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The fully deprotonated anion of 1,3,5-benzene-triphosphonic acid 1,3,5-C6H3[PO32−]3 gives rise to deceptively simple 1H and 31P NMR spectra due to a corresponding [AX]3 spin system. The 13C{1H} NMR...

Synthesis redesign and derivatisation of Fe(ii)-hydroxyphosphonoacetate, incorporating different ammonia loads and M(ii) isomorphic substitutions (M = Mn, Co and Zn), have been implemented. The NH3 adsorption led to materials with enhanced proton conductivity, up to ∼10-3 S cm-1, although it caused a progressive amorphization. The Pair Distribution Function (PDF) analysis for this material confirmed the loss of crystallinity but the local order appeared to be maintained. The parent compound was shown to be an efficient photocatalyst for phenol, 4-chlorophenol and methylene blue even under mild conditions, with TOC removal of 75-90% at 50-150 min of reaction. The M(ii)-substituted derivatives displayed similar behaviour in properties, and therefore their multifunctional character, as the parent compound, although with slightly reduced capabilities.

We study the interaction of six systematically varied tetraphosphonate molecules with carbon steel surfaces by XPS at pH 3. All tetraphosphonates [EDTMP (C2), TDTMP (C4), HDTMP (C6), ODTMP (C8) and DDTMP (C12)] belong to the aminomethylene-phosphonate family, and they possess systematically elongated backbone (from two to twelve methylene groups separating the N atoms). XPS studies were performed on powdered samples and also on immersed carbon steel specimens in aqueous solutions. The XPS results also suggest that the tetraphosphonic acid molecules become significantly deprotonated upon interaction with the carbon steel surface and that the surface interaction of the tetraphosphonic acid family leads to additive adsorption on the steel surface via the phosphonate groups. The mode of corrosion inhibition was studied by potentiodynamic polarization and electrochemical impedance spectroscopy. The changes observed in the impedance parameters, like charge transfer resistance (Rct) and constant phase element (CPE) confirm the strong adsorption on the metal surface. The nature of the protective layer formed on the carbon steel surface was examined by Attenuated Total Reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy and optical microscopy.

The synthesis, structural characterization, topological analysis, proton conductivity, and catalytic properties are reported of two Cu(II)-based compounds, namely a dinuclear Cu(II) complex [Cu2(μ-VPA)2(phen)2(H2O)2]·8H2O (1) (H2VPA = vinylphosphonic acid, phen = 1,10-phenanthroline) and a 1D coordination polymer [Cu(μ-SO4)(phen)(H2O)2]∞ (2). Their structural features and H-bonding interactions were investigated in detail, showing that the metal–organic structures of 1 and 2 are extended by multiple hydrogen bonds to more complex 2D or 1D H-bonded architectures with the kgd [Shubnikov plane net (3.6.3.6)/dual] and SP 1-periodic net (4,4)(0,2) topology, respectively. These nets are primarily driven by the H-bonding interactions involving water ligands and H2O molecules of crystallization; besides, the (H2O)4/(H2O)5 clusters were identified in 1. Both 1 and 2 are moderate proton conductors, with proton conductivity values, σ = 3.65 × 10–6 and 3.94 × 10–6 S·cm–1, respectively (measured at 80 °C and 95% relat...

In our effort to develop new synthetic strategies for isolation of new phosphonate frameworks, we exploited the possibility to simultaneously utilize benzene-1,3,5-triphosphonic acid (H6btp) and di-2-pyridyl ketone (py2CO) which is a major player in the field of polynuclear metal complexes. This ligand blend in the Cu(II) chemistry afforded a two-dimensional framework comprising tetranuclear, [CuII4], secondary building units. The thorough investigation of the CuII / di-2-pyridyl ketone / benzene-1,3,5-triphosphonic acid reaction system also afforded a hydrogen bonded framework. The structure of the latter comprises the cationic [Cu{py2C(OH)2}2]2+ complex [py2C(OH)2 is the hydrate of py2CO], the dianion of benzene-1,3,5-triphosphonic acid (H4btp2-) and water solvates. The magnetic properties of the layered material were rationalized on the basis of magnetically isolated [CuII4] units dominated by antiferromagnetic interactions.

Recalcitrant barium sulfate (BaSO4) scale deposits are commonly encountered in industrial applications. They are hard to remove because of the pH-independence of their solubility. The formation of BaSO4 from supersaturated solutions was studied in two series of experiments: (a) the first series was performed under conditions of high supersaturation to determine the domain of stability of the system and (b) the second at low supersaturations, under conditions in which the supersaturated solutions were stable (seeded growth experiments). From the first series, the stability diagram of the system was determined. Through the second series of precipitation experiments, the effect of two types of triphosphonic acid additives on BaSO4 formation was assessed: the rigid aromatic 1,3,5-benzenetriphosphonic acid (BTP) and the flexible aliphatic amino-tris(methylenephosphonic) acid (AMP). Initially, the pH of the solutions was adjusted at 9.5 so that all phosphonate groups were deprotonated. For both additives, the rate of crystal growth of BaSO4 was inhibited. At low pH (3.60) a decrease of the rate of crystal growth with increasing additive concentrations was found. At pH 9.50 however, an irregular trend was observed showing a relative increase of the rates of crystal growth with increasing inhibitor concentration. These inconsistencies were attributed to changes of the solubility of BaSO4 in the presence of additives. The solubility changes in the presence of each test additive were quantified by measuring the apparent solubility of BaSO4 seed crystals. The measurements showed that the changes were negligible at pH 3.60. Kinetics measurements in the presence of the test additives suggested that their adsorption on the BaSO4 seed crystals was responsible for the inhibition. Modelling the adsorption according to the Freundlich isotherm gave a satisfactory fit of the kinetics data in the presence of BTP and AMP at pH 9.50. The presence of the test additives at both pH values did not affect the morphology of the growing BaSO4 crystals.

