Intercalation of Group(IV) Layered Phosphates

Abstract

The intercalation behavior of layered phosphates of tetravalent metals has been examined by the combined techniques of 31P n.m.r., i.r., thermal analysis and x.r.d. For a series of monoamine intercalates, the measured 31P chemical shifts correlate with the protonation state of the ≡P-OH groups and hydrogen bonding effects. The use of 31P n.m.r. to probe the intercalate structure, together with x.r.d., allowed amine orientations to be deduced for the phases formed during the batch titration of n-propyl- and n-butylamines and for a series of amine saturated intercalates. Linear polyamines were also studied in order to determine the effects that the disposition of functional groups in a molecule could have on intercalation. Differences in the ease of intercalation was observed between amines containing three methylene linkages between amino groups and those having only two methylene linkages. The importance of the match between the amino group separation and the =P-OH groups of the phosphate layers is noted for the first time. Orientations of the amine in the phases formed during the batch titrations are given, based on the 31P, 13C n.m.r. spectra, and basal spacing data. The presence of multiple functional groups in the intercalant leads to phases in which only half the interlayer space is occupied by amine. These materials should have substantial levels of porosity Formation of polyamine-metal complexes in the interlayer was difficult to achieve. The layered phosphates destabilize the metal complexes either by acting as better ligands or by the protonation of the amine ligands. Intercalates of 1,10-phenanthroline and 2,2’bipyridyl with α-zirconium phosphate and the γ-layered phosphates of zirconium and titanium have been prepared. These amines become diprotonated upon intercalation and are oriented lengthwise, parallel to the. phosphate layers, angled at 50-90° for 1,10-phenanthroline and <50° for 2,2’-bipyridyl. The coordination of these amines to iron(II) was followed in detail by 57Fe Mössbauer spectroscopy and x.r.d. Reaction of iron(II) with the intercalated phosphates produced a mixture of the tris amine complex as well as iron(II/III) coordinated to the phosphate layers. The increase in surface area was small. When polyoxochromium(III) species are intercalated into α-zirconium phosphate expanded phases are formed. The small increase in surface area indicates that the chromium species are tightly packed in the interlayers. The novel materials thus formed closely resemble chlorites, smectite clays that contain a continuous polyoxometal interlayer. When polyoxochromium(III) species are intercalated into the γ-layered phosphates of zirconium and titanium,similar products are obtained This thesis shows that 31P n.m.r. and x.r.d can be used to assign interlayer amine orientations and thus contribute to the understanding of intercalation into layered acid phosphates. The characterization of some iron(II) immine intercalates has added to present knowledge concerning interlayer complex formation. A series of novel intercalates with continuous polyoxochromium(III) interlayers has been synthesized. None of the materials have appreciable surface areas as measured by the N2 B.E.T. method. These results suggest that the high charge density of the layered phosphates investigated here is a major impediment to the formation of porous solids pillared by inorganic species.