Inorganic-organic hybrid materials [Ni(py) 4 ] 2 V 10 O 29 (1) and [Ni 2 (py) 5 (H 2 O) 3 ]V 4 O 12 (2) have been synthesized and characterized by infrared spectroscopy, thermogravimetry, magnetometry, and complete single crystal structure analysis. The crystal structures of 1 and 2 exhibit novel three-dimensional covalent networks. The framework structure in 1 contains polyoxometallate groupings of stoichiometry {V 10 O 29 } which are constructed from two cyclic {V 4 O 12 } units bound to centrosymmetric {V 2 O 7 } species. V-O-Ni bridges in the a-and b-directions join these units to two crystallographically independent trans-[Ni(py) 4 O 2 ] octahedra. The nickel-and vanadium-based moieties occupy alternating channels along the c-direction. The structure of 2 consists of octahedral species [Ni(py) 3 (H 2 O)O 2 ] and [Ni(py) 2 (H 2 O) 2 O 2 ] which are linked into a three-dimensional covalent network by the sharing of oxygen atom vertices with tetrahedral {VO 4 } groups. Compounds 1 and 2 are thermally stable up to 200 and 175 °C, respectively.Both compounds show Curie-Weiss type magnetic behavior over the temperature range 1.9-300 K. The effective magnetic moment in both cases is 3.0 µ B , revealing the presence of significant orbital contribution. Single ion magnetization as a function of magnetic field showed linear behavior for 1 and 2 over the range of 0-1 T. At a magnetic field of 9 T, 1 approaches saturation at 2 µ B per Ni 2+ ion, whereas 2 does not approach saturation well.
Catalytic properties of a series of new class of catalysts materials-[Co 3 (H 2 O) 12 V 18 O 42 (XO 4 )].24H 2 O (VNM-Co), [Fe 3 (H 2 O) 12 V 18 O 42 (XO 4 )].24H 2 O (VNM-Fe) (X = V, S) and [H 6 Mn 3 (H 2 O) 12 V 18 O 42 (VO 4 )].30H 2 O for the oxidative dehydrogenation of propane is studied. The open-framework nanostructures in these novel materials consist of three-dimensional arrays of {V 18 O 42 (XO 4The effect of change in the heterometallic center M (M = Mn, Co, Fe) of the linkers on the catalyst performance was studied. The catalyst material with Co in the linker showed the best performance in terms of propane conversion and selectivity at 350°C. The material containing Fe was most active but least selective and Mn containing catalyst was least active. The catalysts were characterized by Temperature Programmed Reduction (TPR), BET surface area measurement, Diffuse Reflectance Infrared Fourier Transform Spectroscopy, and X-ray Absorption Spectroscopy. TPR results show that all three catalysts are easily reducible and therefore are active at relatively low temperature. In situ X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure spectroscopy (EXAFS) studies revealed that the oxidation state of Co(II) remained unchanged up to 425°C (even after pretreatment). The reduction of Co(II) into metallic form starts at 425°C and this process is completed at 600°C.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.