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

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 42(1) 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.