The reaction of MoO42- with a number of phosphonic acids [bis(phosphonomethyl)glycine, R,S-hydroxyphosphonoacetic acid, 1-hydroxyethane-1,1-diphosphonic acid, phenylphosphonic acid, aminotris(methylene phosphonic acid), and 1,2-ethylenediphosphonic acid] under oxidizing (H2O2) hydrothermal conditions at low pH leads to rupture of the P-C bond, release of orthophosphate ions, and generation of the octanuclear, phosphate-bridged, polyoxometalate molybdenum cluster (NH4)5[Mo8(OH)2O24(μ8-PO4)](H2O)2 (POMPhos). This cluster has been fully characterized and its structure determined. It was studied as a proton conductor, giving moderate values of σ = 2.13 × 10-5 S·cm-1 (25 °C) and 1.17 × 10-4 S·cm-1 (80 °C) at 95% relative humidity, with Ea = 0.27 eV. The POMPhos cluster was then thermally treated at 310 °C, yielding (NH4)2.6(H3O)0.4(PO4Mo12O36) together with an amorphous impurity containing phosphate and molybdenum oxide. This product was also studied for its proton conductivity properties, giving rise to an impressively high value of σ = 2.43 × 10-3 S·cm-1 (25 °C) and 6.67 × 10-3 S·cm-1 (80 °C) at 95% relative humidity, 2 orders of magnitude higher than those corresponding to the "as-synthesized" solid. The utilization of POMPhos in catalytic reduction of different sulfoxides was also evaluated. POMPhos acts as an efficient homogeneous catalyst for the reduction of diphenyl sulfoxide to diphenyl sulfide, as a model reaction. Pinacol was used as a low-cost, environmentally friendly, and highly efficient reducing agent. The effects of different reaction parameters were investigated, namely the type of solvent and reducing agent, presence of acid promoter, reaction time and temperature, loading of catalyst and pinacol, allowing to achieve up to 84-99% yields of sulfide products under optimized conditions. Substrate scope was tested on the examples of diaryl, alkylaryl, dibenzyl, and dialkyl sulfoxides and excellent product yields were obtained.

M.T is supported by funding from the European Union’s Horizon 2020 research and innovation program under the Marie Skłodowska-Curie grant agreement No 663830. In September 2018, the First European Workshop on Metal Phosphonates Chemistry brought together some prominent researchers in the field of metal phosphonates and phosphinates with the aim of discussing past and current research efforts and identifying future directions. The scope of this perspective article is to provide a critical overview of the topics discussed during the workshop, which are divided into two main areas: synthesis and characterisation, and applications. In terms of synthetic methods, there has been a push towards cleaner and more efficient approaches. This has led to the introduction of high-throughput synthesis and mechanochemical synthesis. The recent success of metal–organic frameworks has also promoted renewed interest in the synthesis of porous metal phosphonates and phosphinates. Regarding characterisation, the main advances are the development of electron diffraction as a tool for crystal structure determination and the deployment of in situ characterisation techniques, which have allowed for a better understanding of reaction pathways. In terms of applications, metal phosphonates have been found to be suitable materials for several purposes: they have been employed as heterogeneous catalysts for the synthesis of fine chemicals, as solid sorbents for gas separation, notably CO2 capture, as materials for electrochemical devices, such as fuel cells and rechargeable batteries, and as matrices for drug delivery. Publisher PDF

Silica-mineralizing organisms such as diatoms manage several aspects of silica chemistry when polymerizing monomeric silicic acid into amorphous silica. Silicic acid is undersaturated in the diatoms’ habitats and mechanisms of enrichment and prevention of uncontrolled mineralization are not well understood. Diatom-biosilica is associated with organic compounds, including polycationic, post-translationally modified peptides termed silaffins, which induce the condensation of silicic acid under supersaturated conditions. Here, we report the pleiotropic action of the designed silaffin-like peptide P5S3, which (i) stabilizes 4–8x silicic acid (in supersaturated conditions of 8.3 mm), (ii) decelerates silica hydrolysis in non-saturated conditions (1 mm) and (iii) enhances silica precipitation at 15–30x supersaturation (30 mm), forming a composite precipitate. Abundant cationic amino acids in P5S3 can interact with silica, though blocking experiments with selected anions also indicate a role of non-electrostatic (e. g. amide-silica) interactions. This shows how silaffin-like peptides could potentially contribute to both keeping silica soluble, and forming peptide-silica precipitates.

Phosphonate ligands demonstrate strong affinity for metal ions. However, there are several cases where the phosphonate is found non-coordinated to the metal ion. Such compounds could be characterized as salts, since the interactions involved are ionic and hydrogen bonding. In this paper we explore a number of such examples, using divalent metal ions (Mg2+, Ca2+, Sr2+ and Ni2+) and the phosphonic acids: p-aminobenzylphosphonic acid (H2PABPA), tetramethylenediamine-tetrakis(methylenephosphonic acid) (H8TDTMP), and 1,2-ethylenediphosphonic acid (H4EDPA). The compounds isolated and structurally characterized are [Mg(H2O)6]&middot, [HPABPA]2&middot, 6H2O, [Ca(H2O)8]&middot, [HPABPA]2, [Sr(H2O)8]&middot, [HPABPA]2, [Mg(H2O)6]&middot, [H6TDTMP], and [Ni(H2O)6]&middot, [H2EDPA]&middot, H2O. Also, the coordination polymer {[Ni(4,4&rsquo, bpy)(H2O)4]&middot, H2O}n was synthesized and characterized, which contains a bridging 4,4&rsquo, bipyridine (4,4&rsquo, bpy) ligand forming an infinite chain with the Ni2+ cations. All these compounds contain the phosphonate anion as the counterion to charge balance the cationic charge originating from the metal cation.

Novel pillared-layered framework materials were synthesized by high-throughput or microwave-assisted methodology that contain Mg2+ and the zwitterionic linker HDTMP (hexamethylenediamine-N,N,N&prime, N&prime, tetrakis(methylenephosphonic acid)). Three compounds were structurally characterized by X-ray powder diffraction. In the compound {Mg[(HO3PCH2)2N(CH2)6N(CH2PO3H2)2]&middot, (H2O)}n(1), obtained at 140 &deg, C by hydrothermal or microwave-assisted reaction, the layers are built by isolated Mg2+ octahedra coordinated by oxygen atoms from six different zwitterionic HDTMP ligands. Each amino-bis(methylenephosphonate) moiety links three Mg2+ ions, bridging two of them through one phosphonate group and connecting the third polyhedron in a monodentate fashion. In Compound 2, {Mg[(HO3PCH2)2N(CH2)6N(CH2PO3H2)2]}n, hydrothermally synthesized at 180 &deg, C, the layers are composed of bidentate amino-bis(methylenephosphonate) moieties connected to three Mg2+ ions, with one of the phosphonate groups acting as a bridging ligand. Various subtle structural changes are noted for the other two compounds. Thermodiffraction of 1 reveals that a crystalline-to-crystalline phase transformation occurs concomitantly with its dehydration, leading to a new anhydrous phase, namely, {Mg[(HO3PCH2)2N(CH2)6N(CH2PO3H2)2]}n(1deh). This process is fully reversible upon equilibrating the solid at room temperature. The reported compounds can adsorb ammonia and CO2. Compound 1 exhibits a moderate proton conductivity, ~1.5 &times, 10&minus, 5 S&middot, cm&minus, 1 at 80 &deg, C and 95% RH, that increases a half order of magnitude after experiencing a complete dehydration/rehydration process, 1&rarr, 1deh&rarr, 1.

