Montse Bazaga-García

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.

Influence of Proton Conducting Cations on the Structure and Properties of 2D Anilate-Based Magnets

The syntheses, structures, magnetic, and proton conductivity properties of a family of bimetallic anilate-based compounds with inserted alkylammonium cations are presented. The structures of (Me2NH2)[MnIICrIII(Br2An)3]·2H2O (1), (Et2NH2)[MnIICrIII(Br2An)3] (2), (Et3NH)[MnIICrIII(Cl2An)3] (3), and [(Et)(i-Pr)2NH][MnIICrIII(Br2An)3]·(CHCl3)0.5·(H2O) (4) contain a 2D anionic network formed by Mn(II) and Cr(III) ions linked through anilate ligands. In 1, 2, and 3, the hexagonal holes of this network are occupied by Me2NH2+, Et2NH2+, or Et3NH+ cations. Interestingly, the small increase of size of the templating cation in 4 ([(Et)(i-Pr)2NH]+ in the place of Me2NH2+, Et2NH2+ or Et3NH+), gives rise to a different structure with half of the cations placed within the layers and the other one in the space between the layers. This leads to bilayers with an interlayer separation similar to those of 1, 2, and 3 separated by larger interbilayer distances. Compounds 1, 2, and 3 show a ferrimagnetic ordering with a Tc of 8.0 K (1), 8.9 K (2), and 8.0 K (3). In 4, the presence of different interlayer distances leads to a metamagnetic behavior when the sample is measured in contact with the mother liquor. The behavior changes in the dry sample, which shows a ferrimagnetic ordering as that of 1, 2, and 3 due to collapse of the structure as confirmed by powder X-ray diffraction. Interestingly, the metamagnetic behavior is recovered after reimmersing the crystals in the mother liquor proving the reversibility of the process. All solids are Grotthuss-type proton conductors with conductivity values ranging between 2.3 × 10-6 S·cm-1 for 3 and 2.4 × 10-5 S·cm-1 for 1 measured at 70 °C and 95% relative humidity and activation energies of ∼0.2 eV.

Three-Component Copper-Phosphonate-Auxiliary Ligand Systems: Proton Conductors and Efficient Catalysts in Mild Oxidative Functionalization of Cycloalkanes

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% relative humidity). Compounds 1 and 2 are also efficient homogeneous catalysts for the mild oxidative functionalization of C5-C8 cycloalkanes (cyclopentane, cyclohexane, cycloheptane, and cyclooctane), namely for the oxidation by H2O2 to give cyclic alcohols and ketones and the hydrocarboxylation by CO/H2O and S2O82- to the corresponding cycloalkanecarboxylic acids as major products. The catalytic reactions proceed under mild conditions (50-60 °C) in aqueous acetonitrile medium, resulting in up to 34% product yields based on cycloalkane substrate.

From Light to Heavy Alkali Metal Tetraphosphonates (M = Li, Na, K, Rb, Cs): Cation Size-Induced Structural Diversity and Water-Facilitated Proton Conductivity

A family of alkali metal-based frameworks containing the tetraphosphonate ligand hexamethylenediamine-N,N,N′,N′-tetrakis(methylenephosphonic acid), HDTMP, is reported. A cation size-induced structural diversity, from monodimensional solids (Li+ and Na+) through layered (K+) to pillared-layered (Rb+ and Cs+) structures, was found. The proton conductivity properties of the Li compounds (hydrated and dehydrated) are reported and the influence of dehydration/rehydration processes in enhancing proton transfer processes is highlighted. Reversible changes in the dimensionality occurred upon full dehydration/rehydration with minor rearrangements in the framework, implying variations in the Li+–ligand connectivity but preserving the tetracoordination of the metal ion. The reversibly dehydrated–rehydrated sample displayed the highest proton conductivity (5 × 10−3 S cm−1 at 80 °C and 95% RH), a behavior attributed to reversible formation/reformation of P–O(H)–Li bonds that, in turn, provoked changes in the acidity of acid groups and water mobility in the temperature range of impedance measurements.

CCDC 1491091: Experimental Crystal Structure Determination

Related Article: Mario Palacios-Corella, Alejandro Fernandez-Espejo, Montse Bazaga-Garcia, Enrique R. Losilla, Aurelio Cabeza, Miguel Clemente-Leon, Eugenio Coronado|2017|Inorg.Chem.|||doi:10.1021/acs.inorgchem.7b01965