Nonaaquapraseodymium triiodide–thiourea (1/2)

The title compound, [Pr(H2O)9]I3·2CS(NH2)2, an adduct of nonaaquapraseodymium triiodide with two thiourea molecules, is composed from [Pr(H2O)9]3+ cations (polyhedron: monocapped tetragonal antiprism), noncoordinated thiourea molecules and iodide anions. The components are evidently connected by hydrogen bonds but in the presence of heavy atoms water H atoms have not been located. The complex cation and one of the two independent iodide anions are located on a twofold axis.

The title compound, [Pr(H 2 O) 9 ]I 3 Á2CS(NH 2 ) 2 , an adduct of nonaaquapraseodymium triiodide with two thiourea molecules, is composed from [Pr(H 2 O) 9 ] 3+ cations (polyhedron: monocapped tetragonal antiprism), noncoordinated thiourea molecules and iodide anions. The components are evidently connected by hydrogen bonds but in the presence of heavy atoms water H atoms have not been located. The complex cation and one of the two independent iodide anions are located on a twofold axis.
Supplementary data and figures for this paper are available from the IUCr electronic archives (Reference: RK2319).

Comment
The structure investigation of the interaction products of metal salts with thiourea CS(NH 2 ) 2 is very promising, because it allows to predict the possible ways of thermal decomposition of these compounds yielding oxide, sulfide and oxosulfide derivatives (Suponitsky et al., 1988). The lanthanide derivatives are very promising objects of research in this regard, since the corresponding sulfides and oxosulfides are used as the activators of materials with the luminescent properties. To the present time the structure of only some thiourea derivatives of lanthanide salts has been studied in details. Systematic investigation of the previously synthesized thiourea derivatives allowed us to conclude that there are two isostructural series of lanthanide acetates (La-Pr and Nd-Lu) (Romanenko et al., 1980;Romanenko et al., 1981a;Romanenko et al., 1986), and three isostructural series of lanthanide propionates (La-Pr, Nd-Tm, Yb-Lu) (Romanenko et al., 1981b;Romanenko et al., 1985). It was established the existence of complex cations in the structures, involving coordinated water molecules as well as bidentate and bridging acetate or propionate ions. It was noted that thiourea is not included into the internal sphere of complexes. The information about the synthesis and structure of thiourea derivatives of lanthanide halides is much smaller. We have obtained the compounds of thiourea with LnI 3 (Ln = Eu, Ho, Er) at room temperature (Antonenko et al., 2011). X-ray data have been demonstrated that in the solid state these compounds are composed from [Ln(H 2 O) 9 ] 3+ cations (polyhedron: monocapped tetragonal antiprism), non-coordinated thiourea molecules and iodide-ions.
Herein we report the structure of thiourea adduct of nonaaquapraseodymium triiodide I (Fig. 1). In the solid state I is composed from [Pr(H 2 O) 9 ] 3+ cations (polyhedron: monocapped tetragonal antiprism), thiourea molecules and iodide anions. All mentioned species are evidently connected with H-bonds but in the presence of heavy atoms water H atoms have not been located and thus can not be discussed. The complex cation and one of the two independent iodide anions are located on a twofold axis. There is no coordination of thiourea by the lanthanide atom as through the atom S, and through the atom N as well as in the cases of compounds which have been obtained previously (Antonenko et al., 2011). A packing diagram is shown in Fig. 2.

Experimental
The synthesis of title compound was carried out at room temperature by mixing PrI 3 ×9H 2 O and CS(NH 2 ) 2 at a molar ratio 1:1.7. Few drops of water were added to the reaction mixture to the formation of clear solution. After 30 days the light green crystals were identified from it. These crystals are hygroscopic; they are decomposed by water with the release of the initial thiourea. The crystals of title compound suitable for X-ray analysis were dried over the alkali in the desiccator. By complexometric titration with 0.1 M Edta and reverse iodometric titration with 0.1 M Na 2 S 2 O 3 (Patrovsky, 1959;Kolthoff & Belcher, 1957) we established that the molar ratio of nonaaquapraseodymium triiodide and thiourea in this compound is 1:2.

Refinement
In the presence of heavy atoms water H atoms could not be located. The hydrogen atoms bound to N atoms were placed in calculated positions with N-H = 0.86Å and refined as riding with U iso (H) = 1.2U eq (N). Fig. 1. Crystal structure of I with the atom numbering scheme. Displacement ellipsoids are shown at the 50% probability level. Only independent iodide anions are shown. Symmetry code: (i) 1-x, y, 1/2-z.  on-profiled ω scans h = −30→24 Absorption correction: ψ scan (North et al., 1968) k = 0→10  Geometric parameters (Å, °)