Andrea Dei - Academia.edu (original) (raw)

Papers by Andrea Dei

Inorganica Chimica Acta, 2008

The results of a sub-picosecond transient absorption spectroscopy study on a mononuclear and two ... more The results of a sub-picosecond transient absorption spectroscopy study on a mononuclear and two dinuclear low-spin iron(II) complexes is reported. The dinuclear derivatives are homonuclear (i.e. Fe-Fe) and heterodinuclear (Fe-Zn) in nature. The ligands we used were 2-pyridylmethyl-ketazine and 2-pyridylmethyl-hydrazone. Irradiation was made on the metal-to-ligand CT band occurring around 500 nm. The observed pattern of the relaxation decays is consistent with the population of the metastable 5 T 2 ligand field state within the first 100 fs after the photon absorption from the three different chromophores. The suggested implication of triplet intermediate states was not detected. The ground state recovery was observed to occur with a time constant of 350 ps for the mononuclear complex and 1600-1800 ps for the two dinuclear complexes.

Chemical Physics Letters, 2006

A cobalt(III)-polydioxolene polymer undergoing valence tautomeric interconversion was irradiated ... more A cobalt(III)-polydioxolene polymer undergoing valence tautomeric interconversion was irradiated at cryogenic temperatures. Magnetic and EPR data suggest the occurrence of photoinduced VT interconversion, with a maximum degree of about 10%. The kinetics data evidence a larger amount of cooperativity than previously observed in simple monomer, a phenomenon that we attribute to the 1D nature of the system. In the range 9–40K the relaxation time follows two different regimes, both temperature dependent. The small values of the activation energies suggest the existence of phonon assisted relaxation mechanisms based on a tunneling process involving the totalsymmetric breathing mode of the complex.

Dalton Transactions, 2007

The reaction of 3,3,3',3&... more The reaction of 3,3,3',3'-tetramethyl-5,5',6,6'-tetrahydroxy-1,1'spiro-bis(indane), L, with cobalt salts in the presence of diazine ligands affords polymeric derivatives of general formula [CoL(diazine)]infinity . nH2O, L being coordinated as a mixed-valence SQ-Cat species. The bipiridyl and o-phenantroline derivatives have been characterised by means of magnetic, EPR and calorimetric measurements. The characterisation showed that both systems are obtained in a metastable charge distribution, presumably trapped due to the class I character of the mixed valence form of the ligand. The occurrence of entropy-driven valence tautomeric interconversion induces the transition to the most stable charge distribution. The photomagnetic characterisation evidenced that valence tautomeric process can be photoinduced and that the lifetime of the photoinduced metastable state, obtained in low yield, is of ca. 2 x 10(5) s at 9 K.

Journal of Physics: Conference Series, 2005

The valence tautomerism of low-spin CoIII(Cat-N-BQ)(Cat-N-SQ) was investigated by means of UV-vis... more The valence tautomerism of low-spin CoIII(Cat-N-BQ)(Cat-N-SQ) was investigated by means of UV-vis pump-probe transient absorption spectroscopy in chloroform. By exciting the CT transition of the complex at 480 nm, an intramolecular electron transfer process is selectively triggered. The photo-induced charge transfer is pursued by a cascade of two main molecular events characterized by the ultrafast transient absorption spectroscopy: the first

Journal of the Brazilian Chemical Society, 2006

... [ Links ]. 48. Carbonera, C.; Dei, A.; Sangregorio, C.; Letard, J.-F.; Chem Phys. Lett. 2004,... more ... [ Links ]. 48. Carbonera, C.; Dei, A.; Sangregorio, C.; Letard, J.-F.; Chem Phys. Lett. 2004, 396, 198 [ Links ]. 49. Carbonera, C.; Dei, A.; Létard, J.-F.; Sangregorio, C.; Sorace, L.; Angew. Chem. Int. Ed. 2004, 43, 3136. [ Links ]. 50. Tao, J.; Maruyama, H.; Sato, O.; J. Am. Chem. Soc. ...

