Treatment of a suspension of (P2O5)∞ in acetonitrile with excess DABCO leads to rapid formation of a precipitate consisting of a mixture of 3 and 4 (Figure ). Conducting this reaction at suitable dilution results in slow precipitation of crystalline solids and the ability to filter out any insoluble impurities. However, the resulting product was always found to be a mixture of 3 and 4. Extensive attempts to vary conditions or effect purification of the mixture resulted in limited impact on the ratio of the two products. However, careful selection of a crystal for X-ray diffraction provided structural analysis of 4 (Figure ), validating our initial assignment of this impurity. Both 3 and 4 can be viewed as two different neutral building blocks of (P2O5)∞ that have been cut out of the polymeric structure 22 by DABCO.