William J. McCarthy

Highly conductive metallophthalocyanine assemblies. Structure, charge transport, and anisotropy in the metal-free molecular metal H2(Pc)I

Abstract That a metal ion is not required for high electrical conductivity is unequivocally demonstrated by structural, charge transport, optical, and magnetic characterization of the simplest phthalocyanine “molecular metal” H 2 (Pc)I. The crystal structure consists of staggered H 2 (Pc) +0.33 units stacked at 3.251(3) A intervals and parallel chains of I − 3 counterions. At 300 K, σ ‖ = 700 Ω −1 cm −1 and σ ‖ σ⊥ > 500 . At 15 K, σ ∼ reaches a maximum of ca. 4000 Ω −1 cm −1 and falls only to ca. 3500 Ω −1‖ cm −1 at 1.5 K. Analysis of single crystal polarized specular reflectance data (ir to uv) yields ω p = 6360(30) cm −1 and a tight-binding bandwidth of 1.3(1) eV. The magnetic susceptibility is Pauli-like ( X S = 2.21(5) × 10 −4 emu mol −1 ) except for a small, sample dependent Curie component.

Unusual band-filling and counterion ordering effects in a phthalocyanine molecular metal. Single crystal studies of Ni(Pc) (C104)y

The phthalocyanine molecular metal Ni(Pc) (C104)y, y=0.39−0.47 for most crystals, has been synthesized by electrocrystallization techniques. The structure of a crystal with y=0.42 consists of staggered (39.5°) Ni(Pc)+0.42 units stacked at 3.233(1) A separations and disordered, off-axis C10-4 ions. At lower temperatures, the C10-4 ions undergo a transition to an ordered arrangement. At 300°K, σ‖=700±200Ω-1 cm-1 with metal-like (dσ/dT<0) behavior as the temperature is lowered. A broad maximum in σ(T) is found near 200°K, with discontinuous conductivity behavior observed in all samples at lower temperatures. The cause appears to be domain wall phenomena associated with C104 ordering rather than macroscopic fracturing. Thermoelectric power data are also metal-like (S≈T) with no evidence of the aforementioned discontinuities. Room temperature values of S=20−35 μVK-1 are in accord with the relatively high degree of Ni(Pc)+ρ partial oxidation. Polarized single crystal reflectance data reveal a plasma edge, the high energy of which is also explicable in terms of the relatively high degree of partial oxidation. Analysis of the thermoelectric power and optical data yields, in both cases, a tight-binding bandwidth of ca. 1.5 eV.

Structural and electronic anisotropy in polycrystalline compactions of the high-Tc superconductor EuBa2Cu3O7−δ

Abstract X-ray diffraction studies show that simple cold-pressing of EuBa2Cu3O7−δ polycrystalline compactions, as practiced by numerous researchers, leads to very large microstructural anisotropy, with the crystallographic c axis preferentially oriented parallel to the axis of pressing. As shown by variable-temperature resistivity and thermoelectric power measurements, the direction of greatest metallic character at temperatures above the superconducting transition temperature is that perpendicular to the pressing direction, i.e., that parallel to the direction in which the (CuO)n sheets and chains are preferentially oriented. Both ϱ(T) and S(T) are only weakly temperature-dependent, with the transition to the superconducting state taking place in both measurements over a slightly narrower temperature range in the perpendicular direction. Above Tc, the S(T) data are positive and give no obvious evidence for phonon-drag or precursor phenomena. A tentative analysis using a Hubbard/Heikes approach yields an average copper oxidation state in good agreement with experiment.

Phthalocyanine-based electrically conductive, processible molecular/macromolecular hybrid materials

Abstract This contribution relates new information on the properties of electrically conductive, processible Ni(Pc)/polymer/I 2 hybrid materials. Both the temperature and composition dependence of the electrical conductivity of Ni(Pc)/Kevlar/I 2 fibres are strongly reminiscent of the behaviour of composites. Using a variant of our fibre spinning methodology, it is also possible to produce Ni(Pc)/Kevlar/I 2 ribbons. Polarized resonance Raman spectroscopy indicates that the ribbons are structurally anisotropic (Ni(Pc)I c axes are preferentially aligned in the extrusion direction), while four-probe transport measurements indicate significant anisotropy in the conductivity ( σ ‖ σ hu ≈ 8 where ‖ denotes the extrusion direction). This anisotropy is nearly temperature independent. Electrically conductive fibres can also be prepared using Nomex or poly( p -phenylene-2,6-benzobisthiazole) (PBT) instead of Kevlar as the host polymer.

