MONONUCLEAR AND BINUCLEAR OXO-BRIDGED IRON(III) COMPLEXES OF N,N'-BIS(2-PYRIDYLMETHYL)ETHANE-1,2-DIAMINE (BISPICEN)

The syntheses and characterization of a series of iron(III) complexes of the ligand N,N'-bis(2-pyridylmethyl)ethane-1,2-diamine (bispicen), C14H18N4 are described. The monomeric complexes [(bispicen)FeCl2]ClO4 (1) and the corresponding chloride salt [(bispicen)FeCl2]Cl (1a) have been isolated and the structure of the perchlorate salt (1) has been d etermined from three-dimensional crystallographic data. The complex cr ystallizes in space group P2(1)/c of the monoclinic system with four m ononuclear species in a cell of dimensions a=7.323(2), b=14.370(3), c= 18.103(4) angstrom, beta=90.71(2)degrees. The structure has been refin ed to a final R factor of 0.0496 based on 2948 observed independent re flections. The central iron(III) atom is pseudo-octahedrally bonded to the four nitrogen atoms of the ligand and to two cis chloride ligands . The mu-oxodiiron(III) complex {[bispicen)(Cl)Fe]2(mu-O)}(I3)2 (2), C 28H36Cl2Fe2I6N8O, crystallizes in space group P2(1)/n of the monoclini c system with two binuclear species in a cell of dimensions a=8.570(2) , b=14.756(3), c=17.083(3) angstrom, beta=99.68(2)degrees. The structu re has been refined to a final R factor of 0.0417 based on 2272 observ ed independent reflections. The complex contains a linear Fe-O-Fe unit with Fe-O and Fe...Fe separations of 1.798(1) and 3.596(2) angstrom, respectively. The mu-oxo, mu-acetatodiiron(III) complex {[bispicen)Fe] 2(mu-O)(mu-OAc)}I3.2H2O (3), C30H43Fe2I3N8O5, crystallizes in space gr oup P1BAR of the triclinic system with two binuclear species in a cell of dimensions a=10.785(2), b=12.378(2), c=15.834(2) angstrom, alpha=8 7.060(10), beta=87.180(10), gamma=70.630(10)degrees. The structure has been refined to a final R factor of 0.0386 based on 4739 observed ind ependent reflections. The complex contains a bent Fe-O-Fe unit with a bridging Fe-O-Fe angle of 129.8(2)degrees and associated average Fe-O and Fe...Fe separations of 1.794(1) and 3.248(2) angstrom, respectivel y. The Fe-O (acetato) distances are 2.009(3) and 2.040(4) angstrom. Th e mu-oxo, mu-carbonatodiiron(III) complex {[bispicen)Fe]2(mu-O)(mu-CO3 )}I2.6H2O (4), C29H48Fe2I2N8O10, also crystallizes in space group P1BA R of the triclinic system with two binuclear species in a cell of dime nsions a=10.158(2), b=13.459(2), c=15.712(3) angstrom, alpha=73.020(10 ), beta=85.290(10), gamma=79.230(10)degrees. The structure has been re fined to a final R factor of 0.0348 based on 4294 observed independent reflections. The structure of the complex cation is very similar to t hat in 3, and contains a bent Fe-O-Fe unit with a bridging Fe-O-Fe ang le of 129.0(2)degrees and associated average Fe-O and Fe...Fe separati ons of 1.796(11) and 3.241(2) angstrom, respectively. The Fe-O (carbon ato) distances are 1.962(4) and 1.963(4) angstrom. The binuclear compl exes exhibit antiferromagnetic interactions with J values of -102.1, - 118.2, and -113.6 cm-1 for 2, 3 and 4, respectively. The electronic sp ectra are similar to those observed in related species.