2,6-DIMETHYLPHENYL ( XYLYL ) ISOCYANIDE COMPLEXES OF IRON: PREPARATION AND CRYSTAL AND MOLECULAR STRUCTURES OF trans-DICHLOROTETRAKIS(XYLYL ISOCYANIDE)IRON(II), AND CHLOROPENTAKIS(XYLYL ISOCYANIDE)IRON(II) TETRACHLOROFERRATE(III),

Article abstract of DOI:10.1016/0022-328X(86)80361-8

The reation of FeCl2 and xylyl isocyanide (L) (L=2,6-Me2C6H3NC) gives two products viz. purple FeCl2L4 (1) and orange Fe2Cl5L5 (2).The structural identity of these complexes has been determined by single crystal X-ray diffraction studies.Crystals of 1 are tetragonal, space group P4nc, Z=2, in a unit cell of dimensions a 13.853(8), c 8.803(8) Angstroem.The structure has been refined to R 0.068 (R_w 0.071) for 613 independent reflections above background.The structure comprises octahedral Fe^II units with the two chlorines mutually trans. (Fe-Cl 2.318(7), 2.288(6) Angstroem).The four isocyanide ligands, in a cis arrangement around the metal, are essentially linear (Fe-C-N 177.9(7), C-N-C 173.8(8) deg).Crystals of 2 are monoclinic, space group P2₁/a, Z=4, in a unit cell of dimensions a 10.310(8), b 20.468(17), c 23.026(23) Angstroem, β 99.0(1) deg.The structure has been refined to R 0.077 (R_w 0.081) for 2950 independent reflections above background.The complex is a 'mixed' Fe(II)/Fe(III) species and consists of octahedral (1+) cations based on Fe(II), and tetrahedral (1-) anions based on Fe(III).For the cation, variations in Fe-C bond lengths between isocyanide ligands trans to one another and trans to chloride are discussed in terms of a trans-effect dominated by the strong ?-acceptor ability of the isocyanide ligands.Further comparisons are drawn with Fe-C bond lengths observed in 1 and in similar cationic Fe(II) systems.The (1-) anion has tetrahedral symmetry (mean Fe-Cl 2.157 Angstroem, mean Cl-Fe-Cl 109.3 deg).Previous studies of the tetrahedral (1-) anion (high spin Fe(III)) show a mean Fe-Cl of 2.180 Angstroem.