| Abstract
| - Good bonding of M6X12 clustercompositions generally requires that half of the 12 edge-bridging Xalso bond exo to the vertexes of other clusters(Xi-a), and vice versa. Theneed to accommodate both additional cations and an open-shell clusterin the electron-poorK2La6I12Os alters thestructure considerably. Both a new array of clusters with someobviously strained bridging and a tetragonally compressed, closed-shellcluster are revealed in the present structure shown in projection(right) with solid La6Os clusterrepresentations.
- Reaction of KI, La, LaI3, and Os in a weldedniobium tube at 800 °C yields black, air-sensitive crystals ofK2La6I12Os. The phase was characterizedby single-crystal X-ray diffraction (monoclinic,P21/c, Z = 2,a = 9.890(3) Å, b = 19.319(5) Å, c =10.047(4) Å, β = 108.69(3)° at 23 °C). Thestructure contains tetragonally compressedLa6I12 clusters centered by Os and interbridgedby Ia atoms according to the general pattern of(R6Z)Ii6Ii-a6/2Ia-i6/2for all examples with X:R ratios of 2:1. However, the detailedpattern of three-bonded Ii-a andIa-i bridging isnew owing to the need to accommodate a relatively large, distortedcluster and two potassium ions in a moreopen structure. One type ofIi-a andIa-i bridging defines zigzagchains of clusters with strain evident in theinterconnections. EHMO calculations show that the observed 0.49 Åtetragonal compression of the 16-electroncluster (relative to an optimal 18-e) splits the nominalt1u4 HOMO into a two-below-one pattern andgives aclosed-shell configuration. The compound accordingly exhibits onlya small and typical temperature-independentparamagnetism, ∼6 × 10-4 emumol-1.
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