This contribution reports an integrated chemical and physicochemical study of the effects of halogen (I2, Br2) doping on the cofacially joined metallomacrocyclic polymers [M(Pc)0]. Resonance Raman and transmission infrared spectroscopy indicates the formation of [formula omitted]materials for y < 1.1. In contrast, for M = Sn, evidence is presented for the destruction of the tin-oxygen bonds upon doping. For M = Si and Ge, the transmission infrared spectra also reveal the progressive growth of electronic absorption with incremental doping; the effect is somewhat stronger for Si than for Ge. Transmission optical spectra of these materials reveal the formation of phthalocyanine π radical cation species and chains of I3“ counterions. EPR spectra are also in accord with the ligand-centered π radical character of the halogen oxidation. Studies of the doping process (M = Si, Ge) by X-ray diffractometry indicate that it is inhomogeneous and that a single, limiting phase of stoicmometry y 1.1 is produced upon halogenation. Structural characterization of the ([Si(Pc)0]ILl2), ([Ge(Pc)O]I1.12), and ([Si(Pc)0]Bru2) phases by computer analysis of the diffraction data (supported by judiciously selected model compounds) indicates architectural motifs that are essentially isomorphous with Ni(Pc)I, i.e., stacks of staggered M(Pc) units and parallel chains of I3” counterions. The data can be indexed in space group P4/mcc, Z = 2, with a = 13.936 (6) Á, c = 6.488 (3) Á, phthalocyanine staggering angle = 39.5º (Ni); a = 13.97 (5) Á, c = 6.60 (4) Á, staggering angle = 39 (3)º (M = Si); a = 13.96 (5) Á, c = 6.96 (4) Á, staggering angle = 40 (4)º (M = Ge). Evidence is presented that the I3 (or Br3) counterions are disordered along c. Variable-temperature static magnetic susceptibility studies of the ([M(Pc)O]Iy)n polymers reveal a small, sample-dependent Curie component and a Pauli-like, weakly temperature-dependent contribution. The magnitude of the latter is linearly proportional to y and can be associated with the fully doped, y 1.1 phase. The magnitude of the Pauli-like component increases with increasing interplanar ring-ring spacing (Ni – Si -> Ge) while bandwidths (4t) calculated on the basis of a simple tight-binding model decrease. High-resolution 13C NMR spectra (1H decoupled with cross-polarization and magic angle spinning) reveal a downfield shift of [Si(Pc)G] carbon resonances upon doping. Optical reflectivity studies of the M = Si and Ge materials reveal the development of a plasma-like edge in the infrared upon incremental doping with iodine (the effect is stronger for Si than for Ge). Comparison of the data for Ni(Pc)I, ([Si(Pc)0]l! 12), and ([Ge(Pc)0]l1.12) reveals the progressive shift of the edge to lower energy with increasing interplanar spacing (Ni – Si – Ge). This trend is paralleled by plasma frequencies (wp) derived from a Drude analysis and tight-binding bandwidths calculated therefrom. Four-probe electrical conductivity measurements for polycrystalline samples of the Si and Ge polymers reveal a sharp increase in conductivity upon incremental iodine doping. The functional form of the a vs. y plot can be fit to a simple percolation model, in accord with the inhomogeneous character of the doping. For the fully doped materials, the compaction conductivity inversely correlates with the ring-ring interplanar spacings, viz., [formula omitted] The temperature dependence of the conductivity data (4.2-300 K) indicates a region of falling [formula omitted] for M = Ni and Si, suggesting “metal-like” charge transport in the stacking direction near room temperature (already established for M = Ni), while the M = Ge material does not exhibit such behavior. The conclusion for ([Si(Pc)0]l1.12)n is supported by voltage-shorted compaction measurements. The temperature dependence of the M = Ni, Si and Ge powder conductivity data can best be fit to a transport model involving fluctuation-induced carrier tunneling through parabolic potential barriers that separate the high conductivity regions.
ASJC Scopus subject areas
- Colloid and Surface Chemistry