Anna Ciborska

A study of chirality in bis(1,2-dimethoxyethane-κ2O,O′)sodium bis(tri-tert-butoxysilanethiolato-κ2O,S)sodate

This work presents an analysis of self-assembly of a complex molecule from simpler ions, some of which are asymmetric, and is an example of a sodium silanethiolate. The tri-tert-butoxysilanethiolate anion has two helical conformers (P and M), so aggregation of silanethiolates can proceed with recognition of chirality. Alkali metal silanethiolates can form cyclic solvated oligomers (e.g. dimers) or complexes such as sodates with anions of general formula R2Na(-). We note that all known sodates (and lithiates) contain both ligands of the same helicity in the anion, whereas in the dimers the metal atoms are coordinated by silanethiolate ligands of different helicity. The title compound, a new example of a sodate, [Na(C4H10O2)2][Na(C12H27O3SSi)2] or [Na{((t)BuO)3SiS}2][Na(DME)2] (DME is 1,2-dimethoxyethane), is built up of separate ion pairs with no significant interactions. The anion is formed from an Na atom O,S-chelated by two silanethiolate ligands of the same helicity (both P or both M), while the cation contains an Na atom solvated by two DME molecules. Because the structure is centrosymmetric, equal numbers of both conformational enantiomers are present in the crystal lattice.

Variable-temperature X-ray diffraction study of structural parameters of NH---S hydrogen bonds in triethylammonium and pyridinium silanethiolates

Two hydrogen-bonded, well defined compounds were synthesized from tris(2,6-diisopropyl)phenoxysilanethiol (TDST) and triethylamine (TDST-TEA) or pyridine (TDST-py). The crystalline compounds were characterized in the solid state by variable-temperature X-ray diffraction measurements and ATR FT-IR spectroscopy. The toluene solutions of TDST-TEA and TDST-py were studied by NMR spectroscopy. The total hydrogen-bond energies and FT-IR spectra were calculated with the use of BLYP-D/TZP and B3LYP/6-31G(d,p)/GD3BJ methods. Thermochemical parameters and potential energy scans were calculated at the B3LYP/6-31G(d,p)/GD3BJ level. All results point to the higher energy of bonding in TDST-TEA both in the solid state and in solution. At the same time the potential energy scan reveals a very broad double-well hydrogen bond in TDST-py, indicating good stabilization of the system for a wide range of D-H...A distances.