Crystal structure and absorption spectroscopy of a dimeric neodymium(III) complex with triethylenetetraaminehexaacetic acid (H6ttha), Na0.5H5.5[Nd2(ttha)2]·7.5NaClO4·16.83H2O

Abstract

The crystal structure and absorption spectra (IR, UV/VIS) have been determined for Na_0.5H_5.5[Nd₂(ttha)₂]· 7.5NaClO₄·16.83H₂O (H₆ttha = triethylenetetraaminehexaacetic acid). The structure consists of the complex dimer, perchlorate anions, sodium cations and water of hydration. Both neodymium(III) ions are nine-co-ordinate. Each ttha ligand is bonded to one Nd^III through four of its carboxyl oxygen atoms and three of its nitrogen atoms. Two carboxyl oxygen atoms are bonded to the other Nd^III, and the fourth nitrogen atom remains unco-ordinated. The co-ordination spheres of both Nd^III are essentially the same and may be defined as distorted tricapped trigonal prisms. Absorption spectra of a single crystal were measured at room and liquid-helium temperatures. The intensities of the f–f transitions were analysed on the basis of Judd–Ofelt theory. Comparison of the absorption spectra of [Nd(ttha)]^3– in solution to those of single crystals of Na₃[Nd(ttha)]· 2.5NaClO₄·7.617H₂O and Na_0.5H_5.5[Nd₂(ttha)₂]·7.5NaClO₄·16.83H₂O compounds allowed us to estimate the ratio of mono- to di-meric species in solution.