Protonation and olation of 2,2'-bipyridyl and 1,lO-phenanthroline in y-titanium phosphate dihydrate? Carla Ferragina,a M. Antonietta Massucci' and Anthony A. G. Tomlinson' aI.M.A.I., Rome Research Area, C.N.R., P.O. Box 10, Monterotondo Staz., 00016 Rome, Italy bUniversita di Roma 'La Sapienza', P.le A. Moro 5, 00185 Rome, Italy 'Istituto di Chimica dei Materiali, Rome Research Area, C.N.R., P.O. Box 10, Monterotondo Staz., 00016 Rome, Italy 2,2'-bipyridyl (bpy) and 1,lO-phenanthroline (phen) intercalate topotactically into Ti( H2P04)( P04).2H,0 (y-titanium phosphate, y-Tip), the aromatic rings undergoing hydration owing to the strongly acidic character of the >P(OH), groups. For protonated phen, a 'slotted' assembly in the interlayer phosphate surface is given, via NH+ HO-P hydrogen bonding (from indirect spectroscopic results and TG/DSC).Instead, protonated bpy adopts a slanted orientation within the layers, as does 2,9-dimethyl- 1,lO-phenanthroline (dmphen) which remains unprotonated. These differing assemblies lead to differing accessibilities of intercalated amine to metal ion (dmphen >bpy >phen) as confirmed by Cu2+ uptake diffusion rates. Cation exchange of Co2+, + +Ni2 and Cu2 -exchanged composites do not give coordination pillaring, even after dehydration of the materials. Ag + exchanges with Ti( H2P04)( PO4)( phen),.,,.2.5H20 and Ti( H2P04)( P04)(dmphen)o~,, .2.2H20 to give highly expanded composites (dOo2=20-21.3 A). The former has high thermal stability, decomposing only at >450 "C,and may be considered a pillared + + +material.Low Ag -loaded forms give time-dependent staging, ascribed to intralayer Ag diffusion. Ag -phen.y-TiP materials show enhanced selectivities for Cu2+ (Cu2+ >>Ni2+ =Co2+) from binary, ternary and quaternary mixtures and the anhydrous Ni' -exchanged material has a square-planar coordination. Intralayer coordination models are suggested. + The chemistry and applications of metal ion complex moieties supported in/on restricted media interfaces is now well devel- oped' and, as interfacial arrays and geometries are clarified via modern techniques,' there is renewed interest in the supra- molecular chemistry of composite^.^ For zeolites and clays, metal ion surface (or interface) complexes thus supported are of most intere~t.~ However, in situ complex construction in a layered material can also provide a host of 'engineered' small-pore metal-complex pillared materials, promising for applications in fields ranging from optoelectronics5 to pseudo- metalloenzyme catalysk6 We recently found that the well characterised ion-exchanger y-zirconium phosphate gives com- posites different from those of the aform, although details of interface assemblies could not be rationalised in the absence of a structure determinati~n.~ A Rietveld X-ray powder diffrac- tion (XRPD) structure of the y-titanium analogue has since shown that it is best formulated as Ti(H,P04)(P0,)~2H,0, a structure in which a highly acidic, hydrophilic -P(OH), channel alternates with a hydrophobic >P=O channel.' We now report composites formed by the same ligands as before in this matri~,~ with the objective of probing how the surface influences subsequent metal-complex formation and induction of micropores, and site-selectivity.Experimenta1 Materials CrystaJline Ti( H2P04)( P04).2H,0 (basal spacing dm2 = 11.62 A; referred to as y-TiP for convenience) was prepared by treating dried, amorphous titanium phosphate (obtained from reaction between TiC14 dissolved in 2mol dmP3 HC1 and 2mol dm-3 phosphoric acid at room temperature) with 10 mol dm-3 H3P04 under hydrothermal conditions at 300 "C for 48 h. The