L Journal of Alloys and Compounds 323–324 (2001) 678–682 www.elsevier.com / locate / jallcom Absorption spectrum analysis of uranium trichloride heptahydrate a a, b * ~~ ´ M. Karbowiak , J. Drozdzynski , Z. Gajek a Faculty of Chemistry, University of Wrocl «aw, ul. F. Joliot-Curie 14, 50-383 Wrocl «aw, Poland b W . Trzebiatowski Institute of Low Temperature and Structure Research, Polish Academy of Sciences, P .O. Box 937, Wrocl «aw, Poland Abstract 21 A good quality absorption spectrum of a powdered sample of UCl ?7H O was obtained at 4.2 K in the 4000–30 000 cm range. 3 2 Analysis of the spectrum enabled the determination of the crystal-field parameters and assignment of 94 crystal-field levels. The energies of the levels were computed by applying a simplified angular overlap model as well as a semi-empirical Hamiltonian representing the combined atomic and crystal-field interactions.  2001 Elsevier Science B.V. All rights reserved Keywords: Uranium trichloride heptahydrate; Uranium(31); Absorption spectra; Crystal-field analysis 1. Introduction Cary 5 NIR–Vis–UV spectrophotometer in the 4000– 21 30 000 cm range. In order to obtain the spectrum, a This paper presents a crystal-field level analysis per- well-ground mixture of the compound with some chlori- formed on the basis of the low-temperature absorption nated naphthalene oil (refraction index 1.635) was placed spectrum of polycrystalline samples of UCl ?7H O. between two quartz windows, approximately 0.8 cm in 3 2 Spectroscopic crystal-field studies of trivalent uranium, diameter, pressed to obtain a transparent layer, and placed due to experimental difficulties, have so far been exclu- in the cell compartment of an Oxford Instruments Model sively carried out on single-crystal hosts of simple and CF1204 cryostat. The spectrum was recorded at 4.2 and complex lanthanide halides [1–10] and a polycrystalline 300 K. U(HCOO) sample [11]. Most of these investigations, 3 however, exhibit a substantial drawback depending on the appearance of strong, Lapporte-allowed f–d bands in the 3. Parameterization of the crystal-field potential 21 spectra at energies as low as about 16 000–18 000 cm . 31 As a result, the energy level structure of U in different Since no qualitative differences were found [12] be- environments is relatively well established in the 0–16 500 tween the X-ray powder diffraction data of UCl ?7H O 3 2 21 cm region only. Hence, we turned our attention to and LaCl ?7H O it was assumed that these compounds are 3 2 uranium(III) compounds in polycrystalline form, for which isostructural and form similar Cl good quality absorption spectra could also be recorded in [(H O) Mek lMe(H O) ]Cl dimers, where Me5U or 2 7 Cl 2 7 4 21 the 15 000–30 000 cm range. La. The coordination polyhedron approximates two single- capped square antiprisms which share an equitorial edge formed by the bridging chloride atoms [13]. The other four 2. Experimental chloride atoms are not bound to the metal ion. The cells ] are triclinic with space group P1. Due to the lack of The compound was prepared according to the pro- symmetry elements at the metal site in the compound cedures reported in Ref. [12]. The electronic absorption under consideration as many as 27 independent crystal- spectrum of a thin film of the compound was recorded on a field parameters describe the crystal-field (CF) potential. Preliminary estimation of their values is difficult in view of the fact that the first coordination sphere, being of major importance for the CF effect, is especially complex *Corresponding author. Tel.: 148-71-320-4333; fax: 148-71-328- [12,13]. All ligands, i.e. the two chlorine ions and seven 2348. ~~ ´ E-mail address: jd@wchuwr.chem.uni.wroc.pl (J. Drozdzynski). oxygens, are non-equivalent in the sense that any two of 0925-8388 / 01 / $ – see front matter  2001 Elsevier Science B.V. All rights reserved. PII: S0925-8388(01)01087-8