5 research outputs found
2D Corrugated Magnesium Carboxyphosphonate Materials: Topotactic Transformations and Interlayer āDecorationā with Ammonia
In this paper we report the synthesis and structural
characterization
of the 2D layered coordination polymer MgĀ(BPMGLY)Ā(H<sub>2</sub>O)<sub>2</sub> (BPMGLY = bis-phosphonomethylglycine, (HO<sub>3</sub>PCH<sub>2</sub>)<sub>2</sub>NĀ(H)ĀCOO<sup>2ā</sup>). 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 Ā°C
one (of the two) Mg-coordinated water molecule is lost, with the archetype
2D structure maintaining itself. However, the octahedral Mg in MgĀ(BPMGLY)Ā(H<sub>2</sub>O)<sub>2</sub> is now converted to trigonal bipyramidal in
MgĀ(BPMGLY)Ā(H<sub>2</sub>O). Upon exposure of the monohydrate MgĀ(BPMGLY)Ā(H<sub>2</sub>O) 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 MgĀ(BPMGLY)Ā(H<sub>2</sub>O)Ā(NH<sub>3</sub>) 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
Tuning Proton Conductivity in Alkali Metal Phosphonocarboxylates by Cation Size-Induced and Water-Facilitated Proton Transfer Pathways
The structural and functional chemistry
of a family of alkali-metal
ions with racemic <i>R</i>,<i>S</i>-hydroxyphosphonoacetate
(<b>M-HPAA</b>; M = Li, Na, K, Cs) are reported. Crystal structures
were determined by X-ray data (Li<sup>+</sup>, powder diffraction
following an ab initio methodology; Na<sup>+</sup>, K<sup>+</sup>,
Cs<sup>+</sup>, single crystal). A gradual increase in dimensionality
directly proportional to the alkali ionic radius was observed. [Li<sub>3</sub>(OOCCHĀ(OH)ĀPO<sub>3</sub>)Ā(H<sub>2</sub>O)<sub>4</sub>]Ā·H<sub>2</sub>O (<b>Li-HPAA</b>) shows a 1D framework built up by
Li-ligand āslabsā with Li<sup>+</sup> in three different
coordination environments (4-, 5-, and 6-coordinated). <b>Na-HPAA</b>, Na<sub>2</sub>(OOCCHĀ(OH)ĀPO<sub>3</sub>H)Ā(H<sub>2</sub>O)<sub>4</sub>, exhibits a pillared layered āhouse of cardsā structure,
while <b>K-HPAA</b>, K<sub>2</sub>(OOCCHĀ(OH)ĀPO<sub>3</sub>H)Ā(H<sub>2</sub>O)<sub>2</sub>, and <b>Cs-HPAA</b>, CsĀ(HOOCCHĀ(OH)ĀPO<sub>3</sub>H), typically present intricate 3D frameworks. Strong hydrogen-bonded
networks are created even if no water is present, as is the case in <b>Cs-HPAA</b>. As a result, all compounds show proton conductivity
in the range 3.5 Ć 10<sup>ā5</sup> S cm<sup>ā1</sup> (<b>Cs-HPAA</b>) to 5.6 Ć 10<sup>ā3</sup> S cm<sup>ā1</sup> (<b>Na-HPAA</b>) at 98% RH and <i>T</i> = 24 Ā°C. Differences in proton conduction mechanisms, Grothuss
(Na<sup>+</sup> and Cs<sup>+</sup>) or vehicular (Li<sup>+</sup> and
K<sup>+</sup>), are attributed to the different roles played by water
molecules and/or proton transfer pathways between phosphonate and
carboxylate groups of the ligand HPAA. Upon slow crystallization,
partial enrichment in the <i>S</i> enantiomer of the ligand
is observed for <b>Na-HPAA</b>, while the <b>Cs-HPAA</b> is a chiral compound containing only the <i>S</i> enantiomer
Structural Variability in Multifunctional Metal Xylenediaminetetraphosphonate Hybrids
Two new families of divalent metal
hybrid derivatives from the aromatic tetraphosphonic acids 1,4- and
1,3-<i>bis</i>(aminomethyl)Ābenzene-<i>N</i>,<i>N</i>ā²-<i>bis</i>(methylenephosphonic acid),