Inorg Chem, 1979

... (16) G. B. Porter in “Concepts of ... ANDREA DEI,* DANTE GATTESCHI,* and ERMANNO PIERGENTILI ... more ... (16) G. B. Porter in “Concepts of ... ANDREA DEI,* DANTE GATTESCHI,* and ERMANNO PIERGENTILI Received June 26, 1978 2-Pyridyl methyl ketazine (PMK) is known to form dinuclear octahedral complexes of formula M2(PMK)3Y4.nH20 (M = Co, Ni, Cu, Zn; Y = Clod, I, BF4). ...

Journal of the Chemical Society Chemical Communications, 1992

ABSTRACT

Inorganica Chimica Acta, 1988

Inorganica Chimica Acta, 1981

Journal of The Chemical Society, Chemical Communications, 1992

ABSTRACT

The Journal of Physical Chemistry B, 2013

In this work, we studied the valence tautomerism process on two different Co-dioxolene complexes ... more In this work, we studied the valence tautomerism process on two different Co-dioxolene complexes by means of transient infrared spectroscopy (TRIR). The molecules investigated are ls-Co(III)(Cat-N-BQ)(Cat-N-SQ) (DQ2) and [ls-Co(III)(tpy)(Cat-N-SQ)]PF6 (tpy), where Cat-NBQ = 2-(2-hydroxy-3,5-ditert-butylphenyl-imino)-4,6-ditert-butylcyclohexa-3,5-dienone, Cat-N-SQ is the dianionic radical analogue, and tpy = 2,2'-6-2″-terpyridine. DFT calculations of the harmonic frequencies for the two complexes allow us to pinpoint the normal modes to be used as markers of the semiquinonate and benzoquinonate isomers. The photoinduced one-electron charge transfer process from the radical semiquinonate ligand to the metal center leads to a ls-Co(II)(x)(Cat-N-BQ) electronic state (where x is the other ligand). Following this first step, an ultrafast ISC process (τ < 200 fs) takes places, yielding the benzoquinonate isomer (hs-Co(II)(x)(Cat-N-BQ)). In the experiments, we employed different excitation wavelengths on resonance with different absorption bands of the two samples. Excitation in the ligand-to-metal charge transfer (LMCT) band at ∼520 nm and in the semiquinonate band at ∼1000 nm induces the valence tautomerism (VT) in both samples. From the time evolution of the TRIR spectra, we determine the time constants of the vibrational cooling in the tautomeric state (7-14 ps) and the ground state recovery times (∼350 ps for tpy and ∼450 ps for DQ2). In contrast, when the pump frequency is set at 712 nm, on resonance with the benzoquinonate absorption band of the second active ligand of the DQ2, no electron transfer takes place: the TRIR spectra basically show only ground state bleaching bands and no marker band of the tautomeric conversion shows up.

Journal of Inorganic Biochemistry, 1982

Inorganica Chimica Acta, 1982

shift studies can in prmciple provide a powerful tool for mvestlgatmg the structure of paramagnet... more shift studies can in prmciple provide a powerful tool for mvestlgatmg the structure of paramagnetic molecules m solution, since both contact and dipolar shift contributions are related to the geometrical properties of the resonating protons with respect to the paramagnetlc center [ 11. However, because of the difficulties involved in separating these two contributions [2] , the use of the technique IS often limited only to the cases where one of the above quantities is believed to be significantly less important than the other. As a matter of fact, conformational studies on paramagnetic complexes have been extensively carried out only for sixcoordmate nickel(H) complexes [3-61, since, on account of the fact that this octahedral metal ion 1s characterized by an orbitally non-degenerate electronic ground state, dlpolar shifts are expected to be negligible.

