Лако-красочные материалы — производство

The intra — and intermolecular arrangements of the DPP molecules in a DPP crys­tal have been investigated by single X-ray structure analysis [22-28]. Angles and bond distances in the diphenyl DPP 2 are shown in Figure 11.3.

The DPP molecule is practically planar, the phenyl rings being twisted out of the heterocyclic plane by only 7°. The distance between the two hydrogen atoms at N2 and C6 is 2.08 A, while that between the hydrogen atom at C10 and O11 is 2.44 A. For both cases, the sum of the corresponding van der Waals radii is substan­tially larger, being 2.4 A and 2.6 A, respectively, thus implying resonance interac­tion between the DPP chromophore unit and the phenyl rings. This appears to be confirmed by a C3-C5 bond length of 1.43 A, which is shorter and hence possesses even more pronounced double bond character than the bond (1.496 A) between the two aromatic rings of biphenyl. Such resonance interactions, amongst others, would explain the electronic influence of substituents on the earlier mentioned wavelength shifts (see Table 11.1) of maximum absorption, and hence the color of different diaryl DPP derivatives in solution.

Figure 11.4 depicts the projection of the crystal packing on the crystallographic (b, c)-plane, highlighting the intermolecular hydrogen bonding between neighbor­ing lactam NH and carbonyl O atoms. This in turn determines the molecular packing along the a-b diagonal of the crystal lattice. In addition, the weak van der Waals contact between the terminal phenyl group atoms can be viewed.

Figure 11.5 illustrates the geometry of the hydrogen bond between two DPP mole­cules viewed through the phenyl ring at two slightly different angles. The hydrogen bond is slightly angled since the two interacting DPP molecules are not in the same plane. In addition, the p-p interaction between the layers of two DPPs is illustrated.

The crystal packing along the я-axis is determined by p-p interactions between layers of molecules. In Figure 11.6 the p-p interactions are viewed through the H-N bond giving a good illustration of the distances in the crystal.

The interlayer distances between chromophore planes (3.36 A) and between phenyl ring planes (3.54 A) are short enough to warrant significant p-p interac­tions, the growth of crystals investigated being also the strongest along this direc­tion.

11.4