Disordered sodium alkoxides from powder data: crystal structures of sodium ethoxide, propoxide, butoxide and pentoxide, and some of their solvates

Abstract

The crystal structures of sodium ethoxide (sodium ethanolate, NaOEt), sodium n-propoxide (sodium n-propanolate, NaO n Pr), sodium n-butoxide (sodium n-butanolate, NaO n Bu) and sodium n-pentoxide (sodium n-amylate, NaO n Am) were determined from powder X-ray diffraction data. NaOEt crystallizes in space group P 421 m, with Z = 2, and the other alkoxides crystallize in P4/nmm, with Z = 2. To resolve space-group ambiguities, a Bärnighausen tree was set up, and Rietveld refinements were performed with different models. In all structures, the Na and O atoms form a quadratic net, with the alkyl groups pointing outwards on both sides (anti-PbO type). The alkyl groups are disordered. The disorder becomes even more pronounced with increasing chain length. Recrystallization from the corresponding alcohols yielded four sodium alkoxide solvates: sodium ethoxide ethanol disolvate (NaOEt·2EtOH), sodium n-propoxide n-propanol disolvate (NaO n Pr·2 n PrOH), sodium isopropoxide isopropanol pentasolvate (NaO i Pr·5 i PrOH) and sodium tert-amylate tert-amyl alcohol monosolvate (NaO t Am· t AmOH, t Am = 2-methyl-2-butyl). Their crystal structures were determined by single-crystal X-ray diffraction. All these solvates form chain structures consisting of Na+, –O− and –OH groups, encased by alkyl groups. The hydrogen-bond networks diverge widely among the solvate structures. The hydrogen-bond topology of the i PrOH network in NaO i Pr·5 i PrOH shows branched hydrogen bonds and differs considerably from the networks in pure crystalline i PrOH.