Structural, Electrical, Magnetic, and Spectroscopic Properties of Ring-Oxidized Molecular Metals Produced by Iodination of Metal-Free and Nickel Tetrabenzporphyrins

Abstract

Detailed studies of the structure, conductivitity, magnetoresistance, optical spectra, and magnetic properties (susceptibility, EPR) for the new molecular metal tetrabenzporphyrin iodide (H(2)(tbp)I) and the electrical, spectral, and magnetic properties of Ni(tbp)I are reported. Paramagnetic transition-ion impurities were carefully excluded during the synthesis of H(2)(tbp)I and Ni(tbp)I, and both materials show much higher, metal-like conductivites than previously seen for less-pure Ni(tbp)I. Comparison of the specular reflectance data for Ni(tbp)I and H(2)(tbp)I allows a distinction between purely ring pi-transitions and metal-involved charge-transfer transitions, and the spectra fix the energy levels of the pi orbitals involved in conduction. Transport, magnetic, and optical properties show that both H(2)(tbp)I and Ni(tbp)I are ring-based conductors that have metal-like conductivities, varying as approximately 1/T, down to ca. 30-40 K. However, the remaining level of defects is higher in the tbp conductors than in H(2)(pc)I, and whereas the latter is metallic down to the mK temperature range, the defects in the (tbp) compounds localize the conduction electrons at approximately 10 K (Ni(tbp)I) and approximately 30 K (H(2)(tbp)I), leading to transport through one-dimensional variable-range hopping. EPR g-values for H(2)(tbp)I and Ni(tbp)I are close to that for the free electron and are nearly temperature-independent. The line widths for both samples are extremely narrow and also are nearly temperature-independent. These results show that Ni(tbp)I does not display doubly-mixed valence, as thought earlier: Paramagnetic impurities significantly altered the EPR signals of the prior samples. H(2)(tbp)I crystallizes in the space group P4/mcc with cell constants of a = 14.173(10) Å and c = 6.463(4) Å. Full-matrix least-squares refinement of 63 variables gave an R index of 0.061 on F(o)(2).

Acid-Responsive Conductive Nanofiber of Tetrabenzoporphyrin Made by Solution Processing

“…Information on the molecular packing in the nanofibers was obtained by GIXRD and SAED analyses. The sum of out-of-plane and in-plane XRD signals of the BP–TFA fibers on an ITO glass substrate (Figure c, blue and red lines) matches well with the simulated XRD pattern based on a single-crystal structure of needle-crystalline 2BP·BP +• ·I 3 – (Figure c, black line), in which BP and BP +• molecules cofacially π-stack along the needle axis . This matching of the data between BP–TFA and 2BP·BP +• ·I 3 – led us to propose the model structure of the BP–TFA column shown in Figure b.…”

“…The out-of-plane XRD data of BP–TFA (blue line) show a strong peak at 6.08° ( d = 14.54 Å; intercolumnar distance), while the in-plane XRD data (red line) reveal a prominent peak at 27.27° ( d = 3.27 Å; π-stacking distance of the cofacial BP stack), which was not seen in the out-of-plane data. The latter distance is much shorter than the π-stacking distance in the neutral BP crystal (3.359 Å) and slightly longer than the one in the 2BP·BP +• ·I 3 – crystal (3.232 Å) …”

“…Figure b illustrates a schematic columnar structure modeled after a single crystal of 2BP·BP +• ·I 3 – . The BP–TFA fiber has a nominal composition of n BP·(BP +• ·TFA – )· m TFA ( n = 37 ± 2, m = 54 ± 3) as judged by elemental analysis and electron spin resonance (ESR).…”

“…Figure 1b illustrates a schematic columnar structure modeled after a single crystal of 2BP•BP +• •I 3 − . 15 The BP−TFA fiber has a nominal composition of nBP•(BP +• •TFA − )•mTFA (n = 37 ± 2, m = 54 ± 3) as judged by elemental analysis and electron spin resonance (ESR). A π-stacking distance of 3.27 Å and an intercolumnar distance of 14.54 Å were determined by grazingincidence X-ray diffraction (GIXRD) and selected-area electron diffraction (SAED) analyses.…”

Synthesis, crystal structure and charge transport properties of one-electron oxidized zirconium diphthalocyanine, [ZrPc2]IBr2

“…Although the g and C parameters observed in the spectrum of the third partially oxidized zirconium diphthalocyaninato complex [ZrPc 2 ](I 3 ) 2/3 are comparable, the spin concentration is significantly lower [38] ]IBr 2 the g value remains constant with decreasing temperature, but the line width decreases only slightly to a value of 5.4 G at 80 K, the lowest measurement temperature. The narrow line width of the EPR signal within the temperature range is typical for one-dimensional conductors because the direction of spin-lattice relaxation is restricted and slower [83]. The decrease of the line width can be explained in term of enhanced motional narrowing from a reduction in carrier mobility with decreasing temperature.…”