Highly conductive metallomacrocyclic assemblies. Synthetic approaches to molecular metals with variable band-filling

Abstract The enforced cofacial structure of the polymer [Si(Pc)O] n has been employed to introduce new oxidation states in phthalocyanine molecular metals. Thus, oxidative electrochemical techniques have produced materials with doping levels as high as {[Si(Pc)O](BF 4 ) 0.50 } n , {[Si(Pc)O] ( p -toluene-sulfonate) 0.85 } n and {[Si(Pc)O](SO 4 ) 0.09 } n . Controlled potential coulometry and X-ray diffraction studies of the [Si(Pc)O] n /BF 4 − system suggest that ‘break-in’ phenomena have a structural basis (orthorhombic → tetragonal) and that doping is relatively homogeneous. Optical, magnetic, and charge transport properties of the {[Si(Pc)O](BF) 4 y } n series are reported as a function of y . Electrochemical techniques have also been employed to synthesize partially reduced polymers such as {(Et 4 N) 0.25 [Si(Pc)O]} n and {[Li 0.25 [Si(Pc)O]} n . Incremental doping of [Si(Pc)O] n with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) produces materials with doping levels as high as {[Si(Pc)O]DDQ y } n , y = 0.91. Optical and charge transport measurements show that as y is progressively increased, the polymer is transformed from a filled band insulator ( y = 0.00), to a molecular metal ( y ≈ 0.30 – 0.50), to an integral oxidation state Mott insulator (y ⪆ 0.90) .

Phthalocyanine molecular metals by electrocrystallization techniques, unusual anion and oxidation state phenomena

Abstract High-temperature electrocrystallization techniques afford (Ni(Pc) (C10 4 ) y crystals in the stoichiometry range y ≈ 0.39−0.47. The 300 K crystal structure of Ni(Pc)(C10 4 ) 0.42 consists of stacks of Ni(Pc) +0.42 units and disordered, off-axis C10 4 ions. At lower temperature, there is diffractometric evidence for anion ordering. Variable-temperature conductivity data exhibit discontinuous behavior below ca. 150 K which may reflect the anion ordering. Thermoelectric power and optical reflectivity data are characteristic of a low-dimensional molecular metal and are also in accord with sample-dependent y values. Both measurements yield a tight-binding bandwidth of ca. 1.5(1) eV.

Electrochemistry of cofacial phthalocyanine polymers: What can we learn about how molecular metal collective properties respond to wide variations in band filling?

Abstract The oxidative electrochemistry of the cofacially joined phthalocyanine polymer [Si (Pc)O] n to yield molecular “metals” with tunable band filling is described. Initial doping (oxidation) of orthorhombic [Si (Pc)O] n is accompanied by a rearrangement to a tetragonal crystal structure. Once in the tetragonal crystal structure, the conduction band filling can be continuously varied (i.e. doping is homogeneous) over a broad range in y for {[Si (Pc)O]X y ∼ n . For example, materials incorporating BF − 4 as the counterion can be tuned between y = 0.0 and y = 0.50. In fact, the maximum doping level obtainable with a given counterion is largely a function of anion size. Charge transport, optical, and magnetic studies of the {[Si (Pc)O] (BF 4 ) y ∼ n materials reveal an evolution in properties from insulator/semiconductor-like to metal-like with increasing y and an abrupt insulator-to-metal transition at y ≈ 0.20. This change at y ≈ 0.20 appears to be an Anderson-like transition from localized (disordered) states to delocalized states. Physical measurements on {[Si (Pc)-O] (SO 4 ) y ∼ n show no evidence of exceptional electronic effects attributable to the dinegative counterion.

The first molecular metal containing fluoride counterions

Abstract Anhydrous, anaerobic electrocrystallization techniques have afforded (TSeT)F0.25Cl0.50, the first organic molecular metal to contain off-axis fluoride counterions. This material crystallizes in a unique tetragonal motif with stacks of canted TSeT+0.75 molecules. Disordered chloride and fluoride counterions are found in two different types of channels extending parallel to the stacking axis. Interchain Se…Se interactions are shorter than in the analogous (TSeT+y) (X−)y salts (X− = Cl−, Br−, I−). These structural changes are reflected in the electrical [σ (300K) = 1700 S/cm]; σ (40K) = 7000 S/cm, thermoelectrical, and optical properties of this new organic metal.