Kozo Sone

Studies on mixed chelates—III: Mixed copper(II) chelates with N,N,N′,N′-tetramethylethylenediamine and β-diketones[1]

Abstract Ten mixed nickel(II) chelates containing N,N,N′,N′-tetramethylethylenediamine and β-diketonate ions were newly obtained. These chelates can be classified into two types according to their stereochemistries. Under the type [I] fall [Ni tmen aca] (B(C 6 H 5 ) 4 ), [Ni tmen aca] (ClO 4 ), [Ni tmen bzaca] (B(C 6 H 5 ) 4 ), and [Ni tmen bzaca] (ClO 4 ), all of which are red, diamagnetic (or only feebly paramagnetic) square-planar four coordinate chelates. On the other hand, the type[II] chelates are all blue or green, paramagnetic (3·1–3·3 BM.), and apparently octahedral six co-ordinate chelates. They are [Ni tmen aca (OH 2 ) 2 ] (ClO 4 ), [Ni tmen aca (NO 3 )], [Ni tmen aca 2 ], [Ni tmen bzaca (OH 2 ) 2 ] (ClO 4 ), [Ni tmen bzaca (NO 3 )] and [Ni tmen bzaca 2 ]. In the type [I] chelates, an anion of very poor coordination ability (B(C 6 H 5 ) 4 − or ClO 4 − ) acts as the counter ion, while the type [II] chelates contain either two water molecules or a bidentate anion with relatively strong coordinating ability (NO 3 − or a second β-diketonate ion) in their co-ordination spheres. The spectra of these chelates in various organic solvents often depend strongly on the solvent used and temperature, changing from blue (co-ordinating solvents and/or low temperature) to red (inert solvents and/or high temperature). These behaviours can be reasonably explained by assuming the existence of the following equilibria: [Ni tmen (β-dik)] + + 2S ⇄ [Ni tmen (β-dik) (S) 2 ] + . In the case of nitrato-chelates, the equilibria: [Ni tmen (β-dik) (NO 3 )] + 2S ⇄ [Ni tmen ( β -dik) (S) 2 ] + + (NO 3 − ) also seem to exist.

Studies on mixed chelates—IV: Influence of the α-substituent groups in β-diketones on the structure of their mixed nickel(II) chelates with N,N,N′,N′-tetramethylethylenediamine[1]

Abstract Twelve mixed chelates of the general formula, NiTMEN (β-dik) X , containing N,N,N′,N′-tetramethylethylenediamine (TMEN) and various α-substituted β-diketones were prepared. Their magnetic properties, electronic and i.r. spectra, and electric conductivities in nitromethane all show that they are generally quite similar to those of the aca and bza chelates reported; however, it was found that the stereochemistries and relative stabilities of the chelates in solutions are influenced remarkably by the nature of the substituent groups in the β-diketone. Under comparable conditions, an order of the ligands indicating the increase of NiO bond strength and that of the tendency of the square planar chelate to retain its structure in solution was found. This can be reasonably explained by considering the electronic and steric properties of the substituent groups in these ligands.

SOLVATOCHROMISM OF TRANSITION METAL COMPLEXES WITH ORGANIC LIGANDS IN DONOR AND ACCEPTOR SOLVENTS

124 List of Abbreviations 124

Studies on mixed chelates, part IX. A new mixed nickel(II) chelate which assumes 4-, 5-, and 6-coordinate structures in various organic solvents

SummaryA new mixed nickel(II) chelate, Ni(tmen)(acac)(NCS) · 0–1 H2O, was prepared. It was found that this (anhydrous) chelate changes from a 6-coordinate, probably dimeric structure in the solid state to (i) a 5-coordinate square pyramidal, (ii) a 4-coordinate square planar and (iii) 6-coordinate solvated structure, according to the solvent used.

Thermochromic and Chromotropic Phenomena of Cobalt(II) Chloride Solutions and Related Systems

The pink color of an aqueous solution of cobalt(II) chloride is known to be due to that of the 6-coordinate octahedral hexaaqua cation, [Co(H2O)6]2+. However, anhydrous CoCl2 is blue and its solutions in various organic solvents, such as alcohols or acetone, are also blue. In general, the blue color is ascribed to the formation of tetrahedral 4- coordinate complexes. These are often formed when the Co-L (L: ligand) bond is rather weak and ionic, and the ligand is bulky (hence, interhgand repulsion favors a tetrahedral geometry). For example, the spectral and conductometric studies of a number of investigators (e.g. Katzin, Libuś, Osugi, and their collaborators [14,17,31]) have indicated that the blue neutral species of the composition [Co(Solv)2Cl2] predominates in ethanol and higher alcohols (Solv = a solvent molecule; cf. Chap. B.II).

Thermochromism of Nickel(II) Chelates in Solution

The results and discussions in the last chapter may lead to an impression that, although the observed phenomena themselves are quite interesting, most of the theoretical interpretations are far from perfect, and often haunted by numerous ambiguities.

Thermochromism of Transition Metal Complexes in the Solid State

In addition to the thermochromic phenomena observed in solution, numerous changes are also known to occur in the solid state among the transition metal complexes [1, 2]. In this Chapter, we shall first consider some representative examples of irreversible thermochromism. Common reactions of colored complexes will not be treated, since they are, quite naturally, irreversibly thermochromic. Thus, we shall focus our attention on certain reactions of special structural interest, e.g., dehydration reactions, isomerizations and so on, in order to find out some general features of the phenomena. Examples of reversible thermochromism, which are of more specific interest, will then be reviewed.

Miscellaneous Chromotropic Phenomena Observed in Solutions of Metallic Complexes

A large number of chromotropic phenomena in solutions have also been observed and reported for transition metal complexes not covered in the foregoing chapters. In this Chapter we shall concentrate ourselves on several representative examples in which systematic studies led to a reasonably clear-cut understanding of the phenomena. It is interesting to note that the concepts of DN and AN, or of related polarity parameters, appear again and again as unifying principles in many of these examples; it is a proof of their general validity in explaining the changes that occur in solution.

Chromotropic Phenomena of Copper(II) Chelates

A large number of chromotropic phenomena are also observed among the chelates of copper(II). We shall now.compare their structures with those of the Ni(II) complexes discussed in Chapter C in order to illustrate certain points of interest.