Colloidal/amorphous silica (SiO2nH2O, n is variable) is considered as the most undesirable inorganic precipitate that forms during various processes in silica-supersaturated industrial waters. In this paper we present how certain polymeric chemical additives can prevent silicic acid polymerization to form colloidal silica, which may lead to deposition onto industrial equipment. More specifically, stabilization of silicic acid is accomplished by using a cationic polymer, polyallylamine hydrochloride (PALAM), in supersaturated silica solutions (starting silica concentration in the form of silicate 500 ppm, or 8.3 mM sodium orthosilicate, Na2SiO3·5H2O, expressed as SiO2) at pH = 7. PALAM is a linear homopolymer that carries one amine side functional group every two carbon atoms, so it becomes protonated at circumneutral pH, rendering the molecule cationic. Its blends with anionic polymers such as carboxymethylinulin (CMI), poly(acrylamide-co-acrylic acid) (PAM-co-AA) and phosphonomethylated chitosan (PCH) are also studied for their silica scale inhibition efficiency.

Increased interest in the area of metal phosphonate inorganic–organic frameworks is exemplified with a high range of applications and a rich synthetic and structural chemistry of these compounds. The synthesis and potential applications of a novel metal phosphonate, namely Cu(II) phenylvinylphosphonate (PVP) is described in this paper. Syntheses were performed starting from a 1:1 molar ratio of a Cu(NO3)2·6H2O or CuSO4·5H2O and 1-phenylvinylphosphonic acid under hydrothermal conditions at pH values ranging between 2.8 and 3.1. The influence of different counterion for the copper salt used as the Cu(II) source on the structure and crystallinity of the final product was studied. The obtained copper(II) phenylvinylphosphonate compounds were characterized by X-ray powder diffraction, FT-IR spectroscopy, scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and energy-dispersive X-ray spectrometry (EDAX). A possible crystal structure for the copper (II) phenylvinylphosphonate products ...

Mono- and disilicic acids were stabilized by uncharged polyethylene glycols (PEGs) in silica-supersaturated solutions (the starting solution contained 500 ppm/8.3 mM sodium orthosilicate, Na2SiO3·5H2O, expressed as SiO2) at pH = 7, most likely by hydrogen bonding between the silanol groups and -CH2-CH2-O-ether moieties. The stabilization was monitored by measuring molybdate-reactive silica and also by a combination of liquid- and solid-state (29)Si NMR spectroscopy. It depends on PEG concentration (20-100 ppm) and molecular weight (1550-20,000 Da). Two narrow (29)Si NMR signals characteristic for monosilicic acid (Q(0)) and disilicic acid (Q(1)) can be observed in (29)Si NMR spectra of solutions containing PEG 10000 with intensities distinctly higher than the control, that is, in the absence of PEG. Silica-containing precipitates are observed in the presence of PEG, in contrast to the gel formed in the absence of PEG. These precipitates exhibit similar degrees of silica polycondensation as found in the gel as can be seen from the (29)Si MAS NMR spectra. However, the (2)D HETCOR spectra show different (1)H NMR signal shifts: The signal due to H-bonded SiOH/H2O, which is found at 6 ppm in the control, is shifted to ~7 ppm in the PEG-containing precipitate. This indicates the formation of slightly stronger H-bonds than in the control sample, most likely between PEG and the silica species. The presence of PEG in these precipitates is unequivocally proven by (13)C CP MAS NMR spectroscopy. The (13)C signal of PEG significantly shifts and is much narrower in the precipitates as compared to the pristine PEG, indicating that PEG is embedded into the silica or at least bound to its surface (or both), and not phase separated. FT-IR spectra corroborate the above arguments. The H-bonding between silanol and ethereal O perturbs the band positions attributed to vibrations involving the O atom. This work may invoke an alternative way to envision silica species stabilization (prior to biosilica formation) in diatoms by investigating possible scenarios of uncharged biomacromolecules playing a role in biosilica synthesis.

Two new families of divalent metal hybrid derivatives from the aromatic tetraphosphonic acids 1,4- and 1,3-bis(aminomethyl)benzene-N,N′-bis(methylenephosphonic acid), (H2O3PCH2)2−N−CH2C6H4CH2−N(CH2PO3H2)2 (designated herein as p-H8L and m-H8L) have been synthesized by crystallization at room temperature and hydrothermal conditions. The crystal structures of M[(HO3PCH2)2N(H)-CH2C6H4CH2N(H)(CH2PO3H)2(H2O)2]·2H2O (M = Mg, Co, and Zn), M−(p-H6L), and M[(HO3 PCH2)2N(H)-CH2C6H4CH2N(H)(CH2PO3H)2]·nH2O (M = Ca, Mg, Co, and Zn and n = 1−1.5), M−(m-H6L), were solved ab initio by synchrotron powder diffraction data using the direct methods and subsequently refined using the Rietveld method. The crystal structure of the isostructural M−(p-H6L) is constituted by organic−inorganic monodimensional chains where the phosphonate moiety acts as a bidentate chelating ligand bridging two metal octahedra. M−(m-H6L) compounds exhibit a 3D pillared open-framework with small 1D channels filled with water molecules. These channels are formed by the pillaring action of the organic ligand connecting adjacent layers through the phosphonate oxygens. Thermogravimetric and X-ray thermodiffraction analyses of M−(p-H6L) showed that the integrity of their crystalline structures is maintained up to 470 K, without significant reduction of water content, while thermal decomposition takes place above 580 K. The utility of M−(p-H6L) (M = Mg and Zn) hybrid materials in corrosion protection was investigated in acidic aqueous solutions. In addition, the impedance data indicate both families of compounds display similar proton conductivities (σ ∼ 9.4 × 10−5 S·cm−1, at 98% RH and 297 K), although different proton transfer mechanisms are involved. Proyecto nacional MAT2010-15175

The (31)P chemical shift tensor of the phosphonate group [RC-PO(2)(OH)](-) is investigated with respect to its principal axis values and its orientation in a local coordinate system (LCS) defined from the P atom and the directly coordinated atoms. For this purpose, six crystalline metal aminotris(methylenephosphonates), MAMP·xH(2)O with M = Zn, Mg, Ca, Sr, Ba, and (2Na) and x = 3, 3, 4.5, 0, 0, and 1.5, respectively, were synthesized and identified by diffraction methods. The crystal structure of water-free BaAMP is described here for the first time. The principal components of the (31)P shift tensor were determined from powders by magic-angle-spinning NMR. Peak assignments and orientations of the chemical shift tensors were established by quantum-chemical calculations from first principles using the extended embedded ion method. Structure optimizations of the H-atom positions were necessary to obtain the chemical shift tensors reliably. We show that the (31)P tensor orientation can be predicted within certain error limits from a well-chosen LCS, which reflects the pseudosymmetry of the phosphonate environment.

