Gary B. Hix

A silver-based metal–organic framework material as a ‘reservoir’ of bactericidal metal ions

The silver-based MOF material Ag3(3-phosphonobenzoate) was evaluated as a bactericidal material. A sustainable release of Ag+, which was quantified by cathodic stripping voltammetry, was responsible for bactericidal activity against the 6 bacterial strains tested.

Remarkable thermal stability of Eu(4-phosphonobenzoate): structure investigations and luminescence properties

A new 3D rare-earth hybrid material Eu(p-O(3)PC(6)H(4)COO) has been synthesised by a hydrothermal route from Eu(NO(3))(3) x 5 H(2)O and the rigid precursor, 4-phosphonobenzoic acid. The structure of Eu(p-O(3)PC(6)H(4)COO) has been solved by X-ray diffraction on a powder sample and is described as an inorganic network in which both carboxylic and phosphonic acid groups are linked to Eu ions forming a three-dimensional architecture. Thermal analysis performed on this compound has underlined its remarkable stability up to 510 degrees C and an optical study has been conducted to examine its luminescence properties that have been related to the structure of the material. The structural and luminescence properties have also been compared with the related material Eu phenylphosphonate.

Silver-Based Hybrid Materials from meta- or para-Phosphonobenzoic Acid: Influence of the Topology on Silver Release in Water

Three novel silver-based metal-organic frameworks materials, which were synthesized from either 3-phosphono or 4-phosphonobenzoic acid and silver nitrate, are reported. The novel hybrids were synthesized under hydrothermal conditions; the pH of the reaction media was controlled by adding different quantities of urea thereby producing different topologies. Compound 1 (Ag3(4-PO3-C6H4-COO)), synthesized in the presence of urea, exhibits a compact 3D structure in which both phosphonic acid and carboxylic acid functional groups are linked to the silver-based inorganic network. Compound 2 (Ag(4-PO3H-C6H4-COOH)), which was synthesized at lower pH (without urea), has a layered structure in which only the phosphonic acid functional groups from 4-phosphonobenzoic acid moieties are linked to the silver inorganic network; the carboxylic acid groups being engaged in hydrogen bonds. Finally, material 3 (Ag(3-PO3H-C6H4-COOH)) was synthesized from 3-phosphonobenzoic acid and silver nitrate without urea. This material 3 features a layered structure exhibiting carboxylic acid functional groups linked via hydrogen bonds in the interlayer space. After the full characterization of these materials (single X-ray structure, IR, TGA), their ability to release silver salts in aqueous environment was measured. Silver release, determined in aqueous solution by cathodic stripping voltammetry, shows that the silver release capacity of these materials is dependent on the topology of the hybrids. The more compact structure 1 is extremely stable in water with only trace levels of silver ions being detected. On the other hand, compounds 2 and 3, in which only the phosphonic acid functional groups were bonded to the inorganic network, released larger quantities of silver ions into aqueous solution. These results which were compared with the silver release of the previously described compound 4 (Ag6(3-PO3-C6H4-COO)2). The results clearly show that the release capacity of silver-based metal organic framework can be tuned by modifying their topology which, in the present study, is governed by the regio-isomer of the organic precursor and the synthetic conditions under which the hybrids are prepared.

Divalent metal vinylphosphonate layered materials: compositional variability, structural peculiarities, dehydration behavior, and photoluminescent properties

