Aurelio Cabeza

New lead triphosphonates: synthesis, properties and crystal structures

Two new lead nitrilotris(methylene)triphosphonates, Pb[(H 2 O 3 PCH 2 )N(CH 2 PO 3 H) 2 ] I and Pb 2 [(O 3 PCH 2 )N(CH 2 PO 3 H) 2 ]·H 2 O II, have been synthesised. I is triclinic, space group P1, a=8.5077(2), b=11.2363(3), c=5.9484(2) A, α=98.802(2), β=104.955(1), γ=80.911(2)°, Z=2. II is monoclinic, space group Pn, a=7.3614(2), b=11.3889(2), c=7.2541(2) A, β=100.389(2)° and Z=2. Their structures have been solved from laboratory X-ray data by using ab initio powder diffraction methodology. The reliability factors were R wP =9.28%, R P =7.20% and R F =2.67%, for I, and R wP =12.51%, R P =9.38% and R F =4.45%, for II. I shows a new layered structure which has small cavities, inside an inorganic layer, in which the hydrogen phosphonate and the dihydrogen phosphonate groups are located. II is also layered with the water molecule situated in the interlamellar space. Thermal data, IR data and ion-exchange properties are also reported and discussed. II dehydrates to yield orthorhombic Pb 2 [(O 3 PCH 2 )N(CH 2 PO 3 H) 2 ] III. Hydrolysis of I leads to II.

Synthesis and crystal structures of two metal phosphonates, M(HO3PC6H5)2(M = Ba, Pb)

Divalent metal phosphonates, Ba(HO3PC6H5)2 and Pb(HO3PC6H5)2, have been synthesized and structurally characterized [crystal data: a= 32.18(l), b= 5.546(4), c= 8.495(4)A, β= 103.21(3)°, space group C2/c and Z= 4 for Ba(HO3PC6H5)2; a= 31.8302(10), b= 5.5997(2), c= 8.2935(3)A, β= 101.875(2)°, space group C2/c and Z= 4 for Pb(HO3PC6H5)2]. Their structures are isomorphous. The structure of the barium compound was solved from single-crystal data which was then used to refine the-structure of the lead compound by Rietveld methods. In these compounds the metal: phosphonate ratio is 1 : 2 and the phosphonates use all their oxygens to bridge the metal atoms, which are arranged in two-dimensional layers, One of the phosphonate oxygens is protonated. The phosphonate oxygens are involved in both chelation and bridging interactions. The metal atoms are eight-coordinate; four of the binding sites are due to symmetry-related positions of a single oxygen atom and two each from the remaining two oxygen atoms.

Structural complexity and metal coordination flexibility in two acetophosphonates

Two divalent metal acetophosphonates, Pb 6 (O 3 PCH 2 CO 2 ) 4 and Mn 3 (O 3 PCH 2 CO 2 ) 2 , have been synthesised hydrothermally. They crystallise in the triclinic system, space group P, a=11.0064(1), b=12.3604(1), c=8.9783(1) A, α=98.632(1), β=90.474(1), γ=75.629(1)°, Z=2, for M=Pb, and a=10.0146(5), b=6.3942(4), c=8.4796(6) A, α=101.452(4), β=106.254(2), γ=96.431(4)°, Z=2, for M=Mn. The structures were solved ab initio using direct methods from synchrotron powder diffraction data (λ0.4 A) for M=Pb and from laboratory-ray data for M=Mn. The crystal structure of the Pb compound is very complex with 38 non-hydrogen atoms in general positions (114 refined positional parameters), it had been refined by Rietveld method using soft constraints, and converged to R WP =6.8% and R F =1.6%. The structure for M=Mn has a moderate complexity with 19 non-hydrogen atoms (57 refined positional parameters) which was also refined with soft constraints to R WP =8.3%,R F =3.9%. Both compounds show a framework built of alternate metal oxide inorganic layers, pillared by the organic groups. The metal environments in these materials are very distorted. Manganese atoms present three different distorted oxygen environments: four-, five- and six-coordinate. Thermal and IR data are also reported and discussed.

“Breathing” in Adsorbate-Responsive Metal Tetraphosphonate Hybrid Materials

The structures of various layered calcium tetraphosphonates (CaH6DTMP; H8DTMP=hexamethylenediamine tetrakis(methylenephosphonic acid)), have been determined. Starting from CaH6DTMP.2H2O, thermal treatment and subsequent exposure to NH3 and/or H2O vapors led to four new compounds that showed high storage capacity of guest species between the layers (up to ten H2O/NH3 molecules) and a maximum volume increase of 55 %. The basic building block for these phosphonates consists of an eight-membered ring chelating Ca2+ through two phoshonate groups, and the organic ligand is located within the layers, which are held together by hydrogen bonds. The structural analysis revealed that the uptake/removal of guest species (H2O and NH3) induces significant changes in the framework not only by changing the interlayer distances but also through important conformational changes of the organic ligand. An anisotropic breathing motion could be quantified by the changes of the unit-cell dimensions and ligand arrangements in four crystalline derivatives. Complete characterization revealed the existence of interconversion reactions between the different phases upon gas uptake and release. The observed behavior represents, to the best of our knowledge, the first example of a breathing-like mechanism in metal phosphonates that possess a 2D topology.

