Cofacial assembly of partially oxidized metallomacrocycles as an approach to controlling lattice architecture in low-dimensional molecular "metals". Probing band structure-counterion interactions in conductive [M(phthalocyaninato)O]n macromolecules using nitrosonium oxidants

Tamotsu Inabe, John G. Gaudiello, Michael K. Moguel, Tobin J Marks, Robert L. Burton, William J. McCarthy, Carl R. Kannewurf, Tobin J. Marks

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Abstract

This contribution reports an integrated chemical and physicochemical investigation of the consequences of doping the cofacially joined metallomacrocyclic polymers [M(Pc)O]n, M = Si and Ge, with the nitrosonium salts NO+X-, X- = BF4-, PF6-, and SbF6-. In the case of [Si(Pc)O]n, doped products {[Si(Pc)O]Xy}n are obtained with a limiting stoichiometry y ≃ 0.36 (essentially identical with band-fillings obtained with halogen oxidants). In contrast, NO+X- doping results in decomposition of [Ge(Pc)O]n. Upon incremental NO+X- doping of [Si(Pc)O]n, transmission infrared spectra reveal the progressive growth of electronic absorption, and transmission optical spectra reveal the formation of Pc π radical cation species. Studies of the NO+X- doping process by X-ray diffractometry suggest that it is largely inhomogeneous. Computer-assisted analysis of the {[Si(Pc)O]Xy}n powder diffraction data (aided by judiciously chosen model compounds) indicates crystal structures closely analogous to those of {[Si(Pc)O](I3)0.37}n, {[Si(Pc)O](Br3)0.37}n, Ni(Pc)(ClO4)0.40, and Ni(Pc)(BF4)0.35. The data can be indexed in the tetragonal space group P4/mcc, Z = 2, with a = 13.70 (7) Å, c = 6.58 (4) Å, phthalocyanine staggering angle = 40 (2)° (X- = BF4-); a = 13.98 (6) Å, c = 6.58 (4) Å; phthalocyanine staggering angle = 40 (2)° (X- = PF6-); a = 14.31 (4) Å, c = 6.58 (4) Å, phthalocyanine staggering angle = 40 (2)° (X̊ = SbF6-). It appears that the X- ions are disordered along c. ESR spectra reveal nearly free electron g values, in accord with the ligand-centered π radical character of the oxidation. As a consequence of the pronounced unidimensionality and minimal interaction of the carriers with heavy atoms, X-band powder ESR line widths are rather narrow (2.9-0.36 G) and decrease in the order I3- > SbF6- > PF6- > BF4-. For {[Si(Pc)O](BF4)0.36}n, the line width is virtually temperature-independent from 4 to 300 K. Variable temperature (4-300 K) static magnetic susceptibility studies of the {[Si(Pc)O]Xy}n materials reveal a small, sample-dependent Curie-like component and a Pauli-like, weakly temperature dependent contribution. Within experimental error, the Pauli-like susceptibility is independent of X-. Optical reflectivity studies of these materials reveal a plasma edge in the infrared. A Drude analysis of the data yields plasma frequency and tight-binding bandwidth parameters which are essentially independent of X-. Four-probe electrical conductivity studies of polycrystalline {[Si(Pc)O]Xy}n samples reveal a sharp increase of conductivity with increasing y. The temperature dependence of the data can be most convincingly fit to a transport model involving fluctuation-induced carrier tunneling through parabolic potential barriers that separate the high conductivity regions. As for the other collective properties, the charge transport properties are relatively insensitive to X-. A thermochemical analysis (Born-Haber cycle) indicates that the energetics of [Si(Pc)O]n doping with Br2, I2, and NO+X- are surprisingly similar. The small magnitude of the band structure-counterion interactions in the {[Si(Pc)O]Xy}n materials is attributed both to the local electronic and molecular structure of the phthalocyanine subunits as well as the overall stacking rigidity imposed by the -(Si-O-)n chains.

Original languageEnglish
Pages (from-to)7595-7608
Number of pages14
JournalJournal of the American Chemical Society
Volume108
Issue number24
Publication statusPublished - 1986

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  • Chemistry(all)

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