The synthesis of
N,
N'-bis(phosphonomethyl)-1,10-diaza-18-crown-6 tetrahydrate (
6) fromthe corresponding diazacrown ether is described and the crystal structure of this diphosphonicacid determined. The crystals are triclinic,
P with
a = 8.1829(8),
b = 8.3092(10),
c =9.1429(10) Å,
= 85.286(9)
,
= 84.736(9)
,
= 73.158(7)
, and
Z = 1. The center of theazacrown ether ring coincides with the center of symmetry, requiring that the CH
2PO
3Hgroups lie trans to each other. One of the acid protons of each phosphonic acid group resideson the aza nitrogens, resulting in a zwitterion arrangement. There are four water moleculesper unit cell that participate in an extensive system of hydrogen bonding. An importantfeature of the H-bonding is that between adjacent phosphonic acid groups to form linearchains along the unit cell diagonal. Reaction of
6 with Zr(IV) in the presence of H
3PO
4 yieldszirconium phosphate-type layers cross-linked by the crown ether groups. The types of layersformed were deduced by a combination of
31P NMR and X-ray data. Affixing phosphonicacid groups onto the aza crown ether results in a more rectangular shape to the ring, whichis further distorted by the cross-linking of the layers.