Samar K. Das

Open and shut for guests in molybdenum-oxide-based giant spheres, baskets, and rings containing the pentagon as a common structural element

A novel exchange between ligands and/or guest molecules can be accomplished in giant molecular spheres (an example is shown in the picture) which are in equilibrium with the corresponding giant baskets in solution.

A cyclic supramolecular (H2O)4 cluster in an unusual Fe3 complex that aggregates to {Fe3}n with a zig-zag chainlike structure

An aqueous solution containing ferric chloride, acetic acid and 2-hydroxypyridine results in the solid-state isolation of an unusual mixed-ligand trinuclear iron(III) complex [Fe3(μ3-O)(μ2-CH3COO)6(C5H5NO)2(H2O)]ClO4·4H2O, 1, where the iron-coordinated water ligand forms a hydrogen-bonded water tetramer with three other solvent water molecules; the Fe3 clusters aggregate to {Fe3}nvia N–H⋯O type hydrogen bonds, forming a zig-zag chainlike structure.

A cyclic (H2O)4 cluster characterized in the solid state disappears on heating and regenerates from water vapor: A supramolecular reversible gas–solid reaction

An unusual trinuclear iron(III) cluster described herein, [Fe3(μ3-O)(μ2-CH3COO)6(C5H5NO)2(H2O)] ClO4·4H2O (1) (C5H5NO = 2-pyridone), features a cyclic hydrogen bonded supramolecular water tetramer at one of the iron centres, as characterized by X-ray crystallography and thermogravimetry. The water cluster is formed by one iron-coordinated water and three lattice/solvent water molecules. The molecular environment of the water tetramer in the crystal structure consists of a Fe3+ ion (which is covalently bonded to one water of the (H2O)4 cluster), a perchlorate anion and the fourth lattice water. The facile removal of the lattice water molecules was anticipated from the knowledge of the type of interaction of these water molecules with their surroundings. Indeed, this hydrogen bonded water tetramer disappears with the formation of dehydrated solid [Fe3(μ3-O)(μ2-CH3COO)6(C5H5NO)2(H2O)] ClO4 (2), when the compound 1 is heated at ∼135 °C. Interestingly, when the dehydrated solid 2 is exposed to water vapor, it regenerates to 1 in a gas–solid reaction. The exposure of 2 to D2O vapor yields partially deuterated complex [Fe3(μ3-O)(μ2-CH3COO)6(C5H5NO)2(H2O)] ClO4·4D2O (3). As expected, the material 3 changes to 2 on heating at ∼135 °C, which again, on exposure to water vapor, returns to 1. The reversible loss/formation of (H2O)4 cluster in a gas–solid reaction has been established by elemental analyses, IR and X-ray powder diffraction studies including the single crystal X-ray structural analysis of 1.

A New Type of Supramolecular Compound: Molybdenum-Oxide-Based Composites Consisting of Magnetic Nanocapsules with Encapsulated Keggin-Ion Electron Reservoirs Cross-Linked to a Two-Dimensional Network

Nanosized metal-oxide-based composites-novel supramolecular entities-have been assembled and even cross-linked under one-pot conditions. The supramolecular entity (see picture) consists of a paramagnetic icosahedral capsule of the type {Mo VI 72 Fe III 30 } as a host which encloses a potential electron-reservoir noncovalently bonded guest, the reduced Keggin cluster [H 2 PMo 12 O 40 ] 3- .

Linking Icosahedral, Strong Molecular Magnets {Mo} to Layers—A Solid‐State Reaction at Room Temperature

The by no means trivial, solid-state reaction for the condensation of {(Mo)Mo 5 } 12 Fe 30 giant spheres commences through the water ligands and leads to oxo (or hydroxo) bridging. As the discrete icosahedral units approach each other, their oxygen atom bridges ultimately form covalent bonds (Fe-Fe 3.79 A , see picture) to result in a symmetric layered structure.

Giant Ring-Shaped Building Blocks Linked to Form a Layered Cluster Network with Nanosized Channels: [Mo124VIMo28VO429(μ3-O)28H14(H2O)66.5]16−

A novel type of electron-rich (basic!) nanosized channels can be built up by linking giant ring-shaped building blocks, which occur in the layered compound of composition [Mo124VIMo28VO429(μ3-O)28H14(H2O)66.5]16− (see figure). The corresponding sodium salt is obtained by reduction of an acidified aqueous molybdate solution under special reaction conditions.

Discrete polyoxovanadate cluster into an organic free metal-oxide-based material: syntheses, crystal structures, and magnetic properties of a new series of lanthanide linked-POV compounds [{Ln(H2O)6}2As8V14O42(SO3)] x 8 H2O (Ln = La3+, Sm3+, and Ce3+).

