Iron(III) Metallacryptand and Metallacryptate Assemblies Derived from Aroylbis(<i>N</i>,<i>N</i>-diethylthioureas)

Abstract

The reaction of isophthaloylbis( N, N -diethylthiourea), H 2 L 1, with FeCl 3 ·6H 2 O gives the dinuclear tris-complex [Fe 2 (L 1 ) 3 ] ( 5 ), possessing a cryptand-like structure. A similar reaction with the ligand 2,6-dipicolinoylbis( N, N -diethylthiourea), H 2 L 2, however, results in the formation of the anionic, mononuclear Fe(III) complex [Fe(L 2 ) 2 ] − ( 6 ), which could be isolated as its “Tl + salt” by the subsequent addition of Tl(NO 3 ). 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 2 ) 2 ] − } units to infinite chains. When Fe 3+ ions and Tl + ions are added to H 2 L 2 simultaneously in a one-pot reaction, a different product is obtained: a cationic trinuclear complex of the composition {M⊂[Fe 2 (L 2 ) 3 ]} + . It has been isolated as a PF 6 – salt and represents a {2}-metallacryptate with a nine-coordinate Tl + ion in the central void. Structurally related products of the compositions {M⊂[Fe 2 (L 2 ) 3 ]}(PF 6 ) (M = Na +, K +, Rb + ) ( 8 (PF 6 )) could be isolated from analogous reactions with alkaline salts instead of Tl(NO 3 ). {2}-Metallacryptates with larger central voids were synthesized with the ether-spaced aroylbis( N, N -diethylthiourea) H 2 L 3 . The compounds {M⊂[Fe 2 (L 3 ) 3 ]}(PF 6 ) (M = K +, Rb +, Tl + or Cs + ) ( 9 (PF 6 )) were prepared by a similar protocol like those with H 2 L 2 with the simultaneous addition of the metal ions to a solution of H 2 L 3 . 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 2 (L 1 ) 3 ], {K⊂[Fe 2 (L 2 ) 3 ]}(PF 6 ), and {K⊂[Fe 2 (L 3 ) 3 ]}(PF 6 ). The obtained voltammograms indicate the dependence of the redox properties of the oligonuclear systems on the conjugation in the organic backbones of the ligands.