Van der Waals forces are ‘The attractive or repulsive forces between molecular
entities (or between groups within the same molecular entity) other than those due
to bond formation or to the electrostatic interaction of ions or of ionic groups with
one another or with neutral molecules. The term includes dipole–dipole, dipoleinduced dipole, and London (instantaneous induced dipole-induced dipole) forces.
The term is sometimes used loosely for the totality of nonspecific attractive or
repulsive intermolecular forces’ [4] (italics of the author).
In this chapter, the direct electrostatic interactions (dipole-dipole, *1/R
3 ,
quadrupole-quadrupole, *1/R
4 , etc. (see Sect. 6.3.3.2), will not be considered as
van der Waals. Nevertheless, for transition electric dipole-permanent electric dipole,
and transition electric dipole-permanent electric quadrupole interactions, they are
long-range, *1/R
3 and *1/R
4 , respectively (see Sect. 6.3.3.1).
Recently, two types of bonds (complexes), namely, hydrogen and halogen
bonds, began to be considered independently.
‘The hydrogen bond is an attractive interaction between a hydrogen atom from a
molecule or a molecular fragment X–H in which X is more electronegative than H,
and an atom or a group of atoms in the same or a different molecule, in which there
is evidence of bond formation.
A typical hydrogen bond may be depicted as X–H
... Y–Z, where the three centered dots denote the bond. X–H represents the hydrogen bond donor. The acceptor
may be an atom or an anion Y, or a fragment or a molecule Y–Z, where Y is bonded
to Z’ [5].
‘A halogen bond occurs when there is evidence of a net attractive interaction
between an electrophilic region associated with a halogen atom in a molecular
entity and a nucleophilic region in another, or the same, molecular entity. The
halogen bond donor (R-X) are halogen-containing molecules (electrophillic region),
homonuclear or heteronuclear halogens, in particular. The halogen bond is represented conventionally by the three centered dots in R-X
… Y, where the halogen
atom X of the molecule X–R interacts with a nucleophilic acceptor atom/center Y’
[6]. In the gas phase, the halogen bond acceptor (electrophilic region) are Lewis
bases B, such as N 2 , CO, HCN, H 2 O, C 2 H 2 , H 2 S, NH 3 . In this case, the general
notation of halogen bonds would be B
… XY (XY are a homohalogen or heterohalogen) [7].
This book is devoted to gas-phase photoprocesses, that is, electronically excited
states, in particular. Therefore, in this chapter, we consider only those weakly
bound complexes that are weakly bound in electronically excited states, as well. As
far as the author knows, there are no data in the literature on experimental studies of
electronically excited states of complexes with hydrogen and halogen bonds. For
this reason, complexes with hydrogen and halogen bonds in the ground states are
considered briefly.
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6 Weakly-Bound Complexes and Clusters
entities (or between groups within the same molecular entity) other than those due
to bond formation or to the electrostatic interaction of ions or of ionic groups with
one another or with neutral molecules. The term includes dipole–dipole, dipoleinduced dipole, and London (instantaneous induced dipole-induced dipole) forces.
The term is sometimes used loosely for the totality of nonspecific attractive or
repulsive intermolecular forces’ [4] (italics of the author).
In this chapter, the direct electrostatic interactions (dipole-dipole, *1/R
3 ,
quadrupole-quadrupole, *1/R
4 , etc. (see Sect. 6.3.3.2), will not be considered as
van der Waals. Nevertheless, for transition electric dipole-permanent electric dipole,
and transition electric dipole-permanent electric quadrupole interactions, they are
long-range, *1/R
3 and *1/R
4 , respectively (see Sect. 6.3.3.1).
Recently, two types of bonds (complexes), namely, hydrogen and halogen
bonds, began to be considered independently.
‘The hydrogen bond is an attractive interaction between a hydrogen atom from a
molecule or a molecular fragment X–H in which X is more electronegative than H,
and an atom or a group of atoms in the same or a different molecule, in which there
is evidence of bond formation.
A typical hydrogen bond may be depicted as X–H
... Y–Z, where the three centered dots denote the bond. X–H represents the hydrogen bond donor. The acceptor
may be an atom or an anion Y, or a fragment or a molecule Y–Z, where Y is bonded
to Z’ [5].
‘A halogen bond occurs when there is evidence of a net attractive interaction
between an electrophilic region associated with a halogen atom in a molecular
entity and a nucleophilic region in another, or the same, molecular entity. The
halogen bond donor (R-X) are halogen-containing molecules (electrophillic region),
homonuclear or heteronuclear halogens, in particular. The halogen bond is represented conventionally by the three centered dots in R-X
… Y, where the halogen
atom X of the molecule X–R interacts with a nucleophilic acceptor atom/center Y’
[6]. In the gas phase, the halogen bond acceptor (electrophilic region) are Lewis
bases B, such as N 2 , CO, HCN, H 2 O, C 2 H 2 , H 2 S, NH 3 . In this case, the general
notation of halogen bonds would be B
… XY (XY are a homohalogen or heterohalogen) [7].
This book is devoted to gas-phase photoprocesses, that is, electronically excited
states, in particular. Therefore, in this chapter, we consider only those weakly
bound complexes that are weakly bound in electronically excited states, as well. As
far as the author knows, there are no data in the literature on experimental studies of
electronically excited states of complexes with hydrogen and halogen bonds. For
this reason, complexes with hydrogen and halogen bonds in the ground states are
considered briefly.
200
6 Weakly-Bound Complexes and Clusters