Subject: MM3 and simple metal-ligand complexes

From: Patrick Bultinck <[email-masked]>
Date: Mon, 17 Jun 1996 11:21:03 +0200 (DFT)

Dear,

I am doing ab initio work on complexes using ab initio calculations. I 
want to use MM3 for initial geometry searches. I have a question 
concerning an interaction like :

H	H
 \      |
H-C-----N*****Mg2+
 /      |
H       H

I want to know the optimum geometry. I have an input file :

methylamine                                                 0   8 2  0 0  1 10.0
1   1       .0000000         5    0         0    0    0    0    1         1    0
    2    3
    2    4    2    5    3    6    3    7    3    8
   1.74500  -2.10500  -0.73600MG 59(  1)
   0.52600  -1.01100   0.41200 N  8(  2)
  -0.69300   0.08300   1.56000 C  1(  3)
   1.36500  -0.41200   0.08800 H 23(  4)
   0.88700  -1.86500   0.96500 H 23(  5)
  -1.05300   0.93700   1.00600 H  5(  6)
  -0.15000   0.41200   2.43400 H  5(  7)
  -1.52300  -0.53100   1.87400 H  5(  8)
   20   2.00000             0.00000   0.05000    0    0

But this seems to go wrong all the way.... Do I have to put a bond 
between N and Mg (it is mostly electrostatic). Second I get trouble 
because for Mg; valence 6 is expected; not 1 (I gave Mg a 2+ charge in a 
parameter file). If I do put a bond; he complains about missing 
parameters, etc.

How to do this ? I obtained MM3 from QCPE, so cannot look into the 
source. No examples are given for any complexes with an ion involved. Can 
somebody offer a hand, or give me a NH3-M2+ input deck from which I can 
learn,

Thanks,

Patrick

*****************************************************************************
Patrick Bultinck			Macrocycles Quantum Chemical
Ph. D. Student				Calculations
Dept. Inorganic & Physical Chemistry 
University of Ghent			Tel. Int'l code/32/9/264.44.44
Krijgslaan 281 (S-3)			Fax. Int'l code/32/9/264.49.83
9000 Gent				E-mail : [email-masked]
Belgium					http://allserv.rug.ac.be/~pbultink/
*****************************************************************************