Structure and Bonding in Some Gd(III) Metal Complexes Studied by Three-Dimensional X-Ray Analysis and 155Gd Mössbauer Spectroscopy

Abstract

Some functional lanthanide metal complexes, such as acetylacetonato complexes, ethylenediaminetetraacetato complexes, were successfully applied for diagnostic technique. The authors are interested in investigating the structure and bonding in lanthanide and actinide metal complexes using 166Er, 155Gd, and 237Np Mössbauer spectroscopies in connection with single-crystal and/or powder X-ray diffraction, making clear the differences on their structures as well as the differences in the participation of 4f and 5f orbitals in the chemical bonds. In this article, the crystal structures of two novel Gd(III) acetylacetonato complexes, Gd(pta) 3 · 2H 2O (pta = 1, 1, 1-trifluoro-5, 5-dimethyl-2, 4-hexanedione) and Gd(bfa) 3 · 2H 2O (bfa = 1, 1, 1-trifluoro-4-phenyl-2-4-butanedione) were reported. Though both of them were dihydrate and had distorted square antiprismatical structure, Gd(pta) 3 · 2H 2O crystallizes in the P 2 1/n (#14) monoclinic space group and its lattice parameters are a =1.4141(6) nm, b = 1.0708(3) nm, c =2.2344(4) nm, β=95.24(2)°, and Gd(bfa) 3 · 2H 2O crystallizes in P2 12 12 1 orthorhombic space group and its lattice parameters were a= 1.322(1) nm, b =2.295(1) nm, c = 1.0786(8) nm. In the meantime, the authors had finished a systematic investigation on the 155Gd Mössbauer isomer shift (δ) of various Gd(III) metal complexes having a different coordination number (C.N.) and different ratios coordinating oxygen to nitrogen. A tendency for the δ value to decrease with an increase in the C.N, and the number of the nitrogen atom coordinating to Gd was confirmed. This indicated that the Gd-O and/or Gd-N bond in the investigated Gd(III) metal complexes had a small covalent contribution, which was possible to be deduced from the O and/or N atoms of the ligands donating electrons to 6s, 5d, and 4f orbitals of Gd.