Crown compounds for anions. Spectroscopic and theoretical studies of complexation of borohydride anions with cyclic trimeric perfluoro-o-phenylenemercury

Abstract It has been shown by IR and NMR spectroscopy that cyclic trimeric perfluoro- o -phenylenemercury ( o -C 6 F 4 Hg) 3 ( 1 ) is capable of binding borohydride anions in THF and 1,2-dichloroethane solutions to form complexes {[( o -C 6 F 4 Hg) 3 ](BH 4 ) 2 } 2− ( 2 ) and {[( o -C 6 F 4 Hg) 3 ] 2 (BH 4 )} − ( 3 ). According to the IR data, complex 2 contains both terminal and coordinated B–H bonds while all four B–H bonds of the BH 4 − ion are coordinated with the mercury atoms in complex 3 . The use of NMR spectroscopy provided the identification of one more complex of 1 with BH 4 − , which can be formulated as {[( o -C 6 F 4 Hg) 3 ](BH 4 )} − ( 4 ). The stability constants of complexes 2 and 3 have been determined by IR spectroscopy. Quantum-chemical calculations of 2 – 4 by the AM1 method suggest that the complexes have the unusual bipyramidal, sandwich and half-sandwich structures, respectively. In contrast to 1 , the interaction of (C 6 F 5 ) 2 Hg with BH 4 − anions in THF gives a single complex {[(C 6 F 5 ) 2 Hg](BH 4 )} − ( 5 ) independently of the reagent ratio. This complex is much less stable than 2 and 3 .