diamines and metal ion salts were commercial products (Aldrich) and were used as received.t Part 6 of a series entitled 'Pillar Chemistry'. For Part 5, see ref. 7. Intercalation of diamines y-TiP was first pre-swelled with EtOH by agitation of a mixture of y-TiP (1 g) in anhydrous EtOH (100 ml) for 24 h, and centrifugating the suspension at <2000 rpm (to avoid layer collapse). The product was contacted whilst still wet with 100 ml of a 0.01 mol dm-, H,O-EtOH solution of the amine at 40-45 "C (preliminary experiments using 0.1 mol dm -3 concentration solutions gave the same, but less crystalline, solids). After varying contact times, the solids were filtered off and air dried. Table 1 lists stoichiometries, preparation con- ditions and interlayer distances (average of the do,, reflections, which usually go to 1= 3). Phen (but not bpy and dmphen) was subsequently found to intercalate into y-TiP (again at 45°C) without the need for pre-swelling, to give the same final product.Metal ion exchange Batch methods were used, as before." In a typical preparation, a solution of 5mmol dmW3 metal acetate (Co, Ni, Cu) or 10 mmol dm-, AgN03 was agitated with 1mmol of diamine- intercalated material, such that [Amine]:[M"+] =1, where the overbar signifies 'intercalated' ([Amine]: [M"' ]=2 were also investigated for the Ag +-containing suspensions) at 45 "C for 10 days. After filtration, the supernatant was analysed [atomic absorption (AA) spectrophotometry] and the solid dried in air. Ion selectivity experiments were carried out using y-TiPH1.,' [Ago,,,( phen)o.44]*2.5H20 and binary, ternary and quaternary mixtures of transition-metal ions (Co, Ni, Cu, Pd).In a typical experiment, 1 mmol of the Ag-phen derivative was suspended with stirring in 50 ml of water containing 1 mmol in each component (acetate salt) at 45°C for 7 days. The resulting solids were filtered off, air dried and analysed. Analyses and physical methods Chemical analyses [C, H, N; AA spectrophotometry, thermo- gravimetry-differential thermal analysis (TGA-DTA)] and physical measurements [X-ray powder diffraction (XRPD), optical spectra, EPR] were carried out as described pre- J. Muter. Chem., 1996, 6(4), 645-651 645 Table 1 Stoichiometries, preparation conditions and interlayer distances material' contact time/days T/"C d002IA do02 '/A y-TiP(bpy), 43 04H20 15 9 y-TiP(phen), 44 2 5H20 15 8 y-TiP(dmphen), 23 2 2H20 15 9 Stoichiometries deduced from TG and C, H, N analyses Ag+-exchanged viously lo Uptakes in ion-selectivity experiments were followed by UV-VIS spectral methods Several resulting solids were also analysed uza atomic absorption spectroscopy, the two methods gave identical results (within experimental error) Results and Discussion All three amine-intercalated materials give XRPD patterns as expected for grossly topotactic amine diffusion (simple layer expansion) and the limiting products have stoichiometries similar to those in the zirconium analogue' Dmphen is the exception, giving only a single phase-pure product containing ca 1 dmphen per 4 basal units (y-zirconium phosphate, y-ZrP, also gives a single phase, although it contains ca 1 dmphen ligand per 3 basal units7) In addition, the interlayer expansions in y-TiP(phen), 44 2 5H,O and the y-ZrP analogue are similar (6 4 A), although the former differs from the latter in being obtainable from unswelled starting material and also shows high crystallinity even at 400 "C (alFeit with a marked decrease in the interlayer distance, to 14 85 A) Both results suggest that the amines are assembled differently in the two materials Inspection of the y-TiP structure' shows that the distance