[EN] The chemistry of metal phosphonates has been progressing fast with the addition of new materials that possess novel structural features and new properties, occasionally in a cooperative manner. In this paper, we report a new family of functional lanthanide-carboxyphosphonate materials. Specifically, the lanthanide is La, Ce, Pr, Sm, Eu, Gd, Tb, or Dy and the carboxyphosphonate ligand is 2-hydroxyphosphonoacetic acid (H(3)HPA). All reported LnHPA compounds, Ln(3)(H0.73O3PCHOHCOO)(4)center dot xH(2)O (x = 15-16), crystallize in the orthorhombic system. Two types of structures were isolated: series I and II polymorphs. For both series, the three-dimensional (3D) open frameworks result from the linkage of similar organo-inorganic layers, in the ac-plane, by central lanthanide cations, which yield trimeric units also found in other metal-HPA hybrids. Large oval-shaped 1D channels are formed by the spatial separation of the layers along the b-axis and filled with lattice water molecules. LnHPA materials undergo remarkable crystalline-to-amorphous-to crystalline transformations upon dehydration and rehydration cycles, as confirmed by thermodiffraction and NMR spectroscopy. The highest proton conductivity was observed for GdHPA (series II), 3.2 X 10(-4) S cm(-1) at 98% RH and T = 21 degrees C. The dehydration-rehydration chemistry was also followed by photoluminescence spectroscopy. It was shown that loss and reuptake of water molecules are accompanied by clear changes in the photoluminescence spectra and lifetimes of the Eu analog (series II). Our present results reveal a wide family of well-characterized, multifunctional lanthanide-based phosphonate 3D-structured metal-organic frameworks (MOFs) that show reversible crystalline-to-amorphous-to-crystalline transformations and, at the same time, exhibit high proton conductivity., The work at UMA was funded by MAT2010-15175 research grant (Spain), which is cofunded by FEDER. The work at the UoC was supported by a grant from the Research Committee of the University of Crete, ELKE, (KA 3517). The project "Factoria de Crystalizacion, CONSOLIDER INGENIO-2010" provided X-ray structural facilities for this work.

Multifunctional materials, especially those combining two or more properties of interest, are attracting immense attention due to their potential applications. MOFs, metal organic frameworks, can be regarded as multifunctional materials if they show another useful property in addition to the adsorption behavior. Here, we report a new multifunctional light hybrid, MgH6ODTMP·2H2O(DMF)0.5 (1), which has been synthesized using the tetraphosphonic acid H8ODTMP, octamethylenediamine-N,N,N′,N′-tetrakis(methylenephosphonic acid), by highthroughput methodology. Its crystal structure, solved by Patterson-function direct methods from synchrotron powder Xray diffraction, was characterized by a 3D pillared open framework containing cross-linked 1D channels filled with water and DMF. Upon H2O and DMF removal and subsequent rehydration, MgH6ODTMP·2H2O (2) and MgH6ODTMP·6H2O (3) can be formed. These processes take place through crystalline−quasi-amorphous−crystalline transformations, during which the integrity of the framework is maintained. A water adsorption study, at constant temperature, showed that this magnesium tetraphosphonate hybrid reversibly equilibrates its lattice water content as a function of the water partial pressure. Combination of the structural study and gas adsorption characterization (N2, CO2, and CH4) indicates an ultramicroporous framework. High-pressure CO2 adsorption data are also reported. Finally, impedance data indicates that 3 has high proton conductivity σ = 1.6 × 10−3 S cm−1 at T = 292 K at ∼100% relative humidity with an activation energy of 0.31 eV. Proyecto nacional MAT2010-15175 (MICINN, España)

In this paper we report the synthesis and structural characterization of the 2D layered coordination polymer Mg(BPMGLY)(H2O)2 (BPMGLY = bis-phosphonomethylglycine, (HO3PCH2)2N(H)COO2−). The Mg ion is found in a slightly distorted octahedral environment formed by four phosphonate oxygens and two water molecules. The carboxylate group is deprotonated but noncoordinated. This compound is a useful starting material for a number of topotactic transformations. Upon heating at 140 °C one (of the two) Mg-coordinated water molecule is lost, with the archetype 2D structure maintaining itself. However, the octahedral Mg in Mg(BPMGLY)(H2O)2 is now converted to trigonal bipyramidal in Mg(BPMGLY)(H2O). Upon exposure of the monohydrate Mg(BPMGLY)(H2O) compound to ammonia, one molecule of ammonia is inserted into the interlayer space and stabilized by hydrogen bonding. The 2D layered structure of the product Mg(BPMGLY)(H2O)(NH3) is still maintained, with Mg now acquiring a pseudo-octahedral environment. All of these topotactic transformations are also accompanied by changes in hydrogen bonding between the layers. Proyecto nacional MAT2010-15175

The catalytic role of Mg2+ ions in the polycondensation of silicic acid to form amorphous silica has been investigated in detail. This behavior is pH-dependent. As pH increases (herein, the three p...

The effect of various fluorine-containing chemical additives on the dissolution of colloidal silica is systematically studied. These silica scale dissolvers are ammonium bifluoride (NH4·HF2), ammonium fluoride (NH4F), sodium tetrafluoroborate (NaBF4), and disodium fluorophosphate (Na2PO3F). The most effective dissolver was NH4·HF2, which was extensively studied at the pH range 2–7. The highest dissolution efficiency was demonstrated in the pH range 2–4. The dissolution capability of Na2PO3F was monitored not by the silicomolybdate method, but on the basis of a weight-loss approach. It showed substantial dissolution ability at pH’s 7 and 9.

