Weak intra- and intermolecular interactions in a binaphthol imine: an experimental charge-density study on (+/-)-8'-benzhydrylideneamino-1,1'-binaphthyl-2-ol.

The charge density in (+/-)-8'-benzhydrylideneamino-1,1'-binaphthyl-2-ol (1) has been studied experimentally using Mo Kalpha X-ray diffraction at 100 K, and by theory using density-functional thoery (DFT) calculations at the B3LYP/6-311++G** level. The nature of the weak intramolecular peri-C...N, CH...pi, H...H and C(pi)...C(pi) interactions has been examined by topological analysis using the Quantum Theory of Atoms in Molecules (QTAIM) approach. An analysis of the density rho(r), the Laplacian of the density inverted Delta(2)rho(r(b)) and other topological properties at the bond-critical points were used to classify these interactions. The study confirms the presence of the intramolecular CH...pi interaction in (1), which was previously suspected on geometrical grounds. An analysis of the ellipticity profiles along the bond paths unambiguously shows the pi-delocalization between the imine unit and one N-phenyl group. The weak intermolecular interactions in the crystal of (1) were examined experimentally and theoretically through the pairwise interactions of the seven independent dimeric pairs of (1) responsible for the set of unique intermolecular interactions, and also through examination of the Hirshfeld surface d(norm) property. The theoretical dimeric-pair calculations used the BLYP-D functional which supplements the exchange-correlational functional with an empirical dispersion term to provide a more accurate determination of the energies for the weak intermolecular interactions.