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A Thallium Coated Dianion: Trigonal Bipyramidal [F 2 Al(OR) 3 ] 2— Coordinated to Three Tl + Cations in the Ion Pair [Tl 3 F 2 Al(OR) 3 ] + [Al(OR) 4 ] — [R = CH(CF 3 ) 2 ]
Author(s) -
Gonsior Marcin,
Krossing Ingo,
Mitzel Norbert
Publication year - 2002
Publication title -
zeitschrift für anorganische und allgemeine chemie
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.354
H-Index - 66
eISSN - 1521-3749
pISSN - 0044-2313
DOI - 10.1002/1521-3749(200208)628:8<1821::aid-zaac1821>3.0.co;2-3
Subject(s) - trigonal bipyramidal molecular geometry , chemistry , bipyramid , crystallography , stoichiometry , thallium , ion , pentagonal bipyramidal molecular geometry , crystal structure , ionic bonding , ionic radius , atom (system on chip) , inorganic chemistry , organic chemistry , computer science , embedded system
The reproducible synthesis of the unusual ionic aluminum compound [Tl 3 F 2 Al(OR) 3 ] + [Al(OR) 4 ] — ( 1 ) is reported. In the reaction of Li[Al(OR) 4 ] [R = C(H)(CF 3 ) 2 ] with TlF the initially desired Tl[Al(OR) 4 ] only formed with an exact 1:1 stoichiometry, while an excess of TlF led to [Tl 3 F 2 Al(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 [Tl 3 F 2 Al(OR) 3 ] + cation forms a trigonal bipyramid with a pentacoordinate aluminum atom. Three Tl + cations cover the [F 2 Al(OR) 3 ] 2— dianion core and the charge of the resulting [Tl 3 F 2 Al(OR) 3 ] + cation is compensated by a weakly coordinating [Al(OR) 4 ] — anion. Compound 2 contains a centrosymmetric [Al(OR) 3 (μ‐F)] 2 2— dianion core with pentacoordinate aluminum atoms building a distorted edge sharing double trigonal bipyramid. The [Al(OR) 3 (μ‐F)] 2 2— 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 [M 3 F 2 Al(OR) 3 ] + cation upon reaction of Li[Al(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 M[Al(OR) 4 ] with 2 MF giving [M 3 F 2 Al(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 [Cs 3 F 2 Al(OR) 3 ] + [Al(OR) 4 ] — by 95 kJ/mol. It is suggested that in the reaction leading to 1 initially Tl[Al(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 .