%0 Journal Article %A Tacke, Reinhold %A Heermann, Joachim %A Pülm, Melanie %A Richter, Ingo %D 1998 %T (Ammoniomethyl)bis[salicylato(2−)-O1,O2]silicates:  Zwitterionic Spirocyclic λ5Si-Silicates with Two Six-Membered SiO2C3 Ring Systems %U https://acs.figshare.com/articles/journal_contribution/_Ammoniomethyl_bis_salicylato_2_-_i_O_i_sup_1_sup_i_O_i_sup_2_sup_silicates_Zwitterionic_Spirocyclic_sup_5_sup_i_Si_i_-Silicates_with_Two_Six-Membered_SiO_sub_2_sub_C_sub_3_sub_Ring_Systems/3781467 %R 10.1021/om9709852.s001 %2 https://ndownloader.figshare.com/files/5892432 %K zwitterionic spirocyclic λ 5 Si %K enantiomer %K MAS %K acetonitrile %K carboxylate oxygen atoms %K configuration %K 29 Si NMR studies %K trimethoxy %K CH %K CN %K O 2 %K silicate %K Si O 4 C skeleton %K racemate %K crystal %K silicon %K SiO %X The zwitterionic spirocyclic λ5Si-silicate (morpholiniomethyl)bis[salicylato(2−)-O1,O2]silicate (5) was synthesized by reaction of trimethoxy(morpholinomethyl)silane and dimethoxy(morpholinomethyl)phenylsilane, respectively, with salicylic acid (molar ratio 1:2) in acetonitrile at room temperature. Bis[salicylato(2−)-O1,O2][(2,2,6,6-tetramethylpiperidinio)methyl]silicate (6) was obtained analogously, starting from trimethoxy[(2,2,6,6-tetramethylpiperidino)methyl]silane. Compound 5 was isolated as a crystalline product consisting of enantiomorphic crystals, each containing exclusively zwitterions with the same absolute configuration. Crystallization of this product from acetonitrile yielded the crystalline solvate 5·CH3CN (crystals containing a 1:1 mixture of enantiomers with opposite absolute configuration). Compounds 5 (Δ-enantiomer), 5·CH3CN (racemate), and 6 (racemate) were structurally characterized by single-crystal X-ray diffraction. The spirocyclic frameworks of 5 and 6 are built up by two six-membered SiO2C3 ring systems. The zwitterions in the crystal of 5, 5·CH3CN, and 6 contain a pentacoordinate (formally negatively charged) silicon atom (SiO4C skeleton) and a tetracoordinate (formally positively charged) nitrogen atom. The coordination polyhedra around the silicon atoms are distorted trigonal bipyramids, the axial positions being occupied by the carboxylate oxygen atoms. Solid-state MAS NMR studies revealed the following isotropic 29Si chemical shifts:  δ −120.6 (5), −123.1 (5·CH3CN), −120.4 (6). The zwitterion 6 exists also in solution (CDCl3; 1H, 13C, and 29Si NMR studies). %I ACS Publications