Synthesis of neutral binuclear two-chain helicate from the anionic Fe(III) complex of 5-chlorosalicylaldehyde thiosemicarbazone by electrocrystallization

The electrocrystallization of salts of the anionic spin-variable complex [FeIII(L)2]‒ (L is 5-chlorosalicylaldehyde thiosemicarbazone (Н25Cl-thsa)) with cations Cat+ = K+ (I), Me4N+ (II), and Et4N+ (III) affords crystals of the neutral binuclear two-chain helicate [FeIII2(L1)2]0 (IV) (L1 = (L‒2)‒(L‒) are transformed monoanionic and dianionic fragments of L, respectively, linked with each other by the disulfide S–S bridge), which are identified by XRD at 100 and 293 K as the same phase IV · n(H2O) (n ≤ 6) with close lattice parameters. “Fresh” crystals of the complex obtained from salt I correspond to the composition IV · 6(H2O) at 293 K, rapidly lose 50% water molecules, and decrepitate to fine crystalline fragments IV · 3(H2O). The structure of crystals IV · 6(H2O) is monoclinic (space group С2/c) and characterized by cavities filled with disordered water molecules, which amount to more than 20% of the total unit cell volume. Complex IV has the point symmetry group С2 and high-spin geometry of coordination nodes N4O2. As found by cyclic voltammetry, electrochemically inactive complex IV is formed by the two-electron oxidation of the [FeIII(5Cl-thsa)2]– anion via the EEC mechanism.