The structural, electronic, dielectric and vibrational features of two metal-organic frameworks with bispyrazolate ligands are investigated by combining ab initio periodic calculations and experimental techniques. UV-Vis spectroscopy has been used to study the electronic structure, while FTIR spectroscopy to obtain information about the vibrational features of the samples and their adsorptive properties. The examined MOFs contain square-planar Ni(II) nodes bridged either by the 4,4'-bispyrazolato (bpz) or by the 1,4-bis(4-pyrazolato)benzene (bpb) spacers. As expected, they are diamagnetic solids, with Ni(II) in low spin state. This has been confirmed through computations, other magnetic phases being predicted as remarkably less stable. Both materials possess a band gap of similar to 3.4 eV and show interesting dielectric properties due to the microporous structure and the low dielectric constant. Although Ni(II) is coordinatively unsaturated, it does not show any specific interaction with the probe molecules tested, as evidenced by FTIR measurements. This unexpected behavior is explained on the basis of computed results. The high stability of the low spin state of Ni(II) in square-planar coordination and a reduced accessibility of the metal sites due to steric effects are considered to be the reasons for the absence of preferential interactions between the metal centers and the probe molecules adopted.

Theoretical and experimental characterization of pyrazolato-based Ni(II) metal-organic frameworks

PETTINARI, Claudio
2012

Abstract

The structural, electronic, dielectric and vibrational features of two metal-organic frameworks with bispyrazolate ligands are investigated by combining ab initio periodic calculations and experimental techniques. UV-Vis spectroscopy has been used to study the electronic structure, while FTIR spectroscopy to obtain information about the vibrational features of the samples and their adsorptive properties. The examined MOFs contain square-planar Ni(II) nodes bridged either by the 4,4'-bispyrazolato (bpz) or by the 1,4-bis(4-pyrazolato)benzene (bpb) spacers. As expected, they are diamagnetic solids, with Ni(II) in low spin state. This has been confirmed through computations, other magnetic phases being predicted as remarkably less stable. Both materials possess a band gap of similar to 3.4 eV and show interesting dielectric properties due to the microporous structure and the low dielectric constant. Although Ni(II) is coordinatively unsaturated, it does not show any specific interaction with the probe molecules tested, as evidenced by FTIR measurements. This unexpected behavior is explained on the basis of computed results. The high stability of the low spin state of Ni(II) in square-planar coordination and a reduced accessibility of the metal sites due to steric effects are considered to be the reasons for the absence of preferential interactions between the metal centers and the probe molecules adopted.
File in questo prodotto:
Non ci sono file associati a questo prodotto.

I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.

Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11581/329991
 Attenzione

Attenzione! I dati visualizzati non sono stati sottoposti a validazione da parte dell'ateneo

Citazioni
  • ???jsp.display-item.citation.pmc??? ND
  • Scopus 13
  • ???jsp.display-item.citation.isi??? 15
social impact