Lewis Basicity of a Chlorine Atom Bound to an Aliphatic Carbon Atom As Sensed by a Quadruple Chromium-Chromium Bond. Structures of M24*2CH2Cl2, M = Cr, Mo

Article abstract of DOI:10.1021/ja00530a027

Previous studies in this laboratory have shown that the length of the quadruple bond between two chromium atoms is an extremely sensitive function of the amount of ? electron density donated to one or both of the chromium atoms along the outer extensions of the Cr-Cr bond.We report here a compound in which one chlorine atom of a CH2Cl2 molecule approaches one Cr atom of a Cr2<(2,6-xylyl)NC(CH3)O>4 molecule at a distance of 3.354(3) Angstroem, thereby causing the Cr-Cr distance to become 0.076(9) Angstroem longer than it is in the absence of this weak axial Cl...Cl interaction.The structures of the isomorphous compounds, M2<(2,6-xylyl)NC(O)CH3>4*2CH2Cl2, M = Cr, Mo, are reported.The compounds crystallize in the orthorhombic space group Pccn with eight molecules per unit cell.The unit cell constants for the Cr and Mo compounds, respectively, are a = 31.037(7), 31.255(4) Angstroem, b = 15.836(4), 15.928(2) Angstroem, c = 18.288(3), 18.311(3) Angstroem, and V = 8989(5), 9115(4) Angstroem³.The Cr-Cr and Mo-Mo distances are 1.949(2) and 2.083(3) Angstroem, respectively.The average M-O and M-N distances are 1.973(6) and 2.096(6) Angstroem, and 2.08(1) and 2.17(2) Angstroem for the Cr and Mo compounds, respectively.There are two CH2Cl2 molecules which occupy positions along the axial extensions of the M-M bond with M-Cl distances of 3.58(1) and 3.354(3) Angstroem for the chromium compound and 3.59(1) and 3.417 Angstroem for the molybdenum compound.