(H<sub>2</sub>O<sub>3</sub>PCH<sub>2</sub>)<sub>2</sub>āNāCH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>CH<sub>2</sub>āNĀ(CH<sub>2</sub>PO<sub>3</sub>H<sub>2</sub>)<sub>2</sub> (designated herein as <b><i>p</i>-H<sub>8</sub>L</b> and <b><i>m</i>-H<sub>8</sub>L</b>) have been synthesized by crystallization
at room temperature and hydrothermal conditions. The crystal structures
of MĀ[(HO<sub>3</sub>PCH<sub>2</sub>)<sub>2</sub>NĀ(H)ĀCH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>CH<sub>2</sub>NĀ(H)Ā(CH<sub>2</sub>PO<sub>3</sub>H)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]Ā·2H<sub>2</sub>O (M = Mg, Co, and Zn), <b>Mā(<i>p</i>-H<sub>6</sub>L)</b>, and MĀ[(HO<sub>3</sub>PCH<sub>2</sub>)<sub>2</sub>NĀ(H)ĀCH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>CH<sub>2</sub>NĀ(H)Ā(CH<sub>2</sub>PO<sub>3</sub>H)<sub>2</sub>]Ā·<i>n</i>H<sub>2</sub>O (M = Ca, Mg, Co, and Zn and <i>n</i> = 1ā1.5), <b><b>Mā(<i>m</i>-H<sub>6</sub>L)</b></b>,
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 <b><b>Mā(<i>p</i>-H<sub>6</sub>L)</b></b> is constituted by organicāinorganic
monodimensional chains where the phosphonate moiety acts as a bidentate
chelating ligand bridging two metal octahedra. <b><b>Mā(<i>m</i>-H<sub>6</sub>L)</b></b> 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 <b><b>Mā(<i>p</i>-H<sub>6</sub>L)</b></b> 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 <b><b>Mā(<i>p</i>-H<sub>6</sub>L)</b></b> (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 (Ļ ā¼ 9.4 Ć
10<sup>ā5</sup> SĀ·cm<sup>ā1</sup>, at 98% RH and
297 K), although different proton transfer mechanisms are involved
Structural Variability in Multifunctional Metal Xylenediaminetetraphosphonate Hybrids
Two new families of divalent metal
hybrid derivatives from the aromatic tetraphosphonic acids 1,4- and
1,3-<i>bis</i>(aminomethyl)Ābenzene-<i>N</i>,<i>N</i>ā²-<i>bis</i>(methylenephosphonic acid),
(H<sub>2</sub>O<sub>3</sub>PCH<sub>2</sub>)<sub>2</sub>āNāCH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>CH<sub>2</sub>āNĀ(CH<sub>2</sub>PO<sub>3</sub>H<sub>2</sub>)<sub>2</sub> (designated herein as <b><i>p</i>-H<sub>8</sub>L</b> and <b><i>m</i>-H<sub>8</sub>L</b>) have been synthesized by crystallization
at room temperature and hydrothermal conditions. The crystal structures
of MĀ[(HO<sub>3</sub>PCH<sub>2</sub>)<sub>2</sub>NĀ(H)ĀCH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>CH<sub>2</sub>NĀ(H)Ā(CH<sub>2</sub>PO<sub>3</sub>H)<sub>2</sub>(H<sub>2</sub>O)<sub>2</sub>]Ā·2H<sub>2</sub>O (M = Mg, Co, and Zn), <b>Mā(<i>p</i>-H<sub>6</sub>L)</b>, and MĀ[(HO<sub>3</sub>PCH<sub>2</sub>)<sub>2</sub>NĀ(H)ĀCH<sub>2</sub>C<sub>6</sub>H<sub>4</sub>CH<sub>2</sub>NĀ(H)Ā(CH<sub>2</sub>PO<sub>3</sub>H)<sub>2</sub>]Ā·<i>n</i>H<sub>2</sub>O (M = Ca, Mg, Co, and Zn and <i>n</i> = 1ā1.5), <b><b>Mā(<i>m</i>-H<sub>6</sub>L)</b></b>,
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 <b><b>Mā(<i>p</i>-H<sub>6</sub>L)</b></b> is constituted by organicāinorganic
monodimensional chains where the phosphonate moiety acts as a bidentate
chelating ligand bridging two metal octahedra. <b><b>Mā(<i>m</i>-H<sub>6</sub>L)</b></b> 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 <b><b>Mā(<i>p</i>-H<sub>6</sub>L)</b></b> 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 <b><b>Mā(<i>p</i>-H<sub>6</sub>L)</b></b> (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 (Ļ ā¼ 9.4 Ć
