Antiferromagnetic spin-coupling between Mn II and amminium radical cation ligands: Models for coordination polymer magnets

Abstract

One- and two-electron oxidation of the manganese(II) complex [L 2Mn(hfac) 2] (L = 4″,4‴-di- tert-butyl-2′,2″,2‴trimethoxy-{4-(4′-diphenylaminophenyl)pyridine}) were studied by ultra violet/visible/near infra red spectroscopy, cyclic voltammetry and magnetometry. A one-electron oxidation converts the triarylamine ligand to its radical cation and gives a complex in which the antiferromagnetic coupling between the spin on the ligand and that on the metal J/ k b is −1.5 K. In a dilute frozen matrix and at low temperature this behaves as an S = 2 system. A two-electron oxidation gives [L 2Mn(hfac) 2] 2 + which at low enough temperatures behaves as an S = 3/2 system but the spin-coupling between the metal and the ligand is weaker ( J/ k b = −0.3 K). The weakness of these spin-couplings mean that Mn II/amminium radical cation complexes are not promising systems on which to base coordination polymer magnets. The equivalent copper(II) complex [L 2Cu(hfac) 2] was also investigated but this decomposes when an attempt is made to oxidise the ligand to its amminium radical cation.