Comparative studies of geometric and quasielastic characteristics of PP and SS bonds

Abstract

It is demonstrated that density functional theory in B3PW91/aug-cc-pVTZ formulation provides a reasonable estimate of the geometrical and vibrational parameters of various PP and SS bonds. Calculated quasielastic characteristics of SS bonds, such as relaxed force constants f(SS), are approximately twice as large as f(PP). This means much higher elasticity of the PP bond, compared to the SS bond. From the dependence of the relaxed force constants on the formal bond order, the various PP bonds studied represent single bonds. By contrast, the more than twice as high rigidity of the SS bonds implies multiple SS bonding. Pronounced shortening of the SS bond on passing from less electronegative to more electonegative substituents at the sulfur atoms can be ascribed to the corresponding increase of the SS pi interactions. Essentially single PP bonds are not affected by electronic effects of this kind, which is the reason for the small variability of PP bond lengths in the gas phase. At the same time, intermolecular forces acting in crystals may strongly influence the length of highly elastic PP bonds.

PP-Rotation, P-Inversion and Metathesis in Diphosphines Studied by DFT Calculations: Comments on Some Literature Conflicts

“…A destabilising effect is also observed for the anti conformer and apparent in a local elongation of the P-P bond length. The P-P bond length of the gauche conformers of 3 (2.263 Å) is in closer agreement with the literature data, 2.246 Å (X-ray of solid), 2.25 Å (electron diffraction) [22] and 2.259 Å (calculations at the B3PW91/aug-cc-pVTZ level) [23].…”

“…Azofra, et al also obtained the P-P distance for 1-gauche (2.220 Å) at the MP2/aug-cc-pVTZ computational level [20], while Katsyuba et al [23] performed calculations of H 4 P 2 and Me 4 P 2 at different computational levels, HF/aug-cc-pVTZ, B3PW91/aug-cc-pVTZ and BPW91/cc-pVTZ finding P-P distances of 2.422 and 2.231 Å for 1 and 2 respectively at the most accurate level (B3PW91/aug-cc-pVTZ). Although there is an overestimation of the P-P distances by the B3LYP hybrid functional, the agreement between our computational data and the other theoretical methods (such MP2) and the experimental measurements is quite good.…”

Reactivity studies on [Cp′FeI]2: From iron hydrides to P4-activation

“…Furthermore, PP bonds are highly elastic, and can easily be deformed by inter-and intramolecular forces. 88,89 Due to these calculations, the mechanical strength of a typical 2-electron P-P single bond is $1.5 N cm À1 while the value for a 4-electron P]P double bond averages out at $3.3 N cm À1 . Therefore, we expected the value for an aromatic P-P bond to be between 2.1 and 2.4 N cm À1 .…”

Diphosphines with Strongly Polarized P−P Bonds: Hybrids between Covalent Molecules and Donor−Acceptor Adducts with Flexible Molecular Structures

“…The bond lengths associated with a particular atomic environment (“substructure”) are extremely well-defined for covalent bonds between elements of the second row of the periodic table such as carbon, nitrogen, or oxygen, whereas increased variance is found for compounds with “dative” (donor−acceptor) bonds , such as amine-boranes. Much larger deviations from standard bond lengths are, however, also encountered for compounds with elements of the third or higher periods and have, for example, stimulated to attribute certain PP and SS bonds as ”quasielastic . Archetypes are molecules with very bulky substituents, and examples for species with distinctively lengthened homonuclear single bonds connecting two elements of the third period are the disilanes 1a (R = H, Si−Si 2.43 Å, Chart ) and 1b (R = t Bu, Si−Si 2.697 Å) and the diphosphine 2 (P−P 2.310 Å), which all show bond lengths that are substantially larger than standard distances (Si−Si 2.359(12) Å, P−P 2.214(22) Å).…”