Structural study of tetramethylphosphonium-exchanged vermiculite

Vermiculite from Santa Olalla, Spain, was intercalated with tetramethylphos phonium [P(CH3)(4)(+) = TMP], using a TMP-bromide solution at 70 degrees C for three weeks. The resulting TMP-exchanged vermiculite, which contained a small (<5% of a site) amount of residual interlayer la, showed near perfec t three-dimensional slacking. Cell parameters are a = 5.3492(8) Angstrom, b = 9.266(2) Angstrom, c = 14.505(6) Angstrom, beta = 97.08(2)degrees, space group is C2/m, and polytype is IM. Single-crystal X-ray refinement (R = 0. 052, wR = 0.061) located two crystallographically unique sires for the phos phorus atoms (TMP molecule). The phosphorus atoms are occupied partially [P 1 = 0.146(6), P2 = 0.098(5)] and are offset from the central plans of the i nterlayer by 1.23 Angstrom to form two P-rich planes in the interlayer. Ele ctrostatic interactions between the P cations and basal oxygen atoms essent ially balance the negative charge associated with Al for Si substitutions i n the tetrahedral sites. In addition, the orientations of the TMP molecules are probably different owing to packing constraints. The H2O site is locat ed in the center of the interlayer, at the center of the silicate ring, and similar to 3.09 Angstrom from the Ca, which is also located on the central plane of the interlayer. Other H2O molecules are present in the interlayer , but could not be located by the diffraction experiment because they are r andomly positioned in the interlayer. The tetrahedral rotation angle, alpha , is affected by the intercalation of TMP relative to tetramethylammonium ( TMA), thus indicating that 2.1 layers are not simply rigid substrates, and that dynamic interactions occur during reactions involving adsorption and e xchange.