Five compounds based on the versatile pyrazole-4-sulfonate anion (4-SO3-pzH = L−) were synthesized by the reaction of ligand HL with ZnO, CdCO3, Ag2O, NaOH and NH3, respectively. Crystals of Zn(4-SO3-pzH)2(H2O)2, Cd(4-SO3-pzH)2(H2O)2, Ag(4-SO3-pzH), Na(4-SO3-pzH)(H2O) and NH4(4-SO3-pzH) were obtained from aqueous solutions upon evaporation, and were characterized by single-crystal X-ray diffraction, IR and NMR spectroscopy, thermogravimetric analysis and copper corrosion inhibition experiments. We found that the non-isomorphous, 3-dimensional inorganic–organic layered solid state structure of these compounds is determined by an intricate interplay between the size, charge and coordination preference of the cation, and an extended lattice of hydrogen bonds and aromatic interactions. Ligand L− incorporates a host of different binding capabilities (metal coordination through the pyrazole N-atom and/or the sulfonate O-atom, hydrogen-bonding both as donor and acceptor, π–π and C–H⋯π interactions). Thin films formed by these complexes on copper metal surfaces were studied by optical microscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. ZnL2, CdL2, AgL and NH4L, in addition to the free ligand HL, were tested as corrosion inhibitors on copper metal surfaces at three different pH values (2, 3 and 4), and the corrosion rates were quantified. Significant corrosion protection was observed with all compounds at pH 4 and 3.

The effect of various chemical additives (small molecules and polymers) on the dissolution of two kinds of colloidal silica (Aerosil 200 and laboratory-synthesized, SSD) is systematically studied at pH 10. The silica scale dissolvers tested are 5-carboxybenzotriazole (CBZT), amino-tris(methylene phosphonic acid) (AMP), a phosphino-polycarboxylic acid (PPCA), diethylenetriamine pentacarboxylic acid (DETPA), a proprietary polymer (Genesol 40), poly(acrylic acid) (PAA), ethylenediamine-tetrakis(methylenephosphonic acid) (EDTMP), phosphonobutane-1,2,4-tricarboxylic acid (PBTC), sodium metaborate, and N-phosphonomethylimino-diacetic acid (PMIDA). Of the polymeric additives only Genesol 40 shows some dissolution activity, dissolving ∼280 ppm silica at 10 000 ppm dosage after 72 h. PBTC and DETPA are the best-performing additives of all those tested. PBTC is effective even at the 2500 ppm dosage, as it solubilizes ∼290 ppm silica after 72 h. Its efficiency is dosage-dependent. DETPA is also an effective silica d...

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 FTIR, 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 Cu2+ atom, a square planar Cu2+ 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. Proyecto nacional MAT2010-15175 (MICINN, España)

In this report, we demonstrate a topotactic transformation of a [Cu(HPAA)(H2O)2]·H2O one-dimensional (1D) hybrid (HPAA = HO3PCH(OH)CO2, hydroxyphosphonoacetate dianion) to an anhydrous Cu(HPAA) three-dimensional (3D) framework, via the 1D intermediate Cu(HPAA)(H2O)2. Removal of lattice water from 1D [Cu(HPAA)(H2O)2]·H2O yields 1D Cu(HPAA)(H2O)2 and results in alterations in hydrogen bonding interactions (chain···H2O···chain), and, in turn, compaction of the chains as well as “slipping”. These changes are accompanied by creation of a new hydrogen bonding scheme (chain···chain) involving the phosphonate groups and the hydroxyl/carboxy moieties. The initial zigzag 1D chain is retained throughout the dehydration process. In 3D Cu(HPAA) the resulting vacant sites on Cu (generated by removal of both Cu-bound waters) are occupied by phosphonate oxygens from neighboring chains. All three materials have been characterized by X-ray diffraction and a variety of other techniques and their structures have been determined.

In this study, the effect of phosphonate additives oil the crystallization of calcium sulfite dihydrate (CaSO4 center dot 2H(2)O, gypsum) has been investigated in aqueous solutions. Ethylenediamine-tetrakis(methylenephosphonic acid) (EDTMP), hexamethylenediamine-tetrakis(methylenephosphonic acid) (HDTMP), octamethylenediamine-tetrakis-(methylenephosphonic acid) (ODTMP), and dodecamethylenediamine-tetrakis(methylenephosphonic acid) (DDTMP) have been used as additives. It Was found that they are very effective retardants for the crystallization of calcium sulfate dihydrate. The inhibition efficiency is directly proportional to the number of methylene groups in the organic chain that connects the amino-bis-(methylenephosphonate) moieties. The degree of inhibition of crystallization was measured as an increase in induction time and reduction in crystallization rate. Particle size and crystal morphology were determined with a particle-sizer and scanning electron microscopy. According to experimental results, phosphonate additives tested in this study are very effective retardants for the formation of calcium sulfate dihydrate scale. The crystal structure of [Ca(EDTMP)(H2O)(2)]center dot H2O is also reported. This is a one-dimensional coordination polymer in which EDTMP acts as both a bidentate chelate and a bridge for Ca2+ centers.

The constant growth in the area of metal phosphonate materials is exemplified with rich chemistry and a variety of applications. From the multitude of subjects related to metal phosphonates, we have decided to focus on metal phosphonate coordination polymers as corrosion inhibitors in the present Comment. A plethora of metal phosphonate organic-inorganic polymeric hybrid materials have been synthesized, structurally characterized, and evaluated for their anticorrosion properties for the protection of carbon steels. These materials are composed of a metal ion (usually Zn2+, Ca2+, Sr2+, Ba2+, etc.) and polyphosphonate ligands such as AMP (amino-tris(methylenephosphonate) and HDTMP (hexamethylenediamine-tetrakis(methylenephosphonate), or carboxyphosphonate ligands, such as PBTC (2-phosphonobutane-1,2,4-tricarboxylate) and HPAA (hydroxyphosphonoacetate). Their corrosion inhibition performance has been evaluated and some interesting conclusions are drawn relating molecular structure to inhibitory activity.

Syntheses and structures of alkaline earth metal ions and EDTMP, ethylenediamine-tetrakis(methylenephosphonate), are reported. The isostructural Ca2+ and Sr2+ analogs have 1D topologies, with EDTMP acting as both chelating and bridging ligand. The M-EDTMP compounds act as Fe-oxide removers from corroded surfaces.

