POM-based Organic Inorganic Hybrids Research Articles

Polyoxometalate-based nanocomposites for antitumor and antibacterial applications.

Polyoxometalates (POMs), as emerging inorganic metal oxides, have been shown to have significant biological activity and great medicinal value. Nowadays, biologically active POM-based organic–inorganic hybrid materials have become the next generation of antibacterial and anticancer drugs because of their customizable molecular structures related to their highly enhanced antitumor activity and reduced toxicity to healthy cells. In this review, the current developed strategies with POM-based materials for the purpose of antibacterial and anticancer activities from different action principles inducing cell death and hyperpolarization, cell plasma membrane destruction, interference with bacterial respiratory chain and inhibiting bacterial growth are overviewed. Moreover, specific interactions between POM-based materials and biomolecules are highlighted for a better understanding of their antibacterial and anticancer mechanisms. POMs have great promise as next-generation antibacterial and anticancer drugs, and this review will provide a valuable systematic reference for the further development of POM-based nanomaterials.

Insights into organic-inorganic hybrid molecular materials: organoimido functionalized polyoxomolybdates.

Polyoxometalates (POMs) are polyatomic anions that comprise transition metal group 5 (V, Nb, Ta) or group 6 (Mo, W) oxyanions connected together by shared oxygen atoms. POMs are fascinating because of their exclusive and remarkable characteristics. One of the most interesting features of POMs is their capability to function as an electron relay by performing stepwise multi-electron redox reactions while maintaining their structural integrity. Functionalization of POMs with amino organic compounds results in organoimido derivatives of polyoxometalates, which have aroused interest due to augmentation of their properties. Comprehensive study has shown that the synthesis methodologies to obtain desired organoimido derivatives of POMs by employing various imido-releasing reagents have progressed drastically in recent decades, particularly the innovative DCC-dehydrating technique. These organoimido functionalized POMs have been used as major building blocks to develop unique nanostructured organic-inorganic hybrid molecular materials. Many conventional organic synthesis processes such as Pd-catalyzed carbon-carbon coupling and esterification reactions have been performed with organoimido functionalized POMs where the presence of POM triggered the reaction process. Thus, investigation of the reactivity of organoimido derivatives of POMs foreshadows the intriguing future of POMs chemistry.

Two new Keggin-type polyoxometalate-based organic-inorganic hybrid compounds with metal ions and chelate ligands

Two new hybrid compounds with chemical formulas [Co(L1)2(H2O)2]2[SiW12O40]·6H2O (1) and [Cu2(C9H22 N)2(L2)2][SiW12O40]·2H2O (2) (L1 = 3,3′-diamino-5,5′-bis(1H-1,2,4-triazole), L2 = 1,2-bis(3-(2-pyridyl)pyrazole-1-ylmethyl)benzene, C9H22 N = tripropylamine) were prepared in a hydrothermal reaction system containing Keggin-type polyoxometalates (POMs), transition metal (TM) salts (cobalt salts and copper salts), and chelate L1/L2 ligands. X-ray structural analysis reveals that 1 and 2 possess 3-D supramolecular host frameworks with large cavities and the polyoxoanions SiW12 reside in these cavities as the guest templates. The photocatalytic activities of 1 and 2 were investigated. Both compounds show efficient catalytic activity for degradation of RhB with 1 > 2. The loading amount of the POM units and the structural features of these POM-based organic-inorganic hybrid compounds may be necessary factors that affect the activity of catalysts in the photocatalytic degradation.

Theoretical studies on POM-based organic-inorganic hybrids containing double D-A1-π-A2 chains for high-performance p-type, dye-sensitized solar cells (DSSCs).

Polyoxometalate (POM)-based organic-inorganic hybrid systems are designed as p-type dyes containing double D-A1-π-A2 chains. The A1 spacers are thiophene, 1,2,3-triazole, 1,3,4-oxadlazole, thienothiadiazole units or their combinations and the A2 spacer is hexamolybdate. The electronic structures, absorption spectra, and electronic transition characteristics of systems were systematically studied on the basis of density functional theory (DFT) and time-dependent DFT (TDDFT). The highest occupied molecular orbital (HOMO) levels of systems were below the valence bond (VB) of NiO and the lowest unoccupied molecular orbital (LUMO) levels of studied systems were higher than the I2/I3(-) redox level, which benefit hole injection and dye regeneration. The HOMOs of systems were predominantly delocalized over the organic groups and Mo[triple bond, length as m-dash]N, which are more helpful to hole injection than systems . Introduction of thienothiadiazole units is an effective way to improve the light absorption ability of dyes, and inserting thiophene and 1,2,3-triazole as A1 spacers can increase the efficiency of dye in dye-sensitized solar cells (DSSC).

