Abstract
We present a new coordination polymer, {[VO(pzdc)(H2O)2] H2O}n, built from vanadyl and pyrazine-2,5-dicarboxylate (pzdc) ions. It consists of a one-dimensional chain of vanadyl ions linked by pzdc ions. The carboxylate groups show monodentate coordination, while the pyrazine ring is present both in non-coordinated and coordinated modes. This novel structure is stabilized by an intricate network of hydrogen bonds. The material is highly robust, and thermally stable up to 400 K. It is also antiferromagnetic, with a maximum magnetic susceptibility at ca. 50 K. The orbital shape and population analysis by means of DFT analysis confirm the π-acceptor role of the aromatic nitrogen function of the ligand, while the oxygen-based moieties (carboxylates from pzdc, the aqua ligands and oxo from V=O group) behave as normal donors. Charting the density flow related with significant transitions computed by time-dependent DFT, we determined the ligand-to-metal charge transfer processes. The topology of the chain complex implies two different types of connecting bridges. Using Broken Symmetry DFT modelling gives evidence for two different exchange coupling mechanisms between the vanadyl ions along each of these two molecular bridges. One is strongly antiferromagnetic, practically reducing the chain to 'vanadyl dimers'. The other is almost uncoupled, due to the large distance between the vanadyl ions.
Highlights
Vanadium compounds are widely studied in chemistry and applied in industry
One interesting emerging area is the synthesis of vanadium-based metal–organic frameworks (V-MOFs)
V-MOFs, we discovered a new coordination polymer built of vanadyl and pyrazine-2,5-dicarboxylate ions, {[VO( pzdc)
Summary
Vanadium compounds are widely studied in chemistry and applied in industry. They are studied for their redox chemistry, which enables a variety of applications in oxidation catalysis,[1,2,3,4] including its largest application in sulfuric acid synthesis.[2,5,6,7,8] Among these, epoxidation of aliphatic or cycloalkenes is highly relevant because it is a straightforward route for producing various chemicals.[1,2,3] such reactions are mainly performed in homogeneous media, making the catalyst recycle impossible. The weight loss of 6.6% observed between 200 °C and 300 °C is typical for vanadyl compounds containing water molecules coordinated at equatorial positions.[43] The weight loss above 380 °C is due to the decomposition of the organic ligand. Several reports[7,46,47] showed that octahedral vanadyl complexes containing both N- and O-donor ligands often prefer the N-donor in trans position with respect to the VvO bond.
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