betyeen the OH groups of adjacent >P(OH), groups is ca 3 5 A The lower icpic radius of Ti4+ (068 A) with respect to that of Zr4+ (0 90 A) suggests that in the former the >P(OH), groups are more laterally flexible than in the latter (as also indicated by the thermal amplitudes'), allowing an interlayer assembly for phen in which one aromatic benzene ring is slotted into the layers via strong hydrogen bonding with an adjacent >P(OH)2 group The IR spectrum does indeed show evidence for the presence of both protonated phen and specifi- cally bound water molecules A band at 3537cm-1 with a shoulder at 3487 cm-' are assignable to vsym and vaSym modes of lattice H20 and they virtually disappear on dehydration to be replaced by a single band at 3350cm-', ascribable to v(NH+) modes [Fig l(b)] There is also significant splitting of the broad v3(P02-)band on intercalation, further evidence for specific interaction of phen with Po43-groups More interesting is the appearance of bands at 1240 and 1474 cm-I which are due neither to matrix nor to phen modes, they can be assigned to the 0-H and C-H vibrations of a C(H)(OH) group," suggesting that a covalent hydration has occurred in one aromatic ring The UV spectra of bpy- and phen-loaded materials provide further support for both diprotonation and olation, since UV spectra are very sensitive to ring modifi- cation12 Thus, apart from the expected shifts of the phen bands to 224 and 277 nm and the appearance of low-energy shoulders characteristic of [H,phen12+ ,I2 there is also a large low-energy shift of the characteristic [H,phen12+ shoulder (which lies at 318nm in [H2phenI2') to 357nm which is ascribable to loss of aromatic character in a ring [see Fig 2(b)] Turping to y-Tip( bpy), 43 0 4H@, the interlayer distance (14 5 A) is similar to that in the y-zirconium analogue, suggest- ing that a slanted interlayer orientation is given (The layer 'thickness' in ?-Tip, which includes the bimetal-phosphate layer, is cu 903 A, which leaves a van der Waals distance of Ad,,, =5 2 A for the bpy composite ) Again, UV spectral evidence suggests that bpy is also present in the diprotonated 646 J Muter Chem, 1996,6(4), 645-651 25 14 45 1447 (0 18) 43 25 18 00 20 50 (044) 43 25 17 40 21 30 (0 23) 43 Mole ratio in parentheses vlcm ' Fig. 1 FTIR spectra of (a) y-TiP(bpy), 43 0 4H20, (b) y-TiP(phen),,, 2 5H2O -, As-prepared, ---, after dehydration at 120°C for 2 h A/nm Fig.2 UV-VIS spectra TiP(phen), 44 2 5H20 -, 120°C for 2 h of (a) y-TiP(bpy), 43 04H,O, (6) y-As-prepared, --, after dehydration at form [H2bipy12+.Intense bands characteristic of [H2bipy12+ are observed at 220 and 285 nm, with a further band at 315 nm and a much less intense band at 390nm, and an indistinct plateau between 450 and 600 nm [see Fig. 2(u)]. Bands at 1240 and 1474 cm-' are again present in the IR spectra. We conclude that bpy also undergoes ring hydration, and Scheme 1rational-ises the results for both materials. Details from the TG-DTA results also support the sugges-tion that olation occurs on intercalation, and they are particu-larly clear for bpy-loaded materials.Gross thermal losses are analogous to those in a-and y-ZrP: zeolitic water is lost between 25 and 250"C, and organics loss overlaps with final water loss due to phosphate-to-pyrophosphatecondensation. Final, small losses at 600-1 100"Care probably due to carbon-isation of remaining organic residues, and the sharp exotherm at 810°C is due to a phase change to cubic TiP207 (as confirmed by XRD).I3 Turning to the mid-temperature range, between 300 and 450 "C,y-Tip(bpy),~,,-0.4H20 (but not phen and dmphen) gives two exothermic peaks [see Fig. 3(a)] and the corresponding mass losses are in very close agreement with scission of bpy, the C(H)(OH) product being lost first (Scheme 2). This result is not surprising if proton-assisted scission of the H,2+bpyC(H)(OH) by close-lying hydrogen bonds is involved.Analogous scission of bpy after coordination to acidic groups has been reported for alumina surfaces.14 Conversely, y-Tip(phen),.,,.2.5H20 loses zeolitic water in a series of steps up to 200"C, (some water being lost only at ca. 330 "C, as expected for specific hydrogen-bonded H20). $!--40-v) IIIIllllII TIT Fig. 3 TG (-) and DTA (---) curves of (a) y-TiP(bpy)043-0.4Hz0; (b)y-TiP(phen), ,,-2.5H20 Scheme 1 Slotted assembly of modified phen in y-TiP (a) and orientation of (Hzbpy)'+ (b) J. Muter. Chern., 1996, 6(4), 645-651 647 weak H bonding I OH I H+ OH /[\ / Scheme 2 Decomposition pathway of bpy in y-TiP Anomalies in the acid-base characteristics of bpy and phen have long been known,15 and their presence in y-TiP under- lines the strongly acidic nature of the =P(OH), groups The formulations agree with the low water content in Ti(H2P04)( PO,)( bpy), 43 0 4H20, the lengthwise orientation means virtually all =P(OH), sites are occupied, leaving only hydrophobic PO, channels y-TiP(dmphen), 23 2 2H20 shows no spectroscopic or TG evidence for other than a vertically slanted onentation, as expected because p-aromatic sites are occupied by Me groups Dmphen assembly seems to be controlled by the steric hindrance of Me groups Metal-ion uptake Differing amine assemblies and the presence of an extra intralayer coordinating moiety [the C(H)(OH) group] in y-TiP(phen), ,, 2 5H20 are expected to lead to large changes in cation-exchange behaviour Cu2+ uptake shows that exchange is fastest in yTiP(dmphen), 23 2 2H20 (though somewhat slower than in the y-ZrP analogue, shown in Fig 4 for compari- son) as expected, naively, for a higher intercalant interlayer density in the former Dmphen is also the only ligand giving rise to a solid with final [Cu] [L] = 1, yTiP(phen), ,, 2 5H20 gives a final material with [Cu] [L] <O 4, even after 12 days of exchange (see Fig 4) Closer inspection of Fig 4 shows that (I) Cu2+ uptake rates for bpy and phen are inverted between y-TiP and y-ZrP matrices, and (11) the uptake rates follow different laws l6 Initial stage for intercalation is as expected (eg as in the well investigated dichal~ogenides'~) We suggest that the inversion is due to the inaccessibility of strongly hydrogen-bonded P-OH groups in slotted phen, whereas the (al (b)...dmphen 08 differing slopes are due to changes in pore accessibility brought about by amine orientation Cavity vs. pillaring in metal-ion exchanged phases It is of interest to monitor whether metal-exchanged materials are pillared (or become so on dehydration) and, if so, how this influences microporosity For Co2+-, Ni2+- and Cu2+-exchanged matenals, dOo2remains constant after exchange (so coordination to ligand and/or layer must be inferred from spectroscopic data, as before") For all three metal ions, the only clear evidence for N-coordination is obtained for y-TiCu, 23(dmphen), 23 2 2H20, where d-d bands at 725 and 1025 nm follow diagnostics for N-coordination [The band at 450nm with a shoulder at 525nm in y-TiCu, 23(dmphen), 23 2 2H20 is attributable to Cu+-N metal- to-ligand charge-transfer transitions 18] We recall that tetra- gonal 0-coordinated Cu2+ is expected to give rise to relatively low-energy d-d bands (in a-ZrP itself, the d-d bands are at ca 13000 cm-') l9 Time effects are also evident in the Cu2+- exchanged dmphen composite After 4 h contact, the material is