Photochemical and gas adsorption studies of Keggin polyoxometalate functionalized porous melamine terephthaldehyde material.

A compound containing a microporous melamine-terephthaldehyde framework is protonated by grinding with acetic acid, resulting in a mesoporous protonated melamine-terephthaldehyde network. The Keggin polyanion [PMo12O40]3- is then immobilized into this protonated melamine-terephthaldehyde network through a solid-state reaction. The polyanion interacts with the protonated microporous organic network through electrostatic interaction. Three different Keggin-melamine-terephthaldehyde materials were synthesized by varying the Keggin anion loading of 10 wt%, 15 wt% and 20 wt%. The Keggin-melamine-terephthaldehyde materials exhibit photochromism on irradiation with sunlight. The photochromism of the POM-organic hybrid material is due to reduction of the Keggin anion. The resulting blue reduced Keggin-melamine-terephthaldehyde materials are oxidized back by treatment with hydrogen peroxide. The N2, CO2 and H2 adsorption properties of all the synthesized materials, including protonated melamine-terephthaldehyde materials, were studied. The materials were characterized by IR, PXRD, DRS, TGA, EPR spectroscopy, and FESEM electron microscopy. The elemental composition was analysed with a CHN analyser and ICP-OES analysis.

Light-induced dissolution and concomitant crystallization of a Keggin-type polyoxometalate mimicking a naturally occurring phenomenon.

A suspension of a yellow polycrystalline compound [PPh4]3[PMoVI12O40] in N-methylformanilide (NMF) (in which it is not soluble), on irradiation with sunlight, initiates dissolution via its reduction followed by its crystallization leading to the isolation of single crystals of compound [PPh4]4[PMoVMoVI11O40]·3CH3(C6H5)NCHO (1). Compounds [PPh4]3[PMoVI12O40]·1.75 CH3(C6H5)NCHO (2) and [PPh4]3[PMoVI12O40]·2CH3(C6H5)NCHO (3), each containing an oxidized Keggin anion, are obtained at two different temperatures when the corresponding mother liquor is kept in the dark.

Polyoxometalate-Supported Copper(I)-Pyrazole Complex: Unusual Stability, Geometrical Isomers, Organic Transformation, and Computation.

We have described the synthesis and characterization of a polyoxometalate (POM)-supported copper(I)-pyrazole complex, [CuI(C15H12N2)2] [PW12O40{CuI(C15H12N2)2}2]·CH3OH (1). There are three Cu(I)-pyrazole coordination complexes in compound 1, out of which two are supported by the {PW12O40}3- Keggin POM by coordinate covalent bonds from the POM surface through oxygen donors to the Cu(I) centers of two Cu(I) complexes and one remains uncoordinated to the POM surface, acting as a cationic complex species in the crystals of 1. The POM-coordinated Cu(I) complexes have a T-shaped geometry, and the uncoordinated Cu(I) complex is a linear one. During the solvothermal synthesis of compound 1, remarkably, the associated 1,5-diphenylpyrazole ligand is formed from cinnamaldehyde phenylhydrazone through oxidative cyclization at the cost of Cu(II) reduction to Cu(I), and then, these two (copper(I) and pyrazole ligand) form the coordination complex. Compound 1 undergoes desolvation on heating the single crystals of compound 1 at 55 °C in the aerial atmosphere with the formation of the desolvated compound [CuI(C15H12N2)2][PW12O40{CuI(C15H12N2)2}2] (2). Interestingly, when an aqueous suspension of compound 1 is bubbled with O2 gas at room temperature, it undergoes solid-to-solid transformation, resulting in the formation of the compound [CuI(C15H12N2)2]3[PW12O40] (3). Compounds 1, 2, and 3 have been characterized by routine spectral analyses (including cyclic voltammetry and X-ray photoelectron spectroscopy (XPS) studies) and unambiguously by single-crystal X-ray crystallography. We have performed density functional theory (DFT) calculations on compound 1 to understand the rationale of its unusual stability toward oxidation.

Solvent mediated reversible solid state photochromism of {Mo72Fe30} Keplerate.

