Holmium dodeca-iodidoiron-octa-hedro-hexa-holmium, {FeHo(6)}I(12)Ho.

Single crystals of {FeHo(6)}I(12)Ho were obtained during the reaction of HoI(3) with metallic holmium and iron in a sealed tantalum container. The crystal structure consists of isolated holmium clusters encapsulating a single Fe atom, {FeHo(6)} ( symmetry). The rare earth metal atoms are surrounded by 12 edge-capping and six terminal iodide ligands that either connect the clusters to each other directly or via HoI(6) octa-hedra ( symmetry).

Single crystals of {FeHo 6 }I 12 Ho were obtained during the reaction of HoI 3 with metallic holmium and iron in a sealed tantalum container. The crystal structure consists of isolated holmium clusters encapsulating a single Fe atom, {FeHo 6 } (3 symmetry). The rare earth metal atoms are surrounded by 12 edge-capping and six terminal iodide ligands that either connect the clusters to each other directly or via HoI 6 octahedra (3 symmetry).

Comment
Rare earth cluster compounds of the general formula {Z(RE) 6 }I 12 RE, where Z is an interstitial transition metal or main group element and RE is a rare earth element, have been well explored by Hughbanks and Corbett (1988) for RE = Sc, Y, Pr and Gd. Additionally, compounds of the formula {Z(RE) 6 }I 12+y A x , where A is an alkali metal (Rb or Cs) with x = 1-4 and y = 0-1 and Z = C, C 2 , are known for the rare earth elements Pr and Er that were compiled and studied by Meyer & Wickleder (2000) and Wiglusz et al. (2007). With {FeHo 6 }I 12 Ho we were able to extend the knowledge of this structure type to the element holmium, where only {CHo 6 }I 12 Ho had been synthesized previously by Hohnstedt (1993). Other reviews of reduced rare earth metal halides without and with metal clusters were given, for example, by Corbett (1973Corbett ( , 1996Corbett ( , 2000Corbett ( , 2006, Meyer (1988Meyer ( , 2007, Meyer & Wickleder (2000), Simon (1981) and Simon et al. (1991).
The structure of {FeHo 6 }I 12 Ho is isotypic with {FePr 6 }I 12 Pr (Palasyuk et al., 2006) and consists of isolated {FeHo 6 } clusters, i.e. the metal atoms are not shared with other clusters. The {FeHo 6 } cluster core is surrounded by twelve edge-capping and six terminal iodide ligands that either connect the clusters to each other directly or via HoI 6 octahedra ( Fig. 1).

Experimental
Black, almost cubic crystals of {FeHo 6 }I 12 Ho were obtained by the reaction of HoI 3 (200 mg) with holmium powder (84 mg, Chempur, 99.9%) and iron powder (10 mg, Merck, p.a.) in a tantalum container at 1273 K for 200 h. HoI 3 had been synthesized from stoichiometric amounts of holmium and iodine, followed by sublimation in high vacuum for purification (Meyer, 1991). Due to air and moisture sensitivity of both reagents and products, all handlings were carried out in an argon-filled glove box (M. Braun, Garching, Germany).

Refinement
The displacement parameter for the Fe atom was refined isotropically. The highest peak (2.36 e Å -3 ) in the final difference Fourier map is 1.20 Å from atom Ho1 and the deepest hole (-2.44 e Å -3 ) is 2.40 Å from the same atom.

Special details
Geometry. All e.s. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating Rfactors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.