Water-free samarium(III) iodide complexes can be used as reagents to prepare
samarium(II) iodide, whose use in organic chemistry has grown considerably
during the last 25 years. Such complex with urea (Ur) was found in the SmI3–Ur–
H2O system at 0°C [1]; the SmI2 : Ur ratio in the water-free solid was 1 : 5.
In this work, octaureasamarium(III) iodide [Sm(Ur)8]I3 was synthesized by
the reaction of samarium(III) iodide with urea in an aqueous solution.
The crystal structure of the complex was studied by X-ray diffraction. The
crystals of the complex are triclinic, space group P1; a = 10.597(4) Å, b =
11.996(11) Å, c = 13.046(6) Å, α = 85,58(6)°, β = 73.76(4)°, γ = 76.20(7)°, V =
1546.2 Å3.
The structural units of the crystals are the [Sm(Ur)8]3+ cations and iodide
ions. The samarium atom is coordinated by carbonyl oxygen atoms of eight urea
molecules. The Sm–O distances vary from 2.378 to 2.448 Å.
Both nitrogen atoms (and corresponding hydrogen atoms) of one urea
ligand are disordered in two positions. One N–O bond is noticeably shorter than
another (1.271–1.281 and 1.350–1.356 Å, respectively). The positions of the
“jumping” ligand are stabilized by hydrogen bonds of the N–H...I type involving
two iodine atoms. The N–I distances are 3.511 and 3.365 Å. The third iodine
atom forms no hydrogen bonds.
Other ligands are involved in intramolecular H-bonding, the N–O distances
varying from 2.895 to 3.030 Å.
The structure of the crystal is layered. The layers are formed of the complex
cations and iodide ions combined by weak interactions.
Octaureasamarium(III) iodide shows the first example of the structure, in
which the coordination sphere of a rare-earth element consists only of urea
molecules and contains no anions and water molecules.
1. Afinogenova, N., Yu, Konovalova, L.N., Kuznetsova, G.P., Yastrebova, L.F. &
Stepin, B.D. (1976). Zh. Neorg. Khim. 21, 2881–2884.