxamazide (NH 2CO CONHNH 2), two copper(II) complexes, [Cu(dapsox)(H 2O)]·H 2O and [Cu(Hdapsox)](H 2O)]ClO 4, (where H 2dapsox = 2′,2‴-(2,6-pyridindiyldiethylidene)dioxamohydrazide) were obtained and characterized. The structure of the former complex was determined by a single-crystal X-ray analysis. Cu II is located in a square pyramidal environment. The polydentate ligand, dapsox 2− is coordinated in dianionic form, as an unsymmetrical quadridentate planar system forming one-membered and two-five-membered metal-chelate rings. The fifth coordination site is occupied by a water molecule.

Stability of Fused Rings in Metal Chelates. XI. Stability of Dipeptide Amide-Copper(II) Complexes

Abstract The structure-stability relationship between the copper(II) complexes of several dipeptide amides consisting of glycine and/or β-alanine has been investigated by potentiometric titration. The amides of glycylglycine, glycyl-β-alanine, and β-alanylglycine (abbreviated as H2L) have been found to form complexes of the type Cu(H2L)2+ with logK1 values 4.80–5.22. The −logKC1 values for deprotonation of the peptide group are 5.05–5.42 and comparable to those of tripeptides, whereas the −logKC2 values for the terminal amide group are 7.96 for glycylglycine amide and 8.99 for glycyl-β-alanine amide. This indicates that, at neutral pH, the –CONH2 group coordinates to copper(II) mainly through the carbonyl oxygen. β-Alanyl-β-alanine amide-copper(II) system gave precipitates at an early stage of titration. The structures and relative stability of the complexes of types Cu(H2L)2+, Cu(HL)+, and CuL have been discussed from comparative studies of their stability constants.

Stability of Fused Rings in Metal Chelates. X. Structures and Stability Constants of the Copper (II) Complexes of Tripeptides Composed of Glycine and/or β-Alanine

Abstract On the basis of comparative studies of the equilibria involving copper(II) and triglycine (G·G·G), glycylglycyl-β-alanine (G·G·β-A), glycyl-β-alanylglycine (G·β-A·G), or β-alanylglycylglycine (β-A·G·G), the structures of the complexes formed at various pH values and the structure-stability relationship between the fusedring chelates have been discussed in reference to the equilibrium constants determined by potentiometric titration at 25°(μ=0.1 (KNO3)) and the properties of the copper(II) chelates isolated. For each tripeptide, the stability constant K1 for the 1: 1 complex and the constants for the deprotonation reactions Kc1 and Kc2 were calculated by the method of non-linear least-squares. For G·G·G, G·G·β–A, and G·β–A·G, the equilibrium indicating the formation of a protonated complex was detected at pH 3.5–4.5. The relatively small difference in the logK1 values (5.25–5.60) and the logKc1 values (5.23–5.36) and the larger difference in the −logKc2 values (5.54–6.73) have been interpreted in terms of the steric requirements around copper(II) in the fused-ring chelates. Relative stabilities of the fused-ring systems in the deprotonated chelates have been inferred from the K1Kc1Kc2 values to be in the order 5-6-5(G.β-A·G-Cu(II))\simeq6-5-5(β-A·G·G-Cu(II))>5-5-6(G·G·β-A-Cu(II))>5-5-5(G·G·G–Cu(II)).

The Stability of Fused Rings in Metal Chelates. IX. Copper(II) and Nickel(II) Complexes of Schiff Bases Derived from Salicylaldehyde and Dipeptides Containing Glycine and/or β-Alanine

Abstract Copper(II) and nickel(II) complexes of Schiff bases derived from salicylaldehyde(Sal) and dipeptides containing glycine and/or β-alanine have been prepared. It has been found that Schiff base ligands containing glycylglycine (Gly·Gly), glycyl-β-alanine (Gly·β-Ala) or β-alanylglycine (β-Ala·Gly) as the peptide moieties give rise to square-planar, quadridentate copper(II)- and nickel(II)-chelates, while the N-salicylidene-β-alanyl-β-alanine (Sal=β-Ala·β-Ala) does not form the same type of copper(II)- or nickel(II)-chelate. It is concluded on the basis of spectrophotometric, polarographic and other measurements that the stability decreases in the order 6-5-5-([Cu(Sal=Gly·Gly)])≥6-5-6-([Cu(Sal=Gly·β-Ala)])≥6-6-5-([Cu(Sal=β-Ala·Gly)])>>6-6-6-([Cu(Sal=β-Ala·β-Ala)])fused-ring system.

Conformational Analysis of Coordination Compounds. II. Dimethyl-substituted Five- and Six-membered Metal Chelate Rings.

Conformational Analysis of Coordination Compounds. II. Dimethyl-substituted Five- and Six-membered Metal Chelate Rings.

The Stability of Fused Rings in Metal Chelates. VIII. Solution Equilibria of the Copper(II) Complexes of Glycinamide and Related Compounds

Abstract The aqueous solution equilibria of the systems containing copper(II) ion and glycinamide, β-alaninamide, glycine-N,N-diethylamide, or β-alanine-N,N-diethylamide have been investigated by potentiometric titration at 25°C (μ=0.1 (KNO3)). The stability constants K1 and K2 and the constants of the deprotonation reactions K1H, Kc1, and Kc2, for the glycinamide-copper(II) systems, and K1 and K2 for the other ligand-copper(II) systerrs were calculated by the method of non-linear least-squares with the aid of a computer. The K1 values were found to be in the order, glycine-N,N-diethylamide (6.17)>β-alanine-N,N-diethylamide (5.5)>glycinamide (5.30)>β-alaninamide (5.1). The sequence reveals that the five-membered chelates are more stable than the six-membered ones. The K1 and Kc1 values for glycylglycine and β-alanylglycine have been determined anew, and the structures of the chelates formed in acid solution have been discussed from comparative studies of the equilibrium constants, which suggest a tridentate nature of the dipeptides in the chelates of the type Cu(HL)+ where HL denotes free dipeptide.

