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The Effects of Ring Expansion and N-Methylation on the Complexation Behaviour of Macrodinucleating Hexaaza-Dithiophenolate Macrocycles: Destabilization of the CoIII Oxidation Level and Lowering of the Coordination Number



The preparation and characterization of 30-membered hexaza-dithiophenolate macrocycles H2L4–H2L6 with different degrees and patterns of N-alkylation and their complexation properties towards cobalt are reported. Three dinuclear {[CoIII2(L4)(µ-OH)]3+ (3), [CoIIICoII(L5)(µ-OH)]2+ (4), [CoII2H2(L6)Cl2]2+ (5)} and one mononuclear complex {[CoII(L6)]2+ (6)} were obtained, isolated as ClO4 or BPh4 salts, and characterized by CHN analysis, ESI mass spetrometry, IR, UV/Vis, and NMR spectroscopy, cyclic voltammetry, magnetic susceptibility measurements (for 46), and X-ray crystallography (36). In contrast to parent N6S2 macrocycles with diethylenetriamine linkers, which support only face-sharing bioctahedral [Co2L(L′)]n+ complexes (L′ = bridging coligand), the new macrocycles show greater structural diversity enabling the formation of triply bridged complexes with octahedral CoIII,IIN3S2O (3, 4), non-bridged dinuclear complexes with tetrahedral CoIIN2SCl (5), and mononuclear complexes with square-pyramidal CoIIN3S2 (6) coordination environments. The increasing stability of the CoII oxidation level across this series of complexes is a consequence of the increasing degree of N-alkylation coupled with a decreasing ligand-field strength of the tertiary amine functions, as demonstrated by significant anodic shifts in the cyclic voltammograms of 3 and 4. The effective magnetic moments of the CoII ions in 4, 5, and 6 (4.67–5.23 µB) are significantly higher than the expected spin-only value of 3.87 µB, indicative of an orbital contribution to the magnetic moment.