green and slowly changes (24 h) to orange-red, the optical spectra indicating that the change is probably due to changing Cu2+ Cu+ ratio, both present simultaneously Although Co2+, Ni2+ and Cu2+ can form complexes with protonated highly basic amine ligands,20 it appears that the protonated N-groups in bpy and phen in y-TiP are not readily accessible The strongly acidic interlayer in y-TiP may also be responsible the modified bpy is fixed in the trans configuration of Scheme 2, ze the exchanged cation cannot bring about the tram+czs rotation necessary for formation of a complex pillar lo Ag exchanges readily (within minutes) into all three mate- + rials, the accompanying solid-state changes being both loading- and time-dependent (Table 1) Most work has concentrated on y-TiP(phen), 44 2 5H20 because of its interesting assembly For example, at [As'] [phen] mole ratios of 1 2 or above, only y-TiPAg, 22(phen)0 44 1 8H20 IS formed whatever the con- tact time (always at 45 "C), and the intensity ratio IdoO4 Idoo2 > 1 Instead, at [Ag'] [phen]=l 1 (6 days contact), y-TiP[Ag, 37(phen), 44] is given, in which Idoo4 Idooz is now ca 1 y-TiPAg, 44(phen), 44 2 5H2O could be obtained only by successively contacting y-Tip( phen), ,, 2 5H20 with AgN03 at high [Ag'] [phen] mole ratios and it was found that Id,, 2~oo,< 1 These trends are reminiscent of staging behav- iour, and since interlayer distances do not change during the XRD changes and no phase de-mixing was detected, they involve changes in intralayer occupation alone The large layer expansion on exchange may be rationalised assuming that Ag' ions exchange = P(OH), protons, being simultaneously positioned close to the C(H)(OH) group, as shown in Scheme 3 (Despite layer expansion, the optical spectrum shows that the Ag+ does not coordinate to N atoms nor does it give I I I 1 I I timeh Scheme 3 Staging behaviour of Ag+ In y-TiP(phen), 44 2 5H20, show-Fig.4 Cu2+ uptake in (a)y-TiP(amines), (b)y-ZrP(amines) (from ref 6) ing coordination to ligand and layer phosphate 648 J Muter Chem, 1996, 6(4), 645-651 rise to Ag clusters,,, see Fig. 5.) As shown by the TG-DTA curves, decomposition of phen occurs at the same temperature whatever the Ag+ exchange, which supports this suggestion (stepwise, lower temperature, decomposition of amine in the dmphen analogue instead probably reflects the higher degree of freedom of the interlayer dmphen; Fig. 6). The XRPD pattern of y-TiPAg0~,,(phen),~,,~2.5H,0 tends further towards a stage 1 behaviour after the material is left to stand for six months.Conversely, on leaving the only half- exchanged material, i.e. y-TiPAg,.,,( phen),,,,.1.8H20, to stand, the XRPD pattern tends slowly towards that expected for stage 2 behaviour, reaching a limit after four years, as seen in Fig. 7. This implies that Ag+ ions are mobile throughout the 400 800 1200 Alnm Fig. 5 Diffuse reflectance optical spectra :(a) y-TiPCu,,,,(dmphen), 23.2H20;(b) y-TiPAg,,,,( phen), ,,.2.5H20, before (---) and after (-) dehydration Fig. 6 TG-DTA curves of (a) y-TiPAg,,,,( phen),.,,.2.5H2O; (b) y-TiPAg,,,,( phen),.,,-1.8H20; (c) y-TiPAg,,,,(dmphen),.,, .2.9H20 1 1 1 I 5 10 15 20 2Oldegrees (Cu-Kct) Fig. 7 XRPD patterns of (a) y-TiPAg,,,,( phen),,,,.2.5H20; (b) y- TiPAg,.,,( phen),,,,.1.8H,O after 4years standing at room temperature interlayer, presumably via a proton exchange mechanism involving free protons.Pore selectivity and geometry in Ag -exchanged phases + The high interlayer expansion in y-TiPAgo.22(phen)o.44.1.8H,0 (11.2 A) and the presence of residual interlayer protons are expected to enhance cation uptake compared with starting amine-intercalated