Inorganica Chimica Acta, 1982

Inorganica Chimica Acta, 1989

Inorganica Chimica Acta, 1980

Inorganica Chimica Acta, 2008

The results of a sub-picosecond transient absorption spectroscopy study on a mononuclear and two ... more The results of a sub-picosecond transient absorption spectroscopy study on a mononuclear and two dinuclear low-spin iron(II) complexes is reported. The dinuclear derivatives are homonuclear (i.e. Fe-Fe) and heterodinuclear (Fe-Zn) in nature. The ligands we used were 2-pyridylmethyl-ketazine and 2-pyridylmethyl-hydrazone. Irradiation was made on the metal-to-ligand CT band occurring around 500 nm. The observed pattern of the relaxation decays is consistent with the population of the metastable 5 T 2 ligand field state within the first 100 fs after the photon absorption from the three different chromophores. The suggested implication of triplet intermediate states was not detected. The ground state recovery was observed to occur with a time constant of 350 ps for the mononuclear complex and 1600-1800 ps for the two dinuclear complexes.

Chemical Physics Letters, 2006

A cobalt(III)-polydioxolene polymer undergoing valence tautomeric interconversion was irradiated ... more A cobalt(III)-polydioxolene polymer undergoing valence tautomeric interconversion was irradiated at cryogenic temperatures. Magnetic and EPR data suggest the occurrence of photoinduced VT interconversion, with a maximum degree of about 10%. The kinetics data evidence a larger amount of cooperativity than previously observed in simple monomer, a phenomenon that we attribute to the 1D nature of the system. In the range 9–40K the relaxation time follows two different regimes, both temperature dependent. The small values of the activation energies suggest the existence of phonon assisted relaxation mechanisms based on a tunneling process involving the totalsymmetric breathing mode of the complex.

Dalton Transactions, 2007

The reaction of 3,3,3',3&... more The reaction of 3,3,3',3'-tetramethyl-5,5',6,6'-tetrahydroxy-1,1'spiro-bis(indane), L, with cobalt salts in the presence of diazine ligands affords polymeric derivatives of general formula [CoL(diazine)]infinity . nH2O, L being coordinated as a mixed-valence SQ-Cat species. The bipiridyl and o-phenantroline derivatives have been characterised by means of magnetic, EPR and calorimetric measurements. The characterisation showed that both systems are obtained in a metastable charge distribution, presumably trapped due to the class I character of the mixed valence form of the ligand. The occurrence of entropy-driven valence tautomeric interconversion induces the transition to the most stable charge distribution. The photomagnetic characterisation evidenced that valence tautomeric process can be photoinduced and that the lifetime of the photoinduced metastable state, obtained in low yield, is of ca. 2 x 10(5) s at 9 K.

Journal of Physics: Conference Series, 2005

The valence tautomerism of low-spin CoIII(Cat-N-BQ)(Cat-N-SQ) was investigated by means of UV-vis... more The valence tautomerism of low-spin CoIII(Cat-N-BQ)(Cat-N-SQ) was investigated by means of UV-vis pump-probe transient absorption spectroscopy in chloroform. By exciting the CT transition of the complex at 480 nm, an intramolecular electron transfer process is selectively triggered. The photo-induced charge transfer is pursued by a cascade of two main molecular events characterized by the ultrafast transient absorption spectroscopy: the first

Journal of the Brazilian Chemical Society, 2006

... [ Links ]. 48. Carbonera, C.; Dei, A.; Sangregorio, C.; Letard, J.-F.; Chem Phys. Lett. 2004,... more ... [ Links ]. 48. Carbonera, C.; Dei, A.; Sangregorio, C.; Letard, J.-F.; Chem Phys. Lett. 2004, 396, 198 [ Links ]. 49. Carbonera, C.; Dei, A.; Létard, J.-F.; Sangregorio, C.; Sorace, L.; Angew. Chem. Int. Ed. 2004, 43, 3136. [ Links ]. 50. Tao, J.; Maruyama, H.; Sato, O.; J. Am. Chem. Soc. ...

