Characterization of tetra-, penta-, and hexacoordinated high-spin Iron(II) complexes with neutral monodentate sulfur donor ligands. Crystal and molecular structure of Fe(DMTU)7(BF4)2(DMTU = N,Nʹ-Dimethylthiourea)

Abstract

New cationic high-spin iron(II) complexes with substituted thioureas and with perchlorate or tetrafluoroborate anions (X) were obtained: [FeL6]X2(L = N-ethylthiourea, N,N’-di-n-propylthiourea); [FeLn](ClO4)2(L = N,N’-dimethylthiourea, N,N'di-ethylthiourea; n = 4, 6); [Fe(DMTU)n](BF4)2(DMTU = N,N’-dimethylthiourea; n = 4, 5, 7). Tetrahedral ([FeL4]X2), octahedral ([FeL6]X2, [Fe(DMTU)6](BF4)2·DMTU), and pentacoordinate ([Fe(DMTU)5](BF4)2) structures have been identified by using electronic and Mossbauer spectroscopies and magnetic susceptibility measurements. For the last structure, a square-base-pyramidal symmetry around the iron atom is proposed. The DMTU complexes are the first examples in which a soft sulfur-binding monodentate ligand is found in binary iron complexes with three different arrangements. It was possible to evaluate the distortion in the tetrahedral complexes (ΔT~ 800 cm-1) and to correlate the isomer shift with the coordination number: tetracoordinated ~ 0.9, pentacoordinated ~1.1, hexacoordinated ~1.2 mm s"1. The absorption and the line width values are highly dependent on the temperature and the nature of the substituent. The crystal structure of the complex [Fe(DMTU)6](BF4)2-DMTU was determined by heavy-atom methods and refined by least-squares procedures. Crystals are monoclinic, space group C2/c, with a =13.561 (3) Á, b = 24.008 (4) Á, c = 14.290 (4) Á, ß=91.36 (2)°, and Z =4, and the structure was refined to R =0.045 for the 3037 independent reflections greater than 3