The mononuclear macrocyclic Pd^II complex cis-[PdCl₂([9]aneS₃)] ([9]aneS₃ = 1,4,7-trithiacyclo-nonane) converts at 44 kbar into an intensely coloured chain polymer exhibiting distorted octahedral coordination at the metal centre and an unprecedented [1233] conformation for the thioether ligand. The evolution of an intramolecular axial sulfur–metal interaction and an intermolecular equatorial sulfur–metal interaction is central to these changes. High-pressure crystallographic experiments have also been undertaken on the related complexes [PtCl₂([9]aneS₃)], [PdBr₂([9]aneS₃)], [PtBr₂([9]aneS₃)], [PdI₂([9]aneS₃)] and [PtI₂([9]aneS₃)] in order to establish the effects of changing the halide ligands and the metal centre on the behaviour of these complexes under pressure. While all complexes undergo contraction of the various interaction distances with increasing pressure, only [PdCl₂([9]aneS₃)] undergoes a phase change. Pressure-induced I...I interactions were observed for [PdI₂([9]aneS₃)] and [PtI₂([9]aneS₃)] at 19 kbar, but the corresponding Br...Br interactions in [PdBr₂([9]aneS₃)] and [PtBr₂([9]aneS₃)] only become significant at much higher pressure (58 kbar). Accompanying density functional theory (DFT) calculations have yielded interaction energies and bond orders for the sulfur–metal interactions.

The Ni^II complexes [Ni([9]aneNS₂-CH₃)₂]²⁺ ([9]aneNS₂-CH₃=N-methyl-1-aza-4,7-dithiacyclononane), [Ni(bis[9]aneNS₂-C₂H₄)]²⁺ (bis[9]aneNS₂-C₂H₄=1,2-bis-(1-aza-4,7-dithiacyclononylethane) and [Ni([9]aneS₃)₂]²⁺ ([9]aneS₃=1,4,7-trithiacyclononane) have been prepared and can be electrochemically and chemically oxidized to give the formal Ni^III products, which have been characterized by X-ray crystallography, UV/Vis and multi-frequency EPR spectroscopy. The single-crystal X-ray structure of [Ni^III([9]aneNS₂-CH₃)₂](ClO₄)₆⋅(H₅O₂)₃ reveals an octahedral co-ordination at the Ni centre, while the crystal structure of [Ni^III(bis[9]aneNS₂-C₂H₄)](ClO₄)₆⋅(H₃O)₃⋅ 3H₂O exhibits a more distorted co-ordination. In the homoleptic analogue, [Ni^III([9]aneS₃)₂](ClO₄)₃, structurally characterized at 30 K, the NiS distances [2.249(6), 2.251(5) and 2.437(2) Å] are consistent with a Jahn–Teller distorted octahedral stereochemistry. [Ni([9]aneNS₂-CH₃)₂](PF₆)₂ shows a one-electron oxidation process in MeCN (0.2 M NBu₄PF₆, 293 K) at E_1/2=+1.10 V versus Fc⁺/Fc assigned to a formal Ni^III/Ni^II couple. [Ni(bis[9]aneNS₂-C₂H₄)](PF₆)₂ exhibits a one-electron oxidation process at E_1/2=+0.98 V and a reduction process at E_1/2=−1.25 V assigned to Ni^II/Ni^III and Ni^II/Ni^I couples, respectively. The multi-frequency X-, L-, S-, K-band EPR spectra of the 3+ cations and their 86.2 % ⁶¹Ni-enriched analogues were simulated. Treatment of the spin Hamiltonian parameters by perturbation theory reveals that the SOMO has 50.6 %, 42.8 % and 37.2 % Ni character in [Ni([9]aneNS₂-CH₃)₂]³⁺, [Ni(bis[9]aneNS₂-C₂H₄)]³⁺ and [Ni([9]aneS₃)₂]³⁺, respectively, consistent with DFT calculations, and reflecting delocalisation of charge onto the S-thioether centres. EPR spectra for [⁶¹Ni([9]aneS₃)₂]³⁺ are consistent with a dynamic Jahn–Teller distortion in this compound.

The dithiosalicylidenediamine Ni^II complexes [Ni(L)] (R=tBu, R′=CH₂C(CH₃)₂CH₂1, R′=C₆H₄2; R=H, R′=CH₂C(CH₃)₂CH₂3, R′=C₆H₄4) have been prepared by transmetallation of the tetrahedral complexes [Zn(L)] (R=tBu, R′=CH₂C(CH₃)₂CH₂7, R′=C₆H₄8; R=H, R′=CH₂C(CH₃)₂CH₂9, R′=C₆H₄10) formed by condensation of 2,4-di-R-thiosalicylaldehyde with diamines H₂N-R′-NH₂ in the presence of Zn^II salts. The diamagnetic mononuclear complexes [Ni(L)] show a distorted square-planar N₂S₂ coordination environment and have been characterized by ¹H- and ¹³C NMR and UV/Vis spectroscopies and by single-crystal X-ray crystallography. Cyclic voltammetry and coulombic measurements have established that complexes 1 and 2, incorporating tBu functionalities on the thiophenolate ligands, undergo reversible one-electron oxidation processes, whereas the analogous redox processes for complexes 3 and 4 are not reversible. The one-electron oxidized species, 1⁺ and 2⁺, can be generated quantitatively either electrochemically or chemically with 70 % HClO₄. EPR and UV/Vis spectroscopic studies and supporting DFT calculations suggest that the SOMOs of 1⁺ and 2⁺ possess thiyl radical character, whereas those of 1(py)₂⁺ and 2(py)₂⁺ possess formal Ni^III centers. Species 2⁺ dimerizes at low temperature, and an X-ray crystallographic determination of the dimer [(2)₂](ClO₄)₂⋅2 CH₂Cl₂ confirms that this dimerization involves the formation of a SS bond (S⋅⋅⋅S=2.202(5) Å).