Robust 1D open rack-like architecture in coordination polymers of Anderson POMs [{Na4(H2O)14}{Cu(gly)}2][TeMo6O24] and [{Cu(en)2}3{TeW6O24}]: synthesis, characterization and heterogeneous catalytic epoxidation of olefines.
Two novel organic-inorganic hybrid tungsto- and molybdo-telurates having formula [{Na(4)(H(2)O)(14)}{Cu(gly)}(2)][TeMo(6)O(24)] (1){gly = glycine} and [{Cu(en)(2)}(3){TeW(6)O(24)}]·6H(2)O {en = ethyline-diamine} (2) based on Anderson type heteropolyoxometalates (POMs) have been synthesized and characterized by X-ray crystallography. Common structural feature of both 1 and 2 is the presence of a unique 1D open rack-like architecture, where the disc shaped Anderson POMs act as steps and cationic Cu-organic complexes act as handles of the rack. In 1 the independent structural unit is a 1D coordination polymer with the above mentioned rack type architecture, while in 2, these independent rack-like architectures are further extended to a 2D coordination polymer. Heterogeneous catalysis for the epoxidation of cyclohexene and styrene by complexes 1 and 2 showed very good catalytic efficiency resulting epoxides of ~60% yield, with dialcohol formed by the hydrolysis of epoxides, as the other major product (~28%). Cyclic voltammetric studies of [{Na(4)(H(2)O)(14)}{Cu(gly)}(2)][TeMo(6)O(24)] (1) in aqueous KCl solution indicates that the redox changes occur only on the copper centers and supported by carrying out parallel experiments on the precursors like ([Cu(gly)(2)](2+) and [TeMo(6)O(24)](6-), under the identical experimental conditions. The E(1/2) = 0.662, -0.142 and -0.332 V(vs. SCE) correspond to Cu(III) → Cu(II), Cu(II) → Cu(I) and Cu(I) → Cu(0) reductions, respectively. Thermal analyses reveal identical phase transition reactions with an exothermic peak in the DTA curve at 380 °C for 1 and an endothermic peak appears at comparatively higher temperature (408 °C) for 2 manifesting the higher stability of tungstane based POM over the molybdenum ones. EPR as well as magnetic moment results indicate that both the complexes 1 and 2 are paramagnetic with one unpaired electron per copper(II) ion.
Department of Chemistry, Jadavpur University, Kolkata, 700 032, India.
Daipayan
D
Dutta
Atish D
AD
Jana
Mainak
M
Debnath
Asim
A
Bhaumik
Jaromir
J
Marek
Mahammad
M
Ali
D000475:Alkenes / Q000737:chemistry*; D002384:Catalysis; D056831:Coordination Complexes / Q000138:chemical synthesis* / Q000737:chemistry; D003300:Copper / Q000737:chemistry*; D018360:Crystallography, X-Ray; D004578:Electron Spin Resonance Spectroscopy; D008968:Molecular Conformation; D008982:Molybdenum / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D010084:Oxidation-Reduction; D011108:Polymers / Q000737:chemistry*; D013691:Tellurium / Q000737:chemistry*
D000475:Alkenes; D056831:Coordination Complexes; D009942:Organometallic Compounds; D011108:Polymers; D003300:Copper; D008982:Molybdenum; D013691:Tellurium