Dalton Transactions Dynamic Article Links Cite this: DOI: 10.1039/c2dt30537b www.rsc.org/dalton PAPER ε-Keggin-based coordination networks: Synthesis, structure and application toward green synthesis of polyoxometalate@graphene hybrids† L. Marleny Rodriguez-Albelo, a Guillaume Rousseau, b Pierre Mialane, b Jérôme Marrot, b Caroline Mellot-Draznieks, c A. Rabdel Ruiz-Salvador, a Shiwen Li, d Rongji Liu, e Guangjin Zhang, e Bineta Keita* d and Anne Dolbecq* b Received 6th March 2012, Accepted 22nd June 2012 DOI: 10.1039/c2dt30537b Four coordination networks based on the {ε-PMo V 8 Mo VI 4 O 40 (OH) 4 Zn 4 } Keggin unit (εZn) have been synthesized under hydrothermal conditions. (TBA) 3 {PMo V 8 Mo VI 4 O 36 (OH) 4 Zn 4 }[C 6 H 4 (COO) 2 ] 2 (ε(isop) 2 ) is a 2D material with monomeric εZn units connected via 1,3 benzenedicarboxylate (isop) linkers and tetrabutylammonium (TBA) counter-cations lying between the planes. In (TPA) 3 {PMo V 8 Mo VI 4 O 37 (OH) 3 Zn 4 }[C 6 H 3 (COO) 3 ](TPA[ε(trim)] ∞ ), 1D inorganic chains formed by the connection of εZn POMs, via Zn–O bonds, are linked via 1,3,5 benzenetricarboxylate (trim) ligands into a 2D compound with tetrapropylammonium (TPA) cations as counter-cations. (TBA) {PMo V 8 Mo VI 4 O 40 Zn 4 }(C 7 H 4 N 2 ) 2 (C 7 H 5 N 2 ) 2 ·12H 2 O(ε(bim) 4 ) is a molecular material with monomeric εZn POMs bound to terminal benzimidazole (bim) ligands. Finally, (TBA)(C 10 H 10 N 4 ) 2 (HPO 3 ) {PMo V 8 Mo VI 4 O 40 Zn 4 } 2 (C 10 H 9 N 4 ) 3 (C 10 H 8 N 4 )(ε 2 ( pazo) 4 ) is a 1D compound with dimeric (εZn) 2 POMs connected by HPO 3 2− ions and terminal para-azobipyridine ( pazo) ligands. In this compound an unusual bond cleavage of the central NvN bond of the pazo ligand is observed. We report also a green chemistry- type one-step synthesis method carried out in water at room temperature using ε 2 ( pazo) 4 and ε(isop) 2 as reducing agent of graphite oxide (GO) to obtain graphene (G). The POM@G hybrids were characterized by X-ray photoelectron spectroscopy, Raman spectroscopy, powder X-ray diffraction, energy dispersive X-ray analysis, infrared spectroscopy, scanning electron microscopy, transmission electron microscopy and cyclic voltammetry. Introduction Metal organic frameworks (MOFs) 1 have attracted intensive interest because of their structural diversity as well as their potential applications, for example in gas storage, separation, catalysis, drug delivery and imaging. 2 Their properties depend both on the nature of their constituent inorganic building units and their spatial arrangement. In this respect, polyoxometalates (POMs), a large family of soluble anionic metal oxide clusters of d-block transition metals in high oxidation states (W VI , Mo V,VI , V IV,V ), with a wide range of magnetic, 3 redox, 4 and catalytic properties, 5 constitute ideal building blocks for multifunctional materials, combining the properties of POMs and those of MOFs. POMs can be easily functionalized by organic molecules either by direct linking to the oxygen atoms of the POM or via transition metal or rare earth ions grafted at the surface of the POM. 6 Connections of the POMs can then be achieved via the use of multidentate ligands, leading to the formation of oligo- mers 7 or polymers, depending on the number of coordination sites and their geometric orientation. The polymers can be described as POM-based MOFs, so-called POMOFs. 8 Note that this name has also been used for fully inorganic POM-based frameworks as an abbreviation of polyoxometalate open frame- work. 9 An increasing amount of POM-based coordination polymers have been reported over the last decade, with a diver- sity of structures ranging from 1D to 3D frameworks. 10 Some of them exhibit catalytic properties 11 but their electrocatalytic prop- erties have rarely been exploited. 12 Another promising approach consists of building MOF materials around inorganic POM † Experimental conditions for the synthesis and characterizations of POM@G hybrids, bond distances and BVS calculations, figures of the crystallographic structures and of the hypothetical structure of ε(bim) 4 , PXRD patterns, XPS, Raman and IR spectra, TEM and SEM images, CVs. CCDC 870381–870384. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c2dt30537b a Group of Materials Developed by Design, Division of Chemistry and Technologyof Materials, Institute of Materials Research and Engineering (IMRE), University of Havana, Havana, 10400, Cuba b Institut Lavoisierde Versailles, UMR 8180, Université de Versailles Saint-Quentin en Yvelines, 45 Avenue des Etats-Unis, 78035 Versailles cedex, France. E-mail: dolbecq@chimie.uvsq.fr c Laboratoire de Chimie des Processus Biologiques, FRE 3488, Collège de France, 11 Place Marcellin Berthelot, Paris 75005, France d Laboratoire de Chimie Physique, Groupe d’Electrochimie et de Photoélectrochimie, UMR 8000, CNRS, Université Paris-Sud, Bâtiment 350, 91405 Orsay cedex, France. E-mail: bineta.keita@lcp.u-psud.fr e Key Laboratory of Green Process and Engineering, Institute of Process Engineering, Chinese Academy of Sciences, 100190 Beijing, China This journal is © The Royal Society of Chemistry 2012 Dalton Trans. View Online / Journal Homepage