Enhancing single molecule magnet parameters. Synthesis, crystal structures and magnetic properties of mixed-valent Mn4SMMs

Abstract

A novel synthetic route is reported for the synthesis of three dicubane complexes [MnII2MnIII2(bdea)2(bdeaH)2(O2CCMe3)4] (1), [MnII2MnIII2(bdea)2(bdeaH)2(O2CPh)4] (2), and [MnII2MnIII2(teaH)2(teaH2)2(O2CPh)2](O2CPh)2·0.7MeCN·0.3EtOH (3), obtained from the reaction of N-butyldiethanolamine (bdeaH2, for 1 and 2) or triethanolamine (teaH3, for 3) with Mn(OAc)2·4H2O as manganese source and [M3O(O2CR)6](O2CR) (R = CMe3 for 1, and Ph for 2 and 3 and M: Fe or Mn) compounds as carboxylate source. Complex 1 crystallises in the monoclinic space group P21/c (a = 13.2125(7) A, b = 10.9602(6) A, c = 22.2329(11) A, β = 95.053(1)°, V = 3235.9(3) A3, with Z = 2). Complex 2 crystallises in the monoclinic space group P21/n (a = 16.6894(14) A, b = 8.7360(7) A, c = 21.3378(18) A, β = 92.949(2)°, V = 3106.9(4) A3, with Z = 2). Complex 3 crystallises in the monoclinic space group C2/c (a = 30.242(3) A, b = 8.6710(6) A, c = 26.618(3) A, β = 119.915(9)°, V = 6050.0(10) A3, with Z = 4). The X-ray crystallographic structure analyses revealed that 1–3 are essentially isostructural, each consisting of a planar mixed-valent “butterfly” core lying about an inversion centre and comprising two outer “wingtip” heptacoordinate MnII ions and two inner hexacoordinate MnIII. Magnetic properties have been studied for all three complexes using combined ac and dc measurements, revealing single-molecule magnet (SMM) behaviour for 1–3, with an S = 9 spin ground state. A detailed analysis of the slow relaxation of the magnetisation has been performed to characterise their SMM behaviour.