RESUMEN
Two POM@MOF hybrid materials composed of a copper-based metal-organic framework (MOF) [Cu3(C9H3O6)2(H2O)3]n (HKUST-1) encapsulating vanadium-substituted Keggin polyoxometalates (POM), [α-PVW11O40]4- (PVW11) and [α-PV2W10O40]5- (PV2W10), were prepared and characterized. PVW11@HKUST-1 and PV2W10@HKUST-1 were synthesized hydrothermally by self-assembly of HKUST-1 in the presence of the preformed POMs, [α-PVW11O40]4- and [α-PV2W10O40]5-, respectively. The two POM@MOF composites were characterized by X-ray diffraction, TGA, BET surface area analysis and FT-IR and Raman spectroscopy. The electronic structure of the POM@MOF materials and their respective constituents is surveyed using solid state UV-vis reflectance spectroscopy. The UV-vis spectra order the oxidizing strength of the POM constituents ([α-PV2W10O40]5- > [α-PVW11O40]4-) and reveal the distinct electronic structure of the POM@MOF materials obtained by synthetic encapsulation of mono- and di-vanadium substituted Keggin polyoxotungstates in HKUST-1.
RESUMEN
Organofunctionalized tetranuclear clusters [(MII Cl)2 (VIV O)2 {((HOCH2 CH2 )(H)N(CH2 CH2 O))(HN(CH2 CH2 O)2 )}2 ] (1, M=Co, 2: M=Zn) containing an unprecedented oxometallacyclic {M2 V2 Cl2 N4 O8 } (M=Co, Zn) framework have been prepared by solvothermal reactions. The new oxo-alkoxide compounds were fully characterized by spectroscopic methods, magnetic susceptibility measurement, DFT and ab initio computational methods, and complete single-crystal X-ray diffraction structure analysis. The isostructural clusters are formed of edge-sharing octahedral {VO5 N} and trigonal bipyramidal {MO3 NCl} units. Diethanolamine ligates the bimetallic lacunary double cubane core of 1 and 2 in an unusual two-mode fashion, unobserved previously. In the crystalline state, the clusters of 1 and 2 are joined by hydrogen bonds to form a three-dimensional network structure. Magnetic susceptibility data indicate weakly antiferromagnetic interactions between the vanadium centers [Jiso (VIV -VIV )=-5.4(1); -3.9(2) cm-1 ], and inequivalent antiferromagnetic interactions between the cobalt and vanadium centers [Jiso (VIV -CoII )=-12.6 and -7.5â cm-1 ] contained in 1.