materials or y-TiP itself. This is indeed the case; the Ag +-exchanged material gives higher selectivity and higher loading levels than the unloaded material, as shown in Fig. 8. Inspection of Fig. 8 shows that for binary solutions, Cu2+ exchange is highly favoured over Co2+ and Ni2+ exchange, whilst Co2+=Ni2+ (i.e.each is exchanged to roughly the same extent from a Co2+/Ni2+-containing solution) and the same is the case for Co2+ /Ni2+/Cu2+ ternary solutions. Further, the solids produced after exchange all still have layer structures, although greatly amorphized. The Co2+-and Cu2+- exchanged materials give optical spectra expected for all-0 coordinated species (i.e. cavity coordination alone is present and although pores are larger, there is little evidence for migra tion/coordina tion to the pro tona ted amine). Water molecules are coordinated, as deduced from the (small) band- energy changes on dehydration. On dehydration, Co2+- exchanged materials give optical spectra characteristic of distorted tetrahedral [COO,] coordination (see Fig.9 for example). More interesting is the geometry change on dehy- dration of Ni2+-exchanged y-TiP(dmphen),,,,.2.2H20(again, despite a large change in the optical spectra, do,, remains unchanged). A pseudo-octahedral interlayer species is present (~,=8400cm-~)at 25"C, but after dehydration there is no absorbance at <10000 cm-l, i.e. interlayer tetrahedral, five- coordinate, or pseudo-octahedral NiO, geometries can be excluded [see Fig. 9(b)]. A square-planar geometry fits the optical spectrum (d-d band centred at 14 000 cm-l. [NiN4] chromophores with mainly o-bonding N have a d-d envelope at ca. 22 500 cm-' and [NiO,] ones at 18 000-20000 cm-' 23). We attribute the low energy both to the presence of weak P-0 ligands from the host and to distortion of the NiO, due to the constrained environment. Modelling the position is J.Mater. Chem., 1996, 6(4), 645-651 649 co cu 10 .:.,;...; ........:$.;.:... 5 ..... ...0 ........I co cu ...-.-*.' . ' , ' , ' , ' -*:.. ..*:'.I.: , ,' ;:::.):*.:................................;+:.....: ...... ....................... 500 lo00 I500 2000 hlnm : 1. , ' '....-.,p.:. ' ................. , . ..:p.."..:;:'' . , , . , Co Ni ................. .................................................................................... 0 ......................... -Ni Cu Co Ni Cu 40, 35 30 25 20 15 Fig. 9 Diffuse reflectance optical spectra : (a) NiZ+I I.i-,. TiP(dmphen),,,,.2.2H20; (b)Co2+/.~-TiP(dmphen),,,,.2.2H20.-, AS-.................. prepared; ---, after dehydration at 120°C for 2 h.......................... Co Ni A 501 Ni CU Co Ni Cu 1 Fig. 10 Cation selection from six-component mixtures. A, (a) y-TiP,2H2O; (b) y-TiP(bpy)o,43.0.4H20;(c) ~-TiP(phen),,,,~2.5HzO; (d) j~-TiP(dmphen)~.,,~2.2H,O.(a) y-TiPAgo,,3(bpy)o.,3~0.4HzO;B, (b)y-TiPAg0,,,(phen),,,,.1.5H,0; (c) y-TiPAgo.23(phen),,,4.1.8H20. more difficult because the distance between P(OH)2groups is too large to allow normal Ni-0 bonds (a full molecular modelling of the sites is underway). In multicomponent cation exchange, underivatised ?-Tip selects against a mixture of Ag', Rh3+ and Pd" in the 10 5 0 Co Ni Cu Ag Fig.8 Cation uptakes for A, binary; B, ternary; and C, quaternary mixtures: (a) y-TiP(phen),,,,~l.5HZO;(b)y-TiPAgo.,,( phen)o,,4.1.8H20 650 J. Muter. Chern., 1996, 6(4), 645-651 cationic radii order. However, there are differences in exchange selectivity which are less easily rationalised, such as the enhanced selectivity of y-TiP(phen)o.,4-2.5H20 against Cu2+ , Ni2+ and Co2+ compared with y-TiP(dmphen),.,,-2.2H2O (Fig. 1OA). As expected, the Ag -exchanged materials show