The Stability of Fused Rings in Metal Chelates. VII. Copper(II) Complexes of Schiff Bases Derived from 2-Acetylpyridine or Pyridine-2-aldehyde and Dipeptides Containing Glycine, β-Alanine and/or α-Aminoisobutyric Acid

Abstract Eight new copper(II) complexes of SchifF bases derived from 2-acetylpyridine or pyridine-2-aldehyde and dipeptides containing glycine, β-alanine and/or α-aminoisobutyric acid have been prepared, and their relative stability was discussed on the basis of numerical data obtained by spectrophotometric, polarographic and other measurements. As a result, it was found that the stability of fused-ring systems decreases in the order 5-5-6-\simeq5-6-5->5-5-5->5-6-6-system (the first number represents the number of ring members containing pyridine derivatives and the second and third numbers represent those of ring members containing dipeptide moieties). The conclusion proposed previously that SchifF base chelates of aldehydes are generally less stable than those of corresponding ketones, has been proved to be valid also for the copper(II) chelates. It was found that transamination reactions take place in the copper(II) chelates of Schiff bases with pyridine-2-aldehyde and glycylglycine or glycyl-β-alanine.

Stability of fused rings in metal chelates. VI. Structures and stability constants of the copper(II) chelates of dipeptides containing glycine and/or β-alanine

The reactions of the dipeptides containing glycine and/or β-alanine with an equimolar amount of copper(II) nitrate in acid solution were investigated potentiometrically, and the stability constants for the copper(II) chelates formed in acid solution were determined at 25 °C by the method of Datta and Rabin. The chelates with the composition [Cu.peptide(OH2)] were isolated in the pure state. The dipeptides exhibited analogous reactivities, and the stability constants, log K1, for the charged chelates, CuHL+, were found to be between 5.5–5.7. Comparison of the values for glycylglycine and β-alanyl-glycine with those for glycine and β-alanine suggests that these dipeptides act as terdentate ligands forming fused-ring chelates, where the coordinating sites are probably the amino nitrogen, amide nitrogen, and carboxyl oxygen, although the complexing ability of the amide NH group may be weak. The constants, Kc, for the dissociation of the amide hydrogen from the charged chelates to form the deprotonated chelates, CuL, with the rigid 5-5-, 5-6-, or 6-6-membered ring system decrease in the order glycylglycine > β-alanylglycine > glycyl-β-alanine > β-alanyl-β-alanine. The log K1Kc values indicate that the tendency of forming the deprotonated chelates also decreases in this order.

The Stability of Fused Rings in Metal Chelates. IV. Preparation and Relative Stability of Copper(II) Complexes with Tetradentate Schiff Base Ligands

Abstract Relative stability of sixteen aldehyde- and the corresponding ketone-Schiff base chelates has been investigated in terms of their decomposing temperature and half-wave potential against the reduction of copper(II) at the dropping mercury electrode. The previous conclusion, established for copper(II) tridentate Schiff base complexes, that Schiff base chelates of aldehydes are generally less stable than those of corresponding ketones has been proved to be valid also for copper(II) tetradentate Schiff base complexes if there is no serious steric hindrance in the Schiff base ligand. As a result of this investigation, six new copper(II) chelates were synthesized and characterized.

The Stability of Fused Rings in Metal Chelates. V. Copper(II) Chelates of the Schiff Base Derived from Pyruvic Acid and n-Propanolamine

The Stability of Fused Rings in Metal Chelates. V. Copper(II) Chelates of the Schiff Base Derived from Pyruvic Acid and <i>n</i>-Propanolamine

The Stability of Fused Rings in Metal Chelates. III. The Relative Stability of Copper(II) Complexes of Aldehyde- and Ketone-Schiff Bases

Abstract The relationship between the structure of fused-ring systems and the relative stability of copper(II) Schiff base chelates has been discussed, on the basis of the properties of six copper(II) complexes, in connection with the transamination reaction. As the conclusion it has been suggested that the transamination reaction in fused-ring systems containing copper(II)-glyoxylate- or -pyruvate-Schiff bases may be expected only in such appropriately unstable systems as have two five-membered rings and that it is generally accompanied by a stabilization of the system. The preparation and properties of the two new copper(II) chelates, glyoxylidene-β-alaninatoaquo-copper(II) and pyruvidene-α-alaninatoaquocopper(II), have been described.

The Stability of Fused Rings in Metal Chelates. II. Copper(II) Complexes of Schiff Bases Derived from Pyruvic Acid and Amino Acids or Diamines

Abstract The preparation and some properties of four new copper(II) chelates of Schiff bases produced from pyruvic acid and amino acids or diamines have been reported. The relative stability of these compounds as well as of other rather popular copper(II) chelates has been discussed on the basis of spectroscopic and polarographic investigations. It has been demonstrated that any stress on any individual ring in metal polydentatechelates does not generally tend to be deposited in the same ring, but rather spreads to some extent over the whole fused-ring system,, sometimes strengthened and at other times weakened or even completely cancelled by another stress on another ring in the system. Therefore, the stability of fused rings should not be discussed on the basis of a simple summation of the stability of individual rings contained in the fused-ring system. It has been concluded that the stability of metal polydentate chelates increases with a decrease in stress over the whole fused-ring system.