In contrast to biomineralization phenomena, that are among the most widely studied topics in modern material and earth science and biomedicine, much less is systematized on modern view of demineralization. Biomineralized structures and tissues are composites, containing a biologically produced organic matrix and nano- or microscale amorphous or crystalline minerals. Demineralization is the process of removing the inorganic part, or the biominerals, that takes place in nature via either physiological or pathological pathways in organisms. In vitro demineralization processes, used to obtain mechanistic information, consist in the isolation of the mineral phase of the composite biomaterials from the organic matrix. Physiological and pathological demineralization include, for example, bone resorption mediated by osteoclasts. Bioerosion, a more general term for the process of deterioration of the composite biomaterials represents chemical deterioration of the organic and mineral phase followed by biological attack of the composite by microorganisms and enzymes. Bioerosional organisms are represented by endolithic cyanobacteria, fungi, algae, plants, sponges, phoronids and polychaetes, mollusks, fish and echinoids. In the history of demineralization studies, the driving force was based on problems of human health, mostly dental caries. In this paper we summarize and integrate a number of events, discoveries, milestone papers and books on different aspect of demineralization during the last 400 years. Overall, demineralization is a rapidly growing and challenging aspect of various scientific disciplines such as astrobiology, paleoclimatology, geomedicine, archaeology, geobiology, dentistry, histology, biotechnology, and others to mention just a few.

Dissolution of biologically important sparingly soluble salts, such as calcium carbonate and calcium oxalate, is possible by use of carboxyl- and carboxyl/phosphonate-bearing, anionic additives, citrate, malate, carboxyphosphonate, and butane tetracarboxylate. Calcium-containing dissolution products have been identified, characterized, and independently synthesized. These are polymeric materials composed of calcium and the additive as the ligand. Their full characterization was carried out by single-crystal X-ray crystallography and other techniques.

Reactions of M2+ (M = Mg2+ (1), Ca2+ (2), Sr2+ (3), or Ba2+ (4)) salts with R,S-hydroxyphosphonoacetic acid (HPAA) in aqueous solutions of pH 2.0−2.7 at a 1:1 ratio yield hydrated M−HPAA layered or three-dimensional coordination polymers with varying degrees of hydration (metal-coordinated water or lattice water). The crystal structures of 3 (two different phases, 3a and 3b, formed at slightly different pH) and 4 have been determined by single-crystal X-ray crystallography. Both enantiomers (R and S) of HPAA are incorporated in these metal−HPAA materials. Compounds were also characterized by a plethora of other techniques (ATR-IR, SEM, TGA, elemental analyses, powder XRD). Corrosion experiments were carried out at pH 2.0 and 7.3 to study the effect of combinations of externally added Sr2+ or Ba2+ and HPAA (1:1 ratio) on corrosion rates of carbon steel. It was found that at pH 2.0 Sr/HPAA or Ba/HPAA 1:1 combinations are not able to inhibit corrosion. However, at pH 7.3 quantitative corrosion inhibition is ...

In this work, the effect of a biodegradable, environmentally friendly polysaccharide-based polycarboxylate, carboxymethyl inulin (CMI), on the crystal growth kinetics of calcium oxalate was studied...

Reactions of Mg2+ (1), Ca2+ (2), Sr2+ (3), or Ba2+ (4) salts with hydroxyphosphonoacetic acid (HPAA) at a 1:1 ratio yield M-HPAA layered coordination polymers. The crystal structures of 3 (two phases) and 4 have been determined by single crystal X-ray crystallography. Both stereoisomers (R and S) of HPAA are incorporated in the metal-HPAA materials. Synergistic combinations of Sr2+ or Ba2+ and HPAA at pH 7.3 are effective corrosion inhibitors for carbon steel, but are ineffective at pH 2.0.

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 = La3+, Pr3+, Sm3+, Eu3+, Gd3+, Tb3+, Dy3+, Ho3+, H6NMP = nitrilotris(methylphosphonic acid)], and contain Cl− as the counterion. In the case of Ce3+, 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 Ln3+ 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 H4NMP2− organic group has no measurable absorption or luminescence properties. Proyecto nacional MAT2013-41836-R (MINECO) y Proyecto de la Junta de Andalucía P12-FQM-1656

The effect of citrate and phosphocitrate ions on the spontaneous precipitation of magnesium ammonium phosphate hexahydrate (MgNH4PO4·6H2O, struvite) at pH 8.50 and 25 °C was investigated at conditions of constant solution supersaturation. The supersaturated solutions were prepared in synthetic wastewater. The presence of citrate and phosphocitrate in the working solutions showed reduction of the initial rates of struvite precipitation when compared with solutions in their absence. The parabolic dependence of the rates of precipitation on the relative solution supersaturation suggested a surface-diffusion-controlled mechanism. Presence of citrate and phosphocitrate in the supersaturated solutions at concentration levels from 1 to 10 µM resulted in a drastic increase in induction times. The presence of citrate and phosphocitrate inhibited struvite precipitation up to 75–80%. The reduction of precipitation rates was related to additive concentration following an expression suggested by the kinetic Langmuir-t...

Mineral scale deposits such as calcium carbonate and phosphate, calcium oxalate, barium and strontium sulfate, magnesium silicate and others and colloidal inorganic species such as silica present important challenges for process water applications. When silica is left uncontrolled it forms hard and tenacious deposits that are difficult and hazardous to remove. Conventional phosphonate mineral scale inhibitors do not inhibit silica formation and deposition. Chemical cleaning is not free from hazards and requires operational shut-downs. Another challenge is corrosion of critical metal surfaces of industrial equipment. Last but not least, biofouling due to the development of microorganisms. This paper is focused on the presentation of the general scope of these problems and their solutions. More specifically, it concentrates on (a) inhibition of colloidal silica formation, (b) colloidal silica dissolution, and (c) metallic corrosion, in water applications by use of designed chemical approaches. The additives used for silica inhibition were polyaminoamide dendrimers, polyethyloxazoline and polyethyleneimine polymers. For silica dissolution the dissolvers tested were carboxymethyl inulin (CMI), Genesol 40 (a proprietary blend of additives), polyacrylic acid. In principle, silica inhibition is a function of time and inhibitor dosage. Silica dissolution is dependent in a rather unpredictable fashion on the structure of the dissolver, time and dosage. Mild steel corrosion inhibition has been achieved by synergistic use of zinc ions and polyphosphonate anions that create protective films.

