Arthur E. Martell

Infrared Spectra of Metal Chelate Compounds. VI. A Normal Coordinate Treatment of Oxalato Metal Complexes

The infrared spectra of 10 oxalato complexes have been obtained in the frequency range 4000 to 300 cm—1. A normal coordinate treatment made on the 1:1, metal:ligand model of the chelate ring of tris‐(oxalato)‐Cr(III) resulted in the assignment of metal‐oxygen stretching bands in the range between 600 and 300 cm—1 for various oxalato complexes. The force constants and the band assignments obtained are compared with those of the previous normal coordinate analysis based on the free oxalato ion. Relationships between the metal‐oxygen and the carbon‐oxygen stretching frequencies are discussed.

Infrared Spectra of Metal‐Chelate Compounds. I. A Normal Coordinate Treatment on Bis‐(Acetylacetonato)‐Cu(II)

A normal coordinate treatment on the chelate ring of bis‐(acetylacetonato)‐Cu(II) gives calculated frequencies in good agreement with the observed ones in the 1700 and 350 cm—1 range obtained with NaCl, KBr, and CsBr optics. In order to assign the observed bands and to see the coupling between various vibrational modes, the L matrices and the potential energy distribution, Lii2Fi were calculated for all the in‐plane vibrations. The results reveal that (1) the band at 1580 cm—1 previously assigned to asym. CO stretching is asym. CC stretching, (2) the bands at 684 and 654 cm—1 formerly suggested to be metal‐oxygen stretching modes are metal‐oxygen stretching vibrations coupled with ring deformation and CCH3 bending modes, respectively, and (3) a new band found at 455 cm—1 is the sym. Cu–O stretching mode. By comparing the force constants of the Cu–O stretching vibration with those of metal‐nitrogen and metal‐carbon bonds of other compounds, it is suggested that the Cu–O bond in this compound has double bon...

Infrared Spectra of Metal Chelate Compounds. VIII. Infrared Spectra of Co(III) Carbonato Complexes

The infrared spectra of twenty Co(III) carbonato complexes have been measured in a range between 4000 and 300 cm—1. Normal coordinate treatments were made with a model based on the unidentate and bidentate forms of the 1:1 (metal/ligand) complex. The theoretical band assignments and force constants obtained by these calculations confirm the validity of the previous qualitative conclusions based on the differences of symmetry and the frequency shifts of the unidentate and bidentate complexes. The Co(III)‐O stretching bands were located at 440∼380 (antisymmetric) and at 400∼350 (symmetric) for the bidentate complexes, and at 360∼340 cm—1 for the unidentate complexes.

Infrared Spectra of Metal Chelate Compounds. VII. Normal Coordinate Treatments on 1:2 and 1:3 Oxalato Complexes

Normal coordinate treatments have been made on the square planar 1:2 oxalato complex of Pt(II) and the octahedral 1:3 oxalato complex of Cr(III), and the results were compared with those obtained with simple 1:1 complexes. It was found that coupling between the ligands in the square planar 1:2 complex is small whereas coupling between the ligands in the octahedral 1:3 complex is appreciable. Observed differences of the spectra between 1:1 and 1:2 oxalato complexes of Pt(II) and between 1:1 and 1:3 oxalato complexes of Cr(III) and Co(III) are in good agreement with the results of these calculations.

Metal chelate compounds of glycylglycine and glycylglycylglycine.

Abstract The preparation of copper(II), cobalt(III), and nickel(II) chelates of glyclyglycine and of glycylglycylglycine is described and the structures of the compounds are deduced with the aid of analytical data and titration curves. For both ligands it was found that association with these metal ions was accompanied by the displacement of a hydrogen ion from each peptide linkage.

Studies on pyridoxine and pyridoxal analogs—I : The synthesis of substituted pyridinealdehydes☆

Abstract The preparation, purification and properties of 3-hydroxypyridine-2-aldehyde, 3-methoxypyridine-2-aldehyde, 3-hydroxypyridine-4-aldehyde, 3-methoxypyridine-4-aldehyde and their derivatives and some new intermediates are reported. The preparation of the thio-semicarbazones of the aldehydes, as potential tuberculostatic agents, and of 3-hydroxy-4-hydroxymethylpyridine and 3-methoxy-4-hydroxymethylpyridine as pyridoxine analogs, are described.

