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Alkyl chains with different lengths were covalently grafted onto the surface of hexamolybdate through the postfunctionalization protocol of polyoxometalates. The obtained compounds represent typical structures of the so-called giant surfactants. Unexpectedly, those surfactants with hexamolybdates as polar headgroups are able to crystallize, while single-crystal X-ray diffraction reveals that the crystallization behavior of the surfactants is highly dependent on the length of the alkyl chains. For surfactants with comparatively short alkyl chains (C6 and C10), the alkyl chains prefer to interact with tetrabutylammonium, the countercation of hexamolybdate. However, the alkyl chains tend to pack with each other to form a domain of alkyl chains in the surfactant with a longer alkyl chain (C18). The possible mechanism is that a long alkyl chain cannot be fully compatible with the short chain (C4) of tetrabutylammonium.

A bottom-up approach to obtain nanoclusters and large, uniform vesicle-like structures containing organic functionalized hexamolybdates in solution state were developed. Hexamolybdate functionalized carboxylic acid coordinated with two copper ions to form paddle-wheel tetrapolyoxometalate clusters with the features of macro-ions, which can spontaneously assemble into large, stable blackberry-type structures in suitable solvents, completing a hierarchical organization from small POM molecules to nanoscale complexes and then to supramolecular structures.

Four novel organoimido derivatives of hexamolybdate containing a remote carboxyl group have been synthesized: [Bu4N]2[Mo6O18(N-C6H4-3-COOH)] (1), [Bu4N]2[Mo6O18(N-C6H4-2-CH3-4-COOH)] (2), [Bu4N]2[Mo6O18(N-C6H4-2-CH3-5-COOH)] (3), and [Bu4N]2[Mo6O18(N-C6H4-2-CH3-3-COOH)] (4) with 3-aminobenzoic acid, 4-amino-3-methylbenzoic acid, 3-amino-4-methylbenzoic acid, and 3-amino-2-methylbenzoic acid as the imido-releasing agents, respectively. Their structures have been characterized by IR, UV-vis, (1)H NMR, ESI-MS, and single-crystal X-ray diffraction techniques. Hydrogen bonding interactions play an important role in the supramolecular assemblies of these compounds in the solid state. Although the incorporated organic ligands are similar to each other, their supramolecular assembly behaviors are quite different. For compound 1, the dimer structure is formed via hydrogen bonding between the carboxyl group and the POM cluster of two neighboring cluster anions. For compound 2, the 1D chain structure is formed via hydrogen bonding between the carboxyl groups and the POM clusters of the cluster anions. For compound 3, the 2D plane structure is formed via two types of hydrogen bonding between the aromatic rings and the POM clusters of the cluster anions. For compound 4, the 1D plus 2D structures are formed via three types of hydrogen bonding between the aromatic rings and the POM clusters of the two types of cluster anions with different orientations.

A series of remote hydroxyl functionalized organoimido derivatives of hexamolybdate, (Bu(4)N)(2)[Mo(6)O(18)(Cres)] (1) (Cres = 4-amino-m-cresol), (Bu(4)N)(2)[Mo(6)O(17)(Cres)(2)] x H(2)O (2), (Bu(4)N)(2)[Mo(6)O(18)(Phen)] x i-PrOH (Phen = p-aminophenol)(3), (Bu(4)N)(2)[Mo(6)O(18)(Phen)] x EtOH (4), (Bu(4)N)(2)[Mo(6)O(17)(Phen)(2)] (5), (Bu(4)N)(2)[Mo(6)O(18)(Naph)] (Naph = 5-amino-1-napheynyl) (6), and (Bu(4)N)(2)[Mo(6)O(18)(Chex)] x 1.5 H(2)O (Chex = trans-4-aminocyclohexanol) (7) were synthesized and characterized by single crystal X-ray diffraction, FT-IR spectra, UV-vis spectra, elemental analysis, (1)H NMR, and cyclic voltammetry. X-ray structural study reveals that intermolecular and intramolecular hydrogen bonding plays an important role in their supramolecular assembly; it is found that (i) bridged oxo ligands of hexamolybdate cluster are more inclined to form hydrogen bonds as acceptors than terminal oxo ligands in this system; (ii) small solvent molecules with hydrogen bonding donor and acceptor, such as water, i-PrOH, and EtOH, usually act as hydrogen bonding bridge in their supramolecular assembly; (iii) hydrogen bonding has an important influence on their anion conformation besides cell packing; (iv) the hydrogen bonding supramolecular assembly of compounds 1-7 demonstrate an interesting change from dimer (3), to 1D infinite single chain (4), to 1D infinite double chain (2), and to 2D network (1, 5, 6, and 7) owing to the alteration of the grafting organic ligand, the substituted number, and the crystallized solvent molecule. To explore their potential application in conductivity, the optical band gap of compounds 1-7 were determined upon their solid state reflectance spectra. Our current study not only surveys systematically hydrogen bonding interaction and supramolecular assembly of remote hydroxyl functionalized organoimido-derivatized hexamolybdates but also provides some available precursors for further modification including esterification.

