ISSN:
0009-2940
Keywords:
Metal dithiolenes
;
Dipyridinioethylene dihalides
;
Charge-Transfer complexes
;
Electrical conductivity
;
Chemistry
;
Inorganic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
Charge-Transfer Complexes of Metal Dithiolenes, XIII[1]. - cis-trans-Photoisomerisable Viologens as Redoxactive Acceptors - Synthesis and Electrical ConductivityIon Pair Charge-Transfer (IPCT) complexes of the type [A2+[ML2]2-} (1a-f to 4a-f) are synthesized from dianionic metal dithiolenes [M = Ni, Zn, L = cis-1,2-dicyano-1,2-ethene-dithiolate (mnt2-), 2-thioxo-1,3-dithiol-4,5-dithiolate (dmit2-)] and dicationic viologens [A2+ = 4,4′-(1,2-ethenediyl)bis(1-alkylpyridinium)]. The acceptors can exist as cis/trans isomers and may have coordinating properties in the case of 1-cyanoalkyl groups. The IPCT bands are in the range of 500 to 1200 nm and their energy follows the Hush-Marcus relation. For the nickel complexes the reorganization energy amounts to 73, for the zinc compounds to 115 kJ/mol. As shown by X-ray analysis of {A2+[Ni(mnt)2]2-} (2d), A2+ = trans-4,4′-(1,2-ethenediyl)-bis[1-(3-cyanopropyl)pyridinium], the structure consists of stacks of alternating donors and acceptors with a typical plane-to-plane distance of 350 pm. There is no interaction between the cyano group of the acceptor and the nickel atom of the donor. The electrical conductivities of the nickel compounds are in the range of 5 · 10-6 to 3 · 10-11 Ω-1 cm-1, and the corresponding activation energies vary from 0.24 to 0.61 eV. For the dmit complexes these values agree well with the free activation enthalpy of the electron transfer reaction A2+ + [ML2]2- → A+ + [ML2]- calculated from the Hush-Marcus model. This suggests that charge carrier generation occurs by electron transfer. When a trans acceptor is replaced by its cis isomer in [A2+[NiL2]2-}, conductivity changes from 5 · 10-7 to 5 · 10-6 Ω-1 cm-1 and the activation energy from 0.43 to 0.24 eV, when L - dmit2- but stays at about 1 · 10-8 Ω-1 cm-1 for L = mnt2-.
Additional Material:
6 Ill.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/cber.19941270203
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