A family of M-VP (M = Ni, Co, Cd, Mn, Zn, Fe, Cu, Pb; VP = vinylphosphonate) and M-PVP (M = Co, Cd; PVP = phenylvinylphosphonate) materials have been synthesized by hydrothermal methods and characterized by FT-IR, elemental analysis, and thermogravimetric analysis (TGA). Their structures were determined either by single crystal X-ray crystallography or from laboratory X-ray powder diffraction data. The crystal structure of some M-VP and M-PVP materials is two-dimensional (2D) layered, with the organic groups (vinyl or phenylvinyl) protruding into the interlamellar space. However, the Pb-VP and Cu-VP materials show dramatically different structural features. The porous, three-dimensional (3D) structure of Pb-VP contains the Pb center in a pentagonal pyramid. A Cu-VP variant of the common 2D layered structure shows a very peculiar structure. The structure of the material is 2D with the layers based upon three crystallographically distinct Cu atoms; an octahedrally coordinated Cu(2+) atom, a square planar Cu(2+) atom and a Cu(+) atom. The latter has an unusual co-ordination environment as it is 3-coordinated to two oxygen atoms with the third bond across the double bond of the vinyl group. Metal-coordinated water loss was studied by TGA and thermodiffractometry. The rehydration of the anhydrous phases to give the initial phase takes place rapidly for Cd-PVP but it takes several days for Co-PVP. The M-VP materials exhibit variable dehydration-rehydration behavior, with most of them losing crystallinity during the process.

The synthesis and modification of aluminium phosphonates

Two synthetic approaches to the preparation of mixed aluminium phosphite-phosphonate solids have been made. First, the hydrothermal reaction of aluminium hydroxide (gibbsite) with mixtures of phosphorous and methylphosphonic acids under conditions that give microporous aluminium methylphosphonate-β (AlMePO-β) when methylphosphonic acid alone is used, and secondly, the reaction of AlMePO-β with increasing amounts of molten phosphorous acid. Under hydrothermal conditions there is no evidence that AlMePO-β can be prepared with phosphite groups randomly replacing methylphosphonate groups. Rather, the products are dominated over the intermediate phosphite/phosphonate compositional range by a novel phase that is thought, on the basis of 27 Al and 31 P MAS NMR and FTIR spectroscopies, to contain differing amounts of phosphite and methylphosphonate groups. Reaction of AlMePO-β with levels of molten phosphorous acid at 40% or more of the methylphosphonate content gives mixtures of AlMePO-β and a new phosphite phase, whereas reaction using lower amounts of the molten acid leaves AlMePO-β as the only X-ray visible phase. Extension of the melt method to the separate reaction of gibbsite with methylphosphonic and phosphorous acids yields, respectively, single crystals of a new aluminium methylphosphonate [Al(O 3 PCH 3 )(HO 3 PCH 3 )·H 2 O] and a known aluminium phosphite [Al 2 (O 3 PH) 3 ·4H 2 O], the structure of which had only been solved from powder diffraction data. Single crystal diffractometry improved the accuracy with which the structural parameters of the phosphite are known and enabled structure solution of the new aluminium methylphosphonate [Pnma, a=19.075(6) A, b=5.117(2) A, c=8.439(2) A], which is made up of layers that contain isolated, octahedrally coordinated aluminium linked by methylphosphonate groups.

Synthesis of phosphate–phenylphosphonates of titanium(IV) and their n-butylamine intercalates

Layered compounds of general formula Ti(PhPO3)x(HOPO3)2 –x·yH2O have been synthesized and characterized by X-ray powder diffraction, IR spectroscopy, TG and 31P magic angle spinning NMR spectroscopy. Different sources for the tetravalent metal in the synthetic process have been studied. The overall α-layered structure type is maintained while the ratio of phosphate to phenylphosphonate incorporated into the mixed derivative varies. The intercalation behaviour of mixed derivatives toward n-butylamine was also studied. The synthetic process shows kinetic control as a function of the tetravalent metal source; at low titanium(IV) concentration a mixture of products is obtained (phosphate + phosphonate) rather than a phosphate–phenylphosphonate single phase.

The titanium(I) salt ofN,N-(diphosphonomethyl)glycine: synthesis,characterisation, porosity and proton conduction

A new diphosphonic acid,N,N -(diphosphonomethyl)glycine, has been prepared. The titanium(iv) salt [Ti(dpmg)] of this acid has been characterised by X-ray powder diffraction, thermogravimetry, 31 P MAS NMR spectroscopy, isothermal N 2 adsorption–desorption and ac conductivity measurements. Phosphorus is present in a mixture of bonded phosphonate and free phosphonic acid groups. The material is both amorphous and porous (BET specific surface area=119 m 2 g -1 ), and its water content is relative humidity (RH)-dependent. Ti(dpmg) is a protonic conductor (at 90% RH and 90 °C, σ=3×10 -2 S cm -1 ), with conductivity exhibiting Arrhenius-type behaviour at constant RH. Conductivity and Arrhenius parameters are strongly dependent on the water content.

