1,3,5‐Trideoxy‐1,3,5‐tris(dimethylamino)‐cis‐inositol, an Efficient Ligand for Hard Trivalent Metal Ions. Determination of the stability constants of the Fe^III, Al^III, and Cu^II complexes in aqueous solution

Abstract

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.

The Design of Selective Chelating Agents: 1,3,5‐Trideoxy‐1,3,5‐tris‐(dimethylamino)‐cis‐inositol, a Powerful Ligand for Hard and Highly Charged Metal Ions

“…2. and 7. appropriate amounts of 0.1 M HCI were added to 22 individually sealed and thermostated sample solutions. An equilibration time of 72 h was allowed [9]. Further experimental details are summarized in Tables 5-7.…”

“…Anisotropic displacement parameters were used for all non-hydrogen atoms in the final full-ma- The ionic strength was adjusted by adding appropriate amounts of KNO, or KCI to the test solutions. The potential measurements for the continuous titrations were performed as described previously [2,4,6,9]. In the batch titrations of 1.…”

Selective Blocking of Coordination Modes in 1,3,5-Triamino-1,3,5-trideoxy-cis-inositol: Enforced Formation of a Low-Spin Iron(III) Hexaamine Complex

“…They were used without further purification. [Fe(tdci) 2 ]Cl 3 ·15H 2 O was prepared according to a previously described procedure . tmca·3HCl was prepared by selective O-methylation of 1,3,5-triamino-1,3,5-trideoxy- cis -inositol…”

“…The selectivity of the ligand can be readily tuned by introducing more bulky substituents on either the oxygen or nitrogen donors of taci. In 1,3,5-trideoxy-1,3,5-tris(dimethylamino)- cis -inositol (tdci), the conformer with three axial dimethylamino groups is destabilized by nonbonding ( intra ligand) repulsions and only the conformation with three axial hydroxy groups is available for metal binding. , Also additional inter ligand repulsion between the dimethylamino groups would substantially increase steric strain in a bis-complex of tdci with MN 6 coordination . Consequently, exclusive FeO 6 coordination is observed for [Fe(tdci) 2 ] 3+ ( 2 ).…”

Electrochemical Signature of the Coordination Mode in Metal Complexes With a tris-Ferrocenyl Derivative of the Taci Ligand

“…Unfortunately, ES-MS data allowing the confirmation of this 1:1 binding mode between L and Al 3þ ions could not be obtained from solution containing L and Al 3þ . Similarly to the corresponding complex formed with Taci and other derivatives [36][37][38], the formation of a unique electrochemical signal around þ 175 mV indicates that the hard metal cation is coordinated by the alkoxo groups of L, the protons of the hydroxyl groups in L being transferred to the amino groups with formation of ammonium subunits.…”