Synthesis, Spectroscopy and Structure of the Cobalt(III) Complex of the Hexadentate Ligand 5-(4-Amino-2-thiabutyl)-5-methyl-3,7-dithianonane-1,9-diamine

Abstract

A revised synthesis of the hexadentate ligand 5-(4-amino-2-thiabutyl)-5-methyl-3,7-dithianon- ane-1,9-diamine (N₃S₃) is reported. Reaction between the sodium salt of 2-aminoethanethiol and 1,1,1-tris([( tolylsulfonyl )oxy]methyl)ethane in refluxing ethanol results in the formation of the hexadentate ligand N₃S₃. The preparation of the nickel(II) and cobalt(III) complexes is reported. The crystal structure of [Co(N₃S₃)](ClO₄)₃.H₂O has been determined by X-ray diffraction methods and refined to a residual of 0.044 for 3696 independent observed reflections. The crystals are monoclinic, P2₁/n, a 9.314(4), b 15.581(6), c 17.026(3) Ǻ, β 90.30(4)°. Low temperature (c.10 K) absorption spectra are reported for [Co(N₃S₃)]³⁺ and the analogous encapsulated complex [Co(AMN₃S₃sarH)]⁴⁺ where both the spin-allowed ¹A_1g → ¹T_1g, ¹T_2g and spin-forbidden ¹A_1g → ³T_1g, ³T_2g were observed. Ligand -field calculations based on octahedral symmetry result in the ligand -field parameters B 461, C 3075, Dq 2303 cm^-1, and B 462, C 3085, Dq 2266 cm^-1 for the [Co(N₃S₃)]³⁺ and [Co(AMN₃S₃sarH)]⁴⁺ complexes, respectively. A systematic reduction occurs in the Racah B parameter of between 25 and 30 cm^-1 for each additional thioether donor in the series of complexes N_6-xS_x (x = 0, 1, 2, 3). In addition, there is evidence for a progressive increase in the Racah C/B ratio with increasing number of thioether donors in this series.