Nano/nanocomposite systems: in situ growth of particles and clusters of semiconductor metal sulfides in porous silica-pillared layered phosphates

Silica-pillared metal(IV) hydrogen phosphates formed by the intercalation of octameric aminoalkyl or aryl species from solution into layered zirconium or tin phosphates, followed by thermal degradation of the organic moieties, are crosslinked microporous, nanocomposite materials with surface areas up to 230 m–2 g–1. Their use as templates for size-quantization of metal sulfide particles is described via, the sorption of Zn–2+ and Cd–2+ ions from aqueous solution, followed by reaction with H2S in acetone. Band gaps obtained from optical absorption spectra for occluded ZnS and CdS are significantly increased from those of the corresponding bulk-metal sulfides. These data, and those of X-ray absorption spectroscopic measurements at the zinc and cadmium K edges, allow the metal sulfide aggregates to be described in terms of ‘superclusters’, where discrete ‘molecule-like’ Zn(Cd)S semiconductors confined in the micropores interconnect through windows in the pillar network to form more extended structures of diameter ca. 25 A.

Luminescent and Proton Conducting Lanthanide Coordination Networks Based On a Zwitterionic Tripodal Triphosphonate

The synthesis, structural characterization, luminescence properties, and proton conduction performance of a new family of isostructural cationic 2D layered compounds are reported. These have the general formula [Ln(H4NMP)(H2O)2]Cl·2H2O [Ln = La(3+), Pr(3+), Sm(3+), Eu(3+), Gd(3+), Tb(3+), Dy(3+), Ho(3+), H6NMP = nitrilotris(methylphosphonic acid)], and contain Cl(-) as the counterion. In the case of Ce(3+), a 1D derivative, [Ce2(H3NMP)2(H2O)4]·4.5H2O, isostructural with the known lanthanum compound has been isolated by simply crystallization at room temperature. The octa-coordinated environment of Ln(3+) in 2D compounds is composed by six oxygen atoms from three different ligands and two oxygens from each bound water. Two of the three phosphonate groups act as both chelating and bridging linkers, while the third phosphonate group acts solely as a bridging moiety. The materials are stable at low relative humidity at less at 170 °C. However, at high relative humidity transform to other chloride-free phases, including the 1D structure. The proton conductivity of the 1D materials varies in a wide range, the highest values corresponding to the La derivative (σ ≈ 2 × 10(-3) S·cm(-1) at RH 95% and 80 °C). A lower proton conductivity, 3 × 10(-4) S·cm(-1), was measured for [Gd(H4NMP)(H2O)2]Cl·2H2O at 80 °C, which remains stable under the work conditions used. Absorption and luminescence spectra were recorded for selected [Ln(H4NMP)(H2O)2]Cl·2H2O compounds. In all of them, the observed transitions are attributed solely to f-f transitions of the lanthanide ions present, as the H4NMP(2-) organic group has no measurable absorption or luminescence properties.

Silver-Phosphonate Based Metal Organic Frameworks: Synthesis and Antibacterial Action

Silver based Metal Organic Framework (MOF) materials were synthesized by the reaction of phospho-benzoic acid with silver salts under hydrothermal treatment and with/without urea. According to this procedure, either both functional groups (phosphonic acid and carboxylic acid) were engaged in iono-covalent bonds with silver atoms or, on the contrary, only the phosphonic acid function is engaged. Consequently, these materials exhibited different stability and their ability to release silver salts, when they were placed in water, was different. The antibacterial properties of these materials were attributed to the silver salt, released in solution. GRAPHICAL ABSTRACT