On the molecular structure of [Fe3(CO)12] in the solid state

Synthesis and Characterization of Bidentate Isonitrile Iron Complexes

The divalent iron complexes trans-[FeBr2(BINC)2], [Cp*FeCl(BINC)] (Cp* = Me5C5), and [FeBr2(CNAr3NC)2] with the chelating bis(isonitrile) ligands BINC (bis(2-isocyanophenyl)phenylphosphonate) and CNAr3NC (2,2″-diisocyano-3,5,3″,5"tetramethyl-1,1':3',1″-terphenyl) have been prepared and characterized. Their subsequent reduction yields the di- and trinuclear compounds [Fe3(BINC)6], [Cp*Fe(BINC)]2, [Fe(CNAr3NC)2]2, and [K(Et2O)]2[Fe(CNAr3NC)2]2. The molecular structures of all new species were determined by X-ray crystallography and compared to those of related iron carbonyl complexes, demonstrating that the bidentate isonitrile ligands are capable surrogates for two CO ligands with only minimal distortion of the tetrahedral or octahedral geometry of the parent complexes. The complexes were further characterized by NMR and IR spectroscopy, and the electrochemical properties of selected compounds were analyzed by UV-vis-NIR spectroelectrochemistry.

Remarkable Aspects of Unsaturation in Trinuclear Metal Carbonyl Clusters: The Triiron Species Fe3(CO)n(n= 12, 11, 10, 9)

The trinuclear iron carbonyls Fe(3)(CO)(n) (n = 12, 11, 10, 9) have been studied by density functional theory using the B3LYP and BP86 functionals. The experimentally known C(2)(v) isomer of Fe(3)(CO)(12), namely Fe(3)(CO)(10)(mu-CO)(2), is found to be the global minimum below the unbridged D(3)(h) isomer analogous to the known structures for Ru(3)(CO)(12) and Os(3)(CO)(12). The lowest-energy isomer found for Fe(3)(CO)(11) is Fe(3)(CO)(9)(mu(3)-CO)(2) with iron-iron distances in the Fe(3) triangle, suggesting the one double bond (2.460 A by B3LYP and 2.450 A by BP86) and two single bonds (2.623 A by B3LYP and 2.604 A by BP86) required to give each Fe atom the favored 18-electron configuration. Two different higher-energy dibridged structures Fe(3)(CO)(9)(mu(2)-CO)(2) are also found for Fe(3)(CO)(11). The lowest-energy isomer found for Fe(3)(CO)(10) is Fe(3)(CO)(9)(mu(3)-CO) with equivalent iron-iron distances in the Fe(3) ring (2.47 A by B3LYP or BP86). The lowest-energy isomer found for Fe(3)(CO)(9) is Fe(3)(CO)(6)(mu-CO)(3) with distances in the Fe(3) triangle possibly suggesting one single bond (2.618 A by B3LYP and 2.601 A by BP86), one weak double bond (2.491 A by B3LYP and 2.473 A by BP86), and one weak triple bond (2.368 A by B3LYP and 2.343 A by BP86). A higher-lying isomer of Fe(3)(CO)(9), i.e., Fe(3)(CO)(8)(mu-CO), at approximately 21 kcal/mol above the global minimum, has iron-iron distances strongly suggesting two single bonds (2.6 to 2.7 A) and one quadruple bond (2.068 A by B3LYP and 2.103 A by BP86). Wiberg Bond Indices are also helpful in evaluating the iron-iron bond orders.

High pressure study of Ru3(CO)12 by X-ray diffraction, Raman, and infrared spectroscopy

The single-crystal X-ray structure of Ru(3)(CO)(12) is reported at 8 pressures ranging from 1 atm (0.0 GPa) to 8.14(5) GPa. Although intramolecular bonding parameters remain relatively constant, intramolecular and intermolecular nonbonding contact distances decrease by an average of 4% and 15%, respectively. At 8.14 GPa, O...O, C...O, and C...C intermolecular distances as short as 2.54(4), 2.64(6), and 3.07(4) A, respectively, are observed, and the unit cell compresses to 75% of the ambient pressure volume. Raman and infrared spectroscopic measurements show that carbonyl stretching frequencies shift to higher wavenumber values by as much as 80 cm(-)(1), even though Ru-C and C-O distances stay roughly constant throughout the entire pressure range studied. Compression of the sample to above 18 GPa with laser radiation results in an irreversible transformation due to either decomposition or a total collapse of D(3)(h) molecular geometry accompanied by color darkening.