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Azacrown Ether Pillared Layered Zirconium Phosphonates and the Crystal Structure of N,N‘-Bis(phosphonomethyl)-1,10-diaza-18-crown-6

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journal contribution
posted on 25.08.2000, 00:00 by Abraham Clearfield, Damodara M. Poojary, Baolong Zhang, Baiyi Zhao, Agnes Derecskei-Kovacs
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.