Visible and ultraviolet absorption spectra of metal chelates of para-substituted tetraphenylporphines☆☆☆

The visible and ultraviolet spectra of the Cu(II), Co(II), Ni(II), Pd(II), and Pt(II) chelates of tetraphenylporphine, tetra(p-methoxyphenyl)porphine, and of tetra(p-chlorophenyl)porphine are described, and variations are interpreted on the basis of the influence of ligand structure and nature of the central metal ion on chemical binding. A correlation of the data obtained from infrared studies with the visible and ultraviolet spectra of these chelates is also presented. The coordinate bond strength seems to change in the order Cu(II) p-chlorophenyl > p-methoxyphenyl.

Stabilities of metal chelates of pyridoxamine

Abstract The acid dissociation constants of pyridoxamine, and the formation constants of its 1:1 and 2:1 chelates with Cu(II), Ni(II), Co(II), Fe(III), Mn(II), Zn(II), and Cd(II) ions have been determined by a potentiometric method. The structures of the metal chelate compounds formed are deduced with the aid of the titration curves, and the relative stabilities are interpreted in the light of the tentative mechanism of the transamination reaction.

Chelating agents as metal buffers in biological systems. I. Principles and use of ethylenediaminetetraacetic acid

Abstract The interactions which influence the concentration of free metal ions in aqueous solutions of chelating agents are described. Graphical representation of metal chelate equilibria in the form of pM-pH functions is proposed as the most convenient method of taking into account the effects of interfering substances. This method is applied to metal-ion buffer systems containing ethylenediaminetetraacetic acid, and graphs are presented to illustrate the influence of hydrogen-ion concentration, metal-hydroxide precipitation, and oxalate precipitation.

CHELATION: STABILITY AND SELECTIVITY

This monograph on chelation phenomena embraces a unique variety of subject matter as well as background and interest of the authors represented: among them are chemists interested in chelation as a chemical phenomenon, industrial chemists interested in putting chelates to good use, and other investigators working in the life sciences concerned with the role of chelates in the body and in biological systems generally. Jerome Fredrick is to be congratulated for putting together a program so remarkably varied and yet well integrated as to cover the broad area of research and applications in this ever-expanding field of metal chelate compounds. I like to look upon the conference on which this monograph is based as an entropy process. Each scientist contributing to it has worked along lines of specific interest to him, and produced results that usually have varied considerably from those of other workers. The bringing together of so many specialists with such varieties of information results in a net loss of entropy. In this monograph, the decrease of entropy is especially great. Thus the resulting spontaneous processes, involving the exchange of information and the subsequent applications of this new information in the laboratories of the participants, are characterized by an especially large entropy increase. I t is readily seen, therefore, that this monograph in particular should be highly productive of results, as are all processes involving large increases of entropy. To achieve the highest possible stability, one designs a chelating agent, or ligand, with the lowest possible entropy. Therefore, when this agent combines with a metal ion, also of low entropy, the entropy increase is particularly great, resulting in a highly spontaneous reaction. It is only natural, therefore, to look a little more closely a t this chelation reaction to find out in a general way what information has been gained from it and what one may conclude about its future directions. One of the outstanding advances in coordination chemistry was the determination, about fifteen years ago, of the stabilities of the alkaline earth complexes of aminopolycarboxylic acids, of which ethylenediaminetetraacetic acid (EDTA) and nitrilotriacetic acid (NTA) were and still are the outstanding examples. Until that time it was thought impossible to effect reactions of the type indicated in FIGURE 1. The explanation of the high stability of such complexes of the more basic metal ions gradually became obvious from the determination of the stability constants of numerous metal chelate compounds, and it is based on concepts of the so-called chelate effect and an understanding of the general nature of the reactions involving the combination of positive and negative ions. Perhaps the most important factor in obtaining high stability in metal cheThese entropy changes are analogous to the chelation phenomenon.