Structural studies in the tris(NN-dialkyldithiocarbamato)iron(III)‘cross-over’ system

Abstract

The crystal and molecular structures of ‘high-spin’ tris(1-pyrrolidinecarbodithioato)iron(III)(I){[Fe(CS₂·N-[CH₂]₄)₃], µ(300 K, solid) 5·9 B.M.}, and the predominantly ‘low-spin’ tris(N-methyl-N-phenyldithiocarbamato)-iron(III)(II){[Fe(CS₂·NMePh)₃], µ(300K, solid) 3·0 B.M.} have been determined by single-crystal X-ray diffraction methods, using conventional Patterson–Fourier heavy-atom methods followed by block-diagonal least-squares refinement. Final conventional R values were 0·13 [(I), 1346 reflections] and 0·09 [(II), 1014 reflections]. The compounds both crystallize in the monoclinic system with Z= 4 (I): a= 16·23 ± 0·04, b= 14·53 ± 0·02, c= 10·22 ± 0·03 Å, β= 90·3 ± 0·4°, space-group P2₁/n; (II): a= 25·31 ± 0·05, b= 12·90 ± 0·01, c= 9·48 ± 0·03 Å, β= 116·2 ± 0·2°, space-group P2₁/a.

Both molecules consist of three substantially planar dithiochelate ligands surrounding the central iron atom in an approximately D₃ configuration. The angular FeS₆ geometries are closely comparable but there is a large contraction in the Fe–S distance on passing from the ‘high-spin’ to the ‘low-spin’ configuration. In (I), the iron–sulphur distance ranges from 2·38(1) to 2·44(1)Å, whereas in (II), the range is 2·28(1)–2·33(1)Å. The remainder of the molecular dimensions are normal within the limits of experimental error.