Dipolar host guest interactions and geometrical confinement at the basis of the stability of one-dimensional ice in zeolite bikitaite

One-dimensional chains of hydrogen-bonded water molecules are hosted in the noncrossing channels of bikitaite (Li-2[Al2Si4O12]. 2H(2)O), a rare natura l lithium zeolite [C. S. Hurlbut, Jr, Am. Mineral. 42, 792 (1957); Stahl et al., Zeolites 9, 303 (1989)]. We use first-principles methods to study suc h a mineral with different (Si, Al) ordering in the zeolite framework. The one-dimensional polymer of nondiffusing water molecules, one chain per chan nel, is arranged in such a way as to develop a permanent polarization paral lel to the zeolite channel. We found that the one-dimensional and entropica lly unfavored water chain structure is stabilized by dipolar host/guest int eractions between the dipolar water chain and the (reversed sign) dipolar f ramework. A ditrigonal distortion of the hexagonal arrangement of tetrahedr a in the aluminosilicate bikitaite structure is probably at the origin of t he net polarization of the framework, and is induced by the small-sized Li cations. (C) 1999 American Institute of Physics. [S0021-9606(99)70825-1].