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

A novel synthetic route is reported for the synthesis of three dicubane complexes [(Mn2Mn2III)-Mn-II(bdea)(2)(bdeaH)(2)(O2CCMe3)(4)] ( 1), [(Mn2MnIII)-Mn-II (2)(bdea)(2)(bdeaH)(2)(O2CPh)(4)] ( 2), and [(Mn2Mn2III)-Mn-II(teaH)(2)(teaH(2))(2)(O2CPh)(2)](O2CPh)(2) center dot 0.7MeCN center dot 0.3EtOH ( 3), obtained from the reaction of N-butyldiethanolamine (bdeaH(2), for 1 and 2) or triethanolamine (teaH(3), for 3) with Mn(OAc)(2)center dot 4H(2)O 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 P2(1)/c ( a = 13.2125( 7) angstrom, b = 10.9602( 6) angstrom, c = 22.2329( 11) angstrom, beta = 95.053( 1)degrees, V = 3235.9( 3) angstrom(3), with Z = 2). Complex 2 crystallises in the monoclinic space group P2(1)/n (a = 16.6894( 14) angstrom, b = 8.7360( 7) angstrom, c = 21.3378( 18) angstrom, beta = 92.949( 2)degrees, V = 3106.9( 4) angstrom(3), with Z = 2). Complex 3 crystallises in the monoclinic space group C2/c (a = 30.242( 3) angstrom, b = 8.6710( 6) angstrom, c = 26.618( 3) angstrom, beta = 119.915( 9)degrees, V = 6050.0( 10) angstrom(3), 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 Mn-II ions and two inner hexacoordinate Mn-III. 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.