A series of compounds containing the mononuclear complexes [M(tdci),13Ge, Sn) was prepared and characterized by elemental analysis, NMR spectroscopy, and FAB mass spectrometry. Characteristic fragmentation reactions in the mass spectra were elucidated. X-ray analysis of the Al"', Fe"', Ga"' , and In"' complexes revealed that two neutral, zwitterionic tdci ligands coordinate to the metal cation exclusively through deprotonated alkoxo groups. The six coordinated

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The complexes [Fe(tdci),]CI, and [Al(tdci),]Cl, (tdci = 1,3,5-trideoxy-1,3,5-tris(dimethylarnino)-cis-inositol) were prepared and characterized by mass spectrometry, NMR spectroscopy, and magnetic-susceptibility measurements. The formation constants were determined in aqueous solution (25", 0 . 1~ KCI) by potentiometric titration.pK values of H3(tdci),+: 5.89, 7.62, 9.68; Fe"' complexes: log /IML = 18.8, log /IMLz = 32.6; Al"' complexes: log /JML = 14.3, log /IML2 = 26.4. The protonated complex [FeH(tdci),I4+ has also been identified. In contrast to the high stability of the Fe"' and Al"' complexes, only weak interactions of tdci with Cu" have been observed in aqueous solution (25", 0 . 1~ KNO,).Introduction. -The high affinity of 1,3,5-trideoxy-1,3,5-tris(dimethylamino)-cis-inositol (tdci) for Fe"' has already been recognized in 1984 [I]. In a subsequent study, a variety of metal complexes has been characterized in aqueous solution [2]. However, several hazards prevented the preparation of tdci in the scale required for an unambiguous identification of the metal complexes and a quantitative investigation of the equilibria in solution. Our first attempt was, therefore, to improve the preparation procedure of tdci [3] [4]. Since this ligand is now readily available, a comprehensive investigation of complex formation has been performed in our laboratory. We report here the synthesis and characterization of the solid, crystalline Fe"' and Al"' complexes and the potentiometric determination of the stability constants for Fe"', Al"', and Cu" in aqueous solution.

In a series of recent publications we demonstrated that 1,3,5triamino-l,3,5-trideoxy-ds-inositol (taci) is a useful ligand to elucidate the individual affinity of a metal ion for either nitrogen or oxygen donors.1-5 Taci has four different binding sites which allow the coordination of a metal ion by three nitrogen atoms (i), one oxygen and two nitrogen atoms (ii), one nitrogen and two oxygen atoms (iii), or three oxygen atoms (iv) (Scheme la). Al111, a very hard Lewis acid with a high preference for oxygen donors, forms a bis-type iv complex.4 In contrast, softer metal ions like Nin, Cu11, Zna, Cdn and Tlra all bind exclusively to the nitrogen donors of taci forming a bis-type i structure.2'4,5 For Gam, an intermediate type i-type iv coordination with a GaNa03 sphere has been observed.4 Complex formation with Crra finally resulted in a mixture of the type i-type iv coordination and the bis-type iv coordination.1 The versatility of taci is enlarged due to the possibility to coordinate in different tautomeric forms (Scheme lb). It has been demonstrated that the divalent Mg11, Ca11, Srn, and Ba11 coordinate to OH groups,5 whereas Alm, Crm, and Gam are bound to the zwitterionic form of the ligand.1,4 For these trivalent cations, a proton transfer from OH to NH2 is observed, and these metal ions are

Only corner‐sharing between the seven TaO6 octahedra is observed in the neutral complex [H−11Ta7O12(tdci)6] (tdci = 1,3,5‐trideoxy‐1,3,5‐tris(dimethylamino)‐cis‐inositol). The structure on the right (only one tdci ligand is illustrated) depicts the Ta7O30 double adamantane core. In contrast to previously described structures of polyoxometalate ions, which have a predominantly edge‐shared framework, this compound has an unusually open structure.