Inorg Chem, 1979

... (16) G. B. Porter in “Concepts of ... ANDREA DEI,* DANTE GATTESCHI,* and ERMANNO PIERGENTILI ... more ... (16) G. B. Porter in “Concepts of ... ANDREA DEI,* DANTE GATTESCHI,* and ERMANNO PIERGENTILI Received June 26, 1978 2-Pyridyl methyl ketazine (PMK) is known to form dinuclear octahedral complexes of formula M2(PMK)3Y4.nH20 (M = Co, Ni, Cu, Zn; Y = Clod, I, BF4). ...

Journal of the Chemical Society Chemical Communications, 1992

ABSTRACT

Inorganica Chimica Acta, 1988

Inorganica Chimica Acta, 1981

Journal of The Chemical Society, Chemical Communications, 1992

ABSTRACT

The Journal of Physical Chemistry B, 2013

In this work, we studied the valence tautomerism process on two different Co-dioxolene complexes ... more In this work, we studied the valence tautomerism process on two different Co-dioxolene complexes by means of transient infrared spectroscopy (TRIR). The molecules investigated are ls-Co(III)(Cat-N-BQ)(Cat-N-SQ) (DQ2) and [ls-Co(III)(tpy)(Cat-N-SQ)]PF6 (tpy), where Cat-NBQ = 2-(2-hydroxy-3,5-ditert-butylphenyl-imino)-4,6-ditert-butylcyclohexa-3,5-dienone, Cat-N-SQ is the dianionic radical analogue, and tpy = 2,2'-6-2″-terpyridine. DFT calculations of the harmonic frequencies for the two complexes allow us to pinpoint the normal modes to be used as markers of the semiquinonate and benzoquinonate isomers. The photoinduced one-electron charge transfer process from the radical semiquinonate ligand to the metal center leads to a ls-Co(II)(x)(Cat-N-BQ) electronic state (where x is the other ligand). Following this first step, an ultrafast ISC process (τ < 200 fs) takes places, yielding the benzoquinonate isomer (hs-Co(II)(x)(Cat-N-BQ)). In the experiments, we employed different excitation wavelengths on resonance with different absorption bands of the two samples. Excitation in the ligand-to-metal charge transfer (LMCT) band at ∼520 nm and in the semiquinonate band at ∼1000 nm induces the valence tautomerism (VT) in both samples. From the time evolution of the TRIR spectra, we determine the time constants of the vibrational cooling in the tautomeric state (7-14 ps) and the ground state recovery times (∼350 ps for tpy and ∼450 ps for DQ2). In contrast, when the pump frequency is set at 712 nm, on resonance with the benzoquinonate absorption band of the second active ligand of the DQ2, no electron transfer takes place: the TRIR spectra basically show only ground state bleaching bands and no marker band of the tautomeric conversion shows up.

Journal of Inorganic Biochemistry, 1982

Inorganica Chimica Acta, 1982

shift studies can in prmciple provide a powerful tool for mvestlgatmg the structure of paramagnet... more shift studies can in prmciple provide a powerful tool for mvestlgatmg the structure of paramagnetic molecules m solution, since both contact and dipolar shift contributions are related to the geometrical properties of the resonating protons with respect to the paramagnetlc center [ 11. However, because of the difficulties involved in separating these two contributions [2] , the use of the technique IS often limited only to the cases where one of the above quantities is believed to be significantly less important than the other. As a matter of fact, conformational studies on paramagnetic complexes have been extensively carried out only for sixcoordmate nickel(H) complexes [3-61, since, on account of the fact that this octahedral metal ion 1s characterized by an orbitally non-degenerate electronic ground state, dlpolar shifts are expected to be negligible.

Inorganica Chimica Acta, 1982

Inorganica Chimica Acta, 1989

Inorganica Chimica Acta, 1980