99714-79-1Relevant articles and documents
Organometallic oxides: Preparation and molecular and electronic structure of antiferromagnetic [(η-C5H5)Cr(μ3-O)]4 and [(η-C5H5)Cr]4(μ3-η 2-C5H4)(μ3-O)3
Bottomley, Frank,Paez, Daniel E.,Sutin, Lori,White, Peter S.,K?hler, Frank H.,Thompson, Robert C.,Westwood, Nicholas P. C.
, p. 2443 - 2454 (2008/10/08)
The reaction between (η-C5H5)2Cr and Me3NO gave, as the major product, [(η-C5H5)Cr(μ3-O)]4, (I) (18%) and, as the minor product (overall isolated yield 2%), [(η-C5H5)Cr]4(μ3-η 2-C5H4)(μ3-O)3 (II). I and II were separated by chromatographv on glass beads (120-200 mesh). At 295 K I has a distorted (D2) cubane structure, as determined by X-ray diffraction. The Cr-Cr distances are 2.7114 (6) and 2.7004 (6), 2.8099 (5) and 2.8369 (5), and 2.8933 (5) and 2.8987 (5) A?. The Cr-O-Cr and O-Cr-O angles fall into three sets to conform to the D2 symmetry, but the Cr-O distances lie in a narrow range, 1.922 (2)-1.947 (2) A?. Crystal data: monoclinic, P21/n, a = 10.0465 (7) A?, b = 20.9200 (13) A?, c = 10.4345 (4) A?, β = 115.015 (5)°; R = 0.042 for 274 variables and 6022 observed (I > 2.5σ(I)) reflections with 2θ A?; the Cr-O distances were 1.919-1.945 (2) A?. Crystal data: a = 9.9834 (7) A?, b = 20.7828 (23) A?, c = 10.3521 (10) A?, β = 115.359 (7)°; R = 0.028 for 2830 observed reflections with 2θ B at 500 K. The magnetic behavior of I has been studied in toluene solution by 1H and 13C NMR spectroscopy. The observed shifts and their temperature dependence over the temperature range 215-385 K clearly show intramolecular antiferromagnetism. The electron spin delocalization points to magnetic orbitals that are mainly metal in character. The He I photoelectron spectrum in the gas phase at 440 K and the electronic absorption spectrum (450-1550 nm) of a CCl4 solution of I have been measured; both show considerable low-energy structure. Extended Hu?ckel molecular orbital calculations indicate that the ordering of the 12 nonbonding cluster orbitals for a Td cubane is e 1 2 1 ? 2t2. The spectra and magnetism of I are interpreted on the basis of a static distortion of a [(η-C5H5)M(μ3-O)]4 cubane. The structure of II was previously established by X-ray diffraction as a butterfly cubane derived from I by replacement of a corner oxygen atom with the η2 ligand C5H4 (Matrix Presented) II shows antiferromagnetism between 4 and 120 K. It has a magnetic moment of ca. 2.3 μB at 4 K. The magnetic behavior is explained with use of extended Hu?ckel calculations on various forms of I and II; the ground state of the 12 cluster orbitals of II is 1a221a121b1 21b222a122b 113a11 (in C2ν, symmetry). The ground state is markedly influenced by the Cr-Cr distance spanned by the η2-C5H4 ligand, because the 2b1 orbital is antibonding and the 3a1 orbital bonding with respect to this Cr-Cr interaction. II cannot be reduced but is readily oxidized to I by reagents containing oxygen.
