Extended hybrid architectures based on tetra-CoIIsandwiched polyoxotungstates

Abstract

Three extended hybrid materials containing tetra-CoII sandwiched polyoxotungstates [Co(en)2(H2O)]2[Co(en)(H2O)]2[Co4(en)(SiW9O34)2]·2H2en·6H2O (1), [Co(Hen)(H2O)2]2[Co4(H2O)2(SiW9O34)2]·3H2en·28H2O (2) and [Co(enMe)2]4[Co(enMe)]2[Co4(H2O)2(SiW9O34)2]·22H2O (3) (en = ethylenediamine, enMe = 1,2-diaminopropane), have been hydrothermally synthesized and structurally characterized by IR spectra, UV-vis spectra, elemental analysis, thermogravimetric analysis, and single-crystal X-ray diffraction. Compound 1 is based on the tetra-Co-complex-supported clusters {[Co(en)2(H2O)]2[Co(en)(H2O)]2[Co4(SiW9O34)2]} through the linkage of en in an end-to-end fashion to form a 1-D linear chain, whereas compound 2 is constructed from [Co4(H2O)2(SiW9O34)2]12− building blocks and [Co(Hen)(H2O)2]3+ complexes with (3,6)-network topology. The novel 2-D structure of 3 consists of the building blocks [Co4(H2O)2(SiW9O34)2]12− decorated by two [Co(enMe)2]2+ groups and two types of cobalt complexes as double bridges, which was first observed in 2-D layered hybrid materials based on sandwich polyoxotungstates with a (4,4)-connected topology. Furthermore, at room temperature, the EPR spectra of compounds 1, 2 and 3 display broad signals due to the interaction within CoII ions. The values of the g tensor derived from the EPR spectra are ca. 2.57 for 1, ca. 2.20 for 2 and ca. 2.51 for 3, respectively, which are affected by the different coordination environments of CoII ions.