NH4TlI4 center dot 2(18c6)center dot NH3, a new type of a potential double-shell lattice clathrate

The reaction of TlI, NH4I, copper metal and 18-crown-6 (18c6) in air result ed in the formation of NH4TlI4. 2(18c6). NH3. X-ray diffraction analysis re vealed the close structural resemblance of the compound with the large fami ly of supramolecular complexes [(MX4)-X-II{M-I(18c6)}(4)]((TlX4)-X-III)(2) (M-I = Rb, Tl; M-II = Zn, Cu, Mn, Co; X = Cl, Br). The title compound repre sents a 'pure host' variant of the structure, free from the dianion (MX42-) -X-II, and thus containing large tetrahedral cavities: [{cavity}{NH4(18c6)} 2{NH3(18c6)}(2)](TlI4)(2). This suggests a 'double-shell' clathrate nature of these complexes, in which the first shell for the guest dianion (MX42-)- X-II is supplied by four tetrahedrally disposed crown ether molecules and t he second by a diamond-like array of TlX4-. The existence of the 'pure host ' structure itself offers the possibility of preparing genuine lattice clat hrates with tetrahedral molecules (anions) as the guests. (C) 1999 Elsevier Science S.A. All rights reserved.