Describes Gran's graphical method of end point determination for the precise analysis of acids and bases.

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The crystal structures of bis (glycollato) copper (I I), aquobis-(DL-lactato) copper( I I) hemi hydrate, diaquobis-(2hydroxy-2-methylpropionato) copper( I!), diaquobis(methoxyacetato)copper( I I),and diaquobis( phenoxyacetato) copper(l1) have been determined by three-dimensional X-ray structure analysis. All the complexes contain trans-chelate rings, which, apart from the bow-shaped lactate, are coplanar. The copper ions are in elongated tetragonally distorted octahedral environments with two exceptions : in the lactate, copper ions are in a nearly square-pyramidal five-co-ordinate environment; in the methoxyacetate, the octahedron is compressed. Details of the structures may be rationalised in terms of Jahn-Teller distortions and hydrogen-bonding. MOST bis(monocarboxylato)copper(II) complexes inwhich the ligand is unequivocally unidentate have low magnetic moments (-1.45 B.M. at room temperature) in the solid state and in some non-aqueous solvents,l and may be assumed to have dimeric or polymeric structures. However, in aqueous solution the complexes are mononuclear,2 up to a total copper ion concentration of at least 0 . 1~. The known crystal structures of aminocarboxylatocopper( 11) complexes indicate that 2-and 3-aminocarboxylates are invariably bidentate ligands in the solid state. The high thermodynamic stability and hydration of these copper complexes give little reason to doubt that they are also chelates in aqueous solution. However, for 2-and 3-hydroxy, -alkoxy-, and -aryloxy-carboxylates the situation is less clear. No crystallographic information was available when the present programme was initiated. Copper complexes of the 2-substituted carboxylates R1R2C(OR3)C0,-have magnetic moments of about 1.9 B.M. and are therefore monomeric, though not necessarily chelates. However, complexes of the analogous 3-substituted ligands have low magnetic m~r n e n t s ,~ indicative of the dimeric copper acetate structure.6 Systematic studies of differential proton relaxation in bound ligands indicate that 2-and 3-hydroxycarboxylates and 2-alkoxycarboxylates form chelates with copper(I1) in aqueous solution, but that the 3-alkoxycarboxylates are unidentate ligands. Infrared data in heavy-water solution,s and thermodynamic data are consistent with these deductions. There is a fine balance between the different structures of the complex and between the different functions of the ligand, and we have set out to investigate the structures of hydroxy-and alkoxy-carboxylates in the solid state. In aqueous solution, there is a good linear free-energy relationship of the form

Measurements of the proton relaxation rates of lanthanide( 111) aquo-ion solutions show that the correlation times, which govern the proton relaxation times in these solutions, are very short (ca. 1 0-13 s), and are predominantly due to the efectron-spin relaxation times of the cations. The variations in the relaxation rates for different Ln"I ions are discussed in terms of modulation of the different ligand-field splittings. The temperature dependence of the relaxation rates has also been studied and a relationship to the magnitude of ligand-field splittings of the different Ln"' ions is discussed.

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