CON  Connected ligands (block)

 

This directive serves to fix the angles in the case of anisotropic interaction and to define the two parameters of the phase coupling model and has the form

<ILA> <ILB> [<episd(ILA)> <episd(ILB)>].

<ILA> and <ILB> are the sequence numbers of two ligands whose coordinates and AOM parameters must already be defined. AOMX then calculates the two appropriate angles such that the ligand y axes will be placed perpendicular to the plain containing the metal and the two ligands.

The specifications <episd(ILA)> <episd(ILB)> are necessary if phase coupling shall be included in the calculation; by these two items, the difference of in phase and out of phase parameters will be fixed:

<episd(ILA)>
<episd(ILB)>

In the AOM-Block where usual parameters are read in, the avarage value must have been given before:

<epis0(ILA)>
<epis0(ILB)>

AOMX then computes the in phase and out of phase -parameters according to

<epis0(ILA)> + <episd(ILA)> / 2
<epis0(ILA)> - <episd(ILA)> / 2
<epis0(ILB)> + <episd(ILB)> / 2
<epis0(ILB)> - <episd(ILB)> / 2  .

The unusual parametrization through an avarage parameter and the splitting instead of the in phase and out of phase parameters themselves has technical reasons since this way phase coupling could be implemented more easily as an additional perturbation. How you can, nevertheless, work with und by using variables, is demonstrated by the first of the following examples:

Example 1:

TPP
 65   40
 65  140
115  -40
115 -140

VAR OPT
epis  1000
epis'  700
*
epis_0 = epis / 2 + epis' / 2
epis_d = epis - epis'

AOM
7000 900 200 
7000 900 200 
6000 epis_0 0
6000 epis_0 0

CON
1 2
3 4 epis_d epis_d

A distorted tetrahedron is defined with two symmetrical chelate ligands that both exhibit anisotropic interaction. Ligands no. 1 and 2 form the first chelate, no. 3 and 4 the second; for all ligands, the angle will be calculated. On the second chelate, moreover, phase coupling is present, and shall be optimized.

Example 2:

XYZ
x    y    z
xdum ydum zdum

AOM
esig epis epic
0    0    0

CON
1 2

In this example, not a chelate is defined but a unidentate ligand with anisotropic interaction. The second ligand is a dummy since its contributions to the ligand field are equal to zero; it solely serves for the calculation of the angle by spanning a plane together with the central ion and the coordinating atom of the ligand which fixes the orientation of that orbital which is antibonding with respect to the metal-ligand interaction. Regarding this orbital in an idealizing way as a nonbonding p orbital, the plane defined by the aid of the dummy has to be its nodal plane. Examples: in the H_2O ligand, one of the hydrogen atoms may act as the dummy, in the pyridine ligand one of the carbon atoms in ortho or meta position.