Antiferromagnetic orbital exchange

Table I. Structural and antiferromagnetic orbital exchange parameters...

As in other transition metal oxides such as NiO, the spins on the transition metal ions are coupled via the oxide ions. The Mn " ions couple antiferromagnetically with each other via superexchange as in NiO. The coupling of the Mn " ions varies and can be ferro- or antiferro-magnetic. Mn " ions couple to Mn " ions in a process known as double exchange. In this process, a simultaneous hop of an electron from Mn " to an 0 Ip orbital and from the 0 2p orbital to an Mn ion takes place. 

The complex [(VO)2(dana)2] (dana = l,5-bis(p-methoxyphenyl)-l,3,5-pentanetrionato) was prepared and temperature dependent Xm measurements show antiferromagnetic behaviour with J = —80 cm 1.902 The / value is much lower than with [M2(dana)2(py)2] (M = Co, Cu) and this probably results from a different spatial orientation of the exchanging electrons if the unpaired electron is considered to be initially in a dxy orbital, a direct metal-metal interaction may be possible as the V—V distance is large (ca. 3.0-3.2 A V atoms are probably 0.5-0.6 A out of the plane and possibly one above and one below the ligand plane902), one would expect a weak exchange for the direct V—V interaction. 

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