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 (NEt 4) 6[Si 6O 15] · 40.8H 2O and NEt 4OH · 9H 2O

Abstract

A reinvestigation of the crystal structure of the tetraethylammonium silicate hydrate with the approximate chemical composition (C 8H 20N) 6[Si 6O 15] · 40.8H 2O ( 1) is reported. The crystal structure of tetraethylammonium hydroxide nonahydrate, (C 8H 20N)OH · 9H 2O ( 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(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 [Si 6O 15] 6− oligoanions are stabilized in a specific organic–water environment by O–H ⋯ O hydrogen bonds and electrostatic and van der Waals O ⋯ CH 3 and O ⋯ CH 2( N) anion–cation interactions. The NEt + 4 cations occur as conformers of approximate 4 ̄ 2m(D 2d) and 4 ̄ (S 4) molecular symmetry, depending on the location around the oligoanion. 2 is the first representative of a polyhedral clathrate hydrate of the NEt + 4 cation. The novel host structure is built from hydrogen-bonded water molecules and hydroxide ions.