Organic, phosphorus‐based additives are commonly used in water treatment technologies such as mineral scale and corrosion inhibitors, and dispersing agents. Phosphonates find extensive use as anti‐precipitation inhibitors for sparingly soluble salts such as calcium carbonates and phosphates, calcium/barium/strontium sulfates and others, commonly formed in supersaturated process waters in a wide spectrum of industrial applications. In open recirculating cooling water systems strong oxidizing biocides (eg. ClO−, BrO−, etc.) are also added to control microbiological growth but have detrimental effects on other water treatment chemicals that are sensitive to oxidative degradation. In this paper we report the effect of a hypobromite‐based biocide towards the scale inhibitor AMP (amino‐tris‐(methylene phosphonate)). AMP reacts rapidly with the biocide at room temperature. AMP degradation continues, but it slowly reaches a plateau after 1000 minutes. Even after 50 h the reaction time, only 20% of AMP ha...

Structural changes between [OsIIL3]2+ and [OsIIIL3]3+ (L: 2,2′-bipyridine; 1,10-phenanthroline) and molecular and electronic structures of the OsIII complexes [OsIII(bpy)3]3+ and [OsIII(phen)3]3+ are discussed in this paper. Mid-infrared spectra in the ν(bpy) and ν(phen) ring stretching region for [OsII(bpy)3](PF6)2, [OsIII(bpy)3](PF6)3, [OsII(phen)3](PF6)2, and [OsIII(phen)3](PF6)3 are compared, as are X-ray crystal structures. Absorption spectra in the UV region for [OsIII(bpy)3](PF6)3 and [OsIII(phen)3](PF6)3 are dominated by very intense absorptions (e = 40 000–50 000 M−1 cm−1) due to bpy and phen intra-ligand π → π∗ transitions. In the visible region, relatively narrow bands with vibronic progressions of ∼1500 cm−1 appear, and have been assigned to bpy or phen-based, spin–orbit coupling enhanced, 1π → 3π∗ electronic transitions. Also present in the visible region are ligand-to-metal charge transfer bands (LMCT) arising from π(bpy) → t2g(OsIII) or π(phen) → t2g(OsIII) transitions. In the near infrared, two broad absorption features appear for oxidized forms [OsIII(bpy)3](PF6)3 and [OsIII(phen)3](PF6)3 arising from dπ–dπ interconfigurational bands characteristic of dπ5OsIII. They are observed at 4580 and 5090 cm−1 for [OsIII(bpy)3](PF6)3 and at 4400 and 4990 cm−1 for [OsIII(phen)3](PF6)3. The bpy and phen infrared vibrational bands shift to higher energy upon oxidation of Os(II) to Os(III). In the cation structure in [OsIII(bpy)3](PF6)3, the OsIII atom resides at a distorted octahedral site, as judged by ∠N–Os–N, which varies from 78.78(22)° to 96.61(22)°. Os–N bond lengths are also in general longer for [OsIII(bpy)3](PF6)3 compared to [OsII(bpy)3](PF6)2 (0.010 A), and for [OsIII(phen)3](PF6)3 compared to [OsII(phen)3](PF6)2 (0.014 A). Structural changes in the ligands between oxidation states are discussed as originating from a combination of dπ(OsII) → π∗ (bpy or phen) backbonding and charge redistribution on the ligands as calculated by natural population analysis.

Barium sulfate is a common scale in oil production installations that is treated and controlled with phosphonate inhibitors. A fundamental understanding of how these inhibitors operate, however, is only slowly emerging. In this paper, we investigate the effect on barium sulfate crystallization of two very similar phosphonate molecules that only differ in their backbone spacing, ethylenediamine-N,N,N‘,N‘-tetra(methylenephosphonic acid) (EDTMP) and hexamethylenediamine-N,N,N‘,N‘-tetra(methylenephosphonic acid) (HDTMP). It was found that the inhibitory efficacy of the organic molecules depends on their structural differences but also on the presence of other cations such as Zn2+. It appears that both stereochemical considerations and complexation strength differences between the two phosphonate additives result in different inhibitory powers. In the presence of zinc cations and EDTMP, it is found that inhibition is related to the concentration of uncomplexed (“free”) organic.

Misapplication of chemical water treatment inhibition technologies results in the formation of water-formed scale deposits (notably, CaCO3 and BaSO4) that interfere with proper system operation. These are removed by chemical additives through dissolution. Herein, we report the efficient dissolution of CaCO3 at pH 4 by 2-phosphonobutane-1,2,4-tricarboxylic acid (H5PBTC). We also report the identity of the Ca-containing dissolution product, characterized by single-crystal X-ray crystallography and a variety of spectroscopic techniques, as (Ca(H3PBTC)(H2O)2‚2H2O)n. It is the first metal -PBTC complex reported to date. In the structure of polymeric (Ca(H3- PBTC)(H2O)2‚2H2O)n Ca 2+ is seven-coordinated, bound by two phosphonate oxygens, three carboxylate oxygens, and two water molecules. (Ca(H3PBTC)(H2O)2‚2H2O)n was also prepared by designed synthesis by reacting various Ca 2+ sources and H5PBTC. Studies of anticorrosion properties of Ca2+/H3PBTC2- combinations are also reported. Organic phosphonates are used extensively in a plethora of technological applications. 1 In medical and pharmaceutical applica- tions, organic phosphonates are used extensively as regulators of calcium phosphate metabolism 2 and for treatment of calcium deposition diseases.3 Industrial applications include chemical water treatment, 4 dispersion technology, 5 and metallic corrosion control. 6

Organic additives are broadly used in water-treatment applications such as mineral scale, corrosion inhibitors, and dispersing agents. Phosphonates find extensive use as inhibitors for the formation of sparingly soluble salts such as calcium carbonates, phosphates, calcium sulfates, and others, commonly formed in open recirculating cooling systems. In such systems, biocides also are added to control microbiological growth. Some of these biocides are strong oxidants (e.g., ClO−, BrO−, etc.) and affect other water treatment chemicals that are sensitive to oxidative degradation. This study reports the effect of a hypobromite-based biocide towards the triphosphonate amino-tris-(methylene phosphonate) (AMP). AMP reacts rapidly with the biocide at room temperature. AMP degradation continues, but it slowly reaches a plateau after 1000 min. Even after 50 h of reaction time, only 20% of the AMP has decomposed. AMP reacts with the biocide to give orthophosphate much more rapidly at 43°C than at 25°C due to faster k...

The effect of various environmentally friendly chemical additives on the dissolution of colloidal sil- ica is systematically studied. These silica scale dis- solvers are principally polycarboxylates with one to five -COOH groups, mixed polycarboxylates/phosphonates and aminoacids. Based on these results, an effort is made to link their dissolution performance to struc- tural features in this structure/function study. Presence of additional groups (eg. -PO3H2, -NH2 ,o r-OH) in the dissolver molecule augments the dissolution process.

