Redox-Active Ferrocene as a Tuning Functionality for Magnetic Superexchange Interactions of Bis(oxamato) Type Complexes

The reaction of 1,1′-diaminoferrocene with two equivalents of ethyloxalyl chloride in THF afforded the diethyl ester of N,N′-ferrocenylenebis(oxamic acid) (1,1′-fcbaH2Et2, 1). 1 was converted readily to its saponificated form only, namely [nBu4N]2[(1,1′-fcbaH2)] (2), when treated with 4 equiv of [nBu4N]OH followed by the subsequent addition of [Ni(H2O)6]Cl2, whereas [nBu4N]2[Cu(1,1′-fcba)] (3) was obtained in ca. 70% yield by using CuCl2·2H2O. Oxidation of 3 with I2 led to the formation of [nBu4N][Cu(1,1′-fcba)] (4). A combined study of 4 by ESR and 57Fe Mossbauer spectroscopy, supported by DFT calculations, revealed the iron atom of 4 to possess the oxidation state +3. Treatment of 1 with MeNH2 resulted in the exclusive formation of the methyl ester of ferrocenylene-1-(N-methyloxamide)-1′-(oxamic acid) (1,1′-fcooH3Me2, 5). Successive treatment of 5 with [Cu2(OAc)4(H2O)2] and [nBu4N]OH gave rise to the formation of [nBu4N]2[Cu(fcooMe)]·2H2O (6A·2H2O and 6B·2H2O), for which single crystals of the compositi...