Version 2 2020-12-17, 20:14Version 2 2020-12-17, 20:14
Version 1 2020-12-16, 15:05Version 1 2020-12-16, 15:05
journal contribution
posted on 2020-12-17, 20:14authored byVijith Kumar, Patrick Scilabra, Peter Politzer, Giancarlo Terraneo, Andrea Daolio, Francisco Fernandez-Palacio, Jane S. Murray, Giuseppe Resnati
Experimental
and theoretical studies of fluoro-, chloro-, and bromo-substituted
derivatives of barbituric acid and indandione show that imide protons
form short hydrogen bonds and bromine or, to a lesser extent, chlorine
atoms form halogen bonds. The imide nitrogen atoms act as effective
pnictogen bond donors, while C(sp2) and C(sp3) atoms act as tetrel bond donors; the resulting N···O
and C···O close interactions are a distinctive feature
of crystal lattices in all compounds. Importantly, halogen atoms promote
the electrophilicity of C(sp3) sites and favor the formation
of C(sp3)···O close contacts. Oxygen atoms
of carbonyl groups of barbituric and indandione units or of water
molecules function as the interaction acceptor sites: namely, they
donate electron density to hydrogen, halogen, nitrogen, and carbon
atoms. Modeling of various barbituric acid derivatives indicates that
the positive electrostatic potentials of π-holes orthogonal
to the C(sp2) carbons and σ-holes on the elongation
of quasi-axial F/Cl/Br–C(sp3) bonds merge to produce
a single well-defined point of the most positive electrostatic potential
on one face of the barbituric acids. This single local maximum of
the potential on the molecular face is close to the site occupied
by the oxygen forming the C(sp3)···O, and
C(sp2)···O, short contacts observed in crystals.