consider- + ably enhanced selectivity compared with the amine-intercalated materials themselves, against Ag+, Rh3+ and Pd2+ (i.e. in a multicomponent mixture containing Co2+,Ni2+ and Cu2+, partially Ag -exchanged y-Tip( phen),.,,.2.5H20 preferentially + exchanges Cu2+) (Fig.1OB). It is not immediately obvious why this selectivity should be so high, because the pores are large and there is no clear 'blocking' of pathways (as is found in cation-exchanged pillared clays24). Presumably, the presence of further coordinating groups on the bpy and phen can give rise to synergistic effects because of the variety of geometries which may be adopted by the metal ions. Simulation studies are under way to clarify the site geometries. Conclusions The combination of highly acidic >P(OH)2 and hydrophobic >P=O channels in y-TiP leads to large modifications in protonation and assembly of simple aromatic amines in the interlayer, and also unusual ion-exchange behaviour of the pores generated. Since ring hydration ofbpy and phen to produce intralayer C(H)(OH) groups may lead to the gener- ation of chiral centres, a possible use of the materials in the chiral separation of organics is being investigated.M. A. M. thanks the 'Progetto Finalizzato Chimica Fine 11' of C. N. R., and A. A. G. T. thanks the E.U. (contract no. BRE2-CT93-450) for support. We thank Dr. A. De Stefanis for technical help. References 1 For reviews, see: S. L. Suib, Chem. Rev., 1993, 93, 803; N. J. Turro and M. Garcia-Garibay, in Photochemistry in Organised and Constrained Media, ed. V. Ramamurthy, VCH, New York, 1990, ch. 4. 2 G. A. Ozin, New Muter., 1992,4, 612. 3 Y. Yan and T. Bein, Chem. 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Krogh-Anderson, I. G. Krogh- Andersen, G. Alberti, M. Nielsen and M. S. Lehmann, Acta Chem. Scand., 1990,44, 865. 9 A communication has appeared: C. Ferragina, M. A. Massucci and A. A. G. Tomlinson, in Recent Developments in Zon Exchange 2, ed. P. A. Williams and M. J. Hudson, Elsevier Applied Science Press, New York, 1990, p. 103. 10 C. Ferragina, M. A. Massucci, A. La Ginestra, P. Patrono and A. A. G. Tomlinson, J. Phys. Chem., 1985,89,4762. 11 A. Albert and W. L. F. Armarego, Adv. Heterocycl. Chem., 1965, 4, 1.12 R. G. Gray, J. Ferguson and C. J. Hawkins, Aust. J. Chem., 1969, 22, 209. 13 A. Clearfield, Inorganic Exchange Materials, CRC Press, Boca Raton, FL, 1982, ch. 1. 14 S. A. Bagshaw and R. P. Cooney, J. Muter. Chem., 1994,4,557 and refs. therein. 15 R. D. Gillard, Coord. Chem. Rev., 1975,16,67. 16 E. V. Boldyreva and K. M. Salikhov, React. Solids, 1985,1,3. 17 G. V. S. Rao and M. W. Schafer, J. Phys. Chem., 1975,79,557. 18 C. Ferragina, M. A. Massucci, A. La Ginestra, P. Patrono and A. A. G. Tomlinson, Muter. Res. Bull., 1987,261. 19 C. Ferragina, M. A. Massucci, A. La Ginestra, P. Patrono and A. A. G. Tomlinson, J. Chem. Soc., Dalton Trans., 1988,851. 20 N. F. Curtis, in Comprehensive Coordination Chemistry, ed. G. Wilkinson, R. D. Gillard and J. A. McCleverty, Pergamon, London, 1987, vol. 2, p. 899. 21 E.g. C. Delmas, Y. Borthomieu, C. Faure, A. Delahaye and M. Figlarz, Solid State Zonics, 1989, 32/33, 104; T. Kobayashi, H. Kuratas and N. Uyeda, J. Phys. Chem., 1986,90,2231. 22 G. A. Ozin and S. A. Mitchell, in Inorganic Chemistry, Towards the 21st Century, ed. M. H. Chisholm, ACS, Washington, DC, 1987, p. 303. 23 R. Stomberg, I-B. Svensson and A. A. G. Tomlinson, Acta Chem. Scand., 1973,27, 1192. 24 A. Molinard and E. F. Vansant, Separation Technology, ed. E. F. Vansant, Elsevier, Amsterdam, 1994, p. 423. Paper 5/04318B; Received 4th July, 1995 J. Muter. Chem., 1996, 6(4), 645-651 651