Abstract:
The capability of molecular mechanics for modeling the
wide distribution of bond angles and bond lengths characteristic
of coordination complexes was investigatecl. This was the
preliminary step for future modeling of solvent extraction.
Several tin-phosphine oxide COrnI)le:){es were selected as the test
groUl) for t.he d,esired range of geometry they eX!libi ted as \-vell as
the ligands they cOD.tained r Wllich were c\f interest in connection
with solvation. A variety of adjustments were made to Allinger's
M:M2 force·-field ill order to inl.prove its performance in the
treatment of these systems.
A set of u,nique force constants was introduced for'
those terms representing the metal ligand bond lengths, bond
angles, and, torsion angles. These were significantly smaller than
trad.itionallY used. with organic compounds.
The ~1orse poteIlt.ial energ'Y function was incorporated
for the M-X l')ond lE~ngths and the cosine harmonic potential erlerg-y
function was invoked for the MOP bond angle. These functions were
found to accomodate the wide distribution of observed values
better than the traditional harmonic approximations~
Crystal packing influences on the MOP angle were
explored thr"ollgh ttle inclusion of the isolated molecule withil1 a
shell cc)ntaini11g tl1e nearest neigl1'bors duri.rlg energy rninimization
experiments~ This was found to further improve the fit of the MOP angle.
