Trinuclear lanthanoid complexes of 1,3,5-triamino-1,3,5-trideoxy-cis-inositol with a unique, sandwich-type cage structure

A variety of trinuclear complexes [M-3(H-3L)(2)](3+) [M = Y, La, Eu, Gd, Dy; L = 1,3,5-triamino-1,3,5-trideoxy cis-inositol (taci) and 1,3,5-trideoxy-1,3,5-tris(dimethylamino) (tdci)] was prepared as solid materials of the composition M-3(H-3L)(2)X-3. pH(2)O . qEtOH (X = Cl, NO3; 2.5 less than or equal to p less than or equal to 9; q = 0, 0.33) and characterized by elemental analyses, NMR spectroscopy, and FAB(+) mass spectrometry. The crystal structures of [La-3(H(-3)taci)(2)-(H2O)(4)Cl] Cl-2. 3H(2)O and [Gd-3(H-(3)taci)(2)(H2O)(6)]Cl-3. 3H(2)O were elucidated by single-crystal X-ray diffraction studies. The La complex crystallizes in the orthorhombic space group Pbca, a = 17.10(2) Angstrom, b = 16.20(4) Angstrom, c = 20.25-(4) Angstrom, z = 8 for C12C13H38La3N6O13 The Gd complex crystallizes in the monoclinic space group P2(1)/n, a = 10.294(3) Angstrom, b = 15.494(5) Angstrom, c = 19.994(6) Angstrom, beta = 95.36(2)degrees, Z = 4 for C12C13Gd3H42N6O15 The two complexes exhibited a unique, sandwich-type cage structure, where the two triply deprotonated taci ligands encapsulate an equilateral triangle of the three metal centers. The metal cations are coordinated to the equatorial, terminal amino groups and are bridged by the axial mu(12)-alkoxo groups. The coordination spheres are completed by additional peripheral ligands such as H2O or Cl- counterions. The coordination number of the metal cations is 8. Magnetic susceptibility measurements of the Gd complex revealed very weak antiferromagnetic coupling interactions between the three Gd centers. Complex formation and species distribution in aqueous solution was investigated by potentiometry and pD-dependent NMR spectroscopy. An exclusive formation of the [Eu-3(H-(3)taci)(2)](3+) unit in solution was found in the range 7 less than or equal to pH less than or equal to 10. The formation constants were determined for the Y, Eu, Gd, Dy, and Lu complexes with taci. The stability of the lanthanoid complexes increased monotonically with decreasing ionic radius of the metal center.