Magnetic interactions in alkyl substituted cyclohexane diradical systems: a broken symmetry approach.

Magnetic interactions in alkyl substituted cyclohexane diradical systems have been investigated within the framework of spin flip density functional theory. The investigations suggest a ferromagnetic interaction for both the alkyl substituted cyclohexane-1,3-diyls and cyclohexane-1,4-diyls. However, in the case of cyclohexane-1,3-diyls, the ferromagnetic interaction is much stronger than its 1,4 analogue. Interestingly, it has been observed that this interaction is reduced to almost half the value from the butyl to the decyl substituted unit relative to the lower homologues up to the propyl substituted unit in cyclohexane-1,3-diyls. On the other hand, in case of alkyl substituted cyclohexane-1,4-diyls, the ferromagnetic interaction for the higher homologues, i.e., butyl to decyl substituted units, substantially reduces to almost 5-6 times the value of its lower homologue (methyl and ethyl substituted unit). In both these cyclohexane diradical systems, beyond butyl substituted unit, a saturation effect in the magnetic coupling constant (J) value is observed. The rapid decrease followed by a saturation in the singlet-triplet gap and J as well may be explained by considering positive inductive effect of the alkyl substituent.