This paper is focused on a dual approach for silica scale control, inhibition and dissolution by use of designed chemical approaches. Inhibitors that are tested include the polyaminoamide STARBURST dendrimers (PAMAM) of generations 0.5, 1.0, 1.5, 2.0, and 2.5. Of these, only the NH2-terminated ones (PAMAM-1.0 and 2.0) show significant inhibitory activity, in contrast to COOH-terminated ones (PAMAM-0.5, 1.5, and 2.5), which show virtually no inhibition performance. The synergism between the above dendrimers and an anionic polyelectrolyte (poly(acrylamide-co-acrylate) copolymer) is also described. Addition of poly(acrylamide-co-acrylate) copolymer in silica supersaturated solutions containing PAMAM-1 or 2 alleviates the appearance of silica-PAMAM insoluble precipitates, resulting in stable colloids. The paper also describes silica dissolution approaches, as an alternative to inhibition, by using nonhazardous additives based on polycarboxylates with one to five −COOH groups (acetate, oxalate, citrate, diethy...

Amino-tris-(methylenephosphonate) (AMP, N(CH2PO3H2)3) forms various organic–inorganic hybrids with divalent metal cations. Zn2+ reacts with AMP at a 1:1 ratio by replacing two of the six phosphonic acid protons, while amino N maintains its proton, thus forming a zwitter ion. The product is a polymeric material, Zn[HN(CH2PO3H)3(H2O)3]. Its crystal is monoclinic, space group P21/c, with a = 9.1908(7) A, b = 16.0054(12) A, c = 9.6791(7) A, β = 115.2890(10)°, V = 1287.37(17) A3, and Z = 4. The Zn2+ ions form zig-zag chains bridged by two of the three phosphonate groups. The third phosphonate group is non-coordinating and involved in hydrogen bonding. The Zn2+ centers are located in a slightly distorted octahedral environment and are coordinated by three H2O molecules in a mer fashion, two phosphonate oxygens from the same AMP ligand forming an eight-member chelate and another phosphonate oxygen from a neighboring AMP. Adjacent chains are hydrogen-bonded to each other through P–O–H and H–N donors, and the additional participation of all H2O hydrogens in H-bonding results in a corrugated sheet-like structure. Zn2+ and AMP form a synergistic combination of additives that acts as corrosion inhibitor for carbon steel surfaces. The composition of this protective layer is a Zn–AMP material based on spectroscopic comparisons (FT-IR, XRF and EDS) with authentically prepared Zn–AMP.

Dendrimers have attracted immense attention during the last decade due to their interesting properties both from a basic and an applied research viewpoint. Encapsulation of metal nanoparticles for catalysis, drug delivery and light harvesting are only some applications of dendrimers that are breaking new ground. A novel application of dendrimer technology is described in the present paper that relates to industrial water treatment. Industrial water systems often suffer from undesirable inorganic deposits. These can form either in the bulk or on metallic surfaces, such as heat exchangers or pipelines. Silica (SiO2) scale formation and deposition is a major problem in high-silica-containing cooling waters. Scale prevention rather than removal is highly desired. In this paper, benchtop screening tests on various silica inhibition chemistries are reported, with emphasis on materials with a dendrimeric structure. Specifically, the inhibition properties of commercially available STARBURST  polyaminoamide (PAMAM) dendrimers generations 0.5, 1, 1.5, 2, and 2.5 are investigated in detail together with other commonly-used scale inhibitors. Experimental results show that inhibition efficiency largely depends on structural features of PAMAM dendrimers such as generation number and nature of the end groups. PAMAM dendrimers are effective inhibitors of silica scale growth at 40ppm dosage levels. PAMAM dendrimers also act as silica nucleators, forming SiO2-PAMAM composites. This occurs because the SiO2 formed by incomplete inhibition interacts with cationic PAMAM-1 and -2. The general scope of silica formation and inhibition in industrial waters is also discussed.  2005 Society of Chemical Industry

Aminomethylene phosphonates are important scale inhibitors applied in diverse areas of technology. This study adds to the existing body of information on this subject and reports the crystal and molecular structures of tetrasodium 2-hydroxyethylamino- bis (methylene-phosphonate) decahydrate ([Na 4 (HOCH 2 CH 2 N(CH 2 PO 3 ) 2 )]·10H 2 O, 1). The crystal structure of 1 could be described as two-dimensional polymeric layered structure hydrogen bonded into a 3D supramolecular polymeric network. The structure of the tetraanion consists of a “three-arm” backbone stemming from the N atom. Two “arms” are deprotonated methylene phosphonate (–CH 2 PO 3 2− ) moieties and the third is a hydroxyethyl (–CH 2 CH 2 OH) moiety. One Na cation forms an intramolecular complex with two oxygens from separate phosphonate groups, a hydroxyl oxygen, the nitrogen and two lattice water molecules. The position of this Na cation points to a possible coordination site for Ca in a proposed Ca–HEABMP complex (HEABMP=2-hydroxyethylamino- bis (methylene-phosphonate).

This paper describes the synthesis, characterization and crystal structure of an organic–inorganic polymeric hybrid composed of Ca, Na, and phosphocitrate (CaNaPC). CaNaPC is synthesized by reaction of CaCl2 � 2H2O and Na4ðHPC Þ� 3H2O in water, at pH 2. Its structure is polymeric with CaðPCÞ2ðH2OÞ ‘‘monomers’’ connected through Na þ bridges. The 9-coordinate Ca occupies the center of an irregular polyhedron defined by four phosphate, four carbonyl, and one H2O oxygens. CaAOð@CÞ distances are in the 2.446(2)–2.586(2) A range. There is a short distance of 2.477(1) A between Ca and the ester O from C–O–PO3H2. All –COOH groups are protonated. There are three dissociated protons per two PC molecules, all coming from –PO3H2. Na ions are six-coordinate surrounded by –COOHs. The anticalcification properties of CaNaPC on plaque growth were studied in vivo using rats as model systems. Na–phosphocitrate is an effective inhibitor, but its effectiveness diminishes when a lower dose is used (9.7 mg as H5PC), resulting in only 30% plaque reduction. Superior inhibition activity becomes evident by following treatment with CaNaPC, at an equal dose (9.6 mg as H5PC) giving nearly quantitative (95%) plaque inhibition. 2003 Elsevier Science B.V. All rights reserved.