Michael Y. Ogawa

Porphyrinic Molecular Metals

Porphyrinic molecular metals rival the organic metals in the range of their properties and surpass them in the tunability of these properties. Such Such tunability is illustrated here by the change...

Controlled Formation Of Emissive Silver Nanoclusters Using Rationally Designed Metal- binding Proteins

The metal-binding properties of rationally designed, synthetic proteins were used to prepare a series of emissive silver nanoclusters having predictable sizes and emission energies. Metal-binding α-helical coiled coils were designed to exist as peptide trimers, tetramers, and hexamers and found to uniquely bind 6, 8, and 12 Ag(+) ions, respectively. Subsequent treatment with a chemical reducing agent produced a series of peptide-bound Ag(0) nanoclusters that display a strong visible fluorescence whose emission energies depend on the number of bound metal ions in excellent agreement with theory.

Cd2+-induced Conformational Change Of A Synthetic Metallopeptide: Slow Metal Binding Followed By A Slower Conformational Change

A two-stranded alpha-helical coiled coil was prepared having a Cys 4 metal-binding site within its hydrophobic interior. The addition of Cd2+ results in the incorporation of 2 equiv of metal ion, which is accompanied by a conformational change of the peptide, as observed by circular dichroism (CD) spectroscopy. Isothermal titration calorimetry (ITC) shows that the addition of Cd2+ is accompanied by two thermodynamic events. A comparison of the time dependence of the ITC behavior with those of the UV absorption and CD behavior allows the assignment of these events to a preliminary endothermic metal-binding step followed by a slower exothermic conformational change.

Magnetic transitions in a molecular metal with embedded local moments: Cu(pc)I

Abstract We discuss the low temperature magnetic properties of (phthalocyaninato)-copper(II) iodide (Cu(pc)I). This molecular metal contains conductive stacks that incorporate a one-dimensional array of local Cu +2 moments strongly coupled to conduction electrons. Below 20K, the EPR g-value of the coupled spin system increases anomalously and at 8K the EPR signal broadens abruptly and becomes unobservable. Anomalies in the proton NMR spin-lattice relaxation times are observed at the transition temperature. Preliminary EPR experiments conducted on a newly synthesized series of materials, Cu x Ni 1−x (pc)I, indicate the existence of a similar low temperature transition in the presence of various concentrations of loca moments.

Microwave dielectric properties of Cu(tatbp)I

Abstract Cu(tatbp)I (tatbp = triazatetrabenzporphyrinato) is a quasi-one-dimensional molecular conductor that incorporates in its structure a dense array of S = 1 2 moments localized on a metal spine Cu+2 sites and interacting strongly with charge carriers on the p-π molecular orbitals of the tatbp aromatic ring. The microwave dielectric properties have been measured at 13 GHz between 2 and 300K. The a.c. conductivity is in agreement with the d.c. measurement, and its magnitude is similar to that found in other good molecular conductors. The conductivity increases from a room temperature value of σ ∼ 3 × 10 2 Ω −1 cm −1 to a maximum of ca. 7 × 102Ω−1cm−1 at T ∼ 90K; it decreases by almost three orders of magnitude at lower temperatures, but remains practically constant below 6K at σ ∼ 1Ω −1 cm −1 . In the same range the dielectric constant decreases with temperature, the slope being less pronounced below 7K. This temperature behaviour of both properties is not believed to be associated with a normal metal-insulator or semiconductor transition but to be related to the presence of local moments on the metal spine.

Metallic Conductivity and Magnetic Interactions in Nickel and Copper Phthalocyanine Iodides

Abstract We discuss the charge transport and magnetic properties of the titled molecular metals. Replacement of the diamagnetic Ni(+2) by paramagnetic Cu(+2) introduces a novel coupling between local Cu(+2) spins the mobile charge carriers, and produces a coupled transition at 8 K.

Evidence for a One Dimensional Indirect Interaction between Localized Moments in Copper Phthalocyanine Iodide Mediated by Itinerant Electrons

Measurements on Copper phthalocyanine iodide Cu(pc)I indicate that this material is an excellent one dimensional conductor with parallel arrays of localized moments that interact strongly with the conduction electrons. The result is an antiferromagnetic indirect interaction between localized spins mediated by the itinerant electrons. A comparison is made between ESR, magnetic susceptibility, and NMR measurements for a number of materials with the phthalocyanine architecture: Ni(pc)I, Cu(pc) and Cu(pc)I.