Seven-co-ordination in metal complexes of quinquedentate macrocyclic ligands. Part 7. Synthesis and properties of some manganese(II), iron(III), iron(II), zinc(II), and cadmium(II) complexes of an N3O2 macrocycle and the crystal and molecular structure of {2,13-dimethyl-6,9-dioxa-3,12,18-triazabicyclo[12.3.1]octadeca-1(18),2,12,14,16-pentaene}di-isothiocyanatomanganese(II)

Abstract

Reaction of 2,6-diacetylpyridine and 3,6-dioxaoctane-1,8-diamine in methanol in the presence of a stoicheiometric amount of a salt of Mn^II, Fe^III, Fe^II, Zn^II, or Cd^II gives metal complexes of the 15-membered N₃O₂ macrocyclic ligand L⁴ in good yield. Vibrational and electronic spectra as well as electrical-conductance data for solutions provide strong evidence for a seven-co-ordinate, approximately pentagonal-bipyramidal, structure in each case with the macrocycle occupying the pentagonal plane and the axial positions being filled by halide or pseudohalide ion. This is confirmed by a single-crystal X-ray structure determination of the title complex [MnL⁴(NCS)₂] which is triclinic, with a= 13.834(4), b= 7.403(2), c= 10.645(3)Å, α= 91.0(1), β= 71.3(1), γ= 100.8(1)°, Z= 2, space group P. 1427 Independent reflections above background have been measured by counter methods and refined to R 0.075. Metal–nitrogen(macrocycle) distances are 2.244(9), 2.214(8). and 2.254(10)Å and the metal–oxygen distances are 2.296(8) and 2.270(7)Å. The metal–nitrogen(NCS) bond lengths are 2.254(13) and 2.277(13)Å with Mn–N–C bond angles of 130.4(10) and 126.1 (9)°. From magnetic and Mössbauer measurements, the complexes of Fe^III, Fe^II, and Mn^II are shown to be high-spin. Electrochemical data for the iron and manganese complexes are reported; in the case of the iron complexes the oxidation state II is significantly stabilised relative to that in complexes of the analogous N₅ macrocycle.