Exploring the influence of electron donating/withdrawing groups on hexamolybdate-based derivatives for efficient p-type dye-sensitized solar cells (DSSCs)

A series of POM-based organic–inorganic hybrids with different substituting groups are investigated as sensitizers for application in dye-sensitized solar cells (DSSCs).

Two new hybrid compounds assembled from Keggin phosphotungstates, cobalt/zinc cations and V-shaped imidazole ligands

Two new inorganic–organic hybrid compounds, [Co(H2O)2(bimb)2]2[PWVWVI11O40] (1) and [Zn3(H2O)4(bimb)4][PWV3WVI9O40] (2) (bimb = 1,3-bis(1-imidazoly)benzene) have been obtained and characterized by routine methods. Compounds 1 and 2 are synthesized under the same hydrothermal conditions except for alternation of the metal cations, however, their eventual structures are different. Compound 1 exhibits a 1D chain, whereas 2 shows a complicated 3D framework. The distinct structural features of the two compounds indicate that metal cations should have great effects on the structures of POM-based organic–inorganic hybrid compounds. The electrochemical properties of 1 and 2 have been also investigated, and the results show that 1 has a good electrocatalytic activity toward reduction of hydrogen peroxide (H2O2) molecules ascribed to W-centers.

Theoretical studies on organoimido-substituted hexamolybdates dyes for dye-sensitized solar cells (DSSC)

A series of POM-based organic–inorganic hybrids with different π-conjugated bridges are investigated as sensitizers for application in dye-sensitized solar cells (DSSCs). A combination of density functional theory (DFT) and time-dependent DFT (TDDFT) approaches is employed. The effects of π-conjugated spacer size and π-conjugation length on the spectra of designed systems are demonstrated. The results show that the absorption spectra are systematically broadened and red-shifted with increasing sizes of the π-conjugated spacer and the length of π-conjugation. The theoretical examination was performed on the key parameters of incident photon-to-electron conversion efficiency (IPCE), light harvesting efficiency (LHE) and electron injection efficiency (Φinj). The result suggests that system 2 with thieno[3,2-b]thiophene demonstrates a balance of the two crucial factors and may result in the highest IPCE of DSSCs. This study is expected to deepen our understanding of POM-based organic–inorganic hybrid dyes and assist the molecular design of new dyes for the further optimization of DSSCs.

DFT studies on the electronic properties of organometallic-polyoxomolybdate anions [ [formula omitted]Mo 6O 19−n] (2−n)− ( n = 1 or 2): Revealing bonding features of Cp ∗–Mo

In this paper, the electronic properties of organometallic-polyoxomolybdate anions [Cp ∗Mo 6O 18] − (Cp ∗Mo 6), [ Cp 2 ∗ Mo 6O 17] 0 ( Cp 2 ∗ Mo 6), and [Cp ∗TiMo 5O 18] 3− (Cp ∗TiMo 5) are investigated by density functional theory calculations, and several principles for structure–property relationship are obtained. The bonding energy calculations show that the cis-isomer of anion Cp 2 ∗ Mo 6 is more stable than the trans-isomer due to large orbital mixing effect. The phenomena that central oxygen atom largely moves to Mo atom bearing Cp ∗ fragment and extra surface charges likely extend to the trans-position terminal oxygen atoms in anions Cp ∗Mo 6, Cp 2 ∗ Mo 6, and Cp ∗TiMo 5 are explained by trans-influence. Compared with [Mo 6O 19] 2−, the energy gap between highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital of anion Cp ∗Mo 6, as well as Cp 2 ∗ Mo 6, is narrowed due to the raised HOMO which is mainly localized on Cp ∗ fragment. Fragment analysis reveals that Cp ∗–Mo bond characterizes two nonclassical σ bonds and two π bonds, while only π bonds contribute to the bond order. The static first hyperpolarizabilities of Cp ∗Mo 6 and Cp 2 ∗ Mo 6 are smaller than that of [Mo 6O 18NPh] 2− due to weak intramolecular charge transfer. The peculiar Cp ∗–Mo bond would provoke the studies on novel POM-based organic–inorganic hybrid materials.