Probing the magnetic superexchange couplings between terminal Cu(II) ions in heterotrinuclear bis(oxamidato) type complexes

The reaction of one equivalent of [n-Bu(4)N](2)[Ni(opboR(2))] with two equivalents of [Cu(pmdta)(X)(2)] afforded the heterotrinuclear Cu(II)Ni(II)Cu(II) containing bis(oxamidato) type complexes [Cu(2)Ni(opboR(2))(pmdta)(2)]X(2) (R = Me, X = NO(3)(–) (1); R = Et, X = ClO(4)(–) (2); R = n-Pr, X = NO(3)(–) (3); opboR(2) = o-phenylenebis(NR-substituted oxamidato); pmdta = N,N,N’,N”,N”-pentamethyldiethylenetriamine). The identities of the heterotrinuclear complexes 1–3 were established by IR spectroscopy, elemental analysis and single-crystal X-ray diffraction studies, which revealed the cationic complex fragments [Cu(2)Ni(opboR(2))(pmdta)(2)](2+) as not involved in any further intermolecular interactions. As a consequence thereof, the complexes 1–3 possess terminal paramagnetic [Cu(pmdta)](2+) fragments separated by [Ni(II)(opboR(2))](2–) bridging units representing diamagnetic S(Ni) = 0 states. The magnetic field dependence of the magnetization M(H) of 1–3 at T = 1.8 K has been determined and is shown to be highly reproducible with the Brillouin function for an ideal paramagnetic spin = (1)/(2) system, verifying experimentally that no magnetic superexchange couplings exists between the terminal paramagnetic [Cu(pmdta)](2+) fragments. Susceptibility measurements versus temperature of 1–3 between 1.8–300 K were performed to reinforce the statement of the absence of magnetic superexchange couplings in these three heterotrinuclear complexes.