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 co mposition M-3(H-3L)(2)X-3. pH(2)O . qEtOH (X = Cl, NO3; 2.5 less than or eq ual to p less than or equal to 9; q = 0, 0.33) and characterized by element al analyses, NMR spectroscopy, and FAB(+) mass spectrometry. The crystal st ructures of [La-3(H(-3)taci)(2)-(H2O)(4)Cl] Cl-2. 3H(2)O and [Gd-3(H-(3)tac i)(2)(H2O)(6)]Cl-3. 3H(2)O were elucidated by single-crystal X-ray diffract ion studies. The La complex crystallizes in the orthorhombic space group Pb ca, 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 sp ace group P2(1)/n, a = 10.294(3) Angstrom, b = 15.494(5) Angstrom, c = 19.9 94(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. Th e 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 wea k antiferromagnetic coupling interactions between the three Gd centers. Com plex formation and species distribution in aqueous solution was investigate d by potentiometry and pD-dependent NMR spectroscopy. An exclusive formatio n 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 sta bility of the lanthanoid complexes increased monotonically with decreasing ionic radius of the metal center.