Trimethylphosphine reacts with protons in acidic zeolites to form [(CH3)3P−H]+ complexes within the cavities and channels. The mobility of the protonated adduct strongly depends on the available space, which is a function of the amount of (CH3)3P in the zeolite and the size of the guest molecule relative to the cavity or channel dimensions. In an H-Y zeolite containing one molecule per large cavity, the motion is sufficiently rapid to average out a large P−H dipolar interaction, such that even in a static NMR experiment the lines due to J P - H coupling are well resolved. The motional rate is greater than 100 kHz. By contrast, the geometric constraints imposed by the smaller channels in ZSM-5, which are comparable in size to trimethylphosphine, severely restrict the motion. The chemical shift and J coupling values were determined for H-ZSM-5 and dealuminated H-Y zeolites, which are known to be strongly acidic, and for a normal H-Y zeolite, which is less acidic. The 31P chemical shift values were the same within experimental error, but a smaller J coupling in H-ZSM-5 is opposite from what one might expect on the basis of the extent of proton donation. The latter observation suggests that other factors, such as the radius of curvature of the cavities and channels, may play a role in acid−base interactions.

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The synthesis of N,N‘-bis(phosphonomethyl)-1,10-diaza-18-crown-6 tetrahydrate (6) from the corresponding diazacrown ether is described and the crystal structure of this diphosphonic acid determined. The crystals are triclinic, P1̄ with a = 8.1829(8), b = 8.3092(10), c = 9.1429(10) Å, α = 85.286(9)°, β = 84.736(9)°, γ = 73.158(7)°, and Z = 1. The center of the azacrown ether ring coincides with the center of symmetry, requiring that the CH2PO3H groups lie trans to each other. One of the acid protons of each phosphonic acid group resides on the aza nitrogens, resulting in a zwitterion arrangement. There are four water molecules per unit cell that participate in an extensive system of hydrogen bonding. An important feature of the H-bonding is that between adjacent phosphonic acid groups to form linear chains along the unit cell diagonal. Reaction of 6 with Zr(IV) in the presence of H3PO4 yields zirconium phosphate-type layers cross-linked by the crown ether groups. The types of layers formed were deduced by a combination of 31P NMR and X-ray data. Affixing phosphonic acid groups onto the aza crown ether results in a more rectangular shape to the ring, which is further distorted by the cross-linking of the layers.

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