Pressure-frozen benzene I revisited

Abstract

The crystal structure of benzene, C6H6, in situ pressure-frozen in phase I, has been determined by X-ray diffraction at 0.30, 0.70 and 1.10 GPa, and 296 K. The molecular aggregation within phase I is consistent with van der Waals contacts and electrostatic attraction of the positive net atomic charges at the H atoms with the negative net charges of the C atoms. The C-H...aromatic ring centre contacts are the most prominent feature of the two experimentally determined benzene crystal structures in phases I and III, whereas no stacking of the molecules has been observed. This specific crystal packing is a likely reason for the exceptionally high polymerization pressure of benzene. The changes of molecular arrangement within phase I on elevating the pressure and lowering the temperature are analogous.

Rational Control of Conformational Distributions and Mixed‐Valence Characteristics in Diruthenium Complexes

“…Closer inspection reveals that the conformers in which Ω =33, 98° for [ 2 ] + and Ω =36, 105° for [ 3 ] + exhibit a T‐shaped quadrupolar CH⋅⋅⋅π interaction (distance 2.80 Å) between the aromatic rings of the dppe ligands on the two half‐sandwich moieties (Figure ). Similar interactions are recognisable in the herringbone packing pattern of crystalline benzene (centre of mass separation 4.95–5.00 Å), and this is known as the most stable conformation of the benzene dimer (due to dispersion and quadrupole/quadrupole interactions) . At the level of theory used in this study (BLYP35‐D3/def2‐SVP, gas phase), the T‐shaped benzene dimer has a centre of mass separation of 4.96 Å, which is comparable to the distances observed in the optimised structures of [ 2 ] + and [ 3 ] + (4.73–4.95 Å).…”

“…[43] This resulted in the identification of at otal of six local minima for each of [2] (Figure 4). Similar interactions are recognisable in the herringbone packing pattern of crystalline benzene (centre of mass separation 4.95-5.00 ), [44,45] and this is known as the most stable conformation of the benzene dimer (due to dispersion and quadrupole/quadrupolei nteractions). [46] At the level of theory used in this study (BLYP35-D3/def2-SVP,g as phase), the T-shapedb enzene dimer has ac entre of mass separation of 4.96 ,w hich is comparable to the distances observed in the optimised structures of [2] + and [3] + (4.73-4.95 ).…”

Relations between compression and thermal contraction in 1,2,4-trichlorobenzene and melting of trichlorobenzene isomers

“…6). This latent molecular-volume change of 16 Å 3 corresponds to that of benzene (14 Å 3 ), 21 and it is also similar, for example, to that of 3-aminopropan-1-ol, where a conformational conversion between an H-bonded pseudo-cyclamer and an extended molecule takes place on freezing. 22 After freezing, the solid 124TCB is initially strongly compressed until about 0.25 GPa; then the compression monotonically decreases, and at 1 GPa, the volume reaches about 80% of the liquid at 0.1 MPa and 90% of the solid at 0.06 GPa.…”

Van der Waals and Polar Intermolecular Contact Distances: Quantifying Supramolecular Synthons

“…The actual structure of benzene at ambient and higher pressures is more complex and is distinct from the structure in Figure 2. [3,[40][41][42][43] What are the features that bring about such a change? It is apparent that stereoelectronic features associated with the size of atoms are important.…”

“…The structure of benzene between 1.4 and 4.5 GPa is described as a yet-unrefined phase II structure. [42] In the experimental high-pressure phase III (Figure 4), there are intermolecular C···C distances (indicated by thin and thick lines) that are 346-350 pm long; these distances [a] n v is the number of "extra-bonding" valence electrons that contribute to a decrease in the size CR by a term F S = [1 + {SA C H T U N G T R E N N U N G (S+1)} 1/3 ], [28][29][30][36][37][38] in which S = n v /2. The term F S accounts for the decrease in bond length with an increase in bond order (= n v + 1).…”