SYNTHESIS AND MOLECULAR STRUCTURE OF HYDROGEN-BONDED CYCLIC ANIONIC SILICATES ISOELECTRONIC WITH PHOSPHORANES. STRUCTURAL PRINCIPLES OF FIVE-COORDINATED SILICON

Abstract

Abstract The new five-coordinated silicon compounds, pyridinium bis(2,3-naphthalenediolato)phenylsilicate(IV), [(C10H6O2)2SiPh][C5H6N], 11, pyridinium bis(1,2-benzenediolato)-1-naphthylsilicate(IV), [(C6H4O2)2SiC10H7][C5H6N], 12, and pyridinium bis(1,2-benzenediolato)(2- and 4-chlorophenyl)silicate(IV) (2-Cl, 0.85; 5-Cl, 0.15), [(C6H4O2)2SiC6H4Cl][C5H6N], 13, were synthesized and their X-ray structures determined. The structure of 11 is nearly an ideal rectangular pyramid (RP) and 12 is displaced about halfway between the RP and trigonal bipyramid (TBP), while 13 is closer to a TBP. A quantitative assessment of these and related pentacoordinated cyclic anionic silicate structures reveals a continuous change in ring Si[sbnd]O bond lengths that vary from 1.78 (axial) and 1.68 A (equatorial) for the idealized TBP to 1.73 A (basal) for the RP. The results for these compounds, all of which follow the Berry pseudorotational coordinate, suggest a structural nonrigidity at least as great as found for phosphoranes...