Synthesis and structure of [ K – ( 12 - crown - 4 ) 2 ] 2 [ K – ( 12 - crown - 4 ) ] 2 [ Sn 9 ] · 4 en †

The new compound [K–(12C4)2]2[K–12C4]2[Sn9]·4en (1), where 12C4 is 12-crown-4 polyether, was crystallized from an ethylenediamine solution of an intermetallic precursor with nominal composition K4Li2Sn8. The structure of the compound (orthorhombic, Cmca, a = 21.763(4), b = 16.030(3), c = 51.85(1) Å, Z = 8) contains isolated deltahedral clusters of [Sn9]4−. The clusters are of Cs symmetry and are nido according to the number of bonding electrons. The potassium countercations are sequestered by the very small 12C4 ether: half of them are sandwiched between a pair of molecules and the other half are coordinated by a single molecule. The latter potassium cations also bridge edges of the tin clusters, and each cluster has two such coordinated cations. Coordination of potassium cations by such small crown ethers is quite rare. Copyright  2003 John Wiley & Sons, Ltd.