Controlled Thiolate Coordination and Redox Chemistry: Synthesis, Structure, Axial‐Binding, and Electrochemistry of Dinickel(II) Dithiolate Macrocyclic Complexes

A single crystal X‐ray analysis of [Ni 2 L1](ClO 4 ) 2 · MeCN · 1/4 H 2 O, 1a [formed directly from a mixture of nickel(II) template ions, 2,6‐diformyl‐4‐methyl‐thiophenolate, and 1,4‐diaminobutane] reveals that the nickel(II) ions are in square‐planar N 2 S 2 environments and that the four “bowed” dinickel macrocycles in the asymmetric unit pack around a single central perchlorate template ion encapsulating it to form “star” clusters of stoichiometry {[Ni 2 L1] 4 (ClO 4 )} 7+ . These “stars” stack together, via π–π‐stacking interactions, to form two‐dimensional sheets, which are separated from one another by layers of the remaining perchlorate anions and solvent molecules. Reduction, by NaBH 4 , of the four imine bonds in [Ni 2 L2](ClO 4 ) 2 2a (analogous to 1a but formed from 1,3‐diaminopropane not 1,4‐diaminobutane) or [Ni 2 L2](CF 3 SO 3 ) 2 2b to amine bonds produces the corresponding tetra‐amine complex, [Ni 2 L3](ClO 4 ) 2 3 . These complexes are shown to contain diamagnetic nickel(II) ions by a combination of magnetic, NMR and UV/Vis spectroscopic results. The 1 H NMR spectra of 1–3 run in [D 3 ]MeNO 2 and in [D 3 ]MeCN are consistent with increasing axial binding ability in the order: 3 < 2 < 1 . Thiocyanate ion binding studies reveal that 1 and 2 are able to coordinate two thiocyanate ions, forming [Ni 2 L1(NCS) 2 ] 4 and [Ni 2 L2(NCS) 2 ] 5 respectively, whereas 3 does not. Single crystal X‐ray analyses of complexes 4 · 2 MeCN and 5 · MeCN show that adjacent square‐planar and octahedral nickel(II) ions result. Two one‐electron oxidations and two one‐electron reductions are a feature of the electrochemistry of 1–3 in MeCN: curiously, the potentials for the oxidation processes are almost invariant whereas those for the reduction processes vary as anticipated. EPR spectroscopy shows that the first one‐electron reduction process and the first one‐electron oxidation process are metal centred. Spectroelectrochemical studies and redox titrations indicate that a purplish‐coloured complex is produced by one‐electron oxidation of 2 (λ = 870 nm, ϵ = 1320 L mol cm –1 ). The synthesis of a phenolate analogue, [Ni 2 L′(MeCN) 4 ](ClO 4 ) 2 ( 6 ), of the thiophenolate complex 2a is also detailed. Complex 6 undergoes two one‐electron oxidations in MeCN, but, in contrast to the thiophenolate complexes 1–3 , these occur at much higher potentials. Only a single one‐electron reduction process is observed and this occurs at a more negative potential than for any of 1–3 .