Synthesis, structure and electrochemical characterization of the isopolytungstate (W4O16) held by MnII anchors within a superlacunary crown heteropolyanion {P8W48}

An isopolyanion {W4O16} within archetypal {P8W48} heteropolyanion assembly [(P8W48O184)(W4O16)K10Li4Mn10Na(H2O)50Cl2] 15- (Mn10W4-P8W48) has been synthesized by the reaction of the cyclic superlacunary anion [H7P8W48O184] 33− and Mn(ClO4)2.6H2O in I M LiCl soultion medium at pH 8. The isolated compound has been characterized by single crystal X-ray crystallography, powder X-ray diffraction (PXRD), Fourier-transform infrared (FTIR) spectroscopy, elemental analysis and thermogravimetric analysis. Electrochemical studies were also performed on Mn10W4-P8W48 confirmed the presence of Mn centres bonded to the tunsgtic framework. The novel polyanion [(P8W48O184)(W4O16)K10Li4Mn10Na(H2O)50Cl2] 15- is the first example of macrocyclic complex where an isopolyanion (W4O16) 8- is embedded within in the inner cavity of the {P8W48} and is placed in position by six MnII cations as anchors. Whereas, the exocyclic coordination of the four MnII atoms to {P8W48} yields extended structure by linking neighbouring polyanions through {W−O−Mn−O−W} bridges. Further, the polyanion Mn10W4-P8W48 is the first derivative of {P8W48} with six MnII ions (largest) coordinated to the inner side the crown ring as anchors

Comparative NMR Relaxivity Study of Polyoxometalate-Based Clusters [Mn4_{4}(H2_{2}O)2_{2}(P2_{2}W1S_{1S}O56_{56})2_{2}]16−^{16-} and [{Dy(H2_{2}O)6_{6}}2_{2}Mn4_{4}(H2_{2}O)2_{2}(P2_{2}W15_{15}O56_{56})2_{2}]10−^{10-} from 20 MHz to 1.2 GHz

Nuclear Magnetic Resonance relaxivities are a measure for the sensitivity of a contrast agent (CA), i.e. the potential of a paramagnetic moiety to enhance longitudinal and transverse relaxation of molecules in its near neighbourhood. The underlying mechanism is called Paramagnetic Relaxation Enhancement (PRE). The relaxivity, characterizing PRE, depends not only on the external applied magnetic field but also depends on numerous factors, such as number of coordinated water molecules, water exchange rate, rotational diffusion, first and second coordination hydration sphere, electronic and magnetic properties of paramagnetic centers and the molecular shape/size of the CA. Relaxation rates are usually normalized to the concentration of the contrast agent to provide the relaxivities. To investigate the influence of these factors on PRE of newly synthesized potential CA, two paramagnetic metals containing polyoxometalates (POMs) [Mn$_{4}$(H$_{2}$O)$_{2}$(P$_{2}$W$_{15}$O$_{56}$)$_{2}$]$^{16-}$ (Mn$_{4-}$P$_{2}$W$_{15}$) and [{Dy(H$_{2}$O)$_{6}$}$_{2}$Mn$_{4}$(H$_{2}$O)$_{2}$(P$_{2}$W$_{15}$O$_{56}$)$_{2}$]$^{10-}$ (Dy$_{2}$Mn$_{4}$-P$_{2}$W$_{15}$) were selected as models to be studied at $^{1}$H Larmor frequencies from 20 MHz to 1.2 GHz. Structurally, the POM Dy$_{2}$Mn$_{4}$-P$_{2}$W$_{15}$ is similar to the tetra-nuclear manganese(II)-substituted sandwich-type POM Mn$_{4}$-P$_{2}$W$_{15}$, with the two coordinated Dy$^{III}$ cations acting as linkers connecting Mn$_{4}$-P$_{2}$W$_{15}$ units, thus forming a 1D ladder-like chain structure based on sandwich-type rungs strung together by the dysprosium cations. This study shows that POM (Dy$_{2}$Mn$_{4}$-P$_{2}$W$_{15}$) is a promising CA at high magnetic fields and proves that the use of heterometallic clusters is an effective strategy to increase PRE due to the synergistic effects from different metal ions

Synthesis and Characterization of a Heterometallic Extended Architecture Based on a Manganese(II)-Substituted Sandwich-Type Polyoxotungstate

The reaction of [α-P2W15O56]12− with MnII and DyIII in an aqueous basic solution led to the isolation of an all inorganic heterometallic aggregate Na10(OH2)42[{Dy(H2O)6}2Mn4P4W30O112(H2O)2]·17H2O (Dy2Mn4-P2W15). Single-crystal X-ray diffraction revealed that Dy2Mn4-P2W15 crystallizes in the triclinic system with space group P 1 ¯ , and consists of a tetranuclear manganese(II)-substituted sandwich-type phosphotungstate [Mn4(H2O)2(P2W15O56)2]16− (Mn4-P2W15), Na, and DyIII cations. Compound Dy2Mn4-P2W15 exhibits a 1D ladder-like chain structure based on sandwich-type segments and dysprosium cations as linkers, which are further connected into a three-dimensional open framework by sodium cations. The title compound was structurally and compositionally characterized in solid state by single-crystal XRD, powder X-ray diffraction (PXRD), Fourier-transform infrared spectroscopy (FTIR), thermogravimetric (TGA), and elemental analyses. Further, the absorption and emission electronic spectra in aqueous solutions of Dy2Mn4-P2W15 and Mn4-P2W15 were studied. Also, magnetic properties were studied and compared with the magnetic behavior of [Mn4(H2O)2(P2W15O56)2]16−

Synthesis, Characterization, Electrochemistry, Photoluminescence and Magnetic Properties of a Dinuclear Erbium(III)-Containing Monolacunary Dawson-Type Tungstophosphate: [{Er(H2O)(CH3COO)(P2W17O61)}2]16−

Reaction of the trilacunary Wells−Dawson anion {α-P$_{2}$W$_{15}$O$_{56}$$^{12-}$ with ErIII ion in a 1 M LiOAc/HOAc buffer (pH 4.8) solution produces a dinuclear erbium(III) substituted sandwich-type structure [{Er(H$_{2}$O)(CH$_{3}$COO)(P$_{2}$W$_{17}$O$_{61}$)}$_{2}$]$^{16-}$ (1). The isolated compound was structurally characterized using single crystal and powder X-ray diffraction, FTIR spectroscopy, mass spectrometry and thermogravimetric analysis. The electrochemical, electrocatalytic, photoluminescence and magnetic properties of 1 were investigated