The tetraethylammonium cation in a double three-ring silicate heteronetwork clathrate and a polyhedral clathrate hydrate:: low-temperature single-crystal X-ray diffraction studies on (NEt4)6[Si6O15]•40.8H2O and NEt4OH•9H2O

A reinvestigation of the crystal structure of the tetraethylammonium silicate hydrate with the approximate chemical composition (C8H20N)(6)[Si6O15] . 40.8H(2)O (1) is reported. The crystal structure of tetraethylammonium hydroxide nonahydrate, (C8H20N)OH . 9H(2)O (2), has been determined for the first time. The structure of 1 has been refined to much higher precision in the centrosymmetric space group P (1) over bar (Z = 2) with a considerable degree of disorder, compared to a previous structure analysis in the non-centrosymmetric space group P1 without disorder (Sov. Phys. Crystallogr. 29 (1984) 421). 1 may be considered as a host-guest compound, in which trigonal-prismatic double three-ring silicate anions and water molecules form a complicated hydrogen-bonded host structure. The organic guest cations reside in straight channels and very irregular, not completely closed cages. The [Si6O15](6-) oligoanions are stabilized in a specific organic-water environment by O-H . . . O hydrogen bonds and electrostatic and van der Waals O . . . CH3 and O . . . CH2(N) anion-cation interactions. The NEt4+ cations occur as conformers of approximate (4) over bar 2m(D-2d) and (4) over bar (S-4) molecular symmetry, depending on the location around the oligoanion. Z is the first representative of a polyhedral clathrate hydrate of the NEt4+ cation. The novel host structure is built from hydrogen-bonded water molecules and hydroxide ions. (C) 2001 Elsevier Science B.V. All rights reserved.