Three rigid-rod conjugated organic−inorganic hybrid nanodumbbells (Bu4N)4[O18Mo6N(C6H4)NMo6O18] (1), (Bu4N)4[O18Mo6N(C12H8)NMo6O18] (2), and (Bu4N)4[O18Mo6N(C14H12)NMo6O18] (3) bearing terminal polyoxometalate (POM) cages, with different lengths of approximately 2−3 nm and different substituents on the rod, have been synthesized via one-pot reaction of octamolybdate and the appropriate aromatic diamine dihydrochloride with N,N′-dicyclohexylcarbodiimide (DCC) as a dehydrating agent. These complexes have been characterized with UV−vis, IR, 1H NMR, ESI mass spectrometry, cyclic voltammetry, differential pulse voltammetry, and X-ray single-crystal diffraction techniques. The influence of the rod length and substituents on properties of these complexes has been investigated. In addition, the self-assembly of these nanorods has also been explored.

The present article investigates a reversible structural phase transition, and related physical properties change in a new quasi-one-dimensional (1D) organic semiconductor crystal, DBA(TCNQ)2 [DBA = dibutylammonium, TCNQ = 7,7,8,8-tetracyanoquinodimethane]. Differential scanning calorimetry traces reveal the DBA(TCNQ)2 single crystal undergoes a first-order reversible phase transition at around 260−270 K, which is accompanied by a dramatic change in both conductivity and magnetic susceptibility. A direct correlation of physical properties with crystal structure is established. Detailed X-ray structure analyses indicate a reversible structural change related to dimer−tetramer transition along the TCNQ chain and disruption of the hydrogen-bonding chains as the temperature decreases from 270 to 253 K, which is the origin of the electronic and magnetic transition.

Superparamagnetic nanocomposite particles composed of maghemite nanocrystal (ca.15 nm) and deposited Pt nanoclusters (ca. 2.5 nm) were synthesized by a low temperature catalytic method. The magnetic properties of iron oxides species can be easily tuned with different redox atmosphere in the presence of Pt nanoclusters. In this convenient preparation, Pt nanoclusters were first captured on Fe(OH)3 nanoparticles by electrostatic interaction. Then at 80 °C the Fe(OH)3 nanoparticles was catalytically reduced with glycol acid to Fe3O4 nanophase which were finally catalytically oxidized to maghemite (γ-Fe2O3) nanophase in the air at 80 °C. The as-synthesized Pt/Fe3O4 and Pt/γ-Fe2O3 nanocomposites were well characterized by chemical analysis, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, transmission electron microscopy, and magnetization measurements. Reversible and efficient transformation between the Pt/Fe3O4 and Pt/γ-Fe2O3 nanocomposites was realized at 80 °C. The Pt/γ-Fe2O3 nanoco...

