Structural Chemistry of Triple-bonded Groups

Bond length relationships in diazo and diazonium compounds

“…N(Csp3)2 systems in which N is sp2-planar [1.371 (3),~] or sp 3pyramidal [ 1.426 (2) A]. These and other comparisons (Allen & Garner, 1994) indicate that the Car--N bond in benzenediazonium compounds (II) is essentially single but is slightly foreshortened by the conjugative interactions that stabilize these systems relative to their highly reactive alkyl analogues. The other important geometrical feature of (II) is the ipso angle in the phenyl group (0435 in Table 2), which is enlarged to the high value of 124.5 (4) ° as a result of the very strong electronwithdrawing properties of the diazo group (Domenicano & Murray-Rust, 1976).…”

“…Thus, in moving from the diazonium compounds (II), through the oe-diazoketones (HI) to the diazoalkanes (IV) we would expect to observe an increase in the N~N bond length (dr, m) and a concomitant decrease in the C--N bond length (deN) in C~N~N systems. A preliminary survey of C--N~N geometry, incorporated in a recent review of triply-bonded functional groups (Allen & Garner, 1994), indicated systematic variations of dr,~ with deN associated with chemical environment. In this short communication, we report a more complete analysis of C--N~N geometry based on a larger dataset retrieved from the Cambridge Structural Database (CSD, Allen et al, 1991).…”

Coupling of Alkynyl Ligands at a Quadruply Bonded Molybdenum Dimer

“…For the Mo 2 (μ,η 2 :η 2 -HC⋮CSiMe 3 ) unit, the MoC and C⋮C bond distances and associated angles are within the normal ranges established for other M 2 (μ,η 2 :η 2 -RC⋮CR) compounds 6 and are similar to those for the compound [Mo 2 (μ-HC⋮CC 6 H 4 -4-Me)(μ-O 2 CMe)(NH 2 CH 2 CH 2 NH 2 ) 4 ] 3+ , which is the only previously reported compound derived from the addition of an alkyne across a Mo−Mo quadruple bond. One structural feature of note is that the bending of the alkyne ligand (∠[C(26)−C(27)−Si(4)] = 118.9(3)°) is much larger than usual (125−156°) . A space-filling model of the structure reveals this to be the result of significant steric repulsion between the alkyne SiMe 3 group and a dmpm ligand; this repulsion is manifested in the latter by the nonplanarity of the Mo 2 P 4 unit (Figure ).…”

Approximate transferability in alkanenitriles

“…In accordance with their utility, its electron structure has been the subject of a tremendous amount of experimental and theoretical studies 1. Many of them concentrated on the structure of the first member of the nitrile series, HCN, which became part of the most usual benchmark systems to test theoretical methods and calculation levels 2, 3. Nitriles, especially HCN, are also important interstellar molecules that had been detected by radioastronomy in various sources 4.…”