When the yellow rhombohedral crystals of Keplerate [Mo72Fe30O252(CH3COO)12{Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O)91]·150H2O (1), on wetting with N,N-dimethylformamide (DMF), are irradiated with sunlight, a remarkable reversible solid state photochromic behaviour is achieved with the formation of green coloured crystals (1red). The reduction of the {MoVI} centres to {MoV} is responsible for the observed colour change from yellow to dark green. Importantly, compound 1 can be activated towards photochromism only in the presence of the DMF solvent. The photochromic phenomenon displayed by Keplerate compound 1 is a classic example of sunlight activated solvent driven photoactivity.

A Reversible Redox Reaction in a Keggin Polyoxometalate Crystal Driven by Visible Light: A Programmable Solid-State Photochromic Switch.

The colourless crystals of (PPh4 )3 [PW12 O40 ]⋅3 C3 H7 NO (1) are converted to the dark blue crystals of {(PPh4 )3 [PW12 O40 ]⋅3C3 H7 NO}0.85 {(PPh4 )3 (C3 H7 NO)+. [PWV WVI11 O40 ]- ⋅2C3 H7 NO)}0.15 (2) upon irradiation with visible light in an interesting single crystal to single crystal transformation. This photochromic conversion is accompanied by the reduction of concerned Keggin anion from {PWVI12 } to {PWV WVI11 }. This redox conversion is characterized by various spectroscopic techniques including single crystal X-ray diffraction studies. The photochromic properties of compound 1 can be controlled reversibly through the dimethylformamide (DMF) molecule as a function of temperature and proton exposure in a gas-solid reaction. The present work can be described as a new concept of programmable photochromism with the formation of photochromic pockets in crystalline 1 host (solid state), wherein a solvent can be plugged at a time to show light induced coloration.

Isolation of Blackberry-Shaped Nanoparticles of a Giant {Mo72Fe30} Cluster and Their Transformation to a Crystalline Nanoferric Molybdate.

When an aqueous solution of sodium molybdate is added to an aqueous solution of ferric chloride, acidified with acetic acid, a giant {Mo72Fe30} cluster is instantaneously formed as the amorphous substance Na2[Mo72Fe30O252(CH3COO)4(OH)16(H2O)108]·180 H2O (1). Compound 1 consists of aggregated nanovesicles of {Mo72Fe30} clusters, as confirmed by field-emission scanning electron microscopy and transmission electron microscopy images of 1. An aqueous suspension of 1 upon moderate heating results in the formation of crystalline nanoferric molybdate, which gives insight into understanding the formation of a yellow coating mineral, ferrimolybdite, frequently found on the ores of molybdenum.

Fate of a giant {Mo72Fe30}-type polyoxometalate cluster in an aqueous solution at higher temperature: understanding related Keplerate chemistry, from molecule to material.

When the giant icosahedral {Mo72Fe30} cluster containing compound [Mo72Fe30O252(CH3COO)12{Mo2O7(H2O)}2{H2Mo2O8(H2O)}(H2O)91]·150H2O (1) is refluxed in water for 36 h, it results in the formation of nanoiron molybdate, Fe2(MoO4)3, in the form of a yellow precipitate; this simple approach not only generates nanoferric molybdate at a moderate temperature but also helps to understand the stability of {Mo72Fe30} in terms of the linker-pentagon complementary relationship.

Solid-to-solid formation at the solid-liquid interface leading to a chiral coordination polymer from an achiral monomer.

An achiral crystal of a simple mononuclear copper complex [Cu(II)(C(6)H(8)N(2))(2)SO(4)]·H(2)O (1), on dipping into an aqueous azide solution, transforms into a chiral crystal of a coordination polymer [Cu(II)(C(6)H(8)N(2))(N(3))(2)](n) (2) in a solid-liquid interface reaction demonstrating replacement of a sulfate anion by an azide anion from an aqueous solution.

Sulfate anion helices formed by the assistance of a flip-flop water chain.

A flip-flop extended water structure assists the formation of sulfate anion helices (both left- and right-handed) in a crystalline hydrate of a simple organic-inorganic compound [C6H10N2]SO4. 1.5H2O (1).