McConnell model

The variation of the signs of intermolecular. b. the absolute values of which decrease with distance R in an exponential manner, can be explained by the extended McConnell model (20). 

Harrington, W and V. McConnell, Modeling In-Use Vehicle Emissions and the Effects of Inspection and Maintenance Programs, J. Air Waste Manage. Assoc., 44, 791-799 (1994). 

The McConnell model can work reasonably well for systems having only dyad contacts with well-aligned spin orbital overlap.152,153 Numerous examples have been described, and will surely continue to be found, since dyad formation is one of the most common exchange motifs between organic radicals. This is probably in part because favorable AFM exchange between spin-paired radicals can be one of the forces to assemble the radicals in a lattice. 

It is immediately apparent from equation (9) that the McConnell model predicts an exponential decay of the magnitude of Ve with increasing number of bridge bonds. From equations (6) and (9) - using n, the number of bonds, in place of the distance r, in the former equation - the damping factor /3el may be expressed in terms of A and t according to equation (10) ... 

The third, and possibly the most important conclusion is that the distance dependence of TB-mediated electronic coupling in 15(h) is much weaker than that predicted by the simple McConnell model. In that model, a /3el value of about 2.3 bond-1 is estimated, whereas the average /3el value of ca. 1.0 bond-1 for 15(/t) is 2.3 times smaller Thus, the attenuation in the ET rate, mediated by superexchange through a saturated hydrocarbon bridge, could be as small as ca. 2.5 bond-1, as opposed to ca. 10 bond-1, predicted from the simple McConnell model. 

There are two important predictions of the McConnell model. Firstly, the splitting due to TB coupling falls off exponentially with the number of bonds in the relay. Equating Eq. 5 with Eq. 3 (bearing in mind that AE n) = 2Vei) gives ... 

K) [68]. Decamethylmanganocenium is a d high-spin (S = 1) system, as opposed to the d low-spin (S = 1/2) ferrocenium cation. Bulk ferromagnetism has also been reported for the decamethylchromocene/TCNQ [69] CT complex and for [MnCpf] [TCNQ] " [70]. These two latter materials have shown that the interpretation of their ferromagnetism cannot be based on the simple McConnell model, which invokes a configurational mixing of a virtual CT state (vide supra). 

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