On isoelectronic fluorides [H3tren]•(AlF6)•H2O, [H3tren]•(AlF6)•HF, [H4tren]•(AlF6)•(F) and the iron analogue [H4tren]•(FeF6)•(F)

[H(3)tren]center dot(AlF6)center dot H2O4 [H(3)tren]center dot(AlF6)center dot HF and [H(4)tren]center dot(MF6)center dot(F) (M = Al, Fe), are obtained by hydrothermal technique and microwave heating in the (Al(OH)(3),FeF3)-tren-(HF/H2O)-ethanol system. Structure determinations are performed from single crystal X-ray diffraction data. All phases are built up from (MF6)(3-) anions linked by hydrogen bonds to [H(3)tren](3+) or [H(4)tren](4+) cations and to water or HF molecules or "isolated" fluoride anions. [H(3)tren](3+) and [H(4)tren](4+) cations adopt a "spider" shape configuration. Surprisingly, the HF molecule is strongly hydrogen bonded with one fluoride ion of the AlF6 octahedron (d(F center dot center dot center dot F) = 2.38 angstrom) in [H(3)tren]center dot(AlF6)center dot HF while "isolated" fluoride ion is weakly coordinated by three hydrogen atoms in [H4tren]-(MF6)-(F). The evolution of the formulations, from (center dot)[H(3)tren]center dot(AlF6)center dot H2O to [H(3)tren]center dot(AlF6)center dot HF and to [H(4)tren]center dot(MF6)center dot(F) (M = Al, Fe), is linked with the increase of the HF content of the starting solution. The volumes per formula unit decrease from 321.3(1) angstrom(3) and 320.6(1) angstrom(3) in [H(3)tren]center dot(AlF6)center dot H2O and [H(3)tren]center dot(AlF6)center dot HF, respectively, to 298.5(4) angstrom(3) in [H(4)tren]center dot(AlF6)center dot(F). (C) 2006 Elsevier SAS. All rights reserved.