Subject: RE: TM force fields - questions

From: "Shobe, Dave" <[email-masked]>
Date: Thu, 03 Aug 2000 09:37:02 -0400

I'm not an expert in molecular mechanics, but I've been following this
discussion and here's my $.02:

The fact that M-L1 bond lengths vary according to the identity and placement
of the other ligands does not mean that molecular mechanics (MM) is
impossible for transiton metal complexes, only that a decent
parameterization would be much more complicated than for p-block elements.
It may mean that MM software that was designed for organic molecules will be
unable to accurately predict metal complex geometries without major
revisions--that it's not just a matter of defining parameters for new atom
types, since the factors influencing the geometry are quite different.  On
the other hand, even from a "pure science" point of view, I think that a
decent MM algorithm/parameterization for transition metal complexes would be
a worthwhile and interesting goal.

--David Shobe
Sьd-Chemie Inc.
phone (502) 634-7409
fax     (502) 634-7724
email  [email-masked]

Any opinions herein are not necessarily representative of Sьd-Chemie.

-----Original Message-----
From: Isaac B. Bersuker [mailto:[email-masked]]
Sent: Wednesday, August 02, 2000 3:34 PM
To: Robert K Szilagyi
Cc: [email-masked]
Subject: CCL:TM force fields - questions

Dear Dr Szilagyi:

Thank you for your message. Your statements seem to be correct except in one
point:
you miss the NONTRANSFERABILITY (NT) of the force field parameters (FFP)
>from one
compound to another which deprives the whole approach of its heuristic
value.

The NT emerges from the fact that in TMS the parameters for the M-L1 bond
depend
very strongly on the presence of other M-L2, M-L3,..., bonds. For instance,
the
Cu-O bond length varies between 1.8 A and 3.0 A dependent on other bonds and
the
next coordination sphere in the TMS (see my 1996 book). What bond length
Cu-O would
you take as a FFP?

[rest of msg. deleted]