Anthony A. G. Tomlinson

Coordination of Co2+, Ni2+ and Cu2+ to 2,9 - dimethyl - 1,10 phenanthroline intercalated in α-zirconium phosphate: Evidence for dimers

2,9-Dimethyl-1,10-phenanthroline (dmp) intercalates into α-Zr(HPO4)2. (2EtOH) to form α-Zr(HPO4)2 (dmp)0.50. 2.5H2O at maximum uptake, at 25°C. This lamellar composite has an interlayer distance of 14.60(5) A, which changes little - to 13.58(5) A - when the pseudo-zeolitic water is lost. An almost vertical orientation of the dmp between the phosphate layers is proposed, as was found previously for the unsubstituted phenanthroline analogue. When the material is exchanged with Co2+, Ni2+, and Cu2+, under conditions such that [M] : [L] = 1:1 there is partial elution of the dmp, giving rise to materials of formulation α-ZrH1.3M(OH2)0.35(dmp)0.35(PO4)2·nH2O, with no change in interlayer distance. Spectroscopic evidence for the formation of dimers to the intercalated dmp is described.

Assembly and polymerisation of some aromatic amines in α-VOPO4·2H2O

Under soft conditions (dry EtOH, 25 °C), pyrazole, pyrazine and phenazine intercalate into α-VOPO4.2H2O as protonated, non-coordinated amines. Intermediates during pyrazine uptake include a metastable phase with d001= 13.3 A, ascribed to bilayer formation. Benzidine (bz) instead gives two bz+ charge transfer (CT) bronzes: VOPO4(bz)0.5·2H2O (dry EtOH) and VOPO4(bz)0.7·3.5H2O (95% EtOH) with interlayer distances lower (7.05 A and 6.65 A, respectively) than in α-VOPO42H2O itself. Interlayer ‘pocket’ orientation with layer shifting and turbostraticity to accommodate bz+ cations is suggested, which differs from the assembly of bz+ in smectites and V2O5. VOPO4(bz)0.5·2H2O shows ‘moving solid’ behaviour, probably due to changes in specific H-bonding between intercalate and sheet with water content. It is concluded that surface ruffling and specific H-bonding influence composite formation and assembly.Pyrrole (pyrr) almost completely polymerises on intercalation into α-VOPO4.2H2O, giving ‘nestled’ polymer composites with differing polypyrrole (Ppyrr) oxidation levels, whereas aniline uptake is governed by base protonation and proton induced reassembly. Both give differently loaded nanocomposites (with interlayer distances in the range 6.4–17.9 A) depending on amine delivery (vapour, liquid, solution) and intercalant state (powder dispersion, film). Pyrrole loadings are higher with dispersions and lower with films, but the opposite is the case for aniline (An). For example, neat An gives VOPO4(An)1.3·13.5H2O (interlayer distance 17.9 A), An-EtOH gives VOPO4(An)0.4(14.8 A), and gaseous An gives VOPO4(An)0.66·2.2H2O (6.65 A). As prepared, the Ppyrr shows mixed-polaron states, and both series give EPR spectra characteristic of highly anisotropic VIV-containing clusters and do not conduct. All become amorphous on calcination (160 °C), the An-containing composites polymerising to completion. Calcined VOPO4(Ppyrr)066·1.4H2O (from neat pyrrole) is a semiconductor, the EPR spectra (cationic amine and separated VIV ions) further supporting strong polymer-sheet electronic interactions with the formation of VIV island clusters. Assemblies of the two amines in VOPO4 are suggested.

Porous chromia-pillared α-zirconium phosphate materials prepared via colloid methods