Structural Mapping and Framework Interconversions in 1D, 2D, and 3D Divalent Metal R,S-Hydroxyphosphonoacetate Hybrids

Reactions of divalent cations (Mg(2+), Co(2+), Ni(2+), and Zn(2+)) with R,S-hydroxyphosphonoacetic acid (HPAA) in aqueous solutions (pH values ranging 1.0-4.0) yielded a range of crystalline hydrated M-HPAA hybrids. One-dimensional (1D) chain compounds were formed at room temperature whereas reactions conducted under hydrothermal conditions resulted in two-dimensional (2D) layered frameworks or, in some cases, three-dimensional (3D) networks incorporating various alkaline cations. 1D phases with compositions [M{HO(3)PCH(OH)CO(2)}(H(2)O)(2)].2H(2)O (M = Mg, Co, and Zn) were isolated. These compounds were dehydrated in liquid water to yield the corresponding [M{HO(3)PCH(OH)CO(2)}(H(2)O)(2)] compounds lacking the lattice water between the 1D chains. [M{HO(3)PCH(OH)CO(2)}(H(2)O)(2)] (M = Mg, Ni, Co, Zn) compounds were formed by crystallization at room temperature (at higher pH values) or also by partial dehydration of 1D compounds with higher hydration degrees. Complete dehydration of these 1D solids at 240-270 degrees C led to 3D phases, [M{HO3PCH(OH)CO(2)}]. The 2D layered compound [Mg{HO(3)PCH(OH)CO(2)}(H(2)O)(2)] was obtained under hydrothermal conditions. For both synthesis methods, addition of alkali metal hydroxides to adjust the pH usually led to mixed phase materials, whereas direct reactions between the metal oxides and the hydroxyphosphonoacetic acid gave single phase materials. On the other hand, adjusting the pH with acetate salts and increasing the ratio M(2+)/HPAA and/or the A(+)/M(2+) ratio (A = Na, K) resulted in 3D networks, where the alkali cations were incorporated within the frameworks for charge compensation. The crystal structures of eight new M(II)-HPAA hybrids are reported herein and the thermal behavior related to dehydration/rehydration of some compounds are studied in detail.

Structure and Electrons in Mayenite Electrides

One major goal in materials chemistry is to find inexpensive compounds with improved capabilities. Stable inorganic electrides, derived from nanoporous mayenite [Ca12Al14O32]O, are a new family that has very interesting properties such as electronic conductivity combined with transparency. However, an intriguing fundamental problem is to understand the structures of these cubic materials and to characterize their free-electron loadings. Here we report an accurate structural study for three members of the series [Ca12Al14O32]O(1-delta)e(2delta) (delta = 0, 0.15, and 0.45), from single-crystal low-temperature synchrotron X-ray diffraction. The complex structural disorder imposed by the presence of the oxide anions into the mayenite cages has been unravelled. Furthermore, the final electron density map for delta = 0.45 black mayenite has shown electron density localized into the center of the cages, which is the first experimental proof of their electride nature. The reported structural findings challenge theorists to improve predictive models in this new family of materials.

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.

Layered and pillared metal carboxyethylphosphonate hybrid compounds

A series of carboxyethylphosphonate hybrid materials has been prepared: Mn(II)(O3PCH2CH2COOH) *H2O (1), Mn(III)(OH)(O3PCH2CH2COOH)*H2O (2), Al3(III)(OH)3(O3PCH2CH2CO2)2 *3H2O (3) and Cr2(III)(OH)3(O3PCH2CH2CO2) *3H2O (4). Compounds 1 and 2 were synthesized from Mn(III)(CH3COO)3 *2H2O under hydrothermal, or refluxing treatments, respectively. The crystal structures of the manganese-bearing solids have been solved ab initio from laboratory X-ray powder diffraction data and refined by the Rietveld method. 1 crystallises in a orthorhombic cell and 2 in monoclinic symmetry. Both solids have inorganic 2D layered structures with the acid carboxylic groups pointing towards the interlayer space, and the layers linked only through hydrogen bonds. The inorganic layers of these compounds are formed by manganese atoms in distorted octahedral environments linked together by the phosphonate groups. The crystal structure of 3 has been solved ab initio from synchrotron X-ray powder diffraction data. This solid shows a pillared structure with the phosphonate and carboxylate groups cross-linking the inorganic layers. These layers contain chains of aluminium octahedra running parallel to each other. 4 is amorphous and the IR-UV-VIS spectra suggest a framework with Cr(III) cations in octahedral environments. Thermal, spectroscopic and magnetic data for manganese and chromium compounds as well as the structural details of these solids are discussed.

Crystal engineering in confined spaces. A novel method to grow crystalline metal phosphonates in alginate gel systems

In this paper we report a crystal growth method for metal phosphonate frameworks in alginate gels. It consists of a metal-containing alginate gel, in which a solution of phosphonate ligand is slowly diffused. Crystals of metal phosphonate products are formed inside the gel. We have applied this for a variety of metal ions (alkaline-earth metals, transition metals and lanthanides) and a number of polyphosphonic acid and mixed carboxy/phosphonic acid ligands.

Layered acid arsenates α-M(HAsO4)2·H2O (M=Ti, Sn, Pb): synthesis optimization and crystal structures

Abstract The syntheses of α-M(HAsO 4 ) 2 ·H 2 O (M=Ti, Sn and Pb) have been optimized to prepare crystalline single phase materials. The crystal structures of M=Sn, Pb have been refined using X-ray powder diffraction data by the Rietveld method. A combined X-ray and neutron powder data refinement for M=Ti has allowed to obtain a very detailed picture of the structure including the hydrogen-bonding network. The results have been compared with those of the phosphates analogs. In addition, detailed characterization of the samples has been carried out by IR spectroscopy, thermal analysis and powder thermodiffractometry.