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

Abstract

The electrochemical reduction of the bis(1,2,67-tetracyano-3,5-dihydro-3,5-diiminopyrrolizinido) palladium(II) complex, Pd(C 11N 7H 2) 2, furnishes the corresponding radical anion, isolated as PdL 2·NEt 4·2CH 3CN·2H 2O ( 1). 1 is a semiconductor of low conductivity ( σ RT = 1.4 × 10 −10 S cm −1), presumably consisting of segregated stacks of radical anions, weakly interacting antiferromagnetically at room temperature ( μ SO = 1.50 μ B, 300 K). Lowering the temperature, the magnetic moment undergoes a gradual reduction ( μ SO = 0.65 μ 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 π→π ∗ transition between adjacent radical anions, delocalised along the anion stacks.