摘要:

Ion pair charge-transfer (IPCT) complexes consisting of dianionic dithiolene metallates [ML2]2-M = Ni, Pd, Pt, Cu, Zn, and dicationic 4,4′- and 2,2′-bipyridinium derivatives (A2+) exhibit IPCT bands in the VIS-NIR region of the electronic absorption spectrum. When both components are planar, the solid state structure consists of mixed donor–acceptor stacks while that is not the case when one or both are non-planar. By proper selection of the two components the driving force of electron transfer (ΔG12) from the dianion to the dication is varied from 0.7 to -0.1 eV. It is shown that the Hush relation between optical and thermal electron transfer is fulfilled for a number of thirty-two complexes. The reorganization energy is in the range of 60 kJ·mol−1for the d8complexes while it is almost two times larger for the d10zinc compounds. The extent of charge delocalization is typical for outer-sphere complexes as indicated by the parameter α2which is in the range of 10−4. Correspondingly, the interaction between the two redox states is rather weak as suggested by the values of 220-360 cm−1calculated for the exchange matrix element. Free activation enthalpies ΔG* of electron transfer, as calculated within the Hush–Marcus model, amount from 0.15 to 0.73 eV. It is found that the electrical dark conductivity of these composite solids can be quantitatively predicted from ΔG* in the range from 10−10to 10−3ω−1cm−1in the case of complexes consisting of planar components (Class I) while in the presence of a nonplanar acceptor or copper as the central metal (Class II) no similar relation is observed. The electrical photoconductivity is wavelength dependent and exhibits a maximum in the region of the IPCT band. Laser excitation of the solids produces a transient photovoltage (Dember Voltage) with a half-life of about 20 milliseconds. The rcsults suggest that charge generation occurs by electron transfer and charge migration by a hopping mechanism. When a photoisomerizable olefinic acceptor is employed, the conductivity is ten times larger for the cis-isomer.

ISSN:0260-3594    

DOI:10.1080/02603599408035855

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

Structures of small organic and coordination compounds may be calculated rather efficiently and accurately with molecular mechanics. Two major, and still largely unsolved, problems of this method are: (i) the environment of the molecules is usually not included, although with a considerable effort this is basically possible; and (ii) it is not possible with certainty to find the global energy minimum with a general method, a problem that is especially annoying for relatively large systems (more than a few hundred conformers), where all minima may not realistically be screened separately. One possibility addressing both problems consists of combining the computation of structures with experimental results related to the output data of molecular mechanics calculations (nuclear coordinates, strain energies and/or vibrational frequencies). Examples of this approach presented and discussed here indicate that relatively accurate solution structures may be obtained via combinations of molecular mechanics calculations with solution spectra or experimentally determined isomer distributions.

ISSN:0260-3594    

DOI:10.1080/02603599408035856

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

A major challenge facing the synthetic inorganic chemist is the synthesis of solid materials with specifically designed properties. However, small soluble molecular building blocks with well-defined reaction chemistries which would allow low-temperature assembly into crystalline solid state inorganic materials are not well known. Low temperature strategies which show some promise for the rational design of solids include solvothermal reactions, consensation/hydrolysis, and the introduction of templates or guest molecules for the organization of more complex structures. By exploiting these techniques, the rich structural chemistries of the V/O/PO43-and related organically derivatized V/O/RPO3−2systems with a variety of organic and inorganic templates have begun to emerge. Several features of this chemistry are outlined.

ISSN:0260-3594    

DOI:10.1080/02603599408035857

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor

摘要:

This is a scanned image of the original Editorial Board page(s) for this issue.

ISSN:0260-3594    

DOI:10.1080/02603599408035854

出版商:Taylor & Francis Group    

年代:1994

数据来源: Taylor