Simultaneous Introduction of Two Nitroxides in the Reaction: A New Approach to the Synthesis of Heterospin Complexes.

Abstract

A new approach to the synthesis of multispin compounds has been developed, namely, the simultaneous introduction of two different stable nitroxides (nitronyl nitroxide and imino nitroxide) in a reaction with a metal ion. An important characteristic of the new method is that nitronyl nitroxide and imino nitroxide introduced in the reaction with the metal are the products of different series; i.e., the nitronyl nitroxide molecule differs from the imino nitroxide molecule not only in one additional oxygen molecule per molecule but also in another substituent in the side chain of the organic paramagnet. This possibility was demonstrated on the synthesis of multispin compounds [Ni2(A1)(L2)2(Piv)(MeOH)], [Ni2(L1)(A2)2(Piv)(H2O)], [Co2(A1)(L2)2(Piv)(MeOH)], and [Co3(L1)2(A2)2(Piv)2], in which Ln and An differ in the substituent in the phenyl ring. The number of multispin compounds that can be synthesized by the proposed method is almost unlimited. The heterospin complexes of transition metals with coordinated nitronyl nitroxide and imino nitroxide in one molecule contain energy-different exchange interaction channels that differ in both magnitude and sign, as confirmed by the quantum-chemical analysis of exchange channels in [Ni(B1)(B2)2](NO3)2. The series of mixed-radical complexes may include compounds with nontrivial magnetic properties such as [Co2(A1)(L2)2(Piv)(MeOH)], which experiences bulk magnetic ordering below 3.5 K.