Ten‐Coordinate Neodymium( III ) Complexes with Triethylenetetraaminehexaacetic Acid

The crystal structures and spectroscopic (IR, Raman, UV/Vis) data for the complexes [C(NH 2 ) 3 ] 2 [Nd(HTTHA)] · 3H 2 O ( I ) and [C(NH 2 ) 3 ] 3 [Nd(TTHA)] · 6H 2 O ( II ) are presented. Crystals of I are triclinic, P $\bar {1}$ , a = 9.998(2), b = 10.730(2), c = 15.557(3) Å, α = 106.89(3)°, β = 90.27(3)°, γ = 93.24(3)°, V = 1594.0(5) Å 3 , Z = 2, while the chiral crystals of II are monoclinic, P 2 1 , a = 10.157(2), b = 15.958(3), c = 12.788(3) Å, β = 112.68(3)°, V = 1912.5(7) Å 3 , Z = 2. Both structures consist of the complex monomeric anions, guanidinium cations and water of hydration. The Nd III ions are ten‐coordinate. The TTHA ligand coordinates to the Nd III ions with six of its carboxyl oxygen atoms and four nitrogen atoms. Although the coordination environments of both Nd III cations are essentially the same, the spectral results of both crystals reveal the influence of the degree of protonation of the ligand on the Nd III ion. The IR and Raman spectra allowed us to assign some important frequencies. A comparison of the electronic absorption spectra of Nd III –TTHA complexes in solution and in single crystals of I and II allows the detection of a small elongation of the Nd–O and Nd–N bonds in these complexes as compared to the [Nd(TTHA)] 3– moiety in the previously reported complex Na 3 [Nd(TTHA)] · 2.5NaClO 4 · 7.617H 2 O and indicates that the coordination geometry of the ten‐coordinate neodymium complex in solution is the same as in the chiral crystal II . The intensities of the f–f transitions in Nd III –TTHA solutions and of crystals I and II were analysed on the basis of the Judd–Ofelt theory. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)