Synthesis, Characterization and Crystal Structure of 2-dicyanomethylene-1,3-bis(ferrocenylmethyl)-1,3-diazolidine


By reaction of N,N′-ethylenebis(ferrocenylmethylamine) 1 with tetracyanoethylene in dichloromethane the yellow compound 2-dicyanomethylene-1,3-bis(ferrocenylmethyl)-1,3-diazolidine 2 can be isolated. The single-crystal structure of 2 has been determined. It crystallizes in the non-centrosymmetric trigonal space group P3 221, a = 12.255(2), c = 13.831(7) Å, Z = 3. Refinement of the atomic parameters by least-squares techniques gave a final R factor of 0.038 (R′ = 0.034) for 1782 observed reflections having I > 2.5δ(I). Anomalous values of the bond distances and the vinyl carbon chemical shift in the 13C NMR spectrum of 2 are explained on the basis of a polarization due to a combination of the electron-donating behaviour of the nitrogen atoms with the electron-acceptor character of the cyano groups in the dicyanovinyl diamine fragment. The non-linear optical properties were investigated. A second harmonic generation signal for 2 was detected by powder techniques with a low efficiency. Electrochemical experiments in dimethyl sulfoxide revealed a two-electron diffusion-controlled oxidation process according to two consecutive one-electron steps involving the two ferrocenyl fragments the potentials of which are separated by 43 mV. A comproportionation constant K c of 5.3 was found by differential pulse voltammetry, indicating that the mixed-valence species [Fe IIIFe II] + is basically not stabilized.



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