title: "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.
abstract: Recrystallization of the previously reported monosolvated bis(phthalocyaninato)niobium(IV), [Pc2Nb].CINP (CINP = 1-chloronaphthalene), has allowed isolation of a single crystal of a new solvated form, i.e. [Pc2Nb]. 3.5CINP, whose structure has been elucidated by X-ray work: space group P2(1)/n (No. 14); a = 16.765(3), b = 23.800(4), c = 19.421(4) A; alpha = gamma = 90 degrees, beta = 92.51(2) degrees; Z = 4. The sandwiched material is a "stapled" molecule, characterized by the presence of two intramolecular interligand C-C sigma 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](l3)(l2)0.5.3.5CINP. [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.
authors.affiliation: Dipartimento di Chimica, Università degli Studi di Roma La Sapienza, p.le A. Moro 5, 1-00185 Roma, Italy.
authors.forename: Elvira M
authors.initials: EM
authors.lastname: Bauer
authors.forename: Maria Pia
authors.initials: MP
authors.lastname: Donzello
authors.forename: Claudio
authors.initials: C
authors.lastname: Ercolani
authors.forename: Enrico
authors.initials: E
authors.lastname: Masetti
authors.forename: Stefania
authors.initials: S
authors.lastname: Panero
authors.forename: Giampaolo
authors.initials: G
authors.lastname: Ricciardi
authors.forename: Angela
authors.initials: A
authors.lastname: Rosa
authors.forename: Angiola
authors.initials: A
authors.lastname: Chiesi-Villa
authors.forename: Corrado
authors.initials: C
authors.lastname: Rizzoli