The reaction of Cr(CH3CO2)3[Cr(OAc)3] with colloidal n-propylammonium α-zirconium phosphate and subsequent calcination of the products have been investigated. Depending on [Cr(OAc)3] : [initial phosphate] ratios and Cr3+ concentrations, a series of polyhydroxy acetato-Cr3+ intercalated precursor materials can be obtained, in which topotactic interface reactions have occurred to give materials with interlayer distances (d002) ranging from 13.0 to 39.0 A. These precursors show higher layer expansions than the analogous pillared clays (PILCS; d001= 16.8–27.6 A). A model invoking ordered in situ polymerisation of the Cr(OAc)3 on the phosphate surfaces is put forward.Calcination of these precursors under N2(400 °C) leads to a series of chromia-pillared materials in which the interlayers do not collapse to a single (much lower) value, as found previously for most PILCS, but instead provide a wide range of interlayer distances (10–27 A). These correspond to free heights of 3.5–20.5 A, the widest ranging and highest yet found for such materials. These nanoscale oxide-pillared materials have N2 surface areas (B.E.T., 77 K) of 250–330 m2 g–1, with pore radii (cylindrical pore method) ranging from 8.5 to 13.8 A, and very narrow pore-size distributions. Calcination conditions are crucial for obtaining porous solids. If calcination is carried out in air at 400 °C, although pillared powders and films are again obtained, surface areas are only ca. 40 m2 g–1(B.E.T., N2, 77 K).Furthermore, higher calcination temperatures (500 °C, under N2) give rise to X-ray amorphous materials, again having high surface areas and narrow pore-size distributions. All the materials can be processed in thin-film form without loss of textural characteristics.

Porous cross-linked materials formed by oligomeric aluminium hydroxides and α-tin phosphate

The intercalation of the tridecameric polyhydroxyaluminium Keggin-type cation, formally [AlO4Al12(OH)24(OH2)12]7+, into α-Sn(HPO4)2·H2O via the colloidal tetramethylammonium-exchanged intermediate α-Sn[NMe4]0.9–1.0H1.1–1.0(PO4)2·4H2O and the alumina-pillared materials obtained after calcination are described. Two different intercalated precursor materials are obtained, depending on whether the Keggin ion inserted derives from the commercial product (‘Chlorhydrol’) or from the polyhydroxyaluminium cation generated in situ. Calcination leads to materials differing in free heights and in alumina contents. Their surface areas (B.E.T., N2, 77 K) are quite high: 190 m2 g–1[chlor-SnP (400 °C)] and 228 m2 g–1[Al13-SnP (400 °C)]. Pore-size calculations show them to be mainly mesoporous, but with some micropore contribution (> 50% of pores in width range 15–40 A). The higher microporosity of the former with respect to the latter is ascribed to lateral-order differences between the alumina pillars.High cation-exchange capacities (for Co2+, Ni2+ and Cu2+) confirm that both solids are porous and have more accessible interlayer sites than does the parent material. Optical spectra of the transition-metal ion-exchanged materials indicate that the sites available in the two solids differ, and that both differ from those present in the starting α-tin phosphate. Site geometries are suggested.

PLS versus zeolites as sorbents and catalysts II. Terpene conversions in alumina-pillared clays and phosphates and medium pore zeolites

Abstract The reactions of α-pinene, limonene, and α-terpinene in several alumina-pillared clays (PILCs) and a layered α-tin phosphate analogue (Al-PILP) have been investigated under Lewis acid conditions and compared with the mid-pore zeolites USY, NH 4 + -ZSM-5 (with SiO 2 /Al 2 O 3 ratios = 35 and 235), and H + -mordenite. The bicyclic α-pinene gives the highest conversion, all catalysts giving > 50% camphene at 100°C. Total yields show that USY is the strongest acid, after which the acidity order is: BP-PILC = ZSM-5 (35) > FAZA > H + -mordenite, and the layered phosphate appears to be less acid than the PILCs. No fenchane carbocation-derived products are produced, indicating that all the solids promote formation of the norbornyl cation intermediate. Selectivities in the unsubstituted PILCs is comparable with those in the zeolites (e.g. both FAZA and USY show selectivity against limonene production in the α-pinene reaction). BP-PILC also shows appreciable activity for α-pinene at 25°C (as does USY) whereas Al-PILP is inactive. Specific carbocation precursors are deduced from the product distributions and a ‘carbocation cascade’ based on pore acidity provides a rationalisation of the results. However, site-selectivity effects do come into play in K + - and Ca 2+ -PILCs and it also appears that limonene occupies a specific site in USY. The reactions provide a means of generating terpene derived carbocations in the solid state.