This article describes the linking propensity of the sulfite encapsulated polyoxovanadate (POV) anion, [As(8)V(14)O(42)(SO(3))](6-), with aqua-lanthanide complex cations [Ln(H(2)O)(6)](3+) in a controlled wet synthesis resulting in a series of organic free metal-oxide-based materials [{Ln(H(2)O)(6)}(2)As(8)V(14)O(42)(SO(3))] x 8 H(2)O, Ln = La(3+) (1), Sm(3+) (2), and Ce(3+) (3). The title compounds have been characterized by elemental analyses, IR, diffuse reflectance, electron paramagnetic resonance, powder X-ray diffraction (XRD), thermogravimetric analysis (TGA), and single-crystal X-ray diffraction studies. All three compounds crystallize in the monoclinic space group P2(1)/n. Crystal data for 1: a = 13.4839(7), b = 12.3388(6), c = 18.3572(10) A, beta = 108.2570 (10) degrees, V = 2900.4(3) A(3). Crystal data for 2: a = 13.4156(3), b = 12.2588(3), c = 18.2501(4) A, beta = 108.049(3) degrees, V = 2853.8(10) A(3). Crystal data for 3: a = 13.4934(3), b = 12.3983(3), c = 18.3992(4) A, beta = 108.025(3), V = 2927.0(10) A(3). Crystal structure shows that each cluster is surrounded by six [Ln(H(2)O)(6)](3+) complex cations, and each [Ln(H(2)O)(6)](3+) cation is coordinated to three surrounding POV cluster anions. The electron spin resonance spectra of compounds 1-3 show a typical single line (g = 1.9671 for 1, g = 1.9669 for 2, and g = 1.9704 for 3), characteristic for a V(4+) (d(4)) ion; in addition, a supplementary signal appears for compound 2 at g = 5.9238 due to the presence of the Sm(3+) (f(5)) ion. All vanadium atoms exit in +4 oxidation states that have been confirmed by bond valence sum calculations. Variable-temperature magnetic studies for all three compounds 1-3 are performed and are discussed in terms of antiferromagnetic coupling interactions, giving importance to linking/assembling the {V(14)} cluster anions. TGA/mass analyses of compounds 1-3 (linked system) have been compared with that of the starting precursor [NH(4)](6)[As(8)V(14)O(42)(SO(3))] (discrete building unit). Interestingly, the evolution of SO(2) gas takes place for the discrete cluster compound [NH(4)](6)[As(8)V(14)O(42)(SO(3))] in a temperature range of 480-520 degrees C with the decomposition of the POV cluster anion, whereas the same evolution occurs at 520-580 degrees C for compounds 1-3. These comparative TGA/mass studies help to understand how the organic free linker elevates the thermal stability of the sulfite encapsulated POV cluster anion in going from a discrete cluster anion to the linked system (molecule to material). It has also been demonstrated that the stability of the sulfite anion increases to a greater extent when it is included in the cluster cage. The powder XRD studies of compounds 1-3 confirm that these are isostructural materials and provide information about the phase purity.

Paramagnetic Keplerate “Necklaces” Synthesized by a Novel Room‐Temperature Solid‐State Reaction: Controlled Linking of Metal‐Oxide‐Based Nanoparticles

Crystal engineering with nanoobjects? Spherical structurally well-defined molybdenum-oxide-based giant clusters can be appropriately functionalized to a crystalline material with the remarkable property of having discrete cluster units which get covalently linked to form chains (see picture) through Fe-O-Mo bonds after having approached each other as a result of the release of crystal water upon drying.

Polymer supported vo2+ schiff base catalyst for hydroxylation of benzene

Abstract Polymer support VO 2+ having schiff base functional group involving L-tyrosine was prepared from which the metal leaching did not occur. Using this recyclable catalyst, the hydroxylation of benzene by H 2 O 2 was carried out at 65 °C.

Facile and Optimized Syntheses and Structures of Crystalline Molybdenum Blue Compounds Including one with an Interesting High Degree of Defects: Na26[Mo142O432(H2O)58H14] · ca. 300 H2O and Na16[(MoO3)176(H2O)63(CH3OH)17H16] · ca. 600 H2O · ca. 6 CH3OH

The syntheses and structures of the two mixedvalence crystalline molybdenum blue compounds Na26[Mo142O432(H2O)58H14] · ca. 300 H2O (1) (containing the maximal number of well defined defects which influence the overall structure and the reactivity of the anionic cluster) and Na16[(MoO3)176(H2O)63(CH3OH)17H16] · ca. 600 H2O · ca. 6 CH3OH (2) (obtained in an optimized high-yield synthesis) are reported with reference to the critical conditions required for the isolation of corresponding crystalline materials.