Four novel fluoro-functionalized arylimido-substituted hexamolybadates, (n-Bu4N)2[Mo6O18(NAr)] (Ar = 2-CH3-4-FC6H3 (1), 3-CH3-4-FC6H3 (2), 4-FC6H4 (3), or 2-FC6H4 (4)), in which fluorinated phenylimido group linked to an Mo of hexamolybdate by a Mo−N triple bond, have been prepared via the DCC (N,N′-dicyclohexylcarbodiimide) dehydrating protocol of the reaction of α-octamolybdate ion with 2-methyl-4-fluoroaniline hydrochloride, 3-methyl-4-fluoroaniline hydrochloride, 4-fluoroaniline hydrochloride, or 2-fluoroaniline hydrochloride in anhydrous acetonitrile. All these compounds have been characterized by elemental analysis, UV−vis, IR, 1H NMR, and single-crystal X-ray diffraction analyses. The preliminary biological activity test indicated that these compounds display potent herbicidal activity, in particular against the roots of some tested plants (such as Brassica campestris L., Eclipta prostrata L., Echinochloa crusgallis L., and Cirsium japonicum DC.).

Two sandwich-type complexes Na9n(Cu(im)4(H2O)2)1.5n(Cu(im)4(H2O))n[{Cu(im)4}{Na(H2O)2}3{Cu3(im)2(H2O)}(XW9O33)2]2n .(xH2O)n (im=imidazole, X=Bi (1), Sb(2), x=42.5 (1), 40 (2)) have been synthesized and structurally characterized. Basic frameworks of 1 and 2 are built from sandwich-type [{Na(H2O) 2} 3{Cu3(im)2(H2O)}(XW9O33)2](9-) (X=Bi or Sb) anions and [Cu(im) 4](2+) cations. The Cu(2+) and Na(+) ions in the central belt are coordinated by alpha-[XW9O33](9-) units, im, and water molecules to form {CuO4(im)}, {CuO4(H2O)}, and {NaO4(H2O)2} groups in which Cu (2+) ions are partially modified with im ligands. These groups connect alternately forming a six-membered ring including six alpha-[XW9O 33](9-) units. Neighboring anions are further linked by [Cu(im) 4](2+) cations to display an unprecedented anionic chain, which is first observed in sandwich-type tungsto-bismuthate (-antimonite) system. Two kinds of isolated copper complexes and sodium ions are located as counterions, which cause three-dimensional packings of 1 and 2 to present interesting cage structures. The magnetic properties for 1 and 2 both indicate dominant antiferromagnetic interactions among trinuclear Cu(II) clusters.

A novel naphthylimido derivative of hexamolybdate, (Bu4N)2[Mo6O18N(Naph-1)] (1), was synthesized for the first time by the reaction of octamolybdate ion and 1-naphthyl amine hydrochloride with DCC (N,N‘-dicyclohexylcarbodiimide) as a dehydrating agent. The ultraviolet−visible absorption spectrum shows the lowest energy electronic transition of 1 occurs at 383 nm, which is dramatically red-shifted compared to that of [Mo6O19]2- and other monosubstituted phenylimido hexamolybdates reported in the literature. Moreover, cyclic voltammetry studies on compound 1 show the reversible reduction wave at −0.53 V, which is cathodically shifted relative to that of [Mo6O19]2-. Another interesting characteristic of 1 is that the cluster anions form supramolecular 1D chains via C−H···O hydrogen bonding interactions.

A kinetically controlled trans bifunctionalized organoimido derivative of hexamolybdate, (n-Bu(4)N)(2){trans-[Mo(6)O(17)(NAr)(2)]} (Ar = 2,6-dimethylphenyl) 1, in which the two 2,6-dimethylphenylimido groups are bonded to hexamolybdate at the trans positions, has been successfully synthesized in ca. 60% yield under mild reaction conditions. Its trans structure has been confirmed by a single-crystal X-ray diffraction study. In the crystals, cluster anions of 1 self-assemble into a 3D netlike structure via two different kinds of C-H...O hydrogen bondings, in which 1D supramolecular rectangular channels containing tetrabutylammonium cations form along the a axis. Compound 1 has also been characterized by (1)H NMR, IR, and UV-vis spectroscopic studies. UV-vis-near-IR reflectance spectroscopy measurements reveal the compound's nature of semiconductivity with an optical energy gap of 2.55 eV.