Porous chromia-pillared α-tin phosphate materials

Abstract The reactions of Cr(OAc)3 (OAc− = CH3OCO−) solutions with colloidal suspensions of tetramethylammonium α-tin phosphate ( α- Sn[Me 4 N] 0.9 – 1.1 H 1.1−0.9 (PO 4 ) 2 · n H 2 O = “Me 4 Nue5f8SnP”) have been investigated over a wide range of [Cr(OAc)3]:[Me4Nue5f8SnP] ratios, Cr(OAc)3 concentrations, and heating conditions. On aging + reflux, Me4Nue5f8SnP takes up oligomeric Cr3+ species to give crystalline, highly expanded materials having interlayer distances between 24 and 33 A. Conversely, Cr(OAc)3 solutions treated in the same way, but separately, and then added to colloidal Me4Nue5f8SnP gave composites with little expansion (interlayer distance, d002 = 15 A), collapsing to nonporous oxide-phosphates (d002 = 10 A) on calcination. Separately polymerized CrCl 3 NaOH or [Cr3O(OAc)6(OH2)3]+ (standard precursors in clay-pillaring) also gave poorly defined delaminated materials. Chemical, TGA/DTA, and visible/near UV spectroscopic evidence shows the intercalates are polyhydroxyacetato-Cr3+ species, and some may be formulated as [Cr3(OH)6(OAc)]2+, [Cr4(OH)7(OAc)3+, and [Cr5(OH)7(OAc)3]5+. They are formed in situ on the α-tin phosphate surfaces; possible orientations within the layers (taking into account the presence of zeolite-type water) is discussed. Calcination under N2 at 400°C gives chromium oxide-pillared materials with d002 in the ranges 12.5–14.0 A (from precursors prepared at higher Cr3+ concentrations) or 15–20 A (from precursors at lower Cr3+ concentrations). The surface areas (BET, N2, 77K): 264–386 m2 g−1, compare well with analogues in clay chemistry (150–400 m2 g−1). Pore-sized distributions (cylindrical pores model) are narrow, >70% of pores having widths

PLS vs. zeolites as sorbents and catalysts. 5. Evidence for Brønsted/Lewis acid crossover and high acidity in conversions of C1–3 alcohols in some alumina-pillared smectite clays

Conversions of methanol, ethanol, and iso-propanol have been investigated in the activated alumina-pillared montmorillonite (BP-PILC), beidellite/montmorillonite (FAZA), and saponite (ATOS)-based PILCs obtained from standard [Al13O4(H2O)12(OH)24]7+ Keggin-ion. Product outcomes for MeOH differ from those on smectite clays themselves and on alumina (or transition metal ion oxides): all give rise to dimethylether, rather than methylformate or formic acid. Systematic study of conversion, yields and selectivity for cation-exchanged FAZA show that the large changes observed must be ascribed to both steric effects and selective blocking of proton-containing active sites. The latter are most important in Ni2+-exchanged FAZA-containing catalysts and are attributed to generation of highly acidic Lewis sites, e.g. hydrocarbons alone (in a distribution similar to the MTG process) are obtained on Ni2+-FAZA. Apart from ethene and acetaldehyde, EtOH conversion also gives diethylether, not obtained on smectites themselves, and produced via a bimolecular reaction. The total dehydration/dehydrogenation ratio varies in the order BP-PILC>FAZA>>AZA=ATOS, BP-PILC being the most acidic and most selective. Dehydration and dehydrogenation activity with temperature go through a crossover point. This is ascribed to “iso-acidity”, i.e. the iso-acidic point is where Lewis and Bronsted acids are equally strong. Trends in iso-acidity with metal-ion exchange in FAZA materials suggest that the Lewis acid sites are at the alumina pillar. Detailed study of reaction kinetics and contact times leads to the conclusion that saponite surfaces have higher dehydration activity than those in montmorillonite.

