Studies on Solute-solvent Interactions Using the Macrocyclic Teramine Nickel Complex as a Probe

環状テトラミンニッケル錯体を用いた溶質-溶媒相互作用

Yokoyama Takashi

The square-planar, macrocyclic tetramine nickel complexion, R,S,R,S-[NiL]2+ (L = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) which has axial sites available for coordination was found to be a useful probe to explore the solvent-solvent and solute-solvent interactions by using the coordination constants of donor solvent., and the characteristic properties of solvents on coordination were investigated.

In Chapter 1, the coordination constants of the donor solvent to the nickel complex in nitrobenzene (NB) were determined spectrophotometrically. These were discussed from the viewpoint of steric hindrance, basicity of the donor solvent, and the solvent-solvent interaction. It was found that R,S,R,S-[NiL]2+ has a sterically unique coordination site.

In Chapter 2, the ion-pair formation constant by conductometry was discussed. Although N,N-dimethylformaniide (DMF) and N,N-dimethylacetamide (DMA) have an almost similar relative permittivity and basicity, DMF was coordinated to R,S,R,S-[NiL]2+, but DMA was not. The first ionic association constant of R,S,R,S-[NiL]2+ with the perchlorate ion in the mixtures with NB decreased with increasing fraction of both DMF and DMA. DMA as well as DMF in NB selectively solvated the axial coordination site of R,S,R,S-[NiL]2+ to change from contact ion-pairs to solvent-separated ion-pairs. Bulky and delocalized negative pole of NB of which the dipole moment is larger than that of DMF and DMA results in a weak ion-dipole interaction, leading to a larger degree of ionic association. The ionic association was discussed from the viewpoint of steric hindrance and ion-dipole interactions.

In Chapter 3, the self-association of dimethyl sulphoxide (DMSO) was described. The dimerization constants of DNSO which are difficult to determine in dipolar solvents such as NB, DMA, propylene carbonate, and pyridine (Py) were obtained by using the dependence of the coordination constant to R,S,R,S-[NiL]2+ on the DMSO concentration. A fraction of coordinated species of DMSO in NB and Py became maximum at ca. 0.5 DMSO mole fraction and decreases with increasing DMSO mole fraction, unlike other coordinating solvents such as acetonitrile and DMF. As the dimerization masks the coordinating oxygen atom of DMSO, the inhibition of coordination of DMSO occurs. The dimerization constants obtained were large, when the dipole moment of diluent solvent is small.

In Chapter 4, the π-back donation of nitrites was described. Coordination of dipolar aprotic solvents to R,R,S,S-[NiL]2+ and [Ni(cyclam)]2+ which form an octahedral complex by axial ligation of two donor molecules was investigated in NB spec trophotometrically. The second coordination constants of nitriles to R,R,S,S-[NiL]2+ were larger than that of other oxygen atom-coordinating solvents, and furthermore, the first coordination constant was smaller than the second coordination constant for the nitrites. This extraordinariness was discussed in terms of the characteristic properties of the square-planar and macrocyclic tetramine nickel complex, and the π-back donation of nitriles.

Chemistry [ 430 ]

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