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Gallophosphonates Containing Alkali Metal Ions. 2. Synthesis and Structure of Gallophosphonates Incorporating Na+ and K+ Ions

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journal contribution
posted on 08.01.1998, 00:00 by Mrinalini G. Walawalkar, Ramaswamy Murugavel, Herbert W. Roesky, Isabel Usón, Ralph Kraetzner
The reactions between t-BuP(O)(OH)2 and equimolar quantities of MGaMe4 (M = Na, K) yield ionic and alkali metal containing molecular gallophosphonates [Na42-OH2)2(THF)2][(Me2GaO3PBu-t)2]2·2THF (2) and [K(THF)6][K5(THF)2{(Me2GaO3PBu-t)2}3] (3), respectively. Compounds 2 and 3 are soluble in common organic solvents and have been characterized by means of analytical and spectroscopic techniques, as well as by single-crystal X-ray diffraction studies. These compounds represent the rare examples of molecular ionic phosphonate cages which contain coordinated Na+ or K+ ions. Compound 2 is constructed from two eight-membered Ga2O4P2 gallium phosphonate rings which sandwich a central Na4(H2O)2 unit. In the case of 3, three eight-membered Ga2O4P2 gallium phosphonate units envelope an aggregated K5 core which exists in the form of a trigonal-bipyramidal polyhedron. The Na+ and K+ ions in 2 and 3 are also coordinated by the endocyclic oxygen atoms of the eight-membered gallophosphonate crowns, apart from the regular exocyclic P−O coordination. Unlike the lithium gallophosphonate [Li4(THF)4][{(MeGaO3PBu-t)33-O2)}2] (1), compounds 2 and 3 do not undergo any clean cage conversion reaction in the presence of 15-crown-5 and 18-crown-6, respectively.