Molecular hieroglyphics: 29Si COSY NMR spectroscopy reveals the fascinating and beautiful array of aqueous silicate anions that exist in dynamic equilibrium under alkaline conditions. Six of the most abundant oligomers are shown above, with each line representing a Si‐O‐Si siloxane linkage.

Addition of cis-1,2-dihydroxycyclopentane to aqueous alkaline silicate solutions results in the spontaneous formation of three organosilicate species, each with a 2:1 ligand to Si ratio and a pentacoordinated silicon centre. By using a mixture of both cis-1,2-dihydroxycyclopentane and 1,4-anhydroerythritol we show unambiguously that all three species are diastereomers of the monomeric bis(diolato)-hydroxo complex, [(L=)(2)SiOH](-)(where L represents the cis-diol ligand), thus clarifying the general assignment of (29)Si NMR spectra reported for silicate solutions containing furanoidic sugars with vicinal cis-diol functionality, such as ribose.

Molekulare Hieroglyphen: Durch 29Si‐COSY‐NMR‐Spektroskopie wurde die faszinierende Vielfalt von Silicationen aufgedeckt, wie sie unter basischen wässrigen Bedingungen im dynamischen Gleichgewicht vorliegt. Sechs der häufigsten Oligomere sind im Bild gezeigt, wobei jede Linie eine Si‐O‐Si‐Siloxanbrücke darstellt.

The effects of aliphatic sugar alcohols (e.g., threitol, xylitol, sorbitol) on the hydration of tricalcium silicate (C 3 S) and ordinary portland cement (OPC) were investigated and compared with those of sucrose, a well-established cement set retarder. Only sugar alcohols which contain threo diol functionality retarded the setting of C 3 S and OPC, their efficacy increasing with the number of threo hydroxy pairs and, to a smaller extent, with the overall population of hydroxy groups. None, however, were as effective as sucrose. The initial and final setting times increased exponentially with the concentration of saccharide, although the hydration of OPC was less inhibited than that of C 3 S. Saccharides function as ''delayed accelerators,'' that is, cement hydration is first inhibited and then proceeds faster than in saccharide-free cement. This behavior is consistent with the theory that the induction period is controlled by slow formation and/or poisoning of the stable calcium silicate hydrate (CSH) nuclei. The early inhibiting influence of saccharides on CSH precipitation is apparently stronger than on the growth of crystalline calcium hydroxide. Saccharides did not negatively affect the degree of hydration and compressive strength of fully set OPC paste; on the contrary, sorbitol yielded modest increases. L. Struble-contributing editorBased in part on the thesis submitted by L. Zhang for the M.Sc. degree in Environmental Engineering, Lakehead

Conspicuous absence: (29)SiNMR studies show that highly condensed, four-coordinate Si-containing anions are common in concentrated alkali-metal silicate solutions, but reveal no evidence for the existence of specialized zeolite building units. The results add to the mounting evidence that silicate polymerization simply proceeds through stepwise condensation of monosilicate tetrahedra.