SPECTROSCOPIC (IR,NMR) AND CONDUCTIMETRIC CHARACTERIZATION OF LITHIUMALUMINUM-HYDRIDE - CROWN-ETHERS COMPLEXES [LI-CE](ALH4)- WITH CE=SYN AND ANTI-ISOMERS OF DC 18-C-6 IN BENZENE SOLUTIONS()

[Li+-CE](AIH(4))(-) complexes with CE=syn and anti-isomers of DC 18-C- 6 have been characterized in benzene solutions by IR, NMR and conducti metry (at 298 K). The properties of these complexes are closely relate d to those of the cation [Li+-CE]. For the anti-isomer, no distorsion of the macrocycle was noticed after complexation, the Li+ trapped cati on is coordinated with four oxygen atoms of the cavity, and the comple x exhibits a covalent behavior. Electrical conductivity of the benzene solution is concentration independent and has a very low mean value ( Lambda = 0,06 Omega(-1).cm(2).mol(-1)). The macrocycle of the syn-isom er is drastically distorted after complexation. A tridimensional cavit y is formed, in which the Li+ trapped cation is coordinated with six o xygen atoms. As a consequence, the species exhibits a high degree of i onic character due to the stretching of the Li+---(AIH(4))(-) bond. El ectrical conductivity is enhanced for dilute solutions (x 10 at C = 0, 01 mol.L(-1)). The regular tetrahedral symmetry of (AIH(4))(-) anion i s retained in the molecular structure of the two complexes. Benzene so lutions of [Li+-syn-DC 18-C-6](AIH(4))(-) appear to be the first examp le of free-(AIH(4))(-) anions in a non-polar organic medium.