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

One- and two-electron oxidation of the manganese(II) complex [L2Mn(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 [L2Mn(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 [L2Cu(hfaC)(2)] was also investigated but this decomposes when an attempt is made to oxidise the ligand to its amminium radical cation. (C) 2007 Elsevier Ltd. All rights reserved.