VAN DER BENT

Deckers, M., Karperien, M., Van Der Bent, C., Yamashita, X, Papapoulos, S., and Lowik, C. 2000. Expression of vascular endotheflal growth factors and their receptors during osteoblast differentiation. Endocrinology 141 1667-74. 

If a critical film thickness is not reached during film drainage, the drops separate from each other. Conversely, if the critical film thickness is reached, the film ruptures—as a result of van der Waals forces—and the drops coalesce. This generally occurs at thin spots, because van der Waals forces are inversely proportional to h (Verwey and Overbeek, 1948). The value of bent can be determined by setting the van der Waals forces equal to the driving force for film drainage, giving (Verwey and Overbeek, 1948)... 

Sn—C is normal, RSnR = 125°-135°, Sn-Cl distances are 236-240 pm while Sn... Cl is around 350 pm. Both coordinations are linked into zigzag chains which are linear at Sn (Cl—Sn... Cl 170-175°) and bent at Cl (Sn—Cl... Sn around 105°). The cyclohexyl-bromide shows similar features (Sn-Br = 250 pm Sn- -Br = 377 pm). While the long Sn- -Cl or Br distances are only 10% less than the van der Waals radii, the interpretation in terms of very weak additional coordination seems justified. By comparison, in truly 4-coordinate (biphenylyl)2SnCl2, Sn-Cl = 238.6 pm and all the intermolecular Sn/Cl distances exceed 600 pm, and in Et2Snl2 the extramolecular Sn/I is 428 pm, distinctly outside the van der Waals limit. In the end the matter is one of interpretation175. When R2 = Ph2 or MePh, tetrameric units are found containing both 5- and 6-coordinate Sn. 

Hexachlorobenzene is also planar in its crystalline state as shown by an X-ray diffraction study189). It is of interest to point out that the distance between the two vicinal chlorine nuclei (3.12A) in hexachlorobenzene is shorter than the sum of the van der Waals radii (3.60A). This fact prompted one author to comment ... it is reasonable to assume that the ring of perchlorobenzene is puckered with the C—Cl-bonds being bent alternatively upwards and downwards from its mean plane 190). 

According to Lonsdale et al., the four aromatic bridgehead atoms C8, Cg, Cu and C14 are bent out of the plane of the remaining benzene carbon atoms by about 0.168 A (14°) at 291 °K (see Fig. 1) the aromatic nuclei are deformed into a boat conformation. The distance between the aromatic bridgehead atoms C3, C14 and Cg, Cu has shrunk to 2.751 A. The intramolecular distance between the plane formed by atoms C4, C5, C7, Cg and that formed by atoms C12, C13, C15, Ci6 is only 3.087 A the van der Waals distance between two parallel benzene nuclei is usually at least 3.4 A. There must therefore be considerable transannular -overlapping in compound 2. To compensate for this the CH2-CH2 bond length is unusually large 1.630 A at 291 °K at 93°K it is only 1.558 A. 

The crystal structure of pentathiepino [6,7- indole has been determined <1994TL5279>. X-Ray crystal structure analysis revealed that 4,5-ethylenedithio-4,5-pentathiotetrathiofulvalene <1999AM758> moiety has a bent structure resembling the molecular structure of neutral bis(ethylenedithio)tetrathiafulvalene and that the pentathio group adopts a chair-formed conformation. The intradimer interplane distance is 3.35 A, which is much shorter than the interdimer one (4.45 A). In a molecule, there are many intermolecular S-S contacts shorter than the sum of the van der Waals radii (3.7 A), and a two-dimensional network of sulfur atoms was developed between the pentathio groups and tetrathiafulvalene moieties. Furthermore, chlorobenzene molecules are beside the anion and occupy the void space as the interstitial solvent. They are also located on the mirror plane and are disordered at two positions with inversion symmetry because of the cavity structure of the void space. 

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