Self-assembled decanuclear (Na2Mn4Mn4III)-Mn-I-Mn-II complexes: from discrete clusters to 1-D and 2-D structures, with the (Mn4Mn4III)-Mn-II unit displaying a large spin ground state and probable SMM behaviour

The synthesis, magnetic characterization and X-ray crystal structures are reported for five new manganese compounds, [Mn-III(teaH(2))(sal)]center dot 1/2H(2)O (1), [(Na2Mn4Mn4III)-Mn-I-Mn-II(teaH)(6)(sal)(4)(N-3)(2)(MeOH)(4)]center dot 6MeOH (2), [(Na2Mn4Mn4III)-Mn-I-Mn-II(teaH)(6)(sal)(4)(N-3)(2)(MeOH)(2)](n)center dot 7MeOH (3), [(Na2Mn4Mn4III)-Mn-I-Mn-II(teaH)(6)(sal)(4)(N-3)(2)(MeOH)(2)](n)center dot 2MeOH center dot Et2O (4) and [(K2Mn4Mn4III)-Mn-I-Mn-II(teaH)(6)(sal)(4)(N-3)(2)(H2O)(2)](n)center dot 5MeOH (5). Complex 1 is a mononuclear compound, formed via the reaction of Mn(NO3)(2)center dot 4H(2)O, triethanolamine (teaH(3)) and salicylic acid (salH(2)) in a basic methanolic solution. Compound 2 is a mixed-valent hetero-metallic cluster made up of a Mn8Na2 decanuclear core and is formed via the reaction of sodium azide (NaN3) with 1. Compounds 3-5 are isolated as 1- or 2-D coordination polymers, each containing the decanuclear Mn8M2 (M = Na+ or K+) core building block as the repeating unit. Compound 3 is isolated when 1 is reacted with NaN3 over a very short reaction time and forms a 1-D coordination polymer. Each unit displays inter-cluster bridges via the O-atoms of teaH(2-) ligands bonding to the sodium ions of an adjacent cluster. Increasing the reaction time appears to drive the formation of 4 which forms 2-D polymeric sheets and is a packing polymorph of 3. The addition of KMnO4 and NaN3 to 1 resulted in compound 5, which also forms a 1-D coordination polymer of the decanuclear core unit. The 1-D chains are now linked via inter-cluster potassium and salicylate bridges. Solid state DC susceptibility measurements were performed on compounds 1-5. The data for 1 are as expected for an S = 2 Mn-III ion, with the isothermal M vs. H data being fitted by matrix diagonalization methods to give values of g and the axial (D) and rhombic (E) zero field splitting parameters of 2.02, -2.70 cm(-1) and 0.36 cm(-1) respectively. The data for 2-5, each with an identical (Mn4Mn4III)-Mn-II metallic core, indicates large spin ground states, with likely values of S = 16 (+/-1) for each. Solid state AC susceptibility measurements confirm the large spin ground state values and is also suggestive of SMM behaviour for 2-5 as observed via the onset of frequency dependent out-of-phase peaks.