Iron(III) Metallacryptand and Metallacryptate Assemblies Derived from Aroylbis(N,N-diethylthioureas).

The reaction of isophthaloylbis(N,N-diethylthiourea), HL, with FeCl·6HO gives the dinuclear tris-complex [Fe(L)] (5), possessing a cryptand-like structure. A similar reaction with the ligand 2,6-dipicolinoylbis(N,N-diethylthiourea), HL, however, results in the formation of the anionic, mononuclear Fe(III) complex [Fe(L)] (6), which could be isolated as its "Tl salt" by the subsequent addition of Tl(NO). A tighter view to the solid state structure of the obtained product, however, characterizes compound 6 as a one-dimensional coordination polymer, in which four-coordinate Tl ions connect the {[Fe(L)]} units to infinite chains. When Fe ions and Tl ions are added to HL simultaneously in a one-pot reaction, a different product is obtained: a cationic trinuclear complex of the composition {M⊂[Fe(L)]}. It has been isolated as a PF salt and represents a {2}-metallacryptate with a nine-coordinate Tl ion in the central void. Structurally related products of the compositions {M⊂[Fe(L)]}(PF) (M = Na, K, Rb) (8(PF)) could be isolated from analogous reactions with alkaline salts instead of Tl(NO). {2}-Metallacryptates with larger central voids were synthesized with the ether-spaced aroylbis(N,N-diethylthiourea) HL. The compounds {M⊂[Fe(L)]}(PF) (M = K, Rb, Tl or Cs) (9(PF)) were prepared by a similar protocol like those with HL with the simultaneous addition of the metal ions to a solution of HL. Due to the larger spacer between the aroylthiourea units, the coordination number of the central M ions is 12 by six carbonyl and six ether oxygen atoms. All products were characterized by elemental analysis, IR spectroscopy, and X-ray structure analysis. Cyclic voltammetric studies were carried out with the three representative complexes [Fe(L)], {K⊂[Fe(L)]}(PF), and {K⊂[Fe(L)]}(PF). The obtained voltammograms indicate the dependence of the redox properties of the oligonuclear systems on the conjugation in the organic backbones of the ligands.