Layered basic copper anion exchangers: chemical characterisation and X-ray absorption study

The local structure around copper in Cu2(OH)3OAc·H2O, and in the anhydrous iodide analogue prepared by ion exchange, has been determined by X-ray absorption spectroscopy at 77 K. For both compounds, the copper environment is compatible with a botallackite-type Cu2(OH)3Br arrangement, in which two crystallographically distinct copper atoms lie in 4 + 2 (oxygen + X) and 4 + 1 + 1 (oxygen + oxygen + X) environments (X = exchangeable anion OAc, I, Br etc.). Interatomic distances between copper and the exchangeable anion have been determined to be 2.78 and 3.15 A in Cu2(OH)3OAc·H2O and Cu2(OH)3I, respectively, the latter representing an unusual example of a direct CuII—I bond. At least two Cu—Cu distances could be identified in the radial distribution function: r(CuCu)= 3.16 and 6.32 A, signals from second and more distant neighbours being reinforced by a focussing effect along the linear chain of copper atoms in the layers.

Pillared layered structures vs. zeolites as sorbents and catalysts. Part 1.—Hydrocarbon separations on two alumina-pillared clays and an α-tin phosphate analogue

The dynamic sorption of a series of hydrocarbons in an alumina-pillared montmorillonite (AZA), its mixed Fe3+–alumina-pillared analogue, (FAZA) and an alumina-pillared a-tin phosphate analogue (AI-PILP) has been investigated. Separations between binary mixtures of cyclic non-aromatic/aromatic, linear chain/cyclic non-aromatic hydrocarbons, among others, have been performed in the temperature range 200–350 °C. Aromatic chlorohydrocarbons can also be separated from one another and from their ternary mixtures with hydrocarbons. Although they are the most efficient in these separations (requiring lower temperatures), the AI-PILP samples show enhanced acid-catalysis characteristics at higher temperatures. In addition, naphthalene and biphenyl are sorbed by the montmorillonite-based PILCs, but separated by the AI-PILP, confirming that shape-selection behaviour is involved. The anomalous sorption of cyclohexane by the AI-PILP demonstrates that lateral oxide-pillar ordering differs between pillared smectite clays and phosphates.Catalytic cracking phenomena observed for n-heptane differ between AZA and FAZA, indicating that in-pillar Fe in FAZA is involved, and this is confirmed via cracking of 3-methylhexane. That adsorbate–wall (i.e. pillar) interactions are important, and differ from adsorbate interactions in medium-sized zeolites, is supported by the fact that AZA and FAZA act as weak Lewis-acid reaction ‘vessels’ in the isomerisation of p-xylene.

Pillar chemistry. Part 5. Intercalation of 2,2′-bipyridine, 1,10-phenanthroline, and 2,9-dimethyl-1,10-phenanthroline into γ-zirconium phosphate and formation of interlayer copper(II) complexes

2,2′-Bipyridine (bipy), 1,10-phenanthroline (phen), and 2,9-dimethyl-1,10-phenanthroline (dmphen) can be intercalated into γ-Zr(HPO4)2·2H2O as such (i.e. without first pre-swelling the matrix) to give materials having the final formulation γ-Zr(HPO4)2Lx·n H2O (x= 0.48–0.50). With dmphen, if the γ-Zr(HPO4)2·2H2O is first pre-swelled using ethanol, a further, pure layered phase of composition γ-Zr(HPO4)2(dmphen)0.28·2H2O is obtained; bipy and phen do not give this latter phase. Indirect evidence, X-ray diffraction and i.r. spectroscopy, indicates that the orientations of the amines in the interlayer are different from those in the α-Zr(HPO4)2·H2O analogues, probably due to the presence of specific hydrogen bonding by the interlayer water molecules. All four materials exchange CuII. As expected, given its lower interlayer ligand density compared with the other materials, γ-Zr(HPO4)2(dmphen)0.28·2H2O takes up CuII most readily. Further, within the series γ-Zr(HPO4)2Lx·n H2O the order of uptake, phen > dmphen > bipy, is not that expected from ligand steric requirements alone and the uptake is in all cases slower than that in the α-Zr(HPO4)2·H2O analogues, both results indicating the importance of ligand–matrix interactions. The final pure layered materials obtained have [Cu2+]: [] ratios of 1:1 [γ-(dmphen)0.28] and 1:2 [γ-dmphen)0.48 and γ-(bipy)0.48]; γ-(phen)0.50 gave [Cu2+] : []= 0.8:1. Spectroscopic evidence shows that CuII co-ordinates to the amine ligand only in the bipy and phen cases, whereas both dmphen-containing materials exchange Cu2+ into cavities widened by the dmphen but without co-ordination to the intercalated ligand.