A novel organic−inorganic hybrid solid, (n-Bu4N)2[Mo6O17(NAr)2] (Ar = o-CH3OC6H4) 1, has been prepared by refluxing of (n-Bu4N)2[Mo6O19] and appropriate o-anisidine in acetonitrile with N-N‘-dicyclohexylcarbodiimide (DCC) as the dehydrating agent. Compound 1 has been characterized by single-crystal X-ray diffraction. Both of the two terminal o-anisidido ligands are linked, respectively, to an Mo atom of the hexamolybdate in a terminal fashion and exhibit an almost linear coordination mode of the Mo⋮N triple bond character. The two o-anisidido aryl rings on the hexamolybdate cluster lie in the cis position, allowing π−π stacking of phenyl ring among the anions. In the crystal, the cluster anions of 1 aggregate into an interesting 1D double chain along the a-axis through π−π stacking and C−H···O hydrogen-bonding interactions. Compared to the hexamolybdate parent, this solid has a smaller optical band gap of 2.25 eV from UV−visible-near-IR reflectance spectroscopy studies. It has also been characterized by 1...

The eight-nickel-capped polyoxoazonickelate, [Ni(20)(OH)(24)(MMT)(12)(SO(4))](NO(3))(2).6H(2)O (1; MMT = 2-mercapto-5-methyl-1,3,4-thiadiazole), has been synthesized, which has an alpha-Keggin structure with eight nickel caps. In this structure, the polyatom is the late transition metal Ni(II); the central heteroatom is S, and the organic terminal ligand becomes the primary part of the Keggin structure. This is a Keplerate-type cluster, which shows a central Ni(II)(12) cuboctahedron formed by the 12 Ni(II) centers of the classical alpha-Keggin core and a Ni(II)(8) hexahedron formed by the eight nickel caps.

The first polyoxometalatocyclophanes have been synthesized by the covalent linkage of a hexamolybdate cluster and bisarylimido ligands containing flexible chains. These metallamacrocycles are chiral, and some of them can undergo spontaneous resolution. The work provides a new protocol for preparing chiral polyoxometalates (POMs) and chiral metallamacrocycles from achiral building blocks by fastening both ends of a flexible chain onto an achiral POM to remove the symmetric center and mirror.

The assembly of two achiral POMs of Lindqvist and Anderson through strong covalent linkages, using bifunctional TRIS with a rotatable C-N single bond, gives two nanoscale rod-like chiral molecular triads with C(2) symmetry, the chirality of which were confirmed by the single crystal X-ray diffraction analyses and solid CD spectroscopy measurements. The enantiopure crystals of these compounds have been obtained by spontaneous resolution upon crystallization in the absence of any chiral source. The present work opens a way to make chiral nanostructures from achiral polyoxoanions, which may have potential applications in asymmetric catalysis, NLO, and ferroelectric materials.

In this communication, we demonstrate that polyoxomolybdates can activate sp3 C−H bonds in aliphatic amines. Unexpectedly, a carbon−carbon double bond is formed from two aliphatic primary amines via the activation and dehydrogenative coupling of two sp3 C−H bonds near the nitrogen atom bearing a hexamolybdate. Detailed experiments including 1H NMR, 13C NMR, IR, UV−vis, ESI-MS, and especially X-ray single-crystal diffraction substantially confirm the existence of carbon−carbon double bonds in a class of so-resulting organic−inorganic hybrid molecules, which are made up of two terminally substituted imidohexamolybdate cages bridged by a trans-tetrasubstituted, conjugated, rigid ethylene system. This discovery perhaps opens an interesting road to elaborate the CC double bond directly via the functionalization of saturated C−H bonds.

Organoimido derivatives of the mixed-metal [MoW5O19]2- cluster anion can be prepared by the functionalization of the parent cluster with aromatic amines.