Synthesis of Neutral Binuclear Two-Chain Helicate from the Anionic Fe(III) Complex of 5-Chlorosalicylaldehyde Thiosemicarbazone by Electrocrystallization

Abstract

The electrocrystallization of salts of the anionic spin-variable complex [Fe^III(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 [\({\text{Fe}}_{2}^{{{\text{III}}}}\)(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 [Fe^III(5Cl-thsa)₂]^– anion via the EEC mechanism.