to 110◦ and t torsion angles similar to 0◦ (or 180◦) should show
the most antiferromagnetic interactions.
The sign of the exchange coupling agrees with previous work
and as expected, every compound reported in Table 6, including
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compound 3, show antiferromagnetic behaviour, with J values
ꢀ
in the range -2.7 to -11.7 cm-1(H = -J ij Si·Sj). However,
comparing the three factors mentioned before, it is not possible
to find direct magneto-structural correlations among them; it
appears that the three parameters are relevant but none of them
leads the strength of the exchange. From all of the above, one may
conclude that compound 3 shows a long Mn–N distance, and one
the greatest a values found for this type of Mn(III) systems, but
the Mn–N1–N2–N3–Mn core is almost planar (t ~ 180◦), and as a
result exhibits a moderate antiferromagnetic behaviour.
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Conclusion
Although the room-temperature preparation of m-1,3 azide
bridged Mn(III) complexes with salen or salpn type Schiff bases is
common in the literature, introduction of a phenylene diamine
moiety in the ligand prevented the formation of polynuclear
compounds as a result of molecular rigidity, and mononuclear
compounds resulted. In the present study, we have demonstrated
for the first time that polynuclear compounds can also be
prepared, using the ‘so-called’ rigid ligands, simply by increasing
the temperature of the system which helps to overcome the
activation energy. Thus the work opens up a new vista in
preparing polynuclear complexes which was hitherto believed to
be impossible to prepare. However, we have also showed that if
sterically demanding substituents are adjacent to the phenolic
oxygen of the N2O2 donor Schiff bases, the transition state becomes
practically inaccessible and refluxing is not sufficient to overcome
the kinetic barrier of polymerisation. On the other hand, magnetic
studies do illustrate the relevance of the supramolecular features
for compounds 1 and 2, where their magnetic susceptibility data
are better described in terms of dinuclear species. Complex 3 shows
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Acknowledgements
This work was supported by CSIR, India (Fellowship for Pras-
anta Bhowmik, Sanction No. 09/096(0607)/2010-EMR-I, dated
27.1.10) and University Grants Commission, New Delhi (Minor
Research Project sanctioned to S. Chattopadhyay, F. No. 37-
577/2009 (SR) dated 12.01.2010). The work was also supported
by the Ministerio de Educacio´n y Ciencia (CTQ2009-07264/BQU
and CTQ2009-06959/BQU), the Comissio´ Interdepartamental de
Recerca i Innovacio´ Tecnolo`gica de la Generalitat de Catalunya
(CIRIT) (2009SGR1454) and ICREA (Institucio´ Catalana de
Recerca i Estudis Avanc¸ats).
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