Abstract:
The mass spectra of compounds of t he series (C6F5 )3-n
MP~ (n = 1,2,3, M = P and As ), (C6F5>3Sb, Ph) Sb and
(C6F5 )2SbPh have been studied in detail and the important
modes of fragmentation were e1ucidated, a ided by metastable
ions. Various trends attributed to the central atom
and or the . substituent groups have been noted and, where
applicable, compared to recent studies on related phenyl
and pentafluorophenyl compounds of groups IV and V. The
mass spectra of fluorine containing organometallic compounds
exhibit characteristic migrations of fluorine to t he
central atom, giving an increasing abundance of MF+, MF2+'
and RMF+ (R = Ph or C6F5) ions on descending the group_
The mass spectra of pentafluorophenyl , antimony, and arsenic
compounds show a greater fragmentation of the aromatic ring
than those of phosphorus. The mixed phenyl pentafluorophenyl
derivatives show a characteristic pattern depending
on the number of phenyl grm.lps present but show t he general
characteristics of both the tris(phenyl) and tris(pentafluorophenyl)
compounds. The diphenyl pentafluorophenyl
der ivatives show the loss of biphenyl ion as the most import
ant step, the los s of phenyl t o give the i on PhMC6F5 +
being of secondary importance. The ,bis(pentafluorophenyl)
phenyl derivatives fragment primarily by loss of PhC6F5 to
give C6F5M+ ions, the abundance of t hese increasing r apidly
from phosphorus to arsenic. This species then, exhibits a
characteristic fragmentation observed in the tris(penta-
fluorophenyl ) compounds. However, the abundance of (C6F5)2M+ species in these compounds i s small. I ons of the type
C6H4MC6F4 + and tetrafluorobiphenylene ions C6H4C6F4 + also
are observed on substitution of a phenyl group for a penta-
fluorophenyl group. The fully fluorinated species (C6F4)2M+
is not observed, although octafluorobiphenylene ions ,
(C6F4)2+' are evident in several spectra .
The appearance potentials of the major ions were obtatned
from the ionisation efficiency curves. Attempts were
made to correlate these to the effect of the central atom in
substituent groups, but the large errors involved prevented
the reaching of quantitative conclusions, although it would
appear that the electron is removed from the ligand in the
ionisation of t he parent molecule .
