title: The lengths of molybdenum to molybdenum quadruple bonds: correlations, explanations, and corrections.
abstract: A systematic search of the Cambridge Crystallographic Database has yielded structures of 467 molecules containing, or reported to contain, a molybdenum to molybdenum quadruple bond, Mo[quadruple bond]Mo. We have arranged these data as a histogram, in order to determine the "normal" range of Mo[quadruple bond]Mo lengths, 2.06-2.17 A, as well as to examine molecules in which the Mo[quadruple bond]Mo length deviates from the norm. We discuss 24 molecules with exceptionally long Mo[quadruple bond]Mo lengths. Another molecule, Mo(2)(pyNC(O)CH(3))(4), was previously reported to have an unusually short Mo[quadruple bond]Mo bond. However, the structure is highly disordered (probably twinned); thus we have prepared and determined the structure of an analogous molecule, Mo(2)(pyNC(O)CH(2)CH(3))(4), which displays a completely normal Mo[quadruple bond]Mo bond length of over 2.08 A.
authors.affiliation: Department of Chemistry and Laboratory for Molecular Structure and Bonding, PO Box 30012, Texas A&M University, College Station, Texas 77842-3012, USA. cotton@tamu.edu
authors.forename: F Albert
authors.initials: FA
authors.lastname: Cotton
authors.forename: Lee M
authors.initials: LM
authors.lastname: Daniels
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Hillard
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Murillo