Recrystallization of the previously reported monosolvated bis(phthalocyaninato)niobium(IV), [Pc2Nb]âClNP (ClNP ) 1-chloronaphthalene), has allowed isolation of a single crystal of a new solvated form, i.e. [Pc2Nb]â 3.5ClNP, whose structure has been elucidated by X-ray work: space group P21/n (No. 14); a ) 16.765(3), b ) 23.800(4), c ) 19.421(4) Å; R ) ç ) 90°, â ) 92.51(2)°; Z ) 4. The sandwiched material is a "stapled" molecule, characterized by the presence of two intramolecular interligand C-C ó bonds and highly strained phthalocyanine units, as formerly observed by crystallographic work for its Ti(IV) analogue, [Pc2Ti], and the +1 corresponding fragment, [Pc2Nb]+, present in the species [Pc2Nb](I3)(I2)0.5â3.5ClNP. [Pc2Nb] appears to be reluctant to undergo further oxidation above the +1 oxidation state. Detailed theoretical studies by DFT and TDDFT methods have been developed on [Pc2Nb] and [Pc2Nb]+, also extended for comparison to the Ti(IV) complex [Pc2Ti], and an adequate picture of the ground-state electronic structure of these species has been achieved. Moreover, the excitation energies and oscillator strengths calculated for the closed-shell systems, [Pc2Ti] and [Pc2Nb]+, provide a satisfactory interpretation of their characteristic visible optical spectra and help to rationalize the similar features observed in the visible spectrum of the open-shell "stapled" complex, [Pc2Nb]. Thin solid films (100-250 nm) of [Pc2Nb] deposited on ITO (indium-doped tin oxide) show a reversible redox process in neutral or acidic aqueous electrolytes. The electrochemical and electrochromic properties of the sandwiched complex, combined with impedance and UV/visible spectral measurements, are presented and discussed. The achieved electrochemical information, while substantially in keeping with the observed chemical redox behavior and theoretical predictions, qualifies [Pc2Nb] as an "optically passive" electrode and a promising material for its use in electrochromic devices.
"Stapled" Bis(phthalocyaninato)niobium(IV), Pc2Nb: X-ray Crystal Structure, Chemical and Electrochemical Behavior, and Theoretical Studies. Perspectives for the Use of Pc2Nb (Thin Films) as an "Optically Passive Electrode" in Electrochromic Devices
Elvira M Bauer;
2003
Abstract
Recrystallization of the previously reported monosolvated bis(phthalocyaninato)niobium(IV), [Pc2Nb]âClNP (ClNP ) 1-chloronaphthalene), has allowed isolation of a single crystal of a new solvated form, i.e. [Pc2Nb]â 3.5ClNP, whose structure has been elucidated by X-ray work: space group P21/n (No. 14); a ) 16.765(3), b ) 23.800(4), c ) 19.421(4) Å; R ) ç ) 90°, â ) 92.51(2)°; Z ) 4. The sandwiched material is a "stapled" molecule, characterized by the presence of two intramolecular interligand C-C ó bonds and highly strained phthalocyanine units, as formerly observed by crystallographic work for its Ti(IV) analogue, [Pc2Ti], and the +1 corresponding fragment, [Pc2Nb]+, present in the species [Pc2Nb](I3)(I2)0.5â3.5ClNP. [Pc2Nb] appears to be reluctant to undergo further oxidation above the +1 oxidation state. Detailed theoretical studies by DFT and TDDFT methods have been developed on [Pc2Nb] and [Pc2Nb]+, also extended for comparison to the Ti(IV) complex [Pc2Ti], and an adequate picture of the ground-state electronic structure of these species has been achieved. Moreover, the excitation energies and oscillator strengths calculated for the closed-shell systems, [Pc2Ti] and [Pc2Nb]+, provide a satisfactory interpretation of their characteristic visible optical spectra and help to rationalize the similar features observed in the visible spectrum of the open-shell "stapled" complex, [Pc2Nb]. Thin solid films (100-250 nm) of [Pc2Nb] deposited on ITO (indium-doped tin oxide) show a reversible redox process in neutral or acidic aqueous electrolytes. The electrochemical and electrochromic properties of the sandwiched complex, combined with impedance and UV/visible spectral measurements, are presented and discussed. The achieved electrochemical information, while substantially in keeping with the observed chemical redox behavior and theoretical predictions, qualifies [Pc2Nb] as an "optically passive" electrode and a promising material for its use in electrochromic devices.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
