From Weak Interactions to Covalent Bonds:  A Continuum in the Complexes of 1,8-Bis(dimethylamino)naphthalene

Abstract

Experimental charge density distributions in a series of ionic complexes of 1,8-bis(dimethylamino)naphthalene (DMAN) with four different acids: 1,2,4,5-benzenetetracarboxylic acid (pyromellitic acid), 4,5-dichlorophthalic acid, dicyanoimidazole, and o-benzoic sulfimide dihydrate (saccharin) have been analyzed. Variation of charge density properties and derived local energy densities are investigated, over all inter- and intramolecular interactions present in altogether five complexes of DMAN. All the interactions studied [[O...H...O](-), C[bond]H...O, [N[bond]H...N](+), O[bond]H...O, C[bond]H...N, C pi...N pi, C pi...C pi, C[bond]H...Cl, N[bond]H(+)] follow exponential dependences of the electron density, local kinetic and potential energies at the bond critical points on the length of the interaction line. The local potential energy density at the bond critical points has a near-linear relationship to the electron density. There is also a Morse-like dependence of the laplacian of rho on the length of interaction line, which allows a differentiation of ionic and covalent bond characters. The strength of the interactions studied varies systematically with the relative penetration of the critical points into the van der Waals spheres of the donor and acceptor atoms, as well as on the interpenetration of the van der Waals spheres themselves. The strong, charge supported hydrogen bond in the DMANH(+) cation in each complex has a multicenter character involving a [[Me(2)N[bond]H....NMe(2)](+)....X(delta-)] assembly, where X is the nearest electronegative atom in the crystal lattice.

Experimental studies of charge density distribution in the crystals of cytisine and N-methylcytisine. Inside the Fake Tobacco

“…Figure 10 shows the plot of the chosen characteristics of the intermolecular BCPs vs. R ij distance. This plot, after removing the debatable H···H interactions, fits quite well into exp.-type dependence, as postulated, e.g., by Wozniak et al [29,30].…”

Molecular Recognition in Organic Crystals: Directed Intermolecular Bonds or Nonlocalized Bonding?

“…To a good approximation, the electron density at bond critical points follows a negative exponential dependence on the H···X distance until it merges with the background density at an H···X distance of about 2.5 . [36,56,65] For short, strong, hydrogen bonds of the OÀH···O or O···H···O type, for example, as in carboxylic acid dimers or the hydrogen maleate anion [34,66] the Laplacian operator 5 2 1 BCP is negative, indicative of some covalent character in the bond, whereas for longer hydrogen bonds the Laplacian operator is positive, indicative of a closed-shell interaction. The crossing point seems to occur at an H···O distance of about 1.33 , [36] which may be regarded as the approximate boundary between electron-sharing and closed-shell interactions.…”

Models for incomplete nucleophilic attack on a protonated carbonyl group and electron-deficient alkenes: salts and zwitterions from 1-dimethylamino-naphthalene-8-carbaldehyde

“…Cross-polarisation, magic-angle-spinning (CPMAS) 1 H-13 C and 1 H-15 N NMR measurements in the solid state were undertaken at 11.7 T using a Bruker Avance III-500 spectrometer producing 1 H, 13 C and 15 N Larmor frequencies of 500.10, 125.76 and 50.68 MHz, respectively. A Bruker 4 mm HXY probe in dual channel mode was utilised to enable MAS frequencies of 700, 900 and 12 000 Hz.…”

“…A Bruker 4 mm HXY probe in dual channel mode was utilised to enable MAS frequencies of 700, 900 and 12 000 Hz. All 13 C CPMAS data were acquired with an initial 1 H π/2 pulse time of 2.5 μs, a 1 H-13 C contact time of 1 ms and a recycle time of 8 s. These 13 C data were indirectly referenced to neat TMS (δ iso 0 ppm) via a secondary solid reference of 13 C labelled alanine which provided three distinct resonances for the methyl, backbone and carboxyl carbons at isotropic shifts of δ iso 20.5, 50.5 and 178 ppm, respectively. 24 All 15 N CPMAS data were acquired with an initial 1 H π/2 pulse time of 2.5 μs, a 1 H-13 C contact time of 1.5 ms and a recycle time of 8 s. Similarly, all 15 N data were indirectly referenced to MeNO 2 in CHCl 3 (δ iso 0 ppm) via a secondary reference of histidine which provided three distinct resonances at −333.1, −204.3 and −191.0 ppm.…”