Electrochemical reduction of the bis(1,2,6,7-tetracyano-3,5-dihydro-3,5-diimino-pyrrolizinido)palladium(II) complex: syntheses and properties of its radical monoanion as the tetraethylammonium salt

The electrochemical reduction of the bis(1,2,6,7-tetracyano-3,5-dihydro-3,5-diiminopyrrolizinido)palladium(II) complex, Pd(C11N7H2)(2), furnishes the corresponding radical anion, isolated as PdL2 . NEt4 . 2CH(3)CN . 2H(2)O (1). 1 is a semiconductor of low conductivity (sigma(RT) = 1.4 X 10(-10) S cm(-1)), presumably consisting of segregated stacks of radical anions, weakly interacting antiferromagnetically at room temperature (mu(SO) = 1.50 mu(B), 300 K). Lowering the temperature, the magnetic moment undergoes a gradual reduction (mu(SO) = 0.65 mu(B), 5 K), due probably to a partial dimerisation of the radical units. Other chemicophysical properties of 1 are in agreement with its proposed solid state structure: (i) the EPR signal is strong and broad (g = 2.005, linewidth = 19G),indicative of a high spin concentration fast relaxing along the anion stacks; (ii) the reflectance spectrum shows a broad band centred at 1200 nm, due to an interanionic pi-pi* transition between adjacent radical anions, delocalised along the anion stacks.