We report the hydrothermal synthesis of 10 µm × 100 µm × 10 µm single crystals of the microporous titanosilicate sodium-ETS-4. The crystallization of large needle-shaped Na-ETS-4 crystals is preceded by the formation and subsequent dissolution of the titanosilicate GTS-1. Large Na-ETS-4 crystals are obtained with purity higher than 97%. The structures of Na-ETS-4 and its Sr ion-exchanged form are solved from single-crystal X-ray diffraction data. It is suggested from the structure solution and further supported by the results of the empirical bond valence model that the bridging unit of ETS-4 contains five-coordinate titanium(IV). Infrared spectroscopy is also used to support the crystallographic results, with regard to the presence of charge-balancing protons and five-coordinate titanium. ETS-4 is, thus, one of only two synthetic titanosilicate materials containing five-coordinate titanium. We also discuss some structural differences between ETS-4 and its natural analogue, zorite.

The new cyclic phosphine O 2 S[(t-Bu)MeC 6 H 2 O] 2 PPh (1) was used to prepare the new cyclic tetraoxyphosphoranes O 2 S[(t-Bu)MeC 6 H 2 O] 2 PPh(O 2 C 6 Cl 4 ) (2) and O 2 S[(t-Bu)MeC 6 H 2 O] 2 PPh(O 2 C 6 H 4 ) (3) by oxidative addition reactions. In similar reactions, the new cyclic pentaoxyphosphoranes O 2 S[(t-Bu)MeC 6 H 2 O] 2 P(OCH 2 CCl 3 ) 3 (4), O 2 S-[Me 2 C 6 H 2 O] 2 P(OPh) 3 (5), and O 2 S[(t-Bu)MeC 6 H 2 O] 2 P(OC 6 F 5 ) 3 ( 6) were formed from acyclic phosphites and the appropriate diol. Yields ranged from 51% to 66%. X-ray studies revealed hexacoordinated representations for 2 and 6 while 3-5 are pentacoordinate in trigonal bipyramidal geometries. For 3 and 4, the eight-membered rings are positioned diequatorially in anti chair conformations, whereas for 5, this ring occupies axial-equatorial sites in a syn twist-boat form. Tetraoxyphosphorane 3 is unique in locating the least electronegative ligand, the phenyl group, in an axial position. Oxygen donor action from the sulfone SO 2 group led to a displacement from a square pyramid to an octahedron to the extent of 82.2% for the highly fluorinated member 6 in comparison with 27.9% for the tetrachlorocatecholate derivative 2. These two pentaoxyphosphoranes provide the longest and shortest P-O distance thus far from a sulfone donor group, 2.646 (5) Å for 2 and 1.936 (7) Å for 6. In comparison with oxyphosphoranes having bridging sulfur atoms in the eight-membered ring, it is apparent that sulfur atom coordination is greater than oxygen atom coordination from the sulfone group as measured by the tendencies toward hexacoordination. 31 P and 1 H NMR data indicate the presence of two isomeric forms for each of the phosphoranes 2-4. Structural comparisons are made with related cyclic phosphoranes containing sulfur atoms and sulfone groups relative to steric and electronic factors that influence the formation of hexacoordination.

The synthesis of a series of cyclic pentaoxyphosphoranes containing a sulfonyl group was carried out by the reaction of either P(OCH2CF3)3 or P(OPh)3 with the appropriate diol in an oxidative addition reaction:  O2S[(t-Bu)MeC6H2O]2P(OCH2CF3)3 (1), O2S[(t-Bu)MeC6H2O]2P(OPh)3 (2), O2S[(t-Bu)2C6H2O]2P(OCH2CF3)3 (4), and O2S[(t-Bu)2C6H2O]2P(OPh)3 (5). Reaction of 2 with catechol yielded O2S[(t-Bu)MeC6H2O]2P(OPh)(C6H4O2) (3). X-ray studies provided the structures of 1−5, although 4 was badly disordered. The geometries of 2, 3, and 5 are octahedral due to P−O coordination provided by the sulfonyl group, whereas 1 and 4 are trigonal bipyramidal. Solution 31P, 1H, and 19F NMR spectra demonstrate that 1 and 4 exist in isomeric modifications. These are formulated as a pentacoordinate structure, as in the solid state, and a hexacoordinate structure. This represents the first study establishing intramolecular intraconversion between penta- and hexacoordinate isomers of phosphorus. An activation free energy of 17 kcal/mol for the exchange process for 1 and 4 was obtained from variable temperature 1H NMR spectra.

A new class of silatranes N[CH 2 (Me 2 C 6 H 2 )O] 3 SiR was prepared by the reaction of organosilanes with tris(2-hydroxy-4,6-dimethylbenzyl) amine (5) in the case of 1, 3, and 4, and by the reaction of Si(OMe) 4 with the same amine (5) to give 2. This is the first series of silatranes containing all six-membered rings. Their structures were established by X-ray analysis and correlated with 29 Si NMR data. VT 1 H NMR spectra reflected fluxional behavior for the chiral molecules 1-3, whereas 4 was a rigid molecule. The activation energies for enantiomeric conversion of the clockwise and anticlockwise orientations of the propeller-like silatranes 1-3 were statistically the same at about 10 kcal/mol. A simultaneous pseudorotation of all three six-membered rings is suggested to cause the racemization process. The Si-N distances for 1-4 show a large dependence on the exocyclic substituent. Over an approximate electronegativity range of 2.3-3.0, the Si-N distance varies from 2.745(4) Å for 1 to 2.025(4) Å for 4. Thus, the influence of substituent effects on nitrogen-silicon donor-acceptor interactions can be readily studied in the absence of constraints imposed by the use of the smaller ring-containing silatranes.

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