| Abstract: | The reproducible synthesis of the unusual ionic aluminum compound Tl3F2Al(OR)3]+Al(OR)4]— ( 1 ) is reported. In the reaction of LiAl(OR)4] R = C(H)(CF3)2] with TlF the initially desired TlAl(OR)4] only formed with an exact 1:1 stoichiometry, while an excess of TlF led to Tl3F2Al(OR)3]+Al(OR)4]— ( 1 ). Additionally the x‐ray single crystal structure of the byproduct (R‐OH)TlAl(OR)3(μ‐F)]2 ( 2 ) was determined. Compounds 1 and 2 were characterized by X‐ray single crystal structure determinations and 1 also by NMR spectroscopy and an elemental analysis. In 1 the Tl3F2Al(OR)3]+ cation forms a trigonal bipyramid with a pentacoordinate aluminum atom. Three Tl+ cations cover the F2Al(OR)3]2— dianion core and the charge of the resulting Tl3F2Al(OR)3]+ cation is compensated by a weakly coordinating Al(OR)4]— anion. Compound 2 contains a centrosymmetric Al(OR)3(μ‐F)]22— dianion core with pentacoordinate aluminum atoms building a distorted edge sharing double trigonal bipyramid. The Al(OR)3(μ‐F)]22— dianion coordinates two Tl(R‐OH)]+ cations giving the non charged molecular (R‐OH)TlAl(OR)3(μ‐F)]2 ( 2 ). Based on BP86/SVP (DFT‐) and lattice enthalpy calculations a pathway of the reaction was proposed to rationalize the formation of the M3F2Al(OR)3]+ cation upon reaction of LiAl(OR)4] with MF for M = Tl but not for M = Cs (cf. Cs+ and Tl+ have very similar ionic radii). Using a suitable BorñHaber cycle and in agreement with the experiment, the enthalpies of the reaction of 2 MAl(OR)4] with 2 MF giving M3F2Al(OR)3]+Al(OR)4]— and MOR were shown to be favorable for M = Tl by 127 kJ/mol but endothermic for the formation of the hypothetical Cs3F2Al(OR)3]+Al(OR)4]— by 95 kJ/mol. It is suggested that in the reaction leading to 1 initially TlAl(OR)4] is formed, followed by an abstraction of TlOR and Al(OR)3. The latter very strong Lewis acid reacts subsequently with an excess of TlF yielding 1 . |
