X-ray Structures and Electronic Spectra of the Halogen Complexes between Halogen Donors and Acceptors with-Receptors - Halogen Bonding: Fundamentals and Applications - page 136

X-ray Structures and Electronic Spectra
of the -Halogen Complexes between Halogen Donors and

Acceptors with

π

π -Receptors

Sergiy V. Rosokha · Jay K. Kochi ( )

Department of Chemistry, University of Houston, Houston, TX 77204, USA
[e-mail]

1 I tr cti n ................................... 138

2 Electronic Spectroscopy and Thermodynamics

of Donor/Acceptor Interactions with Halogen Derivatives ......... 139

2.1 DihalogenComplexeswithArenesandAlkenes ............... 139

2.2 ComplexeswithHalocarbonAcceptors .................... 141

2.3 Complexes of Halide Anions with Aromatic and Olefinic π -Acceptors . . . 142

2.4 Unified Mulliken Correlations of Donor/Acceptor Complexes

withHalogenDerivatives............................ 144

3 Structural Features

of Donor/Acceptor Complexes with Halogen Derivatives .......... 146

3.1 Complexes of Dihalogen Acceptors with Aromatic and Olefinic π -Donors . 146

π

3.2 Complexes of Polyhalogenated Methanes with -Donors .......... 148

3.3 Complexes of Halide Anions with Aromatic and Olefinic π -Receptors . . . 150

3.4 Donor/Acceptor (Structural) Effects on π -HalogenInteractions....... 155

3.4.1 IntermolecularSeparationsRelevanttoHalogenBonding.......... 155

3.4.2 MolecularGeometriesofDonor/AcceptorMoieties.............. 155

4 Summary and Conclusions ........................... 156

References ....................................... 157

Abstract The spectral characteristics and thermodynamics for the formation of inter-
molecular complexes of dihalogens, halocarbons, and halide anions with various organic
(aromatic and olefinic)

π

-receptors show their direct relationship to the more tradi-
tional donor/acceptor complexes. The unified Mulliken dependence indicates the com-
mon (charge-transfer) origin of the long-distance

-bonding of the halogen centers.
X-ray structural analyses of the molecular complexes of various arene donors with di-
halogen (X 2 ) and halocarbon (XR) acceptors reveal that such non-covalent interactions
are characterized mostly by over-the-rim halogen coordination, with the intermolecular
halogen-carbon contacts shortened by about 0.3-0.4A relative to the sum of the van
der Waals radii. The location of dihalogen and halocarbon acceptors generally follow the
position of highest electron density on the aromatic ring, and the X-X or X-R bonds
are directed perpendicular to the aromatic planes. Likewise, the structural arrangements
of the halide donors in the molecular complexes with cyano-substituted arenes (by and
large) follow the LUMO shape of the aromatic acceptor. Such long-distance

π

-bondings
are attributed to the presence of multiple (close-lying) local energy minima, so that the
donor/acceptor arrangements are rather easily modulated by external forces.

π