10<sup>ā5</sup> SĀ·cm<sup>ā1</sup>, at 98% RH and
297 K), although different proton transfer mechanisms are involved
Guest Molecule-Responsive Functional Calcium Phosphonate Frameworks for Tuned Proton Conductivity
We report the synthesis, structural
characterization, and functionality (framework interconversions together
with proton conductivity) of an open-framework hybrid that combines
Ca<sup>2+</sup> ions and the rigid polyfunctional ligand 5-(dihydroxyphosphoryl)Āisophthalic
acid (<b>PiPhtA</b>). Ca<sub>2</sub>[(HO<sub>3</sub>PC<sub>6</sub>H<sub>3</sub>COOH)<sub>2</sub>]<sub>2</sub>[(HO<sub>3</sub>PC<sub>6</sub>H<sub>3</sub>(COO)<sub>2</sub>H)Ā(H<sub>2</sub>O)<sub>2</sub>]Ā·5H<sub>2</sub>O (<b>Ca-PiPhtA-I</b>) is obtained by
slow crystallization at ambient conditions from acidic (pH ā
3) aqueous solutions. It possesses a high water content (both Ca coordinated
and in the lattice), and importantly, it exhibits water-filled 1D
channels. At 75 Ā°C, <b>Ca-PiPhtA-I</b> is partially dehydrated
and exhibits a crystalline diffraction pattern that can be indexed
in a monoclinic cell with parameters close to the pristine phase.
Rietveld refinement was carried out for the sample heated at 75 Ā°C, <b>Ca-PiPhtA-II</b>, using synchrotron powder X-ray diffraction data,
which revealed the molecular formula Ca<sub>2</sub>[(HO<sub>3</sub>PC<sub>6</sub>H<sub>3</sub>COOH)<sub>2</sub>]<sub>2</sub>[(HO<sub>3</sub>PC<sub>6</sub>H<sub>3</sub>(COO)<sub>2</sub>H)Ā(H<sub>2</sub>O)<sub>2</sub>]. All connectivity modes of the āparentā <b>Ca-PiPhtA-I</b> framework are retained in <b>Ca-PiPhtA-II</b>. Upon <b>Ca-PiPhtA-I</b> exposure to ammonia vapors (28% aqueous
NH<sub>3</sub>) a new derivative is obtained (<b>Ca-PiPhtA-NH</b><sub><b>3</b></sub>) containing 7 NH<sub>3</sub> and 16 H<sub>2</sub>O molecules according to elemental and thermal analyses. <b>Ca-PiPhtA-NH</b><sub><b>3</b></sub> exhibits a complex X-ray
diffraction pattern with peaks at 15.3 and 13.0 Ć
that suggest
partial breaking and transformation of the parent pillared structure.
Although detailed structural identification of <b>Ca-PiPhtA-NH</b><sub><b>3</b></sub> was not possible, due in part to nonequilibrium
adsorption conditions and the lack of crystallinity, FT-IR spectra
and DTA-TG analysis indicate profound structural changes compared
to the pristine <b>Ca-PiPhtA-I</b>. At 98% RH and <i>T</i> = 24 Ā°C, proton conductivity, Ļ, for <b>Ca-PiPhtA-I</b> is 5.7 Ć 10<sup>ā4</sup> SĀ·cm<sup>ā1</sup>. It increases to 1.3 Ć 10<sup>ā3</sup> SĀ·cm<sup>ā1</sup> upon activation by preheating the sample at 40 Ā°C
for 2 h followed by water equilibration at room temperature under
controlled conditions. <b>Ca-PiPhtA-NH</b><sub><b>3</b></sub> exhibits the highest proton conductivity, 6.6 Ć 10<sup>ā3</sup> SĀ·cm<sup>ā1</sup>, measured at 98% RH
and <i>T</i> = 24 Ā°C. Activation energies (<i>E</i><sub>a</sub>) for proton transfer in the above-mentioned
frameworks range between 0.23 and 0.4 eV, typical of a Grothuss mechanism
of proton conduction. These results underline the importance of internal
H-bonding networks that, in turn, determine conductivity properties
of hybrid materials. It is highlighted that new proton transfer pathways
may be created by means of cavity āderivatizationā with
selected guest molecules resulting in improved proton conductivity