For a series of polyether/transition metal ion complexes,
collisionally activated dissociation reactions that
are mediated by the flexibility of the polyether and the number of
coordination sites are reported. The metal ions
are generated by a pulsed laser desorption technique, and
collision-activated dissociation methods are used to
characterize the structures of the resulting metal/polyether complexes.
The CAD patterns for the different polyether/metal ion complexes show striking variations depending on the
flexibility of the ether, its number of coordination
sites, and the type of metal ion. For example, (18-crown-6 +
Co+) dissociates by loss of CHCH• or
C2H3O•
radicals, each pathway in conjunction with multiple losses of
C2H4O, and resulting in products incorporating
one
covalent or ionic bond between the Co+ ion and the crown
ether. In contrast, (12-crown-4 + Co+) dissociates
by
loss of CH2CH2 or
C2H4O closed shell neutrals, each pathway in
conjunction with additional losses of C2H4O
and
resulting in products that incorporate no covalent bonds to
Co+. The polyether/Ni+ complexes show
dissociation
behavior that is similar to that observed for the Co+
complexes, but the polyether/Cu+ complexes show
uniform
dissociation trends that seem to be independent of the flexibility and
number of coordination sites of the ether.
These differences are rationalized based on the nature of the
metal ion, and both the flexibility of the crown ether
and its number of coordinating sites, factors which affect the geometry
during coordination of the metal ion. This
idea is supported by comparative dissociation reactions of metal
complexes containing acyclic polyethers (glymes)
which have more flexible structures. MS/MS/MS experiments and CAD